FUNCTIONAL ANALYSIS OF ACTIVE DNA DEMETHYLATION IN TOMATO

Keywords: Tomato, DNA demethylation, fruit ripeing, differently methylated regions, gene expression

DNA methylation is one of the epigenetic mechanisms that lead to stable and heritable changes in gene expression without alteration on DNA sequence. DNA methylation refers to the addition of a methyl group to the fifth position of the cytosine ring. In recent years, DNA methylation is becoming more and more widely studied, because of its importance in mammals and plants. Methylated cytosines distribution can be determined across the genome at singlenucleotide resolution, that is methylome, using whole genome bisulfite-sequencing (BS-seq) approaches. The methylomes of an increasing number of plant species has been well described, revealing that these large-scale patterns of methylation first described for Arabidopsis are shared among flowering plants, although differences exist between plant species. In plants, cytosine methylation which occurs in all sequence context (CG, CHG, CHH, H being A, T or C) is set up and maintained by three different types of DNA methyltransferase. Methylation of symmetric CG and CHG sites can be maintained by METHYLTRANSFERASE1 (MET1) and CHROMOMETHYLASE2 (CMT2/CMT3), respectively. While maintenance of asymmetric CHH methylation relies on RNA directed DNA methylation (RdDM) or CMT2. DNA methylation can also be removed by the bifunctional DNA glycosylase-lyases, also called the DEMETER-like DNA demethylases. In the model plant Arabidopsis, active DNA

Titre: ANALYSE FONCTIONNELLE DE LA DEMETHYLATION D'ADN ACTIF EN

TOMATE

Ré sumé

La mé thylation de l'ADN gé nomique est l'un des principaux mé canismes é pigé né tiques qui conduisent à des changements stables et hé ré ditaires de l'expression des gè nes sans que cela s'accompagne de la modification de la sé quence d'ADN sous-jacente. Elle fait ré fé rence à l'addition d'un groupement mé thyl sur le carbone 5 des cytosines (5meC). Ces derniè res anné es, l'étude des mécanismes régulant la mise en place et le maintien de de cette méthylation est devenu un thè me de recherche importante, en raison de son rôle essentiel dans la ré gulation du fonctionnement du gé nome des plantes et des mammifè res. La distribution des 5meC sur l'ensemble du génome d'un organisme, encore appelé méthylome, peut ê tre dé terminé e par différentes méthodes dont le séquençage de l'ADN génomique après traitement au bisulfite de sodium (WGBS ou mé thyl C sé q). Chez les végétaux, la méthylation de l'ADN peut se produire dans tous les contextes de sé quence incluant les motifs symé triques CG et CHG et le contexte dissymé trique CHH (H pouvant ê tre A, T ou C). En fonction du contexte de sé quence, la mé thylation des cytosines est mise en place et maintenue par trois types diffé rents d'ADN mé thyltransfé rase. Le maintien de la mé thylation aux sites CG et CHG est assuré e par l'ADN Mé thyltransfé rase 1 (MET1) et par la Chromomomé thylase, CMT3, respectivement. La chromomomé thylase 2 (CMT2) est-elle impliqué e dans le maintien des mé thylation de type CHH, de mê me que les Domain Rearanged Methyltransferases (DRM). Ces derniè res sont sont responsables de la mise en place de la mé thylation de novo et sont guidées jusqu'à leur cible par des petits ARNs selon le mé canisme de « RNA directed DNA Methylation » (RdDM). Enfin la mé thylation de l'ADN peut é galement ê tre é liminé e par les ADN glycosylase-lyases bifonctionnelle, é galement appelé e les DEMETER-like DNA demethylases (DML). Chez la plante-modè le Arabidopsis, la dé mé thylation active de l'ADN joue un rôle essentiel dans l'empreinte maternelle et la dé mé thylation l'ADN génomique lors du développement de l'albumen, mais elles ne semblent pas jouer de rôle essentiel pendant le dé veloppement de la plante chez cette espè ce. La méthylation de l'ADN génomique peut aussi être perdue après la réplication de l'ADN, lorsque les mé canismes devant assurer son maintien ne sont pas actifs. On parle alors de dé mé thylation passive de l'ADN génomique.

La tomate (Solanum lycopersicum) est une plante ayant une forte importance agronomique.

Elle est aussi utilisé e comme principal modè le pour l'étude du dé veloppement et du murissement des fruits charnus climaté riques. Des é tudes ré centes ont maintenant montré que le dé veloppement et la maturation de ces fruits reposent sur la mise en place et le maintien de patrons de transcription diffé rentielle, dont la ré gulation est assuré e par un ensemble de processus complexes impliquant à la fois des contrôles gé né tiques et des ré gulations hormonales. Cependant, il semble que la ré gulation du dé veloppement et de la maturation des fruits charnus ne reposent pas basant uniquement sur les modè les gé né tiques, mais impliquent aussi es ré gulations é pigé né tiques. En effet, des travaux ré cents suggè rent que la mé thylation de l'ADN pourrait é galement ê tre impliqué e En particulier, une diminution importante de l'abondance des 5 meC à l'é chelle du gé nome entier et la dé mé thylation à certains promoteurs observé s lors de la maturation des fruits de tomate.

A fin d'analyser les mé canismes molé culaires responsables de la perte de mé thylation survenant lors de la maturation des fruits de tomate, le projet pré senté se concentre sur l'analyse fonctionnelle des enzymes de tomate impliqué es dans la dé mé thylation active de l'ADN gé nomique. Nous avons identifié 4 ADN dé mé thylases putatives (SlDML 1 à 4) qui contiennent toutes trois domaines hautement conservé s comprenant le domaine Glycosylases qui est porteur de l'activité enzymatique et deux domaines supplé mentaires A et B né cessaires à la liaison de ces enzymes à l'ADN. Dans une tentative d'é tude de l'activité des proté ines SlDML, les ADNcs complets codant pour les enzymes SlDML1 et 2 et ainsi que fragments de ces ADNcs codant pour des versions tronqué es de la porté ine SlDML2 tronqué es a é té cloné s. La production des proté ines recombinantes correspondantes dans la bacté rie E Coli, n'a pas permis de démontrer leur activité biochimique.

Pour analyser les fonctions biologiques des ADN dé mé thylases de Tomate, des plants de tomates transgé niques alté ré s dans l'expression des gè nes SlDML ont é té gé né ré s. Ces plantes pré sentent de nombreuses alté rations du dé veloppement, parmi lesquelles des modifications de l'organisation florale des fruits et de la forme des feuilles ainsi qu'une inhibition marqué e de la maturation des fruits. En utilisant ces plantes, nous avons dé montré que la dé mé thylation active de l'ADN est une exigence absolue pour que la maturation des fruits de tomate puisse avoir lieu.

En particulier nous avons mis en é vidence un lien de cause à effet direct entre la dé mé thylation active de l'ADN principalement mé dié e par une des quatres DML de tomate, SlDML 2 et la maturation des fruits. Les plantes dont l'expression du gène SlDML2 est ré duite pré sente une inhibition de la maturation consé cutive à l'hypermé thylation et la ré pression de l'expression des gè nes codant pour les facteurs de transcription contrôlant la maturation des fruits (Ripening Inhibitor, RIN ; Non Ripening NOR ; Colourless Non Ripening, CNR) et pour des enzymes impliqué es dans des processus biochimiques clefs se produisant lors du murissement tels que l'accumulation des caroté noï des (Phytoè ne Synthase 1, PSY1).

A fin de dé terminer si les phé notypes des plantes transgé niques (dé veloppement affectant les fruits, les fleurs ainsi que le dé veloppement des feuilles) sont hé ré ditaires aprè s la perte du transgè ne par sé gré gation, leur stabilité a é té é tudié e sur plusieurs gé né rations. Dans tous les cas, les phé notypes sont perdus et les plantes aprè s perte du transgè ne semblent en tout point identique à des plants de tomate sauvage, ce qui suggè re une absence d'hé ritabilité des modifications induites par la réduction d'expression des gènes SlDML1 et 2. Cependant, nous ne pouvons exclure que certains patrons anormaux de mé thylation, lié s ou non aux phé notypes observé s, sont né anmoins hé rité s. Il est possible que la perte des phé notypes ne soit pas due à une non-hé ritabilité d'empreintes de mé thylation inapproprié es à certains loci spé cifiques. Cela pourrait plutôt reflé ter que la combinaison des é tats de mé thylation à l'ensemble les loci né cessaire au phé notype n'est pas obtenue dans les plantes obtenues aprè s croisement.

L'analyse d'un plus grand nombre de plan, sur plusieurs générations et associé à l'analyse de la distribution des cytosines mé thylé es sera né cessaire pour ré pondre à cette question.

Pour dé terminer, les processus contrôlé s par SlDML2 dans les fruits de tomate, nous avons effectué une analyse comparative du transcriptome et du mé tabolome des fruits des plantes sauvages et des plantes transgé niques RNAi DML à huit é tapes de dé veloppement du fruit. Ces analyses ont ensuite é té corré lé es aux donné es du mé thylome de tomate dé terminé à partir de fruits de tomate de la varié té Ailsa craig. Ces analyses ré vè lent qu'en plus des gè nes RIN, NOR, CNR, PSY1 un nombre important de mé tabolites primaires et secondaires, et de nombreux gè nes pré sentent une accumulation diffé rentielle et des patrons d'expression distincts respectivement chez les fruits transgé niques DML RNAi et chez les fruits sauvages. Par exemple, l'accumulation de caroté noï des, la biosynthè se et la signalisation de l'é thylè ne, la synthè se puis la dé gradation de la paroi cellulaire, mais aussi l'expression des gè nes codant pour divers facteurs de transcription, et pour certains ré gulateurs é pigé né tiques, incluant une DRM, des histones dé -acé tylases et diffé rents histones dé mé thylases sont extrê mement affecté s dans les fruits transgé niques. Ces ré sultats suggè rent que de nombreux gè nes, y parmi lesquels ceux qui jouent des rôles essentiels pour le dé veloppement et la maturation des fruits, né cessitent d'être dé mé thylé s pour leur expression. En consé quence, ces travaux apportent la dé monstration, pour la premiè re fois, que la dé mé thylation active d'ADN a des effets trè s globaux sur le dé veloppement et la maturation des fruits. Il est maintenant né cessaire de valider ce travail en dé terminant le mé thylome des ligné es transgé niques alté ré es dans la dé mé thylation active de l'ADN.

En conclusion, les observations pré senté es dans ce travail fournissent un cadre de travail permettant d'analyser les mécanismes moléculaire responsable de la déméthylation de l'ADN se produisant pendant la maturation des fruits de tomate. Ici, nous pré sentons une analyse complè te des conséquences d'une réduction de l'expression du gène de SlDML2 sur le trancriptome et le mé tabolome des fruits, tout au long de leur dé veloppement. La corré lation entre les profils d'expression de gènes réalisées lors de ce travail ( variété WVA106) et les changements de la distribution de la méthylation de l'ADN telles que décrites chez la variété Ailsa craig montre qu'en plus d'un rôle général dans la régulation des gènes directement impliqué s dans plusieurs voies mé taboliques, plusieurs gè nes codant pour des facteurs de transcription ainsi que des ré gulateurs é pigé né tiques sont é galement susceptibles d'ê tre directement contrôlé s par la mé thylation de leur ré gion promotrice. Cependant, nous ne pouvions pas é tablir une relation stricte entre la diminution de la mé thylation de l'ADN et l'induction de l'expression des gè nes, car de nombreux gè nes pré sentant une diminution du niveau de mé thylation de l'ADN dans leur ré gion promotrice pendant la maturation des fruits sauvages correspondent à des gè nes normalement ré primé s. Ceci suggè re que la mé thylation active de l'ADN serait né cessaire à leur ré pression pendant le processus de maturation. Ainsi la relation entre la dé mé thylation de l'ADN et l'expression des gè nes pourrait ê tre plus complexe et ne se limiterait pas à la simple hypothè se de dé part de ce travail: la dé mé thylation de l'ADN est né cessaire à l'expression de gè nes induits au cours de la maturation. La dé mé thylation de active de l'ADN pourrait é galement ê tre né cessaire à la ré pression de gè nes exrimé s uniquement lors des phases pré coces du dé veloppement des fruits et ré primé s lors du murissement.

Mots clé s :

Tomate ; Déméthylation d'ADN; Mûrissement des fruits; Régions différentiellement méthylées; l'expression du gène demethylation plays a critical role in maternal imprinting and endosperm demethylation, but none of these functions appear to be essential for the development in this species.

Solanum lycopersicum (tomato) is an important agronomic crop and the main model to study the development and ripening process of climacteric fleshy fruit. Recent studies have now shown that the development and ripening of fleshy fruits relies on the establishment and maintenance of differential transcription patterns and complex regulatory pathways that involve both genetic and hormonal controls are operating at these developmental phases. However, it appears that a full understanding of fruit development and ripening will not be achieved based only on genetic models as suggested by recent studies, which showing an important decrease in global methylation level and demethylation at specific promoters during fruit ripening.

In order to analyze the molecular mechanisms responsible for the loss of methylation observed during tomato fruit ripening, the present project focuses on the functional analysis the tomato enzymes involved in the active demethylation of genomic DNA. As it was suggested that DNA demethylases is DNA glycosylase-lyases, which is normally associated with removal of methylated cytosine, nicking the DNA backbone and leaving a single nucleotide gap and filled with an unmethylated cytosine through base excision pathway. As in Arabidopsis, three highly conserved domains were observed including a glycosylases domain as well as two additional domains A and B. These three domains is necessary for DNA binding and catalysis.

In an attempt to study the SlDML protein activity, the tomato full length DNA glycosylaselyases as well as different truncated recombinant proteins have been produced. Unfournatelly, none of the protein show activity in this study, a further expressional condition should be optimized. In addition, to investigate whether hypermethylated epialleles generated in the transgenic plants can be inherited after the transgene has been lost by segregation, the stability across generations of the developmental alterations affecting flower as well as leaf development was studied. As a result, T4 plants show us that the phenotypes reversed to WT phenotype once the transgene was out segregated, suggesting an absence of heritability of the modifications induced by SlDML2 knock down. However, we cannot rule out that some abnormal methylation patterns linked or not to these apparent phenotypes have been inherited. In addition, it is not known how many loci are involved in generating the flower and leaf abnormalities.

Hence, it is possible that lack of phenotypes is not due to the non-heritability of the improper methylation state at specific loci. It may reflect that the correct combination of homozygous methylation state at all required loci was not obtained. Further generation and screening of more important plant population will be necessary to answer this point.

After characterizing the gene family encoding the tomato DNA demethylases, transgenic tomato plants impaired in the expression of SlDML genes have been generated. These plants present several developmental alterations, including inhibition of fruit ripening, modifications of flower, fruit and leaf shape. Using these plants, we have demonstrated that active DNA demethylation is an absolute requirement for tomato fruit ripening to occur. We show a direct cause and effect relationship between active DNA demethylation mainly mediated by one tomato DML, SlDML2, and fruit ripening. RNAi SlDML2 knockdown results in ripening inhibition via hypermethylation and repression of the expression of genes encoding ripening transcription factors (RIN, NOR, CNR) and rate-limiting enzymes of key biochemical processes (PSY1).

In recent years, the coordinated changes during tomato development and ripening was analyzed using combined transcriptome, metabolism and proteome characterization. However, it appears that a full understanding of tomato fruit development and ripening will not be achieved based only on genetic models. In addition epigenetic regulation, mainly genomic DNA methylation may play a key role in this process. Indeed, several evidence point out the importance of DNA methylation and chromatin regulation on fleshy fruit development and ripening ripening. The fruit ripening defect of Cnr mutant is caused by hypermethylation of an upstream region of the CNR promoter. Zhong et al (2013) also detected that, the promoter region of several genes are demethylated during tomato fruit ripening, suggesting that DNA demethylation may play critical role during this phase of development. However, the pathways under the regulation of SlDML2 have not been comprehensively identified. With the aim to obtain a more comprehensive view of the roles of active DNA demethylation on tomato fruit development and ripening, we have performed a comparative analysis of the transcriptome and metabolome of WT and DML RNAi fruits at eight fruit development and ripening stages. These analyses was integrated with tomato epigenome determined in WT Ailsa craig plants. These analyses reveal that in addition to the four genes (RIN, NOR, CNR, PSY1) previously characterized a large number of metabolites and genes present differential accumulation and expression patterns respectively in DML RNAi transgenic fruits. Such as carotenoid, ethylene biosynthesis and signaling, cell wall synthesis and dissembling, transcription factors, and many others are extremely affected in transgenic fruits. These finding suggests that plenty of genes, including those playing essential roles for fruit development and ripening might require demethylation for their expression. Here, we present evidence for the first time that active DNA demethylation has very global effects on fruit development and ripening. Validation of this analysis will now require determining the fruit methylome of the plants impaired in active DNA demethylation.

In conclusion, the observations presented in this work provide a framework for analysis of the molecular mechanism of DNA demethylation during fruit ripening of tomato. Here, we provide a comprehensive analysis of the knock down SlDML2 on the trancriptome, metaoblom and DNA methylation in the promoter analysis. The large transcriptional reprogramming that occured in mutant during fruit ripeing was correlated alterations in DNA methylation. Here we highlight the central role of active DNA demethylation during tomato fruit ripening. In addition to a general role in the regulation of genes directly involved in several metabolic pathways, we also found that several transcription factors as well as epigenetic regulators are also likely under direct methylation control. However, we could not establish a district relationship between DNA reduction of DNA methylation and induction of gene expression, as not all DEGs containing a type-a DMRs (decreased DNA methylation during fruit ripening) do not correspond to genes normally induced in WT and repressed in transgenic plants. Some were corresponding to an opposite situation and in a few cases more complex methylation pattern (several DMRs) were also found. Indeed these conclusions are based on methylation analysis obtained in another variety. They might however reflect the situation of WVA106 fruits, although some variations are expectable when the methylome of DML RNAi fruits will be analyzed. Hence the relationship between DNA demethylation and gene expression might be more complex than expected, and not limited to the starting hypothesis of this work: DNA demethylation is an absolute requirement for the expression of critical ripening induced genes.

This is indeed clearly in this study, but the analysis presented here also suggest that DNA demethylation might also be necessary for the repression of several genes as well.

In addition, from the rencent study in Arabidopsis, ROS1 were found preferentially targets transposable elements (TEs) which are closer to protein coding genes and intergenic regions, which suggesting that ROS1 may prevent DNA methylation spreading from TEs to nearby genes. While in tomato, as our analysis, we found the methylation level of promoter of a number of genes was altered during fruit ripening, therefore, through methylome analysis, we will also get the preference of DNA methylation on TE, this analysis will give us idea that demethylation in fleshy fruit may has other distinct function as it is in Arabidopsis.

I would like to thank my supervisor Philippe Gallusci. I appreciate for his guidance, responsibility and positivity over these three years. He spent much time to disscuss on all the expriments I performed. His knowledge on epigenetic has been most invaluable, professional and inspiring. I also want to thank Emeline Teyssi specifically, for her discussion and guide for most experiments, as well as her particular correction in the introduction of this thesis. Both of them gave me great help on work and life. Many thanks to my group members, Linda Stammitti, Anne Bertrand, Junhua Kong, especially Linda gave me lots of useful suggestions and great help. I have been fortunate to become a member of this group.

I also can't thank my collaborators enough, James Gavannoi for performing RNA seq and bisulifite sequencing, Alisdair Fernie and Takayuki Tohge for wide-scale metabolism analysis, Dominique Rolin for primary metabolism analysis. Yiguo Hong for VIGS silencing, Gram symour for DML expression in tomato mutants measurement. Meanwhile, I'd like to specifically thank Jame to allow me visit his lab. My eyes are widely opened on building BS-librariy during these precious three months. I also want to thanks Tohge and Alis F, who gave me idea how to do metabolism analysis and very useful guidance. Thanks to Mohamed Zouine and Elie Maza to allow me visit their lab and gaudiness on RNA seq analysis. These are precious communication. At same time, I would like to thank members in their lab, who gave me lots of suggestions and discussion. It has been a great pleasure to working with them.

My thanks to people in Ecophysiology and Functional Genomics of Vine as well as Fruit Pathology and Biology Group members, in particular to Cecil Cabassion, Michel Hernould, Pierre Baldet, for outstanding questions discussion, Esabaelle who took care my tomato plants in the last two years. Zhanwu Dai taught me network analysis and guides discussion. Classmates in these two labs were always generously sharing their knowledge and for all the stimulating and fun meetings we have had.

I can not thank enough of the members of my thesis jury, Etienne Bucher, Mohamed Zouine, Serge Delrot, Mark Hooks and Rossitza Atanassova, they gave me valuable comments and proofreading this thesis.

Mostly, I want to thank my family and friends who always support me in my life, this support is so important for me! It's a great pleasure to have spent my time in France. Work and people here have all enriched my life and made my stay here unforgettable.

I

Summary

DNA methylation is one of the epigenetic mechanisms that lead to stable and heritable changes in gene expression without alteration on DNA sequence. DNA methylation refers to the addition of a methyl group to the fifth position of the cytosine ring. In recent years, DNA methylation is becoming more and more widely studied, because of its importance in mammals and plants. Methylated cytosines distribution can be determined across the genome at singlenucleotide resolution, the so-called methylome, using whole genome bisulfite-sequencing (BSseq) approaches. The methylomes of an increasing number of plant species has been well described, revealing that these large-scale patterns of methylation first described for Arabidopsis are shared among flowering plants, although differences exist between plant species. In plants, cytosine methylation which occurs in all sequence context (CG, CHG, CHH, H being A, T or C) is set up and maintained by three different types of DNA methyltransferase. It can also be removed by the bifunctional DNA glycosylase-lyases, also called the DEMETER-like DNA demethylases. In Arabidopsis, active DNA demethylation plays a critical role in maternal imprinting and endosperm demethylation, but none of these functions appear to be essential for the development in this species.

Tomato is the main model to study the development and ripening process of climacteric fleshy fruit. Recent studies have now shown that the development and ripening of fleshy fruits relies on the establishment and maintenance of differential transcription patterns and complex regulatory pathways that involve both genetic and hormonal controls are operating at these developmental phases. However, it appears that a full understanding of fruit development and ripening will not be achieved based only on genetic models as suggested by recent studies, showing an important decrease in global methylation level and demethylation at specific pormoters during fruit ripening.

In order to analyze the molecular mechanisms responsible for the loss of methylation observed during tomato fruit ripening, the present project focuses on the functional analysis the tomato enzymes involved in the active demethylation of genomic DNA. To achieve this goal, after characterizing the gene family encoding the tomato DNA demethylases, transgenic tomato plants impaired in the expression of SlDML genes have been generated. These plants present several developmental alterations, including inhibition of fruit ripening, modifications of flower, fruit and leaf shape. Using these plants, we have demonstrated that active DNA demethylation is an absolute requirement for tomato fruit ripening to occur. We show a direct cause and effect relationship between active DNA demethylation mainly mediated by one tomato DML, SlDML2, and fruit ripening. RNAi SlDML2 knockdown results in ripening inhibition via hypermethylation and repression of the expression of genes encoding ripening transcription factors and ratelimiting enzymes of key biochemical processes. In an attempt to study the SlDML protein activity a recombinant tomato DNA glycosylase-lyases have been produced. In addition, to investigate whether hypermethylated epialleles generated in the transgenic plants can be inherited after the transgene has been lost by segregation, the stability across generations of the developmental alterations affecting flower as well as leaf development was studied.

To identify the global effect of active DNA demethylation on fruit ripening, we have compared the transcriptome and metabolome of RNAi DML plants and WT controls. This demonstrated that multiple aspects of the fruit ripening processes are affected when DNA II demethylation was impaired. Furthermore, we combined differentially methylation regions determined in Ailsa Craig which allow us identify a number of potential targets for active DNA demethylation. Validation of this analysis will now require determining the fruit methylome of the plants impaired in active DNA demethylation.

List of Figures

List of Tables

Introduction

The introduction part of this manuscript is a review of the current state of the art concerning epigenetic in plant. All epigenetic mechanisms are not detailed, and the following text mainly focuses on DNA methylation and demethylation. Histone post-translational modifications (HPTMs) are also briefly considered, because cross-talks have been described between DNA methylation and HPMTs, leading to specific combinations of epigenetic marks along the genome, as revealed by genome-wide studies [START_REF] Roudier | Integrative epigenomic mapping defines four main chromatin states in Arabidopsis[END_REF]

I. Background: Definition of epigenetics

The definition of the term "epigenetics" has evolved over time. In the early 1940s, epigenetics was first defined by Conard Waddington as "the branch of biology which studies the causal interactions between genes and their products which bring the phenotype into being" (Waddintton, 1942;[START_REF] Waddington | Towards a Theoretical Biology[END_REF]. In other words, here epigenetics designs all molecular processes controlling "the expression of a genotype into a particular phenotype" [START_REF] Dupont | Epigenetics: definition, mechanisms and clinical perspective[END_REF]. Obviously, this definition is broad and not precise. It includes many different mechanisms that can modulate phenotype such as post transcriptional regulation, non-coding RNA regulation, [START_REF] Holoch | RNA-mediated epigenetic regulation of gene expression[END_REF]. Since that time, epigenetics has been redefined several times, becoming more and more specific and precise. By the middle 1990s, it has turned from causal interactions between genes and their products to chromosomal modifications that had the potential to modify gene expression during development. But today epigenetics is commonly used to precisely mean "the study of mitotically and/or meiotically heritable changes in patterns of gene expression that occur without alterations in DNA sequence" [START_REF] Iwasaki | Epigenetic memory in plants[END_REF]. This definition is still evolving and was recently suggested to also include stable marks that although not heritable may lead to stable alteration of the transcriptional programing of specific cells [START_REF] Avramova | Transcriptional 'memory' of a stress: transient chromatin and memory (epigenetic) marks at stress-response genes[END_REF] as indicated by the roadmap consortium of epigenomics (http://www.roadmapepigenomics.org/overview).

At present, it is widely accepted that posttranslational histone modifications, DNA methylation and certain non-coding RNA-mediated epigenetic regulations [START_REF] Holoch | RNA-mediated epigenetic regulation of gene expression[END_REF] constitute epigenetic mechanisms which are critically important in modulating the structure of chromatin. Chromatin, which is only found in eukaryotic cells, designs a complex and organized structure made of proteins, DNA and RNA. The structural unit of chromatin, the nucleosome, consists of 146 bp of DNA wrapped around a protein core made of 4 histones dimers. The chromatin allows the organization and compaction of the genetic material into the nucleus. Along each chromosome, chromatin is organized into transcriptionally active less condensed euchromatin, and transcriptionally inactive highly condensed heterochromatin. But chromatin structure is highly dynamic, and may undergo changes during development or in response to environmental signals.

Because epigenetic mechanisms govern these modifications in chromatin structure, they impact DNA accessibility for all DNA-template processes including gene transcription [START_REF] Lauria | Epigenetic control of gene regulation in plants[END_REF], DNA recombination [START_REF] Choi | Meiotic recombination hotspotsa comparative view[END_REF] and transposition [START_REF] Mirouze | Transposable elements, a treasure trove to decipher epigenetic variation: insights from Arabidopsis and crop epigenomes[END_REF]. In the following text, only the role of epigenetic regulations in gene expression is described, the other processes using DNA as a template are not discussed.

The epigenetic regulation of the genome activity relies on different mechanisms. Some of these mechanisms involve chromatin modifiers, which are responsible for covalent modifications in chromatin, including DNA methylation, and histone post-translational modifications (HPTMs), the so-called epigenetic marks. Other epigenetic mechanisms involve chromatin remodelers, which non-covalently modify chromatin structure by changing the nucleosome position, destabilizing nucleosomes, or substituting histone variants to the canonical histones. Both chromatin modifiers and chromatin remodelers usually function in concert, to modify chromatin structure.

Epigenetic marks

Two types of epigenetic marks have been described, DNA methylation and histone posttranslational modifications corresponding both to covalent modifications, affecting respectively the DNA molecules, and the different histone proteins.

DNA methylation

Although DNA covalent modifications have been described since 1948, it was first suggested that these modifications may modulate gene expression much later in 1969 [START_REF] Hotchkiss | THE QUANTITATIVE SEPARATION OF PURINES, PYRIMIDINES, AND NUCLEOSIDES BY PAPER CHROMATOGRAPHY[END_REF][START_REF] Griffith | DNA ticketing theory of memory[END_REF]. DNA methylation refers to the addition of a methyl group to the fifth position of the cytosine ring. This covalent modification is found in procaryotes [START_REF] Adhikari | DNA methyltransferases and epigenetic regulation in bacteria[END_REF] and initially existed in most of the eukaryotic including plants, fungi, protists and animals [START_REF] Zemach | The Arabidopsis Nucleosome Remodeler DDM1 Allows DNA Methyltransferases to Access H1-Containing Heterochromatin[END_REF]. But it appears that the ability to methylate DNA was lost in some organisms. For example, the genomes of the budding yeast Saccharomyces cerevisiae and of the nematode worm Caenorhabditis elegans do not contain methylated cytosine [START_REF] Colot | Eukaryotic DNA methylation as an evolutionary device[END_REF]. DNA methylation is considered as a very stable mark that is maintained by well described mechanisms (Law and Jacobsen 2010;[START_REF] Matzke | RNA-directed DNA methylation: an epigenetic pathway of increasing complexity[END_REF]) and which can be removed by a variety of mechanisms depending on the organism considered [START_REF] Piccolo | Getting rid of DNA methylation[END_REF][START_REF] Chinnusamy | Epigenetic regulation of stress responses in plants[END_REF][START_REF] Kohli | TET enzymes, TDG and the dynamics of DNA demethylation[END_REF]. Recently, another pattern of DNA modification, DNA hydroxymethylation was only found in mammals and was shown to be an intermediate to DNA demethylation. In addition, 5-hydroxymethylcytidine (5hmC) is also though to play regulatory roles in gene expression (Song and Pfeifer, 2016). More recently, DNA N6-adenine methylation (6mA) was also proposed to become a new epigenetic mark in eukaryotes although it is detected at very low amount. The possible regulatory function of 6mA mark was reviewed by [START_REF] Luo | DNA N6-methyladenine: a new epigenetic mark in eukaryotes?[END_REF] [START_REF] Luo | DNA N6-methyladenine: a new epigenetic mark in eukaryotes?[END_REF].

In mammals, DNA methylation mainly happens in the symmetrical CpG context, which occupies approximate 70-80% of CG throughout the genome (Law and Jacobsen 2010). However, recent publications have described that DNA methylation in non CG context (mCH) was also observed in embryonic stem cells, and adult mammalian somatic cells, such as mammalian brain cells. Genome wide methylomes show that the content of mCH in fetal brain cells is very low, but abundant in human adult brain tissue. This increase in mCH is correlated with tissue-specific functions [START_REF] Pinney | Mammalian Non-CpG Methylation: Stem Cells and Beyond[END_REF][START_REF] Schultz | Human Body Epigenome Maps Reveal Noncanonical DNA Methylation Variation[END_REF]. This suggests that, in addition to mCG that plays major roles in mammals development, mCH appears to have important functions during the formation of specific tissues. In plants, the cytosine methylation patterns are distinct: cytosine methylation can occur in all sequence contexts, in CG, CHG symmetrical contexts, and in nonsymmetrical CHH context (where H=A, T or C). The distribution of mC between the different sequence contexts varies between plants. For example, in Arabidopsis methylation occurs predominantly at the CG context (CG:55%; CHG:23%; CHH:22%) [START_REF] Zhang | Genome-wide High-Resolution Mapping and Functional Analysis of DNA Methylation in Arabidopsis[END_REF][START_REF] Lister | Highly Integrated Single-Base Resolution Maps of the Epigenome in Arabidopsis[END_REF], whereas Zhong et al (2013) found that in tomato, CHH is the major context for mC (CG:28%; CHG:23%; CHH:49%) (Zhong et al., 2013). However in most plants, the methylation level in CG context is always higher than in CHG and CHH contexts (calculated as the number of methylated sites over the total number of sites in a genome, i.e., mCG/total CG sites). This indicates that methylation predominantly occurs in CG context compared with other contexts. For example, [START_REF] Niederhuth | Widespread natural variation of DNA methylation within angiosperms[END_REF] found that mCG is always the highest among the three cytosine contexts by comparing 34 different angiosperm species, although there is a large variation in methylation levels in each cytosine context in different species (Fig 1 .1) [START_REF] Niederhuth | Widespread natural variation of DNA methylation within angiosperms[END_REF].

Histone posttranslational modifications

Histones are basic proteins that are essential for the packaging of DNA into chromatin. The nucleosome, which is the structural chromatin unit, consists of 146 bp of DNA wrapped around an octameric histone core made of 4 histones dimers. Among the five major families of histones that have been described H2A, H2B, H3 and H4 are the core histone proteins, while H1 is known as the linker histone (Fig 1 .2) [START_REF] Luger | Crystal structure of the nucleosome core particle at 2.8 A resolution[END_REF][START_REF] Georgopoulos | Haematopoietic cell-fate decisions, chromatin regulation and ikaros[END_REF]. Histone posttranslational modifications (HPTMs) include acetylation, methylation, phosphorylation, sumoylation as well as ubiquitination and occur at amino acid residues (lysines, histidine, etc) located mainly in the amino terminal tail of histone that protrudes from the nucleosome (Fig 1 .3). The Histone PTM's diversity is multiplied by the fact that different amino acid residues can be modified in each single histone, and that some modifications occur at various levels. For example, the lysine K4 of histone H3 may be mono-, di-, or tri-methylated. Histone marks are associated with either activation or repression of gene transcription. For example histones H3 and H4 acetylation, and histone H3 methylation of lysine K4 are associated with gene activation(for a review, see [START_REF] Lauria | Epigenetic control of gene regulation in plants[END_REF]. HPTM can affect chromatin structure in two different ways [START_REF] Bowman | Post-Translational Modifications of Histones That Influence Nucleosome Dynamics[END_REF]. First all marks except methylation modify the net charge of the histones, and might alter the interactions between nucleosomes or between DNA and histones within a single nucleosome. For example … Second, HPTMs constitute signals that are read by other proteins, often organized as protein complexes, able to influence chromatin structure, or to directly regulate gene expression. Indeed the signal recognized by these regulatory proteins may correspond to individual marks, or to a combination of different HPTMs. The information provided by the HPTMs constitutes the so-called histone code whose existence was first postulated by Jenuwein and Allis [START_REF] Jenuwein | Translating the Histone Code[END_REF].

Genome-wide distribution of methylcytosines

Whole genome bisulfite-sequencing (WGBS) approaches enable determination of methylcytosines distribution across the genome at single-nucleotide resolution, revealing the socalled methylomes [START_REF] Laird | Principles and challenges of genome-wide DNA methylation analysis[END_REF].

In mammals, DNA methylation is spread over the entire genome, with the exception of dense clusters known as CpG islands often found near gene promoters [START_REF] Pinney | Mammalian Non-CpG Methylation: Stem Cells and Beyond[END_REF]).

In plants, a majority of DNA methylation occurs at transposable elements (TE) and repetitive sequences that are clustered in heterochromatin in centromeric, and pericentromeric regions, but that may also be found in euchromatin [START_REF] Chan | Gardening the genome: DNA methylation in Arabidopsis thaliana[END_REF]. TEs and other repeats are methylated in all possible contexts (CG, CHG and CHH), and this methylation has been shown to be essential for the repression of transposons transcription and mobility. The genome wide profiling of the Arabidopsis methylome has also shown that the methylation pattern of genes is complex and can be located in various part of genes [START_REF] Zhang | Genome-wide High-Resolution Mapping and Functional Analysis of DNA Methylation in Arabidopsis[END_REF]. Hence, in Arabidopsis, 61.5% of the genes were entirely unmethylated. When present DNA methylation can occur either in the promoter region (5.2% of the Arabidopsis genes) and/or gene bodies (33.3% of the genes). Promoter methylation was associated with genes presenting differential expression pattern, whereas gene body methylation, which is mainly restricted to CGs, is prevalent in constitutively expressed genes with moderate to high transcription level. Hence unlike methylation at transposons, CG methylation in gene bodies does not seem to cause silencing [START_REF] Lister | Highly Integrated Single-Base Resolution Maps of the Epigenome in Arabidopsis[END_REF]. Furthermore in met1 mutants, which lack virtually all CGs methylation (see below), the expression of bodymethylated genes did not appear to be systematically increased when compared to unmethylated genes [START_REF] Zhang | Genome-wide High-Resolution Mapping and Functional Analysis of DNA Methylation in Arabidopsis[END_REF]Law and Jacobsen 2010). Indeed the function of body methylation in plants remains to be further investigated (For a review, see [START_REF] Bewick | Gene body DNA methylation in plants[END_REF]).

The methylomes of an increasing number of plant species are now being described, revealing that these large-scale patterns of methylation first described for Arabidopsis are shared among flowering plants, but some differences also exist [START_REF] Springer | Creating Order from Chaos: Epigenome Dynamics in Plants with Complex Genomes[END_REF]. For example, whereas in Arabidopsis intergenic regions are mostly short and devoid of methylation, this is not true for rice or maize where these regions are dominated by transposons and methylated (Fig 1 .4 ) [START_REF] Springer | Creating Order from Chaos: Epigenome Dynamics in Plants with Complex Genomes[END_REF]. Other differences are related to the repartition of the methylation in the 3 different sequence contexts. For example, in Arabidopis CHG and CHH methylation often occur together and are mostly located at transposons together with CG methylation, but this is not the case in species such as rice, maize or tomato. In maize, where the genome-wide CHH methylation levels are quite low, most transposons lack elevated CHH methylation [START_REF] West | Genomic Distribution of H3K9me2 and DNA Methylation in a Maize Genome[END_REF]. The analysis of the maize methylome furthermore revealed limited regions often located close to genes, characterized with high CHH methylation and low level of CG and CHG methylation [START_REF] Gent | CHH islands: de novo DNA methylation in near-gene chromatin regulation in maize[END_REF]. Li et al (2015) raised the hypothesis that these so-called CHH islands may act as epigenetic insulators, preserving the silencing of transposons from activity of nearby genes [START_REF] Gent | CHH islands: de novo DNA methylation in near-gene chromatin regulation in maize[END_REF]Li et al., 2015a). In rice, CHH methylation is mainly located in euchromatic regions where it essentially targets small TE such as miniature inverted transposable elements (MITEs), which are located with high frequency at the 5' and 3' end of protein-coding genes [START_REF] Zemach | Local DNA hypomethylation activates genes in rice endosperm[END_REF]. The analysis of tomato methylomes also revealed such enrichment in CHH methylation in the 5' regions of genes, associated with MITEs (Zhong et al., 2013), although in tomato there is also a substantial level of CG and CHG methylation in the same regions (Fig 1.5). Interestingly two recent studies in maize have shown the association between the insertion of a MITE in the promoter region of the Vegetative to generative transition 1 (Vgt1), a specific regulatory gene and a characteristic trait, early flowering time [START_REF] Castelletti | A MITE Transposon Insertion Is Associated with Differential Methylation at the Maize Flowering Time QTL Vgt1[END_REF] or drought tolerance [START_REF] Mao | A transposable element in a NAC gene is associated with drought tolerance in maize seedlings[END_REF]. In both case a correlation has been established between the presence of the MITE in the promoter, an increase in promoter CHH methylation, and a decrease in gene expression, suggesting that TE insertion can influence neighboring genes expression via an effect on the chromatin state of their promoter regions. Another difference concerns gene body methylation, whereas rice and Arabidopsis correspond only to CG methylation, however, in maize, it also contains CHG methylation .

II. Mechanism of DNA methylation

DNA methylation is catalyzed by enzymes called DNA methyltransferases (DMTs). Different DMTs have been characterized in both mammals and plants, which are involved, either in maintenance of DNA methylation during cell divisions, or in the establishment of new DNA methylation patterns (the so called de novo methylation)

2.1 Enzymes involved in DNA methylation in mammals.

Maintenance of DNA methylation in mammals

In mammals four DNA methyltransferases (DNMTs) have been characterized that are highly conserved. DNMT1 maintains DNA methylation at hemi-methylated DNA after DNA replication during cell division. It is the most abundant DNMTs in adult cells. DNMT3A and NNMT3B are involved in establishing de novo DNA methylation, as they don't require hemi-methylated DNA to bind. DNMT3-like (DNMT3L) is another member of the DNMT3 family, but it has no enzymatic activity by itself. This enzyme binds to DNMT3A or DNMT3B and enhances their catalytic activity [START_REF] Pinney | Mammalian Non-CpG Methylation: Stem Cells and Beyond[END_REF]. In mammals, DNMT1 is the principal enzyme that can mediate the maintenance of CG methylation. This enzyme is required for embryonic development and survival of somatic cells in mice. It has been well summarized that DNMT1 doesn't work alone, but work with some accessory proteins. For example, ubiquitin like PHD and RING finger 1 (UHRF1) were recently shown to be key regulators for maintenance of DNA methylation. The uhrf1 mutant is indeed characterized by a severe decrease in DNA methylation. The current model for UHFR1 action is as follows: UHRF1 recognizes hemi-methylated DNA via its SET and RINGassociated (SRA) domains and H3K9me3 via its TUDOR and PHD domains; UHFR1 ubiquitylates H3K23/H3K18 to facilitate the environment for DNMT1 binding. Then DNMT1 binds ubiquitylated H3K23 inducing a conformational change in DNMT1 which promotes its activation [START_REF] Nishiyama | Regulation of maintenance DNA methylation via histone ubiquitylation[END_REF]. In addition, UHRF1 interacts with DNMT3A and DNMT3B, which suggests a role for UHRF1 in de novo methylation. Maintenance of DNA methylation also requires the chromatin remodeling factor Lymphoid Specific Helicase1, but the precise role of LSH1 in DNA methylation remains unknown [START_REF] Nishiyama | Regulation of maintenance DNA methylation via histone ubiquitylation[END_REF].

Enzymes involved in DNA methylation in plants.

In plants, four DNA methyltransferase classes have been characterized. DNA methyltransferase 1 (MET1) which is the homologue of DNMT1 maintains methylation at CG sites. CHROMOMETHYLASE3 (CMT3) is a plant specific enzyme that maintains CHG methylation and requires histone H3 methylation at the lysine K9 to be recruited at its target sites [START_REF] Yang | Dicer-independent RNA-directed DNA methylation in Arabidopsis[END_REF]. De novo DNA methylation in the different sequence contexts is mediated by two enzymes, one is the homologue of the DNMT3 methyltransferases, DOMAINS REARRANGED METHYLTRANSFERASE 2 (DRM2) and another one is CMT2 [START_REF] Matzke | RNA-directed DNA methylation: an epigenetic pathway of increasing complexity[END_REF].

Maintenance of DNA methylation in plants

It has been well documented that, in plants, MET1 is responsible for CG methylation maintenance [START_REF] Kankel | Arabidopsis MET1 Cytosine Methyltransferase Mutants[END_REF]. The mechanism of maintenance of CG methylation is highly conserved between plants and mammals. MET1 can't work alone but requires additional proteins; recruitment of MET1 at target sites requires two different SRA proteins, VARIANT IN METHYLATION (VIM) and Decrease in DNA Methylation 1 (DDM1). However, in plants whether these proteins behave in a similar way as in mammals, needs further validation [START_REF] Kankel | Arabidopsis MET1 Cytosine Methyltransferase Mutants[END_REF].

CHG methylation is maintained by the plant specific enzyme, CMT3 (chromomethylase 3), and requires the H3K9 methyltransferases KRYPTONITE (KYP/SUVH4), SUVH5 and SUVH6 [START_REF] Lindroth | Requirement of CHROMOMETHYLASE3 for Maintenance of CpXpG Methylation[END_REF]. Genome-wide profiling of H3K9Me2 and DNA methylation showed that these marks are highly correlated [START_REF] West | Genomic Distribution of H3K9me2 and DNA Methylation in a Maize Genome[END_REF]. CMT3 mutant displayed a dramatic loss of DNA methylation as also observed in a suvh4 mutant, SUPPRESSOR OF VARIEGATION 3-9 HOMOLOGUE 4 a histone methyltransferase that is largely responsible for H3K9 dimethylation [START_REF] Cedar | Linking DNA methylation and histone modification: patterns and paradigms[END_REF][START_REF] Du | Mechanism of DNA Methylation-Directed Histone Methylation by KRYPTONITE[END_REF]. Furthermore, two other H3K9 histone methyltransferases, SUVH5 and SUVH6 also contribute to global levels of CHG methylation [START_REF] Ebbs | Locus-Specific Control of DNA Methylation by the Arabidopsis SUVH5 Histone Methyltransferase[END_REF]. Hence, in Arabidopsis CMT3 is recruited to specific sites by binding dimethyl K9 histone H3 (H3K9Me2) [START_REF] Du | DNA methylation pathways and their crosstalk with histone methylation[END_REF]. Reciprocally, KYP binds CHG methylated motives through its SRA domain [START_REF] Johnson | The SRA methyl-cytosine-binding domain links DNA and histone methylation[END_REF] thereby establishing a self-reinforcement loop between CHG methylation and H3K9 dimethylation.

De novo DNA methylation in plants

In plants, de novo methylation is mediated by RNA directed DNA methylation, a process also called RdDM (Law and Jacobsen 2010), which is also responsible of maintenance of CHH methylation. RdDM is mainly dependent on the methyltransferases, DOMAINS REARRANGED METHYLTRANSFERASE1 (DRM1) and DRM2, and it is always associated with 24nt siRNA, which direct DNA methylation at their homologous regions (For a review, see [START_REF] Matzke | RNA-directed DNA methylation: an epigenetic pathway of increasing complexity[END_REF]). Alternatively de novo methylation may rely on the chromatin remodeler DDM1 (DECREASE IN DNA METHYLATION 1), together with the CHROMOMETHYLASE 2 [START_REF] Zemach | The Arabidopsis Nucleosome Remodeler DDM1 Allows DNA Methyltransferases to Access H1-Containing Heterochromatin[END_REF][START_REF] Stroud | Non-CG methylation patterns shape the epigenetic landscape in Arabidopsis[END_REF].

A number of components of the RdDM pathway have been recently identified in Arabidopsis leading to the proposal of a model for this complex epigenetic mechanism (Fig 1 .6) [START_REF] Gallusci | DNA methylation and chromatin regulation during fleshy fruit development and ripening[END_REF]. RdDM depends on specialized transcriptional machinery and involves at least two steps: 24-nt siRNA biogenesis and siRNA-guided de novo methylation (for a review, see [START_REF] Matzke | RNA-directed DNA methylation: an epigenetic pathway of increasing complexity[END_REF][START_REF] Zhou | RNA Pol IV and V in Gene Silencing: Rebel Polymerases Evolving Away From Pol II's Rules[END_REF]. The classic RdDM pathway is initiated by recruitment of Polymerase IV (Pol IV), a plant specific DNA dependent RNA polymerase to the appropriate regions of the genome, including TEs and intergenic regions to transcribe a single strand RNA. The recruitment of Pol IV to target sequences is not fully understood. For a large subset of the RdDM targets, Pol IV recruitment necessitates a homeodomain protein, SAWADEE HOMEODOMAIN HOMOLOG 1 (SHH1) which recognizes chromatin enriched with unmethylated H3K4 and H3K9me2 and interacts with Pol IV [START_REF] Law | Polymerase-IV occupancy at RNA-directed DNA methylation sites requires SHH1[END_REF]Zhang et al., 2013b). The long single strand RNAs produced by Pol IV are rapidly converted into double strand RNAs (dsRNAs) by RNA DEPENDENT RNA POLYMERASE 2 (RDR2). The generation of dsRNAs also involves the putative chromatin remodeling protein CLASSY 1 (CLSY1), but the role of this factor remains unknown. The dsRNAs are then processed into 24-nt siRNAs by Dicer-like 3 ribonuclease III enzyme (DCL3). The doublestranded 24-nt siRNAs are transferred to the cytoplasm and loaded into the Argonaute (AGO) protein AGO4 to form a silencing complex. The silencing complex is transferred back to the nucleus with the help of AGO4, and siRNAs are targeted back to DNA repeats through sequence homology.

The siRNA-guided de novo methylation requires then another plant-specific DNA-dependent RNA polymerase, Pol V, and some associated factors. Pol V generates long intergenic non coding RNAs from target loci. The AGO-loaded siRNAs pair with this Pol V scaffold RNAs, and recruit the de novo DNA methyltransferase DOMAINS REARRANGED METHYLTRANSFERASE 2 (DRM2) which catalyzes de novo DNA methylation at the target locus. Pol V transcription and association with chromatin are facilitated by the DDR complex. This complex comprises the putative chromatin remodeler DEFECTIVE IN RNA-DIRECTED DNA METHYLATION 1 (DRD1), DEFECTIVE IN MERISTEM SILENCING 3 (DMS3), and RNA-DIRECTED DNA METHYLATION 1 (RDM1), which has been shown to interact with both AGO4 and DRM2, and to bind to methylated single-stranded DNA. Some other RdDM components may also be needed to complete this process, including some histone-modifying enzymes that remove active marks.

Recently, alternative RdDM pathways have been suggested. For example [START_REF] Yang | Dicer-independent RNA-directed DNA methylation in Arabidopsis[END_REF] found that the majority of the RdDM loci don't require DCL proteins and 24nt siRNA, but rather 25-50 nt RNAs Pol IV-dependent small RNAs (P4 RNAs,) that may act as trigger RNAs to initiate DNA methylation following the RdDM pathway [START_REF] Yang | Dicer-independent RNA-directed DNA methylation in Arabidopsis[END_REF].

RdDM has been shown to be inhibited by heterochromatin, which is enriched in larger transposons. Furthermore lack of DRM2 causes a relatively modest decrease in CHH methylation, demonstrating that the majority of CHH methylation does not depend on RdDM. Indeed most CHH methylation at heterochromatic sequences is mediated by another pathway, requiring the chromomethylase CMT2 and DDM1 and depending on linker histone H1 [START_REF] Zemach | The Arabidopsis Nucleosome Remodeler DDM1 Allows DNA Methyltransferases to Access H1-Containing Heterochromatin[END_REF].

In Arabidopsis both the DDM1/CMT2 and the RdDM/DRD1 pathways mediate nearly all transposon CHH methylation. Hence both pathways act together to inhibit transposon mobility. But this scheme may not be valid in all plant species. For example in rice, the Osdrm2 mutation was shown to lead to a near complete loss of CHH methylation [START_REF] Tan | The ortholog of DDM1 is mainly required for CHG and CG methylation of heterochromatin and is involved in DRM2-mediated CHH methylation that targets mostly genic regions of the rice genome[END_REF]. Hence, in rice, almost all CHH methylation seems to be established by OsDRM2. Furthermore OsDDM1 is required for the facilitation of OsDRM2-mediated CHH methylation. These results suggest that de novo DNA methylation though mediated by similar pathways, can vary between plant species [START_REF] Tan | The ortholog of DDM1 is mainly required for CHG and CG methylation of heterochromatin and is involved in DRM2-mediated CHH methylation that targets mostly genic regions of the rice genome[END_REF].

Functions of DNA methylation in plants

In eukaryotes, cytosine DNA methylation is a conserved and stable epigenetic mark that plays essential roles in the silencing of transposable elements (TEs) and genes (Law and Jacobsen 2010). A number of articles have reviewed that cytosine methylation is critical for diverse biological process, including the establishment and maintenance of tissue specific gene expression patterns, genomic imprinting and X chromosome inactivation (Laird PW, 2003;[START_REF] Duymich | DNMT3B isoforms without catalytic activity stimulate gene body methylation as accessory proteins in somatic cells[END_REF].

Cytosine DNA methylation plays different roles during plant development

The genome-wide distribution of methylcytosines is subjected to dynamic changes during development

The distribution of methylcytosines has been analyzed at a genome-wide level in different plants and developmental contexts, including endosperm development (Hsieh et al., 2009;[START_REF] Zemach | Local DNA hypomethylation activates genes in rice endosperm[END_REF][START_REF] Lu | Genome-Wide Epigenetic Regulation of Gene Transcription in Maize Seeds[END_REF], male gametophyte development [START_REF] Slotkin | Epigenetic reprogramming and small RNA silencing of transposable elements in pollen[END_REF][START_REF] Borg | Chromatin remodelling during male gametophyte development[END_REF], fruit ripening (Zhong et al., 2013), and flower development [START_REF] Yang | Whole-genome DNA methylation patterns and complex associations with gene structure and expression during flower development in Arabidopsis[END_REF] .

These studies show that DNA methylation patterns are modified during plant development. More precisely, the variations in DNA methylation affect specific regions which are referred to as differentially methylated regions (DMRs).

Correlations could be established between some DMRs and changes in gene expression, . However, not all gene-associated DMRs were associated with to variations in gene expression. This is illustrated for example by the study of [START_REF] Yang | Whole-genome DNA methylation patterns and complex associations with gene structure and expression during flower development in Arabidopsis[END_REF], who compared different samples along flower development (meristems, flowers at early and late development stages). Their results show that methylation variations during flower development are correlated with expression changes of more than 3000 genes, many of which are important for flower development [START_REF] Yang | Whole-genome DNA methylation patterns and complex associations with gene structure and expression during flower development in Arabidopsis[END_REF]. But many more gene-related DMRs were identified, which were not associated with differentially expressed genes. For example, from the comparison of meristems with early flowers, [START_REF] Yang | Whole-genome DNA methylation patterns and complex associations with gene structure and expression during flower development in Arabidopsis[END_REF] identified 2503 genes associated with changes in promoter methylation. But only 141 among these 2503 genes were differentially expressed (Fig 1 .7), clearly revealing that changes in DNA methylation at gene promoters are not systematically associated with changes in gene expression [START_REF] Yang | Whole-genome DNA methylation patterns and complex associations with gene structure and expression during flower development in Arabidopsis[END_REF]. This analysis also revealed that DMRs were more abundant in gene body than in promoter, and it seems that part of the DMR localized in gene-body was associated with differential expression, indicating that the role of gene body methylation in transcription regulation maybe more important than initially thought.

These results suggest that specific changes in DNA methylation could be important for the regulation of gene expression in relation to developmental phase change. This hypothesis is further demonstrated by the analysis of mutants impaired in DNA methylation function. As illustrated in the following part, through a few examples. In Arabidopsis, mutations affecting maintenance of CG methylation (met1-1, met1-2, and met1-3) are recessive [START_REF] Kankel | Arabidopsis MET1 Cytosine Methyltransferase Mutants[END_REF][START_REF] Saze | Maintenance of CpG methylation is essential for epigenetic inheritance during plant gametogenesis[END_REF]. As expected, the plants impaired in MET1 function (mutants or antisens plants) are characterized by a decrease in CG methylation. The more affected plants show pleiotropic developmental defects including reduced apical dominance, smaller plant size, altered leaf size and shape, decreased fertility and altered flowering time [START_REF] Finnegan | Reduced DNA methylation in Arabidopsis thaliana results in abnormal plant development[END_REF][START_REF] Jacobsen | Ectopic hypermethylation of flower-specific genes in Arabidopsis[END_REF]. The late-flowering phenotype is present in met1 heterozygous Arabidopsis plants, and is even more severe in a met1 homozygote background. This phenotype is caused by the hypomethylation of the FWA gene, which controls Arabidopsis flowering time and contains direct-repeats in its promoter [START_REF] Kankel | Arabidopsis MET1 Cytosine Methyltransferase Mutants[END_REF][START_REF] Saze | Maintenance of CpG methylation is essential for epigenetic inheritance during plant gametogenesis[END_REF] .

The knock out of the gene responsible for CG maintenance has a much more severe impact on plant development in rice. Mutation affecting the major CG methyltransferase gene, OsMET1-2, leads to severe defects in seed development and vegetative growth leading to seedlings swift necrotic death [START_REF] Hu | Mutation of a major CG methylase in rice causes genome-wide hypomethylation, dysregulated genome expression, and seedling lethality[END_REF]. This suggests that although DNA methylation in a CG context is conserved in plants its role during plant development may vary among different plant species.

b-mutants affected in non CG methylation

In Arabidopsis drm1 drm2 double mutants show no morphological defects [START_REF] Cao | Role of the Arabidopsis DRM Methyltransferases in De Novo DNA Methylation and Gene Silencing[END_REF][START_REF] Kankel | Arabidopsis MET1 Cytosine Methyltransferase Mutants[END_REF], although DRM2 was shown to have an essential function in the establishment of DNA methylation at genes such as FWA and SUPERMAN (SUP) [START_REF] Cao | Role of the Arabidopsis DRM Methyltransferases in De Novo DNA Methylation and Gene Silencing[END_REF]. Cmt3 mutants also display a wild-type morphology, even though it was found that CMT3 plays an important role in hypermethylation of the promoter of SUP gene in the CHG context, in met1 mutants [START_REF] Lindroth | Requirement of CHROMOMETHYLASE3 for Maintenance of CpXpG Methylation[END_REF].

On the other hand, drm1drm2cmt3 (ddc) triple mutant plants show pleiotropic effects on plant development. Interestingly, some of the developmental alterations observed in met1 mutants were not seen in ddc mutants, as for example, the late flowering phenotype, suggesting that CG and non CG methylation may control different aspects of plant development [START_REF] Cao | Role of the Arabidopsis DRM Methyltransferases in De Novo DNA Methylation and Gene Silencing[END_REF].

The analysis of rice and maize mutants showed that alteration of DNA methylation in crop species may have stronger deleterious effects than in Arabidopsis. For example, in rice, knockdown of OsDRM2 [START_REF] Moritoh | Targeted disruption of an orthologue of DOMAINS REARRANGED METHYLASE 2, OsDRM2, impairs the growth of rice plants by abnormal DNA methylation[END_REF], OsDCL3a [START_REF] Wei | Dicer-like 3 produces transposable element-associated 24-nt siRNAs that control agricultural traits in rice[END_REF], or OsCMT3 [START_REF] Cheng | Loss of function mutations in the rice chromomethylase OsCMT3a cause a burst of transposition[END_REF] causes pleiotropic developmental defects, unlike mutation of their respective homologous gene in Arabidopsis. This suggests DNA methylation in crop plants with complex genome components may play more important role than in Arabidopsis.

DNA methylation under environmental stress

Environmental stress such as salt, drought and other biotic and abiotic factors represent serious challenges for plant breeding as they may impact plant growth, as well as yield and product quality. Recent studies have highlighted the importance of DNA methylation in the regulation of gene expression under biotic and abiotic responses, and also have suggested that DNA methylation may play a role in stress memory.

a-Role of DNA methylation in abiotic stress response

Several studies have described changes in DNA methylation patterns in responses to abiotic stresses. For example, using a methylation-sensitive amplification polymorphism (MSAP) approach, [START_REF] Gayacharan | Epigenetic responses to drought stress in rice (Oryza sativa L.)[END_REF] found that under drought stress, drought-susceptible and drought-tolerant rice genotypes were characterized by different evolutions in DNA methylation level, which was evaluated as a methylation percentage. Furthermore, they showed that the yield and panicle weight were negatively correlated with methylation percentage in rice under drought stress, these changes in DNA methylation correspond to the activation of stress-related genes [START_REF] Gayacharan | Epigenetic responses to drought stress in rice (Oryza sativa L.)[END_REF].

You have other recent articles showing changes in the methylome in response to stress. Other articles show that rice plants that represent different tolerance to stress have different methylome consistent with a role of DNA methylation in the adaptation to stress.

b-Role of DNA methylation in stress memory (abiotic stress)

Plants that have experienced a stress become more tolerant to future stressful conditions, through the acquisition of stress memory. In some cases, this memory is transmitted to the next generations. The molecular mechanisms underlying the memory of stress and its transgenerational inheritance are not well understood but some reports suggest that epigenetic mechanisms may be involved (for reviews, see: [START_REF] Iwasaki | Epigenetic memory in plants[END_REF][START_REF] Bilichak | Transgenerational response to stress in plants and its application for breeding[END_REF].

Most of the studies arguing for a role of DNA methylation in stress memory are based on the demonstration of a correlation between changes in DNA methylation and stress tolerance.

In some reports, this correlation was based on the comparison of different generations of plants submitted or not to stress. As an illustration two studies using rice could be mentioned: nitrogen deficiency and heavy metal stress were shown to induce modifications in DNA methylation patterns, which were partly inherited in the following generations. The inheritance of the modifications was correlated with an enhanced stress tolerance [START_REF] Kou | Heritable alteration in DNA methylation induced by nitrogendeficiency stress accompanies enhanced tolerance by progenies to the stress in rice (Oryza sativa L.)[END_REF] [START_REF] Ou | Transgenerational Inheritance of Modified DNA Methylation Patterns and Enhanced Tolerance Induced by Heavy Metal Stress in Rice[END_REF].

As an alternative, the correlation between changes in DNA methylation and stress tolerance was demonstrated through the comparison of different genotypes characterized by contrasted levels of stress tolerance. For example, using an integrated approach combining BS-SEQ and RNA-SEQ, [START_REF] Garg | Divergent DNA methylation patterns associated with gene expression in rice cultivars with contrasting drought and salinity stress response[END_REF] compared the methylomes of different rice cultivars with contrasted sensitivity to drought and salinity stress. They identified a high number of differentially methylated regions (DMR) among the different cultivars and found that the distribution of many of these DMR was associated with differential expression of genes important for abiotic stress response. Moreover, smRNA abundance was positively correlated with hypermethylated regions [START_REF] Garg | Divergent DNA methylation patterns associated with gene expression in rice cultivars with contrasting drought and salinity stress response[END_REF]. This analysis suggests that long term adaptation of plant to abiotic stress involves modifications in DNA methylation patterns responsible for the regulation of the expression of a specific set of stressresponsive genes.

Using a completely different experimental approach, [START_REF] Shen | Natural CMT2 Variation Is Associated With Genome-Wide Methylation Changes and Temperature Seasonality[END_REF] also obtained results suggesting a role for DNA methylation in long term adaptation. Using a large collection of Arabidopsis thaliana accessions adapted to a wide range of climactic conditions, they performed a genome-wide association analysis, in order to identify loci where the alleles tolerate different climate ranges. Their study revealed that the temperature seasonality is correlated with a specific allele of the CMT2 gene. The reference WT CMT2 allele is mainly found in species growing in areas with less seasonal variability in temperatures, whereas the alternative CMT2 allele exists in both stable and variable regions. Shen et al also demonstrated that Arabidopsis cmt2 mutants display an increased tolerance to heat-stress. Altogether their results suggest that genetic modifications responsible for changes in DNA methylation mechanisms (CMT2-related functions) may participate in natural adaptation to variable temperatures [START_REF] Shen | Natural CMT2 Variation Is Associated With Genome-Wide Methylation Changes and Temperature Seasonality[END_REF].

c-Role of DNA methylation in biotic stress response

The modulation of DNA methylation not only appears to be important for abiotic stress response, but also for biotic stress response. For example, [START_REF] Akimoto | Epigenetic Inheritance in Rice Plants[END_REF] found that experimentally hypomethylated rice was less susceptible to the infection with the pathogen Xantomonas oryzae pv. oryzae. This enhanced tolerance was correlated with an increase in the expression of Xa21G coding for the Xa21-like protein, known to confer resistance to X. oryzae pv. oryzae. The difference in gene expression was associated with a difference in Xa21G promoter methylation: whereas Xa21G promoter was heavily methylated in the control plants, it was almost devoid of methylcytosine in the hypomethylated plants. Acquisition of disease resistance, and promoter hypomethylation were stably inherited, indicating that reprogramming DNA methylation at some loci is an important mechanism for plant defense [START_REF] Akimoto | Epigenetic Inheritance in Rice Plants[END_REF]. This hypothesis was confirmed by [START_REF] Dowen | Widespread dynamic DNA methylation in response to biotic stress[END_REF] in Arabidopsis. Mutants globally defective in maintenance of CG methylation (met1-3) or non-CG methylation (ddc = drm1-2 drm2-2 cmt3-11) were exposed to a bacterial pathogen (P. syringae). All mutants showed global DNA demethylation and an increased resistance to P. syringae. Methylomes were obtained from noninfected and infected plants, revealing many different DMRs, corresponding both to increase or decrease in DNA methylation mainly in CG and CHH contexts. Many infection-related DMRs were associated with differentially expressed genes (DEGs), which were characterized by a strong enrichment for genes involved in plant defense. Moreover, the DEGs associated with hypomethylated DMR tended to be constitutively mis-expressed in met1-3 and ddc mutants, consistent with the increased tolerance of these mutants to P. syringae [START_REF] Dowen | Widespread dynamic DNA methylation in response to biotic stress[END_REF].

III. DNA demethylation in plants

Cytosine methylation of genomic DNA is reversible through DNA demethylation. In plants, DNA demethylation can be achieved passively, when maintenance of methylation after DNA replication is not operating, or actively, by replication-independent processes.

Passive DNA demethylation in plants

Passive demethylation occurs for newly synthesized DNA during replication if the new DNA is not targeted by DNA methyltransferase [START_REF] Agius | Role of the Arabidopsis DNA glycosylase/lyase ROS1 in active DNA demethylation[END_REF].

Is there any situation where this has been described before in animals and plants. If yes you should add a couple of sentence to explain that

Active DNA demethylation in plants

Enzymes involved in DNA demethylation in plants

The first DNA demethylases to be characterized, AtROS1 and DEMETER, were identified in 2002 in Arabidopsis (Choi et al., 2002;Gong et al., 2002). AtROS1 was isolated during a screening for Repressor of Silencing (ROS): ros1 mutants were shown to cause the silencing of a transgene and of a homologous endogenous gene that were originally active. This silencing was correlated with DNA hypermethylation at the affected loci (Gong et al., 2002). Demeter mutants were isolated in the frame of a screen for genes controlling seed viability by their maternal allele (Choi et al., 2002). DEMETER was shown to be expressed exclusively in the central cell of the female gametophyte and in seeds, and to be required for the activation of MEDEA expression in the central cell and in the endosperm. Since 2002, two additional DNA demethylases were described in Arabidopsis, DEMETER-LIKE 2 (AtDML2), DEMETER-LIKE 3 (AtDML3) (Penterman et al., 2007b;[START_REF] Ortega-Galisteo | Arabidopsis DEMETER-LIKE proteins DML2 and DML3 are required for appropriate distribution of DNA methylation marks[END_REF], whereas very few functional studies were performed in other plant species [START_REF] La | A 5-methylcytosine DNA glycosylase/lyase demethylates the retrotransposon Tos17 and promotes its transposition in rice[END_REF].

Machinery of active DNA demethylation in plants

Strong evidence supports that DNA glycosylases-lyases, also called DEMETER-like DNA demethylases, can catalyze the removal of methylated cytosine efficiently through a Base Excision Repair pathway (BER process) (Gong et al., 2002;[START_REF] Gehring | DEMETER DNA Glycosylase Establishes MEDEA Polycomb Gene Self-Imprinting by Allele-Specific Demethylation[END_REF]. DNA demethylases are bifunctional enzymes, which possess both DNA glycosylase and apurinic/apyrimidinic (AP) lyase activities. Four steps were shown to be involved in the BER process: (I) DNA demethylase with DNA glycosylase activity cleaves the phosphodiester backbone at the 5-meC site, generating an abasic site. (II) DNA demethylase with AP lyase activity subsequently nicks the DNA to generate a primary 5Mc excision product, 3'-PUA, as intermediate by β-elimination, or go directly δelimination to generate 3'-phosphate. (III) An AP endonuclease converts the intermediate to 3'-OH to generate a single nucleotide gap. (IV) The gap is repaired by a DNA polymerase and a DNA ligase by adding an unmethylated cytosine. (V) Finally, this biochemical process results in a net loss of cytosine methylation (Fig 1 .8) (Penterman et al., 2007b;Law and Jacobsen 2010;Wu and Zhang 2010) . Base excision repair (BER) through direct excision of 5-methylcytosine (5meC). Initiation of the BER pathway can be carried out by a glycosylase that directly excises 5meC to generate an abasic (apurinic and apyrimidinic (AP)) site. The DNA backbone is nicked by an AP lyase (or by the glycosylase itself if it is bifunctional). The 3′ sugar group is then cleaved by an AP endonuclease and the resulting single nucleotide gap is filled in with an unmethylated C by an unknown polymerase and ligase. It has been well established in plants that the demeter (DME; also known as repressor of silencing 1 (ROS1)) family of enzymes can carry out the 5meC glycosylase reaction. Figure is adapted from Wu and Zhang (2010).

The different components that participate in active DNA demethylation have been well defined. At step (III), Arabidopsis AP endonucleases family members APE1L and ARP are capable of processing the 3'PUA to generate a 3'-OH or either use ARP or a DNA 3' phosphatase ZDP to convert δ-elimination product to 3'-OH [START_REF] Lee | AP endonucleases process 5-methylcytosine excision intermediates during active DNA demethylation in Arabidopsis[END_REF]. DNA ligase LIG1 was also identified as the major DNA ligase that complete the BER pathway in active DNA demethylation [START_REF] Córdoba-Cañero | Arabidopsis ARP endonuclease functions in a branched base excision DNA repair pathway completed by LIG1[END_REF].

All four DNA demethylases from Arabidopsis can target both symmetrical cytosine CG, CHG and asymmetrical cytosine CHH. It is worth pointing out that DME and ROS1 can also remove thymine, but not uracil, and seems to show a preference for CG context [START_REF] Morales-Ruiz | DEMETER and REPRESSOR OF SILENCING 1 encode 5methylcytosine DNA glycosylases[END_REF].

How DNA demethylases are guided to their target loci, is so far not known. However recent studies suggested that specific combinations of epigenetic marks may contribute to the recruitment of DNA demethylases to their targets (Li et al., 2015b). This hypothesis is based on the characterization of a protein complex involved in the repressor of silencing function through the active demethylation pathway, which recognizes and binds to specific epigenetic marks, and is responsible for the acetylation of histone H3. This complex has been shown to contain 4 proteins: MBD7, IDM1, IDM2 and IDL1. MBD7 is a methyl-CpG-Binding protein which is enriched at highly methylated, CG-dense sites throughout the genome. It was shown to prevent aberrant spreading of DNA methylation [START_REF] Wang | Methyl-CpG-Binding Domain Protein MBD7 Is Required for Active DNA Demethylation in Arabidopsis[END_REF]. IDM1 is a histone acetyltransferase which binds methylated DNA at chromatin sites lacking histone H3K4me2/H3K4me3 and acetylates H3 [START_REF] Qian | A Histone Acetyltransferase Regulates Active DNA Demethylation in Arabidopsis[END_REF]. IDM2 and IDM2-like protein (IDL1) are two related α-crystalline domain proteins; IDM2 was shown to be required for the full activity of IDM1 in vivo. ROS5 is a small heat shock protein [START_REF] Zhao | REPRESSOR OF SILENCING5 Encodes a Member of the Small Heat Shock Protein Family and Is Required for DNA Demethylation in Arabidopsis[END_REF], which interacts with MBD7 [START_REF] Wang | Methyl-CpG-Binding Domain Protein MBD7 Is Required for Active DNA Demethylation in Arabidopsis[END_REF] and with IDM1. According to Li et al (2015), the histone acetyltransferase complex creates a feasible chromatin environment to recruit DNA demethylases, which then starts the active DNA demethylation process (Fig 1.9).

In addition to these essential protein factors, a component of the cytosolic iron-sulfur cluster assembly (CIA) pathway, MET18, an anti-silencing factor was shown to interact with ROS1. This suggests that the CIA pathway may play a role in active demethylation, but how MET18 is linked to ROS1 is still unclear [START_REF] Duan | MET18 Connects the Cytosolic Iron-Sulfur Cluster Assembly Pathway to Active DNA Demethylation in Arabidopsis[END_REF]. Another study also identified that, ROS3, a RNAbinding protein, may function in a pathway similar to ROS1, but the link between ROS3 and DNA demethylation needs to be further verified [START_REF] Zheng | ROS3 is an RNA-binding protein required for DNA demethylation in Arabidopsis[END_REF]. Parental imprinting occurs in the endosperm in plants, and is essential for embryo and seed development. Parental imprinting at specific loci means that only one allele is expressed, which is either of maternal or of paternal origin. [START_REF] Bauer | Genome demethylation and imprinting in the endosperm[END_REF] have reviewed imprinted genes in Arabidopsis. Recent work indicate that between 75 and 200 genes are imprinted in the endosperm depending on the species analyzed and sequencing depth and potential co,ntaminations with seed coat or embryo tissues ( For a review, see Ghering et Satyaki 2017) Well characterized imprinted genes in Arabidopsis include FWA, MEA, FIS2, and PHERES1, which are specifically expressed from the maternal genome in the endosperm while the alleles from the paternal genome are silenced. Imprinted genes are regulated on an epigenetic level, involving DNA methylation, DNA demethylation and/or histone modification particularly the trimethylation of lysine 27 of histone H3 which is mediated by the PRC2 complex [START_REF] Bauer | Genome demethylation and imprinting in the endosperm[END_REF]. It was suggested that passive DNA demethylation could also have a function in gene imprinting [START_REF] Bauer | Genome demethylation and imprinting in the endosperm[END_REF]. In most cases the epigenetic mechanisms responsible for gene imprinting are implemented during the formation of the gametophytes, leading to different epigenetic status of the parental alleles in each gamete. The epigenetic status of each allele persists beyond fertilization, resulting in differential expression of the parental alleles in the endosperm.

In Arabidopsis, DEMETER (DME) has been shown to play an important role for imprinting of specific genes as for example MEDEA (MEA). MEA is a maternally expressed gene that controls seed development, and is specifically expressed in the female gametophyte central cells and in seeds [START_REF] Xiao | Imprinting of the MEAPolycomb Gene Is Controlled by Antagonism between MET1 Methyltransferase and DME Glycosylase[END_REF]. The current model suggests that MEA is constitutively repressed in vegetative tissue through MET1-dependent methylation. During the formation of the female gametophyte, DEMETER removes the methylation marks at the maternal allele in the central cell, which results in its expression (Choi et al., 2002;[START_REF] Xiao | Imprinting of the MEAPolycomb Gene Is Controlled by Antagonism between MET1 Methyltransferase and DME Glycosylase[END_REF]. During male gametogenesis the repression of the paternal allele is maintained owing to the lack of DME, and to the Polycomb complex PRC2 activity which is responsible for the addition of repressive H3K27me3 marks at MEA promoter [START_REF] Gehring | DEMETER DNA Glycosylase Establishes MEDEA Polycomb Gene Self-Imprinting by Allele-Specific Demethylation[END_REF]. Additional DNA methylation-independent mechanisms may also be involved as suggested by the identification of a sequence in MEA promoter which is necessary and sufficient to mediate MEA imprinting in a DME and MET1-independent way [START_REF] Wöhrmann | Identification of a DNA methylation-independent imprinting control region at the Arabidopsis MEDEA locus[END_REF]. Another imprinted gene, FWA, which is only expressed in the female gametophyte and in the endosperm, plays key functions in the control of flowering time. The imprinting of this maternally expressed gene is also regulated by DME [START_REF] Soppe | The Late Flowering Phenotype of fwa Mutants Is Caused by Gain-of-Function Epigenetic Alleles of a Homeodomain Gene[END_REF]Choi et al., 2002;[START_REF] Gehring | DEMETER DNA Glycosylase Establishes MEDEA Polycomb Gene Self-Imprinting by Allele-Specific Demethylation[END_REF][START_REF] Wöhrmann | Identification of a DNA methylation-independent imprinting control region at the Arabidopsis MEDEA locus[END_REF].

Comparison of endosperm and embryo methylomes in Arabidopsis, rice and maize have revealed that imprinting may affect more than 100 genes in each of these species (for a review, (Zhang et al., 2013a).

Genome-wide analyses have also shown that DNA hypomethylation in the endosperm was not restricted to loci near imprinted genes, but rather occurred in TE and repeat sequences throughout the genome of Arabidopsis [START_REF] Gehring | Extensive demethylation of repetitive elements during seed development underlies gene imprinting[END_REF]Hsieh et al., 2009), rice [START_REF] Zemach | Local DNA hypomethylation activates genes in rice endosperm[END_REF], maize [START_REF] Lu | Genome-Wide Epigenetic Regulation of Gene Transcription in Maize Seeds[END_REF] and Castor Bean [START_REF] Xu | Genomic DNA Methylation Analyses Reveal the Distinct Profiles in Castor Bean Seeds with Persistent Endosperms[END_REF]. In Arabidopsis DNA global hypomethylation was also shown to occur in the gametophyte central cell and to be DEMETERdependent [START_REF] Ibarra | Active DNA Demethylation in Plant Companion Cells Reinforces Transposon Methylation in Gametes[END_REF]. Altogether these results suggest that gene imprinting may arise in central cell when demethylation events targeting repeats or transposon also affect the expression of neighboring genes.

Two functions were suggested for the decrease in DNA methylation in the central cell and in the endosperm: [START_REF] Law | Establishing, maintaining and modifying DNA methylation patterns in plants and animals[END_REF] it may play a role in endosperm biogenesis. Indeed [START_REF] Zemach | Local DNA hypomethylation activates genes in rice endosperm[END_REF] have shown that genes coding for major storage proteins and starch synthesizing enzymes are hypomethylated in rice endosperm [START_REF] Zemach | Local DNA hypomethylation activates genes in rice endosperm[END_REF]. (2) The decrease in DNA methylation may favor siRNA biogenesis, which would diffuse to neighboring cells, egg cell in the gametophyte, and embryo cells in the seed. There siRNAs would enhance TE and repeat silencing through RdDM, providing an efficient protection against the deleterious effects of TE mobilization (review: (Zhang et al., 2013a)).

Other functions of active DNA demethylation in plant

AtROS1, AtDML2 and AtDML3 function as genome wide DNA demethylases that remove 5mC marks at sites located at the 3' and 5' end of genes, in order to protect genes from potentially deleterious methylation. Indeed nearby TE or repeat sequences are common features of DML gene targets (Penterman et al., 2007a). But ros1, dml2, dml3 single, double or triple mutants showed little or no developmental alterations, suggesting that the functions of DNA demethylases are not essential for development in this species Yu (Yu et al., 2013).

Only recently, Yamamuro found that ros1 mutant and ros1 dml2 dml3 (rdd) triple mutant show overproduction of stomatal lineage cells leading to a small-cell-cluster phenotype (Fig 1 .10) (Yamamuro et al., 2014). Yamamuro et al (2014) suggested that ROS1 negatively regulates the bHLH protein SPCH to prevent establishing the stomatal lineage cells through a control of EPF2 expression. EPF2 is known to negatively regulate SPCH function and ros1 phenotype is very similar to EPF2 loss-of-function phenotype (Yamamuro et al., 2014). Indeed EPF2 was shown to be repressed in ros1 and rdd mutants due to an increase in the methylation status of its promoter. The reduction in EPF2 expression was shown to be responsible for the small-cell-cluster phenotype in ros1 and rdd mutants. Yamamuro et al (2014) proposed a model where EPF2 expression in the WT is regulated through the antagonist actions of RdDM and active demethylation, because of the presence of a TE in the upstream region of its promoter, approximately 1.5 kb 5' from its transcriptional start site. The TE is targeted by RdDM and thus methylated, this methylation tends to spread from the TE into EPF2 promoter but ROS1 ensures EPF2 expression by erasing the spreading DNA methylation. It is unknown how the balance between DNA methylation and demethylation activities is achieved.

Interestingly ROS1 is also located in the vicinity of a TE, and was shown to be regulated through the double action of DNA methylation and demethylation. But each activity has the opposite outcome on ROS1 expression, compared to typical targets of these processes: ROS1 expression is promoted by DNA methylation and inhibited by DNA demethylation [START_REF] Williams | Methylation-Sensitive Expression of a DNA Demethylase Gene Serves As an Epigenetic Rheostat[END_REF]. [START_REF] Williams | Methylation-Sensitive Expression of a DNA Demethylase Gene Serves As an Epigenetic Rheostat[END_REF] propose that owing to this specific regulation, ROS1 may play a role in DNA methylation homeostasis at the genome wide scale scale. Another study suggests that AtROS1 may be involved in stress response. [START_REF] Bharti | AtROS1 overexpression provides evidence for epigenetic regulation of genes encoding enzymes of flavonoid biosynthesis and antioxidant pathways during salt stress in transgenic tobacco[END_REF] produced transgenic tobacco plants over-expressing AtROS1 and submitted them to salt stress. AtROS1 overexpression was correlated to an increase in the expression of genes encoding enzymes involved in flavonoid biosynthesis and antioxidant pathways and these upregulations were linked to a decrease in the methylation status of their promoters. This suggests that active DNA demethylation may participate in the induction of secondary metabolites synthesis in response to salt stress. However the gene expression levels were only 5-6 times higher in transgenics compared to WT. Furthermore, the secondary metabolites (flavonoids) were not measured, therefore further experiments are necessary to confirm this conclusion [START_REF] Bharti | AtROS1 overexpression provides evidence for epigenetic regulation of genes encoding enzymes of flavonoid biosynthesis and antioxidant pathways during salt stress in transgenic tobacco[END_REF].

AtROS1 was shown to have a function in plant defense against pathogens, through the regulation of some TEs related genes. Yu et al (2013) found that AtROS1 can restrict the multiplication and vascular propagation of Pseudomonas syringae in leaves through the induction of some immune related genes that have repetitive sequence in their promoters. This process is tightly linked with the RdDM pathway (Yu et al., 2013).

IV. The importance of epialleles in plants

Heritable epigenetic variants of genes, termed epialleles, are associated with heritable changes in DNA expression without any alteration of the DNA sequence. Epialleles can broaden genetic diversity and may provide a new source of beneficial traits for crop breeding. Assessing the importance of methylated epialleles in plant population require the following determination: (i) the extent of variation in methylation patterns among individuals within a population; (ii) the extent to which natural methylation variants are stably inherited. However, only very few epialleles have been identified until now.

Different epimutants were isolated and characterized in Arabidopsis. The phenotype of the clk epimutant (clark kent) is similar to the phenotype of the superman (sup) mutant, characterized by an increased number of stamens and abnormal fused carpels. Indeed SUP was shown to be modified by an epimutation in the clk epimutant: its promoter is hypermethylated compared to the WT [START_REF] Jacobsen | Hypermethylated SUPERMAN Epigenetic Alleles in Arabidopsis[END_REF]. Another well-known epimutant in Arabidopsis is fwa, which shows late flowering. This phenotype is due to hypomethylation at two direct repeat elements upstream of the FWA locus [START_REF] Kinoshita | One-Way Control of FWA Imprinting in Arabidopsis Endosperm by DNA Methylation[END_REF].

However, the first natural epimutant was found in Linaria vulgaris. The lcyc epimutant shows an hypermethylated region in the promoter of lCYC (Linaria cyloidea-like), which encodes a transcription factor that controls the floral development process. The lcyc phenotype can spontaneously reverse, which corresponds to a change in the methylation status of the promoter (Cubas et al., 1999)(Fig 1.11).

Currently, three natural epialleles were found in rice, Epi-d1, Epi-df and Epi-rav6 (Zhang (Miura et al., 2009;[START_REF] Zhang | Identification and Characterization of an Epi-Allele of FIE1 Reveals a Regulatory Linkage between Two Epigenetic Marks in Rice[END_REF][START_REF] Zhang | Epigenetic Mutation of RAV6 Affects Leaf Angle and Seed Size in Rice[END_REF]. All of them are associated with defects in important agronomic trait. Epi-d1 is a natural mutant, which shows a metastable dwarf phenotype, although this phenotype is chimeric. This is caused by an hypermethylation in the promoter of DWARF1 [START_REF] Miura | A metastable DWARF1 epigenetic mutant affecting plant stature in rice[END_REF]. Epi-df mutant shows a dwarf phenotype together with various floral defects. In this case, the phenotype is caused by an hypomethylation in the promoter of FIE1 (Fertilization-independent endosperm1), coding for one of the component of the Polycomb Repressive complex 2. As expected for a plant affected in the expression of a PcG gene, it was found that H3K27me3 levels were altered in Epi-df mutant [START_REF] Zhang | Identification and Characterization of an Epi-Allele of FIE1 Reveals a Regulatory Linkage between Two Epigenetic Marks in Rice[END_REF]. More recently, [START_REF] Zhang | Epigenetic Mutation of RAV6 Affects Leaf Angle and Seed Size in Rice[END_REF] isolated a spontaneously occurring epimutant, Epi-rav6, with large leaf angle and small seed size. These defects were caused by the ectopic expression of RAV6, coding for a B3 DNA-binding domain containing protein involved in brassinosteroid homeostasis. The alteration in RAV6 expression was furthermore linked to the hypomethylation of its promoter [START_REF] Zhang | Epigenetic Mutation of RAV6 Affects Leaf Angle and Seed Size in Rice[END_REF].

In tomato, an epimutant has also been isolated and studied, the well-known cnr epimutant which produces fruits that never ripe (Fig 1.11). This non-ripening phenotype was correlated with the hypermethylation of the promoter of CNR, which codes for a major regulator of fruit ripening. Interestingly, this epi-phenotype is very strong and stable (Manning et al., 2006) .

Altogether, these findings show that epialleles may have a substantial effect on plant phenotype. Some epialleles may be associated with critically important agricultural traits. So epimutants screening represents an interesting and powerful tool for plant breeding.

V. Physiological changes during tomato fruit ripening

Tomato (Solanum lycopersicum) is an important crop and a model plant for fleshy fruits development and ripening. After fertilization, tomato fruit development proceeds in two main phases that precede fruit ripening. Early fruit development events correspond to fruit growth mediated by an active cell division phase followed by an important increase in cell size associated to the endoreduplication process. Fruit growth essentially ends at the so-called "mature-green stage", when the fruit has acquired its final size, but is still hard, green and acid-tasting. The fruit ripening process then takes place. Several dramatic physiological and metabolic changes occur at the fruit development to ripening transition and during ripening: (i) transition from a partly photosynthetic metabolism to a completely heterotrophic metabolism; (ii) differentiation of chloroplasts into chromoplasts; (iii) changes in cell wall composition, and in sugar and organic acids accumulation, and the dramatic accumulation of carotenoids mainly lycopene (for a review see [START_REF] Tohge | On the regulation and function of secondary metabolism during fruit development and ripening[END_REF]). Altogether these modifications determines nutrient accumulation in the fruits, hence the fruit nutritional quality, motivating intense research efforts to decipher the regulation mechanisms underlying ripening. The availability of extensive genetic, molecular and genomic resources for tomato has contributed to a better understanding of the ripening control. Ripening was shown to be under a strict genetic control in relation with hormonal regulations,

CNR mutant WT

A B

involving especially ethylene [START_REF] Giovannoni | Fruit ripening mutants yield insights into ripening control[END_REF]. Three transcription factors have been identified as central regulators for fruit ripening: RIN (ripening inhibitor), NOR (non-ripening) and CNR (colorless non-ripening) (Giovannoni 2004;[START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF]Vrebalov, et al. 2002) (Fig 1.12). Below, I will describe some of the major physiological events associated with tomato fruit ripening

Tomato fruit softening

Decrease in firmness during ripening involves a coordinated series of modifications of the primary cell wall and middle lamella, resulting in a weaken structure. Since fruit softening is the major determinant of shelf life, understanding the mechanisms responsible for cell wall modifications during ripening is of economic importance.

In tomato, a number of cell wall structure-related genes are expressed during fruit ripening, including more than 50 structural genes encoding cell wall modifying proteins are expressed during fruit development and ripening process [START_REF] Uluisik | Genetic improvement of tomato by targeted control of fruit softening[END_REF]. A few studies have investigated the role of individual cell wall structure-related gene in fruit ripening [START_REF] Smith | Down-Regulation of Tomato β-Galactosidase 4 Results in Decreased Fruit Softening[END_REF][START_REF] Brummell | PRIMARY CELL WALL METABOLISM DURING FRUIT RIPENING[END_REF][START_REF] Godoy | Galacturonosyltransferase 4 silencing alters pectin composition and carbon partitioning in tomato[END_REF], many of them have focused on genes related to pectin biosynthesis, such as PG (POLYGALACTURONASE), whose expression shows a sharp increase during ripening and results in substantial cell wall pectinase activity, during fruit softening [START_REF] Dellapenna | Transcriptional Analysis of Polygalacturonase and Other Ripening Associated Genes in Rutgers, rin, nor, and Nr Tomato Fruit[END_REF]. However specific repression or induction of PG in fruit does not alter fruit softening, indicating that the polygalacturonase activity is not sufficient for fruit softening. It may associate with some other factors to control fruit softening (Giovannoni 2004). The role of another enzyme, the galacturonosyltransferase (GAUT) also involved in pectin biosynthesis, was analyzed. GAUT4 RNAi mutant showed altered pectin composition coincided with an increase in firmness. This indicates that GAUT4 plays a role in fruit softening during fruit ripening, although it was also shown to interfere with carbon metabolism, partitioning and allocation and globally affect plant development [START_REF] Godoy | Galacturonosyltransferase 4 silencing alters pectin composition and carbon partitioning in tomato[END_REF]. More recently, [START_REF] Uluisik | Genetic improvement of tomato by targeted control of fruit softening[END_REF] found that silencing PI

Fruit ripening

encoding pectate lyase, also increased fruit firmness but without altering other aspects [START_REF] Uluisik | Genetic improvement of tomato by targeted control of fruit softening[END_REF]. Indeed, fruit ripening is also characterized by significant changes in changes in the βgalactose content of cell walls. At least seven tomato β-galactosidases (TBG1-7) are thought to play important roles during fruit development and maturation, but only suppression of TBG4 was associated with alteration of fruit firmness, which is associated to a reduced galactose loss. Downregulation of TBG1, 3 and 6 didn't lead to obvious phenotype on fruit ripening [START_REF] Eda | Structural and functional analysis of tomato β-galactosidase 4: insight into the substrate specificity of the fruit softening-related enzyme[END_REF]. The expression of TBG4 was shown to be related with the galactose content [START_REF] Eda | Structural and functional analysis of tomato β-galactosidase 4: insight into the substrate specificity of the fruit softening-related enzyme[END_REF]. Furthermore mutants impaired for expansion function, show delayed fruit ripening and softening, coincident with a modification of hemicellulose structure (Minoia et al., 2016). However, repression of the ripening-related endo-β-1,4-glucanases CEL1 or CEL2 did not change fruit softening. Impaired Exp1 show delayed fruit ripening and softening, which caused by the modification of hemicellulose structure. These studies suggest that several genes encoding cell wall modifying enzymes contribute to cell wall changes during fruit development and ripening. Fruit softening would thus be the result of the concerted action of numerous cell wall-modifying enzymes. The sum of each enzymatic activity could lead to extensive softening and, eventually, tissue disintegration. However, this process is still poorly understood, and requires more investigations.

Ethylene production

Basically, fruits can be categorized into two families depending on their ability to undergo a burst of ethylene production and an associated increase in respiration rate at the onset of ripening. Fleshy fruits such as, strawberry, grape and citrus don't go through this program for ripening: they are categorized as non-climacteric fruits. Contrarily, for tomato, which is as a typical example of climacteric fruit, the ripening process is linked to a dramatic increase of ethylene production and rises in respiration. Some other fruits, such as apple, peach and banana belong to this family, too Osorio et al (2013). Adenosyl L-Methionin (SAM) is the starting point of ethylene synthesis. SAM synthesis is made by the S-adenosyl-methionine (SAM) synthase which catalyzes the adenosylation of the Sulphur atom of methionine. Ethylene synthesis then occurs in two steps initiated by the conversion of SAM into 1 aminocyclopropane-1-carboxylic acid (ACC) followed by the transformation of ACC into ethylene respectively catalyzed by the ACC synthase (ACS) and the ACC oxidase (ACO). In tomato, 14 genes corresponding to putative ACS and 6 to putative ACO have been identified within the tomato genome sequence (Tomato Genome Consortium, 2012;Liu et al, 2015b). A subset of them are operating in fruits and participate either to the ethylene synthesis System 1, operating during early tomato fruit development, either to the system 2 which insures ethylene production during fruit ripening. ACS1A, ACO1, 3, 4 are the main genes participating to system 1 [START_REF] Barry | Ethylene and Fruit Ripening[END_REF][START_REF] Giovannoni | Molecular biology of ethylene during tomato fruit development and maturation[END_REF], whereas, ASC2, ACS4, ACO1 and ACO4 are involved in system 2. System 1 allows the synthesis of ethylene in developing fruits. At the mature green stage, ACS2 and ACS4 are induced and further stimulated by ethylene production, resulting in an auto-catalytic ethylene production. This leads to the repression of ACS1 and ACS6. In addition fruit ripening associated factors, including RIN, CNR play key roles in this process and are necessary for ethylene production at the onset of fruit ripening [START_REF] Giovannoni | Fruit ripening mutants yield insights into ripening control[END_REF].

Ethylene is then perceived by the ethylene receptor, ETR that initiates a signaling cascade that release the blocking of Ethylene Insensitive (EIN) by the Constitutive Triple-Response proteins (CTR). This starts a transcriptional cascade that is initiated by the stabilization of Insensitive3-Like1 (EIL1) that in turn activates the genes encoding the Ethylene Response factor, ERF (Solano et al., 1998). Finally ERF transcription factors control the expression of ethylene-regulated genes by binding to GCC-box type cis-elements (Liu et al., 2015b;[START_REF] Giovannoni | Molecular biology of ethylene during tomato fruit development and maturation[END_REF]. The genes involved in this process during fruit ripening have been identified and include CTR1, EIN2, EIN3/EIL1 and then the ERF family, which in turn control several genes determining various ripening-related traits, including color, firmness, aroma, taste and shelf life.

Color change: chlorophyll degradation and carotenoid synthesis

Tomato color change from green to red is the visible sign indicating the transition from development to ripening. The color change is associated with the degradation of chlorophylls and the shift of the carotenoid composition from lutein and neoxanthin to carotenes, mainly to lycopene and to a lower extend β-carotene.

Chlorophyll is responsible for the green color in the early stages of fruit ripening. The chlorophylls biosynthesis and degradation pathways have been well reviewed [START_REF] Tanaka | Chlorophyll metabolism[END_REF]. The chlorophyll a biosynthetic pathway starts from glutamate. In this phase, the synthesis of 5-aminolevulinic acid (ALA) by glutamyl-tRNA reductase (GluTR) and glutamate 1semialdehyde aminotransferase is a key control point. The interconversion of chlorophyll a to chlorophyll b, the so-called chlorophyll cycle, is catalyzed by the chlorophyllide a oxygenase (CAO). The degradation of chlorophyll a and chlorophyll b is a slow and important process, which corresponds to the transition of green fruit to ripening [START_REF] Tanaka | Chlorophyll a oxygenase (CAO) is involved in chlorophyll b formation from chlorophyll a[END_REF][START_REF] Tanaka | Chlorophyll metabolism[END_REF]. It was suggested that chlorophyll degradation is initiated by the reduction of chlorophyll b into chlorophyll a. This reduction step is catalyzed by non-yellow coloring 1 (NYC1), a chlorophyll b reductase. Mutation on NYC1 or NOL gene (NYC1-like) leads to non-ripening fruit, which always stays green [START_REF] Tanaka | Chlorophyll a oxygenase (CAO) is involved in chlorophyll b formation from chlorophyll a[END_REF][START_REF] Kusaba | Rice NON-YELLOW COLORING1 Is Involved in Light-Harvesting Complex II and Grana Degradation during Leaf Senescence[END_REF][START_REF] Horie | Participation of Chlorophyll b Reductase in the Initial Step of the Degradation of Light-harvesting Chlorophyll a/b-Protein Complexes in Arabidopsis[END_REF][START_REF] Sato | Two short-chain dehydrogenase/reductases, NON-YELLOW COLORING 1 and NYC1-LIKE, are required for chlorophyll b and light-harvesting complex II degradation during senescence in rice[END_REF]. Then chlorophyll a is degraded by sequential elimination of phytol and magnesium, respectively by a chlorophyllase (Chlase), and a Mg dechelatase, producing pheophorbide a (pheide a). Under the activity of pheide a oxygenase (PAO) and red chl catabolite (RCC) reductase, pheophorbide a is converted to primary fluorescent chl catabolite-1 (pFCC-1), which are finally transformed to nonfluorescent chl catabolites (NCCs) [START_REF] Pružinská | Chlorophyll Breakdown in Senescent Arabidopsis Leaves. Characterization of Chlorophyll Catabolites and of Chlorophyll Catabolic Enzymes Involved in the Degreening Reaction[END_REF].

Carotenoids are terpenoid derivatives that are synthesized in fruit tissue during fruit ripening. There are two major classes of carotenoids: (i) xanthophylls, as for example, violaxanthin and nexanthin, and, (ii) carotenes, such as lycopene and β-carotene (See review: [START_REF] Tohge | On the regulation and function of secondary metabolism during fruit development and ripening[END_REF]. In tomato fruits, there is a substantial accumulation of certain carotenoid pigments during the ripening process. Among thosehe dramatic accumulation of lycopene causes the color change from green to orange and red. Transcriptional regulation of the genes involved in carotenoid biosynthesis pathway has been well characterized and 22 genes were demonstrated to play a role in this process in tomato [START_REF] Fraser | Genetic engineering of carotenoid formation in tomato fruit and the potential application of systems and synthetic biology approaches[END_REF][START_REF] Nogueira | Subchromoplast Sequestration of Carotenoids Affects Regulatory Mechanisms in Tomato Lines Expressing Different Carotenoid Gene Combinations[END_REF]. Lycopene biosynthesis from two geranylgeranyl diphosphate molecules has been shown to proceed through the production of phytoene by the phytoene synthase (PSY1). This enzyme plays a key role in lycopene biosynthesis and it is highly induced during fruit ripening at the transcriptional level. Furthermore psy1 mutants show serious defects in carotenoid accumulation [START_REF] Bartley | A tomato gene expressed during fruit ripening encodes an enzyme of the carotenoid biosynthesis pathway[END_REF]Fray andGrierson, 1993, andFraser et al 2000). Several genes coding for enzymes acting upstream of lycopene are also induced during fruit ripening, concomitantly with the accumulation of lycopene [START_REF] Bartley | A tomato gene expressed during fruit ripening encodes an enzyme of the carotenoid biosynthesis pathway[END_REF]. On the contrary, genes coding for enzymes acting downstream of lycopene are mainly turned off during fruit ripening to allow the accumulation of lycopene. Lycopene accumulation in tomato fruits has been shown to be regulated by ethylene signaling and by the developmental regulators RIN, NOR and CNR [START_REF] Klee | Genetics and Control of Tomato Fruit Ripening and Quality Attributes[END_REF][START_REF] Seymour | Regulation of ripening and opportunities for control in tomato and other fruits[END_REF].

Primary metabolites changes during tomato fruit ripening

The combined analysis of tomato fruit transcriptome and metabolome shows that transcriptomic changes are less dramatically than variations in metabolites abundance, suggesting that posttranslational mechanisms dominate metabolic regulation (Carrari et al 2006). However, some strong relationships between ripening-associated transcripts and specific metabolite groups were found too, such as TCA-cycle organic acids and sugar phosphates.

The acid taste of tomato fruits is attributed mainly to organic acids, including citrate and malate. The levels of organic acid in TCA cycle tend to decrease along fruit development. These changes are largely caused by the changes in activity of TCA-cycle enzymes, most of which decline during the chloroplast-chromoplast transition in tomato fruit [START_REF] Bartley | A tomato gene expressed during fruit ripening encodes an enzyme of the carotenoid biosynthesis pathway[END_REF][START_REF] Schauer | Metabolic profiling of leaves and fruit of wild species tomato: a survey of the Solanum lycopersicum complex[END_REF]Carrari et al., 2006). As the precursor of aspartate, malate is an important metabolite for ethylene feedback regulation during tomato fruit ripening and is also an important contributor to starch accumulation. Earlier work showed that starch degradation is also one of the major changes for fruit transition from development to ripening. Starch metabolism has been well demonstrated to have a tense relation with AGPase activity, which is also controlled at the transcriptional level (Osorio et al., 2013a). Moreover, [START_REF] Centeno | Malate Plays a Crucial Role in Starch Metabolism, Ripening, and Soluble Solid Content of Tomato Fruit and Affects Postharvest Softening[END_REF] found that in tomato, malate is a key component in the redox regulation of AGPase. Inhibiting fruit-specific gene of mitochondrial MDH, major tomato fumarase, or cytosolic phosphoenolpyruvate carboxykinase (PEPCK), leads to a decrease in the content of transitory starch in the transgenic plants with the higher malate content. These findings suggested that malate may have an important regulatory function for starch biosynthesis [START_REF] Centeno | Malate Plays a Crucial Role in Starch Metabolism, Ripening, and Soluble Solid Content of Tomato Fruit and Affects Postharvest Softening[END_REF]Osorio et al., 2013b).

The balance and content between organic acids and sugars are important for high quality fruit [START_REF] Bastí As | Modulation of organic acids and sugar content in tomato fruits by an abscisic acid-regulated transcription factor[END_REF]. Glucose, fructose and sucrose are the major sugars after fruit ripening. The levels of fructose and glucose increase during fruit development and ripening, whereas the concentration of sucrose decreases during fruit development. The decrease of sucrose is caused by the activity of invertases, enzymes that hydrolyze sucrose to hexose and thus play a fundamental role in the energy requirements for plant growth and maintenance [START_REF] Dnfna Mirona | Sucrose uptake, invertase localization and gene expression in developing fruit of Lycopersicon esculentum and the sucrose-accumulating Lycopersicon hirsutum[END_REF]. Knock down of a specific gene encoding a sucrose invertase, Line5, induces an increase in the level of sucrose and a decrease in hexose content, resulting in smaller fruits [START_REF] Klann | Antisense acid invertase (TIV1) gene alters soluble sugar composition and size in transgenic tomato fruit[END_REF]. Transcription factors can also affect key primary metabolites. For example, in SlAREB1 overexpressors, citrate, malate, glutamate, glucose and fructose show higher accumulation levels in red mature fruit pericarp compared with those observed in antisense suppression lines. This suggests that an AREB-mediated ABA signal affects the metabolism of these compounds during the fruit developmental program, even if the fruit ripening wasn't affected in these transgenic plants [START_REF] Bastí As | Modulation of organic acids and sugar content in tomato fruits by an abscisic acid-regulated transcription factor[END_REF][START_REF] Tohge | On the regulation and function of secondary metabolism during fruit development and ripening[END_REF].

The transition from tomato fruit development to ripening involves a huge amount of protein degradation. (Carrari et al., 2006;[START_REF] Kahlau | Plastid Transcriptomics and Translatomics of Tomato Fruit Development and Chloroplast-to-Chromoplast Differentiation: Chromoplast Gene Expression Largely Serves the Production of a Single Protein[END_REF]. Therefore, most of the free amino acid contents tend to increase during fruit transition, such as glutamate, aspartate, although their contents are variable in different species. In particular, free glutamate of ripe tomato fruit occupies a central role in the metabolism of amino acid in plants [START_REF] Sorrequieta | Free amino acid production during tomato fruit ripening: a focus on l-glutamate[END_REF]. However, GABA was found to be one of the most abundant free amino acid in the pericarp of mature fruit and to show a rapidly decrease during ripening [START_REF] Takayama | How and why does tomato accumulate a large amount of GABA in the fruit?[END_REF].

VI. Role of DNA methylation / demethylation during fruit development and ripening

As mentionned above, DNA methylation participates in the control of plant development. Several lines of evidence further suggest that DNA methylation plays a role during fruit development and ripening.

The importance of epigenetic regulations in fruit was first suggested by the identification of the tomato epi-mutant Colorless non-ripening (Cnr) (Manning et al. 2006). More recently, several reports have described situations where a differential methylation pattern in fruits was associated with a change in fruit phenotype. For example, Telias et al (2011) have analyzed apple cultivars, such as 'Honeycrisp' or 'royal gala', that produce fruits characterized by striped color patterns. These patterns correspond to the presence of sectors of different colors, green or red, in the peel. The molecular analysis of the two types of sectors has revealed that the color difference is associated with different anthocyanin contents and with the differential expression of MYB10, which codes for a transcription factor that has a key role in anthocyanin accumulation (Telias et al., 2011). The difference in MYB10 expression was shown to depend on the methylation level in the promoter of MYB10, MYB10 promoter is more or less methylated depending on the peel areas (Fig 1.14). The origin of this methylation mosaic is not known. Similar results were obtained by comparing different pear fruits from the cultivar Max Red Bartlett producing both red-and greenskin fruits on the same tree [START_REF] Wang | The methylation of the PcMYB10 promoter is associated with green-skinned sport in Max Red Bartlett pear[END_REF], or by comparing yellow fruits from an apple somatic mutant, 'Blondee', with red-skin apples from its parent 'Kidd's-D8' [START_REF] El-Sharkawy | Transcriptome analysis of an apple (Malus × domestica) yellow fruit somatic mutation identifies a gene network module highly associated with anthocyanin and epigenetic regulation[END_REF]. Working on tomato, Quadrana et al ( 2014) found that the vitamin E content in fruit is correlated with the methylation level in the promoter of VTE3, which encodes a protein involved in vitamin E biosynthesis. Accordingly VTE3 expression is linked to its promoter DNA methylation status. Interestingly, in some species, as for example, the cultivated species solanum lycopersicum, VTE3 5' regulatory region contains a TE and is highly methylated, whereas in some other species, as for example the wild species, S. pennellii, the TE is absent and VTE3 promoter is not methylated (Quadrana et al., 2014).

These different findings show that modification of the DNA methylation level at some specific loci can impact fruit development and ripening, but they don't demonstrate that the regulation of gene expression through DNA-methylation plays a role during fruit development or ripening. 2011) (Telias et al., 2011) Messeguer et al (1991) first suggested that DNA methylation undergo changes during tomato fruit development and ripening. Teyssier et al (2008) then showed that there is a 30% decrease of the global DNA methylation level in pericarp during fruit maturation. The comparison of tomato fruit methylomes at 4 developmental stages further demonstrated that there is a widespread epigenome reprogramming during fruit ripening (Zhong et al., 2013). Zhong et al (2013) found that around 1% of the tomato genome is differentially methylated during tomato fruit ripening, and that DNA demethylation occurs at promoters of fruit ripening-related genes such as NOR and CNR. The global and locus specific loss of DNA methylation during ripening is unlikely to be due to passive DNA demethylation because there is no more cell division and little endoreduplication during this process (Teyssier et al., 2008). This suggested that active DNA demethylation might play an important role during tomato fruit ripening. Because the treatment of immature fruits with a DNA methylation inhibitor induces early ripening before seed maturation, Zhong et al (2013) proposed the following model: (i) methylation inhibits ripening before seed maturation, the promoter of key ripening genes being hypermethylated. (ii) In maturing fruits, these promoters become demethylated, which would induce their expression through the recruitment of specific ripening-related transcription factors like RIN. Indeed RIN binding sites are typically adjacent to DMR and they become demethylated during ripening. This suggests that the binding of RIN to its targets sites occurs in concert with their demethylation (Chen et al., 2015).

A B C

VII. Objectives of the work

Cytosine methylation (5MeC) of genomic DNA is a crucial reversible epigenetic mark that impacts several biological processes. Most notably, DNA methylation is involved in the control of gene expression and provides an epigenetic layer to the genetic information. As introduced above, DNA methylation is a revisable marker. DNA methylation is set up and maintained by three types of DNA methyltransferases, MET1, Chromomethylases (CMT), and small RNA mediated de novel methylation companied with Domain Rearranged Methyltransferase (DRM) in three different contexts, CG, CNG and CHH (H being C, T or A) and can be actively eased by DNA demethylases (DML). DMLs are essential enzymes that protect the genome against extensive methylation, hence removing DNA methylation in the 5' and 3' part of genes and limiting the formation of silenced hyper-methylated epialleles.

As introduced above, over the last 10 years, DNA methylation/demethylation has been shown to be critically important for plant development in the model plant Arabidopsis. Tomato is a model plant of fleshy fruits development and ripening. Indeed, we have shown that tomato plants treated with zebularine, an inhibitor of DNA methylation present pleiotropic phenotypes affecting the vegetative parts of plants, flowers and fruits, therefore highlighting the important function of DNA methylation in this plant as well. Zhong et al (2013) found that more than 4000 genes happens DNA demethylation during fruit ripening, which suggest active DNA demethylation works during fruit ripening process. Therefore, the objective of this project is to address the question of the functions of this class of enzyme during tomato fruit ripening and more generally during tomato plant development and quality.

To achieve this goal, plants modified in their methylation level needs to be generated and analyzed. Therefore, RNAi was used to knockdown genes involved in the control of DNA demethylation. Selected lines were characterized using combined analyses of fruit metabolic composition, transcriptome, small RNA populations and if relevant the genome-wide description of DNA methylation pattern (McrBC-Seq and /or Bisulfite [BS] sequencing) (The strategy used in this project is as following, Fig1.15). This aims at determining which genes/loci targeted by DMLs in tomato fruits impact their phenotype. Identified loci with differential methylation and expression profile were validated using McrBC-PCR or targeted BS sequencing approaches and their expression level from RNA seq data were controlled by quantitative RT-PCR. This project is divided into two parts:

(I: Chapter-2) focuses on the characterization of the functions of active DNA demethylation during tomato fruit ripening and more globally in tomato plants. To achieve this goal, RNAi plants with reduced DNA demethylase gene expression have been generated. This part aims at demonstrating that specific fruit ripening phenotypes observed in these plants are due to the hypermethylation of genes critical for fruit ripening. It also include attempts to characterize the biochemical function of tomato DML proteins. An additional question is to analyze to which extend phenotypes that are induced when DML genes are knocked down can be stably inherited during subsequent generations and therefore questions the stability of demethylation induced changes in methylation patterns.

(II: Chapter-3) presents comprehensive analyses of the impact of active DNA demethylation on the transcriptomes and metabolomes of fruits that have a reduced DML2 gene expression. The aim is to determine amongst the numerous physiological disorder affecting these fruits, those that are directly controlled by methylation. To answer this question RNA seq was combined with the metabolic analysis of fruits. Results were used to determine what genes are both differentially expressed and methylated in the transgenic lines as compared to WT fruits.

Introduction

In plants, genomic DNA methylation at cytosines is a reversible epigenetic mark regulating various aspects of genome functioning, such as transposon mobility and gene expression. Methylation of cytosines can be actively removed by bifunctional DNA glycosylase-lyases, the socalled DEMETER-like DNA demethylases (Choi et al., 2002). In Arabidopsis, active DNA demethylation plays a critical role in the maternal imprinting and endosperm demethylation. However impairing DNA demethylase activities has no major impact on Arabidopsis plants suggesting that these enzymes are not essential for development in this species. However, the functions of this class of enzymes are not known in tomato (Yamamuro et al., 2014,).

It has previously been shown in the laboratory that the genomic DNA of tomato fruit pericarp is massively demethylated during ripening, at a time when cell division and DNA replication are reduced (Teyssier et al., 2008). This makes unlikely that lost of DNA methylation is due to dilution following DNA replication and the inability to maintain DNA. It rather suggests that DNA methylation is actively removed. It was also recently demonstrated that demethylation occurs at specific gene promoters (Zhong et al., 2013). The objective of my project is to study the role of tomato SlDMLs, using transgenic tomato plants impaired in the expression of SlDML genes.

In the first part in this chapter, I will present the functional analysis of SlDML genes, mainly focusing on one of the genes SlDML2, during fruit ripening. Firstly, the four tomato SlDML genes were characterized in details and DML RNAi transgenic plants were generated with the aim to knock down all SlDML genes at once. T0 plants were phenotyped and many of them presented a strong inhibition of fruit ripening. To investigate the consequences of DNA demethylation on the ripening process, we have analyzed the primary metabolites as well as carotenoids and ethylene content, and found that many the aspects of fruit ripening were inhibited and limited in DML RNAi transgenic fruits. To demonstrate a causal relationship between fruit ripening defects of transgenic lines and the impairment of active DNA demethylation, four essential genes (RIPENING INHIBITOR (RIN), NON RIPENING (NOR), COLORLESS NON RIPENING (CNR) and PHYTOENE SYNTHASE 1 (PSY1)) playing important roles in fruit ripening were analyzed to determine their expression level and the methylation level at their promoter.

In a second part of this chapter, I will present the strategy used to characterize tomato SlDML protein activity. Among the four DEMETER-like DNA demethylase genes, SlDML2 was chosen to demonstrate the DNA glycosylase-lyases activity in vitro because it is the most highly expressed of the four SlDML genes in ripening fruits. Attempt to produce the recombinant protein and the use of an in vitro activity test will be described.

The third part in this chapter will present the potential role of active DNA demethylation on other aspects of tomato plant development, namely, flower formation and early leaf development. We found that in some DML RNAi transgenic plants, flower and fruit pericarp were altered, in addition to fruit ripening. This is allowed to investigate the heritability of these phenotypes in the absence of the transgene. We have therefore developed a strategy to segregate out the transgene in order to analyze the eventual transgenerational stability of the flower and fruit phenotypes.

A DEMETER-like DNA demethylase governs tomato fruit ripening Ruie Liu a,1 , Alexandre How-Kit b,1 , Linda Stammitti a,1 , Emeline Teyssier a , Dominique Rolin a , Anne Mortain-Bertrand a , Stefanie Halle a , Mingchun Liu c,d , Junhua Kong e , Chaoqun Wu e , Charlotte Degraeve-Guibault a , Natalie H. Chapman f , Mickael Maucourt a , T. Charlie Hodgman f , Jörg Tost b,g , Mondher Bouzayen c,d , Yiguo Hong e,h , Graham B. Seymour f , James J. Giovannoni i , and Philippe Gallusci In plants, genomic DNA methylation which contributes to development and stress responses can be actively removed by DEMETER-like DNA demethylases (DMLs). Indeed, in Arabidopsis DMLs are important for maternal imprinting and endosperm demethylation, but only a few studies demonstrate the developmental roles of active DNA demethylation conclusively in this plant. Here, we show a direct cause and effect relationship between active DNA demethylation mainly mediated by the tomato DML, SlDML2, and fruit ripeningan important developmental process unique to plants. RNAi SlDML2 knockdown results in ripening inhibition via hypermethylation and repression of the expression of genes encoding ripening transcription factors and rate-limiting enzymes of key biochemical processes such as carotenoid synthesis. Our data demonstrate that active DNA demethylation is central to the control of ripening in tomato. G enomic DNA methylation is a major epigenetic mark that is instrumental to many aspects of chromatin function, including gene expression, transposon silencing, or DNA recombination [START_REF] Law | Establishing, maintaining and modifying DNA methylation patterns in plants and animals[END_REF](2)(3)(4). In plants, DNA methylation can occur at cytosine both in symmetrical (CG or CHG) and nonsymmetrical (CHH) contexts and is controlled by three classes of DNA methyltransferases, namely, the DNA Methyltransferase 1, Chromomethylases, and the Domain Rearranged Methyltransferases (5)[START_REF] Bender | DNA methylation and epigenetics[END_REF][START_REF] Finnegan | Plant DNA methyltransferases[END_REF]. Indeed, in all organisms, cytosine methylation can be passively lost after DNA replication in the absence of methyltransferase activity [START_REF] Law | Establishing, maintaining and modifying DNA methylation patterns in plants and animals[END_REF]. However, plants can also actively demethylate DNA via the action of DNA Glycosylase-Lyases, the so-called DEMETER-Like DNA demethylases (DMLs), that remove methylated cytosine, which is then replaced by a nonmethylated cytosine [START_REF] Hsieh | Genome-wide demethylation of Arabidopsis endosperm[END_REF][START_REF] Gong | ROS1, a repressor of transcriptional gene silencing in Arabidopsis, encodes a DNA glycosylase/lyase[END_REF][START_REF] Zhu | Active DNA demethylation mediated by DNA glycosylases[END_REF][START_REF] Wu | Active DNA demethylation: Many roads lead to Rome[END_REF]. Initially identified as enzymes necessary for maternal imprinting in Arabidopsis thaliana [START_REF] Choi | DEMETER, a DNA glycosylase domain protein, is required for endosperm gene imprinting and seed viability in arabidopsis[END_REF], the role of DMLs has since been established in various processes such as limiting extensive DNA methylation at gene promoters [START_REF] Zhu | The DNA glycosylase/lyase ROS1 functions in pruning DNA methylation patterns in Arabidopsis[END_REF], determining the global demethylation of seed endosperm [START_REF] Hsieh | Genome-wide demethylation of Arabidopsis endosperm[END_REF][START_REF] Gehring | Extensive demethylation of repetitive elements during seed development underlies gene imprinting[END_REF] and promoting plant responses to pathogens [START_REF] Yu | Dynamics and biological relevance of DNA demethylation in Arabidopsis antibacterial defense[END_REF]. Of note, Arabidopsis ros1, dml2, and dml3 single, double, or triple mutants showed little or no developmental alterations [START_REF] Gong | ROS1, a repressor of transcriptional gene silencing in Arabidopsis, encodes a DNA glycosylase/lyase[END_REF][START_REF] Yamamuro | Overproduction of stomatal lineage cells in Arabidopsis mutants defective in active DNA demethylation[END_REF][START_REF] Penterman | DNA demethylation in the Arabidopsis genome[END_REF], suggesting that active DNA demethylation is not critical for development in this species. However, as mentioned above, genomic DNA methylation is an important mechanism that influences gene expression, and methylation at promoters is known to inhibit gene transcription (5,[START_REF] Gehring | DNA methylation dynamics in plant genomes[END_REF]. Hence, it is likely that the active removal of methylation marks is an important mechanism during plant development and plant cell fate reprogramming, leading to the hypomethylation of sites important for DNA-protein interaction and gene expression, as already observed in human cells [START_REF] Bhutani | DNA Demethylation Dynamics[END_REF].

Indeed, accumulating evidence suggests that active DNA demethylation might play a greater role in controlling gene expression in tomato. In support of this idea, recent work describing the methylome dynamics in tomato fruit pericarp revealed substantial changes in the distribution of DNA methylation over the tomato genome during fruit development, and demethylation during ripening at specific promoters such as the NON RIPENING (NOR) and COLORLESS NON RIPENING (CNR) promoters [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF][START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF]. This observation is consistent with previous studies indicating that genome cytosine methylation levels decrease by 30% in pericarp of fruits during ripening, although DNA replication is very limited at this stage [START_REF] Teyssier | Tissue dependent variations of DNA methylation and endoreduplication levels during tomato fruit development and ripening[END_REF].

Significance

This work shows that active DNA demethylation governs ripening, an important plant developmental process. Our work defines a molecular mechanism, which has until now been missing, to explain the correlation between genomic DNA demethylation and fruit ripening. It demonstrates a direct cause-and-effect relationship between active DNA demethylation and induction of gene expression in fruits. The importance of these findings goes far beyond understanding the developmental biology of ripening and provides an innovative strategy for its fine control through fine modulation of epimarks in the promoters of ripening related genes. Our results have significant application for plant breeding especially in species with limited available genetic variation. Here, we investigated active DNA demethylation as a possible mechanism governing the reprogramming of gene expression in fruit pericarp cells at the onset of fruit ripening.

Results

The Tomato Genome Contains Four DNA Glycosylase Genes with Specific Expression Patterns. The tomato genome contains four putative DML genes encoding proteins with characteristic domains of functional DNA glycosylase-lyases ( 23) (SI Appendix, Fig. S1 A and C and Table S1). SlDML1 and -2 are orthologous to the Arabidopsis AtROS1 (Repressor of Silencing 1) gene and SlDML3 to AtDME (DEMETER), whereas SlDML4 has no closely related Arabidopsis ortholog (SI Appendix, Fig. S1B). All four SlDML genes are ubiquitously expressed in tomato plants, although SlDML4 is expressed at a very low level in all organs analyzed. In leaves, flowers, and young developing fruits, the four genes present coordinated expression patterns characterized by high expression levels in young organs that decrease when organs develop. However, unlike SlDML1, SlDML3, and SlDML4, which are barely expressed during fruit ripening, SlDML2 mRNA abundance increases dramatically in ripening fruits, suggesting an important function at this developmental phase (Fig. 1).

Transgenic Plants with Reduced DML Gene Expression Present Various

Fruit and Plant Phenotypes. The physiological significance of tomato DMLs was addressed through RNAi-mediated gene repression using the highly conserved Helix-hairpin-Helix-Gly/Pro rich domain (HhH-GPD) specific to DML proteins as a target sequence (SI Appendix, Fig. S2A). Our goal was to repress simultaneously all tomato SlDML genes, anticipating potential functional redundancy among these four genes; 23 independent T0 transgenic lines were generated and 22 showed alterations of fruit development, including delayed ripening, modified fruit shape, altered color, shiny appearance, parthenocarpy, or combinations of these phenotypes (Fig. 2A).

Lines 2 and 8, which showed delayed and inhibited ripening phenotypes, were chosen to investigate the possible link between ripening and DNA demethylation. In both cases, 10-25 T1 and T2 plants were grown that showed maintenance and strengthening of the nonripening phenotypes in subsequent generations coincident with the presence of the transgene. The loss of the RNAi transgene in segregating lines led to reversion to a wildtype (WT) phenotype, indicating a lack of memory effect across generations when fruit ripening is considered (Fig. 2 A and B and SI Appendix, Fig. S3A). In plants of both RNAi lines, analysis of SlDML gene residual expression in 20 days postanthesis (dpa) fruits indicates that only SlDML1 and SlDML2 are repressed to 40-60% of the WT level, whereas SlDML3 and SlDML4 are either unaffected or induced compared with WT (Fig. 3A). This is most likely attributable to the lower homology level of these two genes, with SlDML1 in the part of the gene used for the RNAi construct (SI Appendix, Fig. S2A). During ripening, SlDML2 expression is reduced to 10% of WT at the Breaker (Br) stage and remains low at 55 dpa (Br + 16) but increases slightly at 70 dpa (Br + 31) (Fig. 3B and SI Appendix, Fig. S2B), coincident with the partial ripening observed in transgenic RNAi fruits (Fig. 2C and SI Appendix, Fig. S3B). Whether the increase in SlDML2 expression at late ripening stages is attributable to a weaker effect of the RNAi remains unclear. None of the three remaining genes, SlDML1, SlDML3, and SlDML4, which are weakly expressed during ripening, displayed significantly reduced (E) VIGS experiment on 47-dpa (Br + 5) fruits injected with PVX/SlDML2 [fruits ( 1) and ( 3)] or PVX [fruits ( 2) and ( 4)] at 12 dpa [fruits ( 3) and ( 4)] inside of fruits ( 1) and ( 2), respectively. (Scale bars: 1 cm.)

expression compared with WT fruits of the same age, indicating that observed ripening phenotypes are likely attributable to SlDML2 gene repression. This hypothesis was further confirmed using virus induced gene silencing (VIGS) to specifically repress the SlDML2 gene; 17.5% of the fruits injected with a PVX/ SlDML2 vector presented non ripening sectors contrary to those injected with a control PVX virus that all ripened normally (Fig. 2E and SI Appendix, Fig. S4B). Indeed, SlDML2 was down-regulated in nonripening sectors of fruits injected with the PVX/ SlDML2 vector, whereas none of the three other SlDML genes was repressed (SI Appendix, Fig. S4C), demonstrating that the specific knock down of SlDML2 is sufficient to inhibit ripening. It was noteworthy that some plants from line 2 developed additional phenotypes affecting plant growth, leaf shape, flower development, and fruit carpel number that were not observed in T0 and T1 generations (Fig. 2D and SI Appendix, Fig. S3 B andC). The screening of additional lines revealed other independent transgenic lines that presented flower, fruit, and plant phenotypes similar to line 2 (SI Appendix, Fig. S3D). These observations indicate that the severity of the phenotypes increases over generations and suggest that DMLs may also be involved in other aspects of tomato plant development beyond fruit ripening.

All Aspects of Fruit Ripening Are Delayed and Limited in RNAi Transgenic Lines. Fruits of transgenic lines 2 and 8 were further analyzed to investigate the consequences of DNA demethylation on the ripening process. Indeed, in fruits of both transgenic lines, the onset of fruit ripening was delayed from 10 to 20 d compared with WT or Azygous revertant fruits, and ripening of transgenic fruits was never completed even after 45 d or longer maturation times (Fig. 2 B and C and SI Appendix, Fig. S3B). The ripening defect is further demonstrated by the late and extremely reduced total carotenoids and lycopene accumulation and the delayed chlorophyll degradation (Fig. 4A). Primary metabolite composition was also modified, as visualized by principal component analysis (PCA) using the absolute concentration of 31 primary metabolites issued from 1 H-NMR analysis (Fig. 4B and SI Appendix, Fig. S5A). The first two principal components (PCs), explain more than 54% of total variability. During early development (20, 35, and 39 dpa), WT and transgenic samples follow parallel trajectories as highlighted by the PCA in which the second PC (PC2) explains 21% of the total variability. However, at 55-dpa and later ripening stages, PC1, which accounts for 33.67% of the global variability, separates WT fruits from all other samples. Hence, WT fruit samples harvested at 55-dpa and older stages are clearly distinct from transgenic fruit samples of the same age. Metabolic differences between ripening WT and transgenic fruits are mainly attributable to overaccumulation of malate and reduction or delayed accumulation of compounds typical of ripening fruits, including glucose, fructose, glutamate, rhamnose, and galactose (SI Appendix, Fig. S5 B-D). Climacteric rise of ethylene production was also dramatically reduced in fruits of both DML RNAi lines, although low ethylene accumulation occurred to a degree and timing consistent with the late and limited ripening process of RNAi fruits (SI Appendix, Fig. S6).

Fruit-Ripening Defects Are Correlated with the Repression and Hypermethylation of Genes Necessary for This Developmental Process.

To demonstrate a causal relationship between fruit ripening defects of transgenic lines and the impairment of active DNA demethylation, the expression of CNR ( 21), RIPENING INHIBITOR (RIN) [START_REF] Vrebalov | A MADS-box gene necessary for fruit ripening at the tomato ripening-inhibitor (rin) locus[END_REF], NOR (25), and PHYTOENE SYNTHASE 1 (PSY1) [START_REF] Bartley | A tomato gene expressed during fruit ripening encodes an enzyme of the carotenoid biosynthesis pathway[END_REF][START_REF] Ray | Cloning and characterization of a gene involved in phytoene synthesis from tomato[END_REF] genes was assessed in RNAi transgenic plants. These genes were selected among others because they are necessary for the overall ripening process (CNR, RIN, NOR), or specifically govern carotenoid accumulation (PSY1), an important quality trait of mature tomato fruit. Moreover, the promoter regions of these genes showed reduced methylation levels during fruit ripening in WT tomato [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF][START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF]. It is noteworthy that CNR gene induction was delayed 15 d in transgenic fruits, and all three other genes showed a dramatic reduction in expression level consistent with the ripening defect of the transgenic lines (Fig. 5A and SI Appendix, Fig. S7). To assess whether repression of CNR, RIN, NOR, and PSY1 gene expression in ripening fruits results from the maintenance of a high cytosine methylation status of their promoter upon down-regulation of SlDML2, methylsensitive-PCR (McrBC-PCR) analysis of the corresponding promoters was performed. This approach revealed a ripening-associated demethylation of the RIN, NOR, and PSY1 promoters in WT and Azygous revertant fruits but not in SlDML RNAi fruits (Fig. 5B). No detectable variations of methylation in the CNR promoter during ripening of WT fruits were revealed with this method. The putative differentially methylated regions (DMRs) in the NOR and PSY1 promoter regions were subsequently analyzed by gene specific bisulfite pyrosequencing [START_REF] How-Kit | Accurate CpG and non-CpG cytosine methylation analysis by high-throughput locus-specific pyrosequencing in plants[END_REF]. Methylation analysis of the CNR promoter was targeted to a region known to be methylated at all stages (CNR1) (SI Appendix, Fig. S9C), used here as a control for methylation and to a previously identified DMR (CNR2) (SI Appendix, Fig. S9C) [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF][START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF]. For all three promoters, cytosines that became demethylated in ripening WT fruits but not in transgenic fruits of the same age were identified (Fig. 6A and SI Appendix, Fig. S9). Two distinct situations were observed: (i) sequences corresponding to putative RIN binding sites (RIN BS) in the CNR and NOR promoters [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF], where methylation is high at 20 and 35 dpa in all plants analyzed and drops to very low levels during ripening of WT fruits but is maintained to high levels in RNAi fruits of the same age; and (ii) sequences that are hypermethylated in transgenic fruits at all stages analyzed compared with WT fruits. These latter sequences include a newly identified DMR in the PSY1 promoter and cytosines upstream and downstream to the RIN BS in the NOR and CNR promoters. These data demonstrate the absolute requirement of promoter demethylation in critical genes for ripening to occur. The data also suggest multiple patterns of cytosine demethylation occurring either specifically during ripening or at earlier stages.

Discussion

Previously reported analysis of DNA cytosine methylation and RIN binding during fruit development in WT and in the rin and Cnr tomato-ripening mutants suggested a significant role for DNA methylation during ripening and a feedback loop between methylation and ripening transcription factors [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF][START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF][START_REF] Chen | Requirement of CHROMOMETHYLASE3 for somatic inheritance of the spontaneous tomato epimutation Colourless non-ripening[END_REF]. Here, we demonstrate for the first time to our knowledge that active DNA demethylation is an absolute requirement for fruit ripening to occur and show a direct cause and effect relationship between hypermethylation at specific promoters and repression of gene expression. In this context, SlDML2 appears to be the main regulator of the ripening associated DNA demethylation process. (i) SlDML2 is the only SlDML gene induced concomitantly to the demethylation and induction of genes that control fruit ripening; (ii) the specific knockdown of SlDML2 in VIGStreated fruits leads to inhibition of fruit ripening similar to DML-RNAi fruits; and (iii) the hypermethylated phenotype described in the Cnr and rin mutants ( 20) is associated with the specific repression of SlDML2, with none of the other SlDML genes being down-regulated (Fig. 6B and Dataset S1). Indeed, we cannot formally rule out that SlDML1, which is repressed in the transgenic RNAi lines, also participates in the genomic DNA demethylation in fruits. However, SlDML1 is mainly expressed at early stages of fruit development and only at very low levels during fruit ripening. Hence, this protein may also be involved in demethylation events but mainly those occurring at the early stages of fruit development.

In addition to genes encoding major fruit ripening regulators, those encoding enzymes involved in various aspects of fruit ripening are also likely to be demethylated, as suggested by the observation that PSY1 gene expression also requires demethylation. Combined transcriptomic, methylomic, and metabolomic analysis of the transgenic lines described here will now be required to determine the network of genes and metabolic processes primarily targeted by demethylation in tomato fruit.

SlDML2 is the likely focal point of a feedback regulation on ripening-associated DNA demethylation, because this gene is clearly down-regulated in fruits of the rin, nor, and Cnr mutants, contrary to the other SlDML genes that are normally expressed (Fig. 6 B and C and Dataset S1). It is plausible that timing and extent of demethylation may represent an important source of variation in the diversity of kinetics and intensity of ripening found among tomato varieties, thus presenting a frontier for further investigation. Controlling the timing and kinetics of active DNA demethylation in fruits may therefore provide new strategies to enhance fruit shelf life. In addition, engineering DNA demethylation in tomato fruits would be an innovative and novel strategy for the improvement of traits of agronomical relevance in a species with little genetic diversity [START_REF] Lin | Genomic analyses provide insights into the history of tomato breeding[END_REF]. Finally, the recent demonstration that hypermethylation of a Myb promoter blocks anthocyanin accumulation during pear and apple ripening [START_REF] Telias | Apple skin patterning is associated with differential expression of MYB10[END_REF][START_REF] Wang | The methylation of the PcMYB10 promoter is associated with green-skinned sport in Max Red Bartlett pear[END_REF] supports the notion of a more general role for demethylation in fruits. However, whether this mechanism occurs similarly during the ripening of all fleshy fruit species now requires further investigation.

Materials Methods

Plant Material and Experimental Plan. All experiments were performed using a cherry tomato variety (Solanum lycopsersicum, cv WVA106) that was grown in greenhouse conditions, except for VIGS experiments, which were performed on Solanum lycopsersicum, cv Ailsa Craig grown in growth chambers as described [START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF]. For the array experiments, fruit pericarp of Ailsa Craig and near-isogenic mutants rin, nor, and Cnr were collected at 13 stages of fruit development and ripening with three independent biological replicates per line and immediately frozen in liquid nitrogen for RNA extraction and array analysis. Details of tomato transformation, selection of line 2 and 8 used in this study, and of VIGS experiments are provided in SI Appendix, Materials and Methods. For all analysis, two independent transgenic T2 plants (DML2A and -B and DML8A and -B for lines 2 and 8, respectively) and an azygous plant obtained from line 8 were used. Additional T2 plants were eventually used as controls for the phenotypes of these four plants. T2 plants from line 2 presented dramatic alterations of flower development, not visible in previous generations, and were backcrossed to allow fruit development. This resulted in a limited number of fruits (see below). For this reason, not all developmental stages could be analyzed for this line.

The experimental plan was designed to span tomato fruit development and ripening in cv West Virginia 106 (WVA106) and transgenic DML RNAi plants over a period of 85 d from fruit set to account for the strongly delayed ripening phenotype of the transgenic fruits. At stages following mature green, the DML RNAi fruits diverge from the WT, because they are significantly delayed in ripening induction and almost completely ripening inhibited. Because it was not possible to select stages equivalent to the Br (39 dpa) or red ripe stages in the transgenic lines, we have chosen to analyze fruits identically staged, which allows comparing changes in the context of a developmental parameter (days postanthesis) that can be precisely mea-sured. Two independent cultures were performed. (i) Plants from line 2 and the relevant WT control (WT1), fruits were harvested at [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF]35,55 (Br + 16), 70 (Br + 31), and 85 (Br + 46) dpa. Because the fruit yield was reduced in line 2, a sufficient number of fruits at the Br stage could not be harvested and older fruits were preferentially selected to allow the analysis of late effects of demethylation inhibition. (ii) Line 8 was grown together with its own WT control (WT2) and an azygous plant. Because there were more fruits available for this line, the Br stage (39 dpa) was harvested in addition of the stages used for line 2.

For all fruit samples, two individual T2 plants were used, and for each sample, a minimum of six fruits separated in three biological replicates were processed and stored at -80 °C until used.

Molecular and Metabolite Analysis. Details of molecular (gene expression, microarrays, McrBC-PCR analysis of gene DNA methylation, and gene-targeted bisulfite sequencing) and metabolite (Carotenoid, ethylene, and 1 H-NMR) analysis are provided in SI Appendix, Materials and Methods.

SI Appendix SI Materials and methods

Tomato transformation

Tomato transformation

For tomato transformation, a 223bp fragment (Fig. S2A) corresponding to part of the highly conserved HhH-GPD domain of DNA glycosylase Lyase was amplified from the SlDML1 cDNA and cloned in sense and antisense orientation in pK7GWIWG2 (I) plasmid to form a hairpin structure necessary for to RNA silencing. The recombinant plasmid named pK7GWSlDML was introduced in the A. tumefaciens strain GV3101. Subsequently, tomato cotyledon transformation was done as described in Gonzalez et al. (S1). Twenty five regenerated shoots were selected from independent calli and cultured as described in How Kit et al. (S2). Twenty five kanamycin resistant T0 plants were transferred to the greenhouse and grown to obtain T1 seeds. Among the 25 independent T0 transgenic plants obtained, 8 including plants 2 and 8, presented delayed and limited ripening phenotypes. Plants 2 and 8 were selected for further studies and self-pollinated and backcrossed, respectively, to generate lines 2 and 8. Backcrossing of the T0 plant 8 was necessary due to flower abnormality. Twenty five T1 plants were grown in each case and were classified based on the level of SlDML expression as determined by semi quantitative RT-PCR on 20 dpa fruits and used for preliminary phenotype characterization. No flower abnormality was observed on T1 plants that were therefore self-pollinated. Complete phenotypic and molecular analyses were performed on T2 plant population obtained after selfing of a single homozygote (line 2) or hemizygote (line 8) T1 plant.

VIGS experiments

For VIGS experiments a 480 bp PCR amplified fragment corresponding to the 5' coding sequence of SlDML2 was inserted into the PVX vector [START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF]. This part of the gene has no significant homology with any of the other tomato SlDML genes. VIGS and analysis of VIGS experiments were as described [START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF], using 80 independent fruits injected at 12 days post anthesis.

Molecular Analysis

Gene expression analysis

Absolute quantification of transcript was performed as described (S3). For each gene, PCR fragments were cloned and controlled by sequencing and a calibration curve was done. For comparative RT-QPCR, experiments were performed as described (S2). Normalization of data was done according to Pfaffl et al. (S4) using EF1 alpha as a reference gene and a reference sample. An ANOVA two ways was performed and difference in gene expression levels between Wild Type and transgenic plants were assessed using a student t test (n=3; *: p<0.05; **: p<0.01; ***p<0.001). All primers used for RT PCR analysis are listed in Table S2.

For microarrays analysis, total RNA was isolated from rin, nor Cnr and wild type Ailsa Craig pericarp samples according to methods as described in [START_REF] Manning | A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening[END_REF]. The concentration of RNA was determined using an Agilent Bioanalyser 2100 (Agilent Technologies). Total RNA was treated with DNA-free (Ambion) as per the manufacturer's instructions. RNA was then hybridized to the Syngenta Tomato Affymetrix GeneChip.™ The microarrays were normalized using the Robust Multichip Average (RMA) method with the Bioconductor Affymetrix package (S5), which both accounts for the background correction using the perfect match (PM) features for quantile normalization of all the arrays (S6) and for condensing probes into probe regions (hereafter referred to as genes) (S7). The expression values are arbitrary units of fluorescence intensity.

A linear mixed model was fitted to the logarithm of the DML data with genotype, developmental stage and gene considered as fixed effects and plant and fruit-withinplant as random terms in the model. The significance of the fixed effects and their interactions were tested using the Variance ratio F-tests output by the mixed model fitting routines within the Genstat 17 statistical package

McrBC-PCR Analysis

For methylation analysis, genomic DNA were purified from fruit pericarp using the illustra DNA extraction kit Phytopure (GE Healthcare, UK), quantified at 260nm and quality control was performed after electrophoresis on a 1% agarose gel. For McrBC-PCR methylation analysis, 1µg of genomic DNA was digested with McrBC (NEB) for 5h according to manufacturer instructions with or without GTP as a negative control. PCR amplification was performed with 50 ng of genomic DNA with the relevant primers shown in Table S2.

Bisulfite sequencing

Gene specific BS sequencing was performed essentially as described in [START_REF] How-Kit | Accurate CpG and non-CpG cytosine methylation analysis by high-throughput locus-specific pyrosequencing in plants[END_REF]. Briefly, PCR primers for bisulfite treated DNA amplification were designed with Primer3 (http://bioinfo.ut.ee/primer3-0.4.0/) using the unconverted genomic DNA sequence as input sequence. As every C nucleotide can be potentially methylated in plants and in order to avoid any sequence selection bias during PCR amplification, "C" and "G" nucleotides were replaced by "Y" and "R" nucleotides in forward and reverse primers respectively. All primers are listed in Table S2.

One microgram of genomic DNA was used for bisulfite treatment conversion using the EpiTect 96 Bisulfite Kit (Qiagen, Courtaboeuf/France) according to manufacturer's instructions. The absence of unconverted genomic DNA was assessed processing a whole-genome amplified sample (Whole Genome Amplification (WGA) kit, Sigma-Aldrich) simultaneously with the bisulfite conversion of all samples, which presented a DNA methylation value of 0% for every C position of each amplicon after pyrosequencing. PCR amplification of the selected promoter fragments, purification of PCR products and pyrosequencing experiments were performed as described (S8). DNA methylation patterns were analyzed with the PyroMArk CpG software (Qiagen) and by an in-house developed Microsoft Excel Visual Basic Application for Cytosines outside CpG sites. For each sample, average DNA methylation value of each cytosine or cytosine group (CC, CCC) obtained by pyrosequencing of the three regions of interest (CNR, NOR and PSY1) were pooled to generate a matrix. Heatmap representation of the data was then performed using "heatmap2" function of "gplots" package of the R software. Hierarchical unsupervised clustering between columns and rows were computed using Euclidean distance and complete linkage method as agglomerative method.

Metabolite analysis

Ethylene production analysis

Ethylene production was assayed on individual fruit after 2 h by withdrawing 1-ml gas samples from sealed jars. Gas samples were analyzed via gas chromatography (7820A GC system Agilent Technologies, Santa Clara, CA, USA, http:// www.chem.agilent.com/en-US/products-services/Instruments-Systems/Gas-Chromatography/7820A-GC/Pages/default.aspx). Ethylene was identified via comigration with an ethylene standard and quantified with reference to a standard curve for ethylene concentration.

Carotenoid analysis

Carotenoid analysis was done as described (S3). Samples from transgenic plants DML2A, B and DML8A, B were compared to those of WT1 and WT2 respectively. Differences between samples were evaluated using an ANOVA and Tukey's test ( n=3, *: p<0.05; **: p<0.01; ***p<0.001).

H-NMR Metabolite analysis

For 1 H-NMR analysis, polar metabolites were extracted from ground Solanum lycopersicum L., cv WVA106 pericarp fruit. Briefly, the frozen powdered samples were lyophilised and polar metabolites were extracted from 15 to 30 mg of lyophilised powder samples with an ethanol-water series at 80°C. The supernatants were combined, dried under vacuum and lyophilized. Each lyophilized extract was solubilized in 500 µL of 300 mM potassium phosphate buffer pH 6.0, in D 2 O. Ethylene diamine tetraacetic acid disodium salt (EDTA) was added at a final concentration of 3 mM. Each extract was titrated with KOD solution to pH 6 and lyophilized again. The lyophilized titrated extracts were stored in darkness under vacuum at room temperature, before 1 H-NMR analysis was completed within one week.

1 H-NMR analysis was performed using 500 µL of D 2 O with sodium trimethylsilyl [2,2,3,3-2 H 4 ] propionate (TSP, 0.01% final concentration for chemical shift calibration) added to the lyophilized titrated extracts. The mixture was centrifuged at 17,700 g for 5 min at room temperature. The supernatant was then transferred into a 5 mm NMR tube for acquisition. Quantitative 1 H-NMR spectra were recorded at 500.162 MHz and 300 K on a Bruker Avance III spectrometer (Wissembourg, FR) using a 5-mm broadband inverse probe, a 90° pulse angle and an electronic reference for quantification The assignments of metabolites in the NMR spectra were made by comparing the proton chemical shifts with literature or database values (S9), by comparison with spectra of authentic compounds and by spiking the samples. For assignment purposes, 1 H-1 H COSY, spectra were acquired for selected samples. For absolute quantification three calibration curves (glucose and fructose: 2.5 to 100 mM, glutamate and glutamine: 0 to 30 mM) were prepared and analysed under the same conditions. The glucose calibration was used for the quantification of all amino-acids, as a function of the number of protons of selected resonances except fructose, glutamate and glutamine that were quantified using their own calibration curve. The metabolite concentrations were calculated using AMIX (version 3.9.10, Bruker) and Excel (Microsoft, Redmond, WA, USA) softwares.

To explore the metabolite multidimensional data set, one unsupervised multivariate statistical method was used on mean-centered data scaled to unit variance: Principal Component Analysis (PCA). PCA was used to visualize the grouping of the different samples without any knowledge of their group. PCA was performed of absolute concentration of 31 metabolites issued from 1 H-NMR analysis of transgenic and corresponding WT controls tomato pericarp fruit harvested at [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF]35,40,55,70,85 and 110 days post pollination (dpa), using SAS software version 8.01 (SAS Institute 1990).

For individual metabolites, means ± standard deviations (sd) were calculated from three biological replicates. For all biochemical analyses two extractions were completed to measure the concentration of each biological replicate, then the mean of three biological replicates was calculated. Mean comparisons were conducted using an ANOVA followed by Tukey's t -test. S1. (B) Phylogenetic analysis. An unrooted dendogram was generated using the Maximum Likelihood method in MEGA v.6 based on the JTT model (S 10). Sequences of DNA glycosylase proteins were aligned using Muscle. The numbers at the branching points indicate the percentage of times that each branch topology was found during bootstrap analysis (n=1000). (C) The Helixhairpin-helix -Gly/Pro rich domain (HhH-GPD) domain of tomato DNA Demethylase was aligned with those of Arabidopsis. Red dot indicates the highly conserved Lysine residue necessary for catalytic activity, blue dot shows the conserved aspartic acid residue present in the active site and green dots show the cysteine residues that constitute a [4Fe-4S] cluster [START_REF] Mok | Domain structure of the DEMETER 5-methylcytosine DNA glycosylase[END_REF]. Accession numbers are indicated in Table S1.

AtDemeter AtROS1 AtDML2 AtDML3 SlDML1 SlDML2 SlDML3 SlDML4 M . S K A A R M K G K N K K K S G K E E K N R R T K S K E G K E L V A T G Q V K A L K G P L E N D K S I G G E K G E T I K K G L K E Q E E E D P K K K D K K K K P K K E Q E K R T A S I N N A E S F V V V I F F Q D D D D D D D W W W W W W W W D D D N D D D D S C S N S S S R L L L L L L L L R R R R R R R R K R K . L L K . D E E R Q Q E K V A A M A A V A E Q E Y E Q Q Y G A S T S A S S N R G K N N K T E A G E G G S G G G R G K K G T R I K . K K K Y Q R R . R R K T E E E S E E E G R K R R K R R S N T T P T T S T K R E E A A K E N S R M N N D S N T T H T T A N M M M M M M M R D D D D D D D D S T T S S S S S I V V V L L L V D D D N D D N N Y W W W W Y Y W E K D S D E E E A A A D A A A A I I L V V V V V R R R R R R R R R A C L C C S H A A T S A A A A S D D G D N A D I V V Q V V V V S K H N N N K K E E K V E E E M I V I L I I I I S A A E S A S F E E N T H H D E A T I T T T A Q I I I I I I I I K K I K R R K K E S K K E E E C R R R R R R R R G G G G G G G G M M M Q M M M Q N N N F N N N G N H N R N N N N M K M I M K M V L L L L L L L L A A A S A A A A V E E E E E E A R R R R R R R K I I I I I I I I K Q K L K Q K K D G A K D A D N F F F F F F F F L L L L L L L L E D N N N N D N R R R D R R R R I L L E I I L S V V V V F V V F K N K N R S R E D D K Q E D D H H H H N H H H H G G G G G G G G G S S N S S S S I I I I I I I V D D D D D D D D L L L L L L L L E E E E E E E E W W W W W W W W L L L L L L L L R R R R R R R R E D D N D D D D AtDemeter AtROS1 AtDML2 AtDML3 SlDML1 SlDML2 SlDML3 SlDML4 S V V A V V V V P P P P P P A P P P P S P P P K D D D H D D D E K K K L K K K D A A A V A A A V K K K K K K K K D E E R E E E E Y Y Y Y Y Y Y Y L L L L L L L L L L L L L L L L S S S E S S S S I F I I I I I I R N N E R R R Y G G G G G G G G L L L I L L L L G G G G G G G G L L L L L L L P K K K K K K K K S S S S S S S S V V V A V V V T E E E E E E E D C C C C C C C C V V V V V V V I R R R R R R R R L L L L L L L L L L L L L L L L T T S G T T T S L L L L L L L L H H H K H H H R N H Q H N H N H L L I H L L L H A A A A A A A S F F F F F F F F P P P P P P P P V V V V V V V V D D D D D D D D T T T T T V T I N N N N N N N N V V V V V V V V G G G G G G G A R R R R R R R R I I I I I I I I A A A A A A A V V V V V V V V V R R R R R R R R M L L L L L L L G G G G G G G G W W W L W W W W V V V V V V V V P P P P P P P P L L L L L L L L Q Q Q E Q Q Q Q P P P P P P P P L L L L L L L L P P P P P P P P E E D N E E E D S S E G S S S G L L L V L L L L Q Q Q Q Q Q Q Q L L M M L L L M H H H H H H H H L L L Q L L L L L L L L L L L L E E E F E E E E L M L E L L L K Y Y Y Y Y Y Y F P P P P P P P P V M V S V I I L L L L M L L L E E E E D E E E S S S S S S S S S I I V I I I I I Q Q Q Q Q Q Q Q K K K K K Q K K F Y Y Y Y Y Y Y L L L L L L L L W W W W W W W W P P P P P P P P R R R R R R R R L L L L L L L L C C C C C C C C K K K K K K K E L L L L L L L L D D D P D D D D Q Q Q Q Q Q Q V R K K E R R R S T T T T T T T T L L L L L L L L Y Y Y Y Y Y Y Y AtDemeter AtROS1 AtDML2 AtDML3 SlDML1 SlDML2 SlDML3 SlDML4 E E E E E E E E L L L L L L L L H H H H H H H H Y Y Y Y Y Y Y Y Q Q H Q H H H H L M M M M M M M I I I I I I I I T T T T T T T T F F F F F F F F G G G G G G G G K K K K K K K K V V V V V V V V F F F F F F F F C C C C C C C C T T T T S T T T K K K K K K K K S S V T S S S K R K K I K K K K P P P P P P P P N N N N N N N N C C C C C C C C N N N N N N N D A A A A A A A A C C C C C C C C P P P P P P P P M M M M M L L L R K K K R R R R G G A S G G A T E E E E E E E E C C C C C C C C R R R K R R R R H H H Y H H H H F F Y F F F F F A A S A A A A A S S S S S S S S A A A A A A A A Y F R Y F F Y F A A A V A A A A S S S S S S S S A A A S A A A T R R R K R R R R L L L V L L L L A A A L A A A R L L L L L L
E E E E E E Q E K E E E E E Q R G S K K K K K S . D M S S S G L . R H I I I E T . T E V V V A S . S P S S S D A . V N A A S S T . M T T T A K
CCC1 C2 C3 C4 C5 C6 C7 CC8 C9 C10 C11 C12 CCC13 C15 CC16 CCC17 C18 C19 C20 C21 C22 0 0,5 1 CCC1 C2 C3 C4 C5 C6 C7 CC8 C9 C10 C11 C12 CCC13 C15 CC16 CCC17 C18 C19 C20 C21 C22 0 0,5 1 C1 CC2 C3 CC4 CC5 C6 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 CCCC24 CC25 0 0,5 1 C1 CC2 C3 CC4 CC5 C6 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 CCCC24 CC25 DMR McrBC 0 0,5 1 1,5 C1 C2 CC3 C4 C5 C6 CC7 C8 CC9 C10 C11 C12 CC13 C14 C15 C16 C17 CCCCC18 C19 C20 C21 C22 CC23 C24 C25 C26 CC27 C28 CC29 CC30 C31 C32 CCC33 C34 C35 C36 CC37 CC38 CCCCC39 RIN ChIP-Seq CNR 1 CNR 2 0 0,5 1 1,5 C1 C2 CC… C4 C5 C6 CC… C8 CC9 C10 C11 CC12 CC13 CC14 C15 C16 C17 C18 C19 C20 C21 0 0,5 1 1,5 C1 C2 CCC3 C4 C5 C6 CCC7 C8 CC9 C10 C11 CC12 CC13 CC14 C15 C16 C17 C18 C19 C20 C21 0 0,5 1
1,5 C1 C2 CC3 C4 C5 C6 CC7 C8 CC9 C10 C11 C12 CC13 C14 C15 C16 C17 CCCCC18 C19 C20 C21 C22 CC23 C24 C25 C26 CC27 C28 CC29 CC30 C31 C32 CCC33 C34 C35 C36 CC37 1

Activity test for tomato SlDMLs protein

As reviewed in chapter 1, in plants, active DNA demethylation is catalyzed by bifunctional enzymes, the DNA Glysosylase-lyases, which possess both DNA glycosylase and apurinic/apyrimidinic (AP) lyase activities. DNA glycosylase cleaves the phosphodiester backbone at the 5-meC removal site by β, δ-elimination, AP lyase subsequently nicks the DNA, and an AP endonuclease generates a 3-hydroxyl to which a DNA repair polymerase adds an unmethylated cytosine. DNA ligase completes the repair process by sealing the nick (Penterman et al., 2007). Finally this biochemical process results in a net loss of cytosine methylation (Chapter 1, Fig 1.8).

In Arabidopsis, four DEMETER-like DNA demethylases were indentified, including Repressor Of Silencing (ROS1), DEMETER, DEMETER-LIKE 2 (AtDML2) and DEMETER-LIKE 3 (AtDML3) (Choi et al., 2002;Gong et al., 2002;Penterman et al., 2007;[START_REF] Ortega-Galisteo | Arabidopsis DEMETER-LIKE proteins DML2 and DML3 are required for appropriate distribution of DNA methylation marks[END_REF]. All these four Arabidopsis DEMETER-like DNA demethylases protein are DNA Glycosylase-lyases, characterized by a highly conserved Glycosylase domain present in both prokaryotic and eukaryotic DNA glycosylases, an iron-sulfur cluster motif, which is suggested critical for DNA glycosylase-lyases activity is located in this domain. Another two additional conserved domains A and B flanks in the central glycosylase domain, these three conserved domain are necessary and sufficient for DNA demethylation activity [START_REF] Agius | Role of the Arabidopsis DNA glycosylase/lyase ROS1 in active DNA demethylation[END_REF][START_REF] Mok | Domain structure of the DEMETER 5-methylcytosine DNA glycosylase[END_REF][START_REF] La | A 5-methylcytosine DNA glycosylase/lyase demethylates the retrotransposon Tos17 and promotes its transposition in rice[END_REF].

The tomato genome contains four DEMETER-like (DML) genes with three characteristic domains of DNA demethylases, suggesting that these proteins are functional DNA Glycosylaselyases. They code for putative proteins of 1702aa, 1824aa, 1869aa and 1538aa (aa = amino acids). SlDML1 (Solyc09g009080) and SlDML2 (Solyc10g083630) are orthologous to AtROS1, SlDML3 (Solyc11g007580) to AtDME, whereas SlDML4 (Solyc03g123440) is distinct from the three other proteins (Fig 2 .1, p58) as have been reported before (Liu et al., 2015). ( Liu et al., 2015).

To assess the biochemical activity of SlDML protein using in vitro assays, three full length cDNA, including SlDML1, SlDML2 and SlDML3 were selected to develop a protein activity test. To address whether the three conserved domains are also necessary and sufficient for SlDML2 DNA demethylases activity, three different truncated cDNA forms (SlDML2-962, SlDML2-845, SlDML2-694) were designed in addition to the reference full length of SlDML2 protein (Fig 2 .2). We hypothesized that SlDML2-694 and SlDML2-845 will be active proteins because they still contain the complete three conserved domains. In contrast SlDML2-962 has a truncated domain A, which may result in a loss of activity.

Together, all of the six cDNAs were cloned into the cloning vector (pENTR) and subsequently subcloned into the expression vector (pET300/NT-DEST) and introduced in E.coli cells (Rosetta2 strain, DE3) with modified codon usage (Fig 2 .3).

Fig 2. 2 Structures of SlDML2 proteins along with their truncated versions used in this study

Fig 2. 3 Cloning vector and expression vector used in this study

To purify recombinant proteins, proteins expression and solubility were first tested. Unfortunately, full length SlDML1 and SlDML2 could not be successfully produced, and the truncated forms SlDML2-962 and SlDML2-694 were not continued after the construction of the recombinant vectors. Only SlDML3 and the truncated SlDML2-845 were successfully expressed although the production remained very low irrespective to the conditions used. Several different conditions were tested, including different incubation temperatures (16°C, 23°C, 26°C) as well as different sonication buffers but the production of SlDML2-845, SlDML2-962 remained very low. (1) DNA substrates: Oligonucleotides used as DNA substrates were synthesized and were purified by PAGE from company. Double-stranded DNA substrates were prepared by mixing a 5 mM solution of a 50 -fluorescein-labelled oligonucleotide (upper-strand) with a 10 mM solution of an unlabelled oligomer (lowerstrand), heating to 95 ℃ for 5 min and slowly cooling to room temperature; (2) Expression and purification of DML2 and DML3 : The full-length cDNA was inserted into the pET300 /NT-DEST expression vector to add a polyhistidine (His6) Tag at the Nterminus of DML2 and DML3 protein. Expression of recombinant genes was carried out in E. coli (Rosetta2 strain, DE3) (Stratagene). A fresh transformant colony was transfereded into 10 mL of LB medium containing kanamycin (50 mg/ml) and chloramphenicol (34 mg/ml), then the culture was incubated for overnight with shaking. A 2.5 ml aliquot of the overnight culture was added into 1L of fresh LB medium with kanamycin (50 mg/ml) and chloramphenicol (34 mg/ml), and incubated at 37℃, 250 rpm, until the A600 was 0.1. The culture was then transfered at 23℃, and 962 962 incubation continued at 250 rpm for 3h. Cells were collected by centrifugation at 13 000 g for 30 min and the pellet was frozen at -80℃. (3) Recombinant protein purification. The stored pellet was thawed and resuspended in 10 ml of Sonication Buffer (SB: 20 mM Tris-HCl pH 8.0, 500 mM NaCl, 20% glycerol, 15 mM b-mercaptoethanol, 1% Tween-20) supplemented with 5 mM imidazole. Cells were disrupted by sonication and the lysate was clarified by centrifugation. The supernatant was loaded onto a Ni2+-sepharose column preequilibrated with SB buffer supplemented with 5 mM imidazole. The column was washed with 10 ml of SB supplemented with 5 mM imidazole, followed by 10 ml of SB supplemented with 100 mM imidazole. Proteins were eluted with a 30 ml gradient of imidazole (100 mM to 1 M) in SB and collected in 2 ml solution. The protein was disalted and disolved in the following buffer (DB: 50 mM Tris-HCl pH 8.0, 500 mM NaCl, 1 mM DTT, 50% glycerol). The protein preparation was divided into aliquots, and stored at -80℃. All steps were carried out at cold room (4℃). Protein concentrations were determined by the Bradford assay. Denatured proteins were analysed by SDS-PAGE (10%) using broad-range molecular weight standards (Bio-Rad). (4) Enzyme activity assays. Double-stranded oligodeoxynucleotides (20 nM, unless otherwise stated) were incubated at 308C for the indicated times in a reaction mixture containing 50 mM Tris-HCl pH 8.0, 1 mM EDTA, 1 mM DTT, 0.1 mg/ml BSA, and the corresponding amount of purified protein in a total volume of 50 ml. Reactions were stopped by adding 20 mM EDTA, 0.6% sodium dodecyl sulphate, and 0.5 mg/ml proteinase K, and the mixtures were incubated at 37 ℃ for 30 min. DNA was extracted with phenol:chloroform:isoamyl alcohol (25:24:1) and ethanol precipitated at -20℃ in the presence of 0.3 mM NaCl and 16 mg/ml glycogen. Samples were resuspended in 10 ml 90% formamide and heated at 95℃ for 5 min. Reaction products were separated in a 12% denaturing polyacrylamide gel containing 7 M urea. Fluorescein-labelled DNA was visualized using the blue fluorescence mode of the FLA-5100 imager.

The activity of purified proteins was tested in a DNA incision assays. SlDML2-845 contains the 3 complete domains, which are necessary for activity, so it is expected to be active. SlDML2-962 with truncated domain A is supposed to have no activity; therefore, it was used as a negative control. The DNA incision assay mechanism as below (Fig 2 .5A). Fluorescein-labeled duplex oligonucleotides containing 5-methylcytosine in different sequence contexts were chosen as the substrates of SlDML2-845 protein. Incubation of SlDML2-845 with an oligonucleotide containing the unmethylated CpXpG site will result in the generation of a cleavage product after incubation with MsP1, which can be visualized in a Fluorescein-labeled DNA imager. The test took MspI as positive control, which will show incision activity on CCGG sites if cytosines are not methylated, but will be inhibited if the second C is methylated. Hence incubating DML with methylated DNA containing a methylated CCGG site will provide a cleavage product after MSP1 incubation, only if the DML are active. If the enzyme is not active, no cleavage product will be obtained. A positive control is done by incubating the same unmethylated DNA with MSP1, which allow visualizing the cleavage product. As a conclusion, we coud not detect any significant activity using either SlDM2-845, or SlDML2-962, although MspI could cleave the substrate very efficiently (Fig 2 .5B). The reasons are unclear and could be due to a lost of activity during the protein purification process associated to the low protein yield.

B

Part III Analysis of the inheritance of phenotypes generated in DML

RNAi plants after transgene out-segregation

The Cnr mutant was the first epimutant identified in tomato. In this epimutant, fruit ripening was inhibited due to an increased methylation at the CNR promoter region, and this phenotype is stably heritable (Manning et al, 2006). We have now shown that repression of SlDML2 expression results in hypermethylation at specific loci that blocks fruit ripening. It is unclear whether these hypermethylated loci are stable through generation and will maintain the phenotypes observed in the transgenic lines.

Preliminary observation have already shown that segregation of the transgene after selfing plants of line 8 heterozygous for the transgene resulted in reversion of ripening phenotype to a WT ). This suggests that hypermethylation of genes controlling fruit ripening is not transmitted to the next generation in the absence of the transgene. However fruit ripening phenotypes are late developmental events. Hypermethylation at these ripening genes occur at the onset of fruit ripening in the pericarp of fruit and therefore cannot be transmitted to the gamete. The demethylation at these pormoters requires to be newly made in each plant during fruit ripening and is therefore unlikely to be stably transmitted to the next generation. .

We have also noticed that other lines present additional phenotypes affecting leaves and flowers. Such phenotypes are likely to be due to early developmental events that may take place in meristems and therefore could be transmitted to the next generation of plants. In order to test the possible transmission of these phenotypes, we have investigated their heritability in Line 2 and Line 1 that present modified floral shape and development that result in fruits with multiple carpel, and alteration of leaf shapet. The experimental plan used for this study was applied to lines The phenotype of all T4 plants was analyzed irrespective to the presence of the transgene. Finally we found that for both line 2, and line 1 plants that had lost the transgene by segregation (table 1) have reversed to WT phenotype (Fig 2 .7), suggesting an absence of heritability of the modifications induced by SlDML2 knock down. However, we cannot rule out that some abnormal methylation pattern, not linked to these apparent phenotypes are inherited. In addition, it is unclear whether the plants obtained present an homozygous epigenetic state. Additional generations obtained after selfing these plants should be analyzed.

A B

Chapter 2 68

Conclusion

In this chapter, we demonstrated that among the four SlDML genes, SlDML2 knockdown results in fruit ripening inhibition via hypermethylation and repression of the expression of ripening related genes. Four essential genes that related to fruit ripening were identified as the potential primary targets of SlDML2, including three fruit ripening transcription factors, RIN, NOR, CNR and a key enzyme of carotenoid biosynthesis PSY1. Our data demonstrate first time that active DNA demethylation is critically important for tomato fruit ripening to occur.

To characterize the SlDML protein activity, SlDML1, 2, 3 full length and three truncated SlDML2 (SlDML2-694, SlDML2-845, SlDML2-962) were successfully cloned into an expression vector and destination vector. The recombinant constructions were expressed in vitro (E.coli), unfortunately, the full length SlDML1, SlDML2 could not be successfully expressed in E.coli. Only a full length SlDML3 and a truncated versions of SlDML2, SlDML2-845 containing the three complete domains) and SlDML2-962 containing a truncated domain A) could be synthesized at low levels in E coli. Unfortunately, SlDML3 full length wasn't successfully purified. SlDML2-845 and SlDML2-962 were obtained, that were subsequently used for an activity test. We could not demonstrate any activity for these two proteins which may be caused by the low production of recombinant protein purification.

To study the potential stability of the phenotypes affecting plant development after transgene segregation, T4 plants of line 1 and line 2 with abnormal flower and pericarp phenotype were analyzed. As a result, T4 plants show us that the phenotypes reversed to WT phenotype once the transgene was out segregated, suggesting an absence of heritability of the modifications induced by SlDML2 knock down. However, we cannot rule out that some abnormal methylation patterns linked or not to these apparent phenotypes have been inherited. Indeed, due to flower abnormalities, hemizygous T2 plants have been back crossed to WT plants generating a heterozygous epigenetic state. Indeed these plants have been selfed for one generation before their analysis as a first step to generate homozygous epigenetic states. In addition, it is not known how many loci are involved in generating the flower and leaf abnormalities. Hence, it is possible that lack of phenotypes is not due to the non-heritability of the improper methylation state at specific loci. It may reflect that the correct combination of homozygous methylation state at all required loci was not obtained. Further generation and screening of more important plant population will be necessary to answer this point.

In this chapter, we have shown that the inhibition of fruit ripening in RNAi SlDML lines is correlated with the hypermethylation of ripening related genes. Four genes (RIN, NOR, CNR and PSY1) were identified to have a direct causal and effect relationship between active DNA demethylation and gene expression. However, in addition to these four genes, how many genes expressed during tomato fruit development and ripening have been impacted in plants knocked down for SlDML2? What is the global impact of impaired active DNA demethylation on tomato fruit ripening? To answer these questions, our next objective is to establish a global regulatory network associated with active DNA demethylation during fruit ripening. For this purpose, metabolome and transcriptome analyses were combined with the analysis of the genome wide distribution of DNA methylation.

Introduction

DNA methylation is a reversible epigenetic modification that plays important roles in transposon silencing, genomic imprinting and regulation of gene expression [START_REF] Bender | DNA methylation and epigenetics[END_REF]. Unlike in mammals which genomic DNA methylation mainly occurs in the CG context; in plants, methylation of cytosine occurs in three sequence contexts: the symmetrical contexts, CG and CHG and in the non-symmetrical context CHH (H=A, C, T). A majority of DNA methylation in plants occurs at transposable elements and repetitive sequence that are clustered in heterochromatin [START_REF] Zhang | Genome-wide High-Resolution Mapping and Functional Analysis of DNA Methylation in Arabidopsis[END_REF]. In Arabidopsis, DNA methylation can also occurs in promoters and in the bodies of expressed genes. In this later case DNA methylation ishighly correlated with gene transcription. Indeed 61.5% of Arabidopsis expressed genes of Arabidopsis are entirely devoid of methylation where 5.2% are methylated within their promoters and 33.3% are methylated within their transcribed regions also called gene body [START_REF] Zhang | Genome-wide High-Resolution Mapping and Functional Analysis of DNA Methylation in Arabidopsis[END_REF][START_REF] Lister | Highly Integrated Single-Base Resolution Maps of the Epigenome in Arabidopsis[END_REF]. Although DNA methylation is essential for Arabidopsis, its impact on plant development may vary between plant species.. For example, DNA methyltransferases 1 (MET1) mutant in Arabidopsis, lateflowering plants were frequently observed among plants heterozygous, and this phenotype is more sever in met1 homozygotes. This is caused by the hypomethylation of the FWA gene, which is specifically controlling Arabidopsis flowering time [START_REF] Soppe | The Late Flowering Phenotype of fwa Mutants Is Caused by Gain-of-Function Epigenetic Alleles of a Homeodomain Gene[END_REF][START_REF] Kankel | Arabidopsis MET1 Cytosine Methyltransferase Mutants[END_REF]Saze and Kakutani 2011). In rice, knocking out the major CG methyltransferase, OsMET1, impaired seed development and vegetative growth and all seedlings underwent swift necrotic death [START_REF] Hu | Mutation of a major CG methylase in rice causes genome-wide hypomethylation, dysregulated genome expression, and seedling lethality[END_REF].

In plants, DNA methylation of cytosine can be removed by DNA demethylase (DMLs). DNA demethylases are bifunctional 5-methylcytosine DNA glycosylase/lyase, which are critical for preventing DNA hypermethylation at hundreds of genomic regions in Arabidopsis. More recently, ros1 mutant was discovered 6902 hypermethylated differentially methylated regions with whole genome bisulfate sequencing (Penterman et al., 2007;Tang et al., 2016). Four genes encoding DNA demethylase have been identified in this species, DEMETER, DEMETER-LIKE 2 (AtDML2), DEMETER-LIKE 3 (AtDML3), and REPRESSOR OF SILENCING1 (AtROS1) [START_REF] Cao | Role of the Arabidopsis DRM Methyltransferases in De Novo DNA Methylation and Gene Silencing[END_REF]Choi et al., 2002;Gong et al., 2002;Penterman et al., 2007;[START_REF] Ortega-Galisteo | Arabidopsis DEMETER-LIKE proteins DML2 and DML3 are required for appropriate distribution of DNA methylation marks[END_REF]. The function of Arabidopsis DNA demethylase family members have been well studied in recent years. In addition, all of these four DNA demethylases can target both symmetrical cytosine CG, CHG and asymmetrical cytosine CHH. It is worth pointing out that, DME and ROS1 can also remove methyl from thymine, but not uracil, and show a preference for CG context [START_REF] Morales-Ruiz | DEMETER and REPRESSOR OF SILENCING 1 encode 5methylcytosine DNA glycosylases[END_REF].

DEMETER is known to be critical for active DNA demethylation in the central cell and thereby for gene imprinting and endosperm development. Heterozygous DME/dme-1 mutant produced 1:1 seeds with normal embryos and enlarged endosperm with aborted embryos (Choi et al., 2002;[START_REF] Xiao | Imprinting of the MEAPolycomb Gene Is Controlled by Antagonism between MET1 Methyltransferase and DME Glycosylase[END_REF]. AtROS1 is required for release of transcriptional silencing of an hypermethylated transgene, and was shown protect the genome against unwanted methylation (Gong et al., 2002;[START_REF] Agius | Role of the Arabidopsis DNA glycosylase/lyase ROS1 in active DNA demethylation[END_REF]. Yamamuro et al (2014) found that AtROS1 can influence the initiation of stomatal lineage cell by regulating EPF2 expression (Yamamuro et al., 2014). AtROS1 may also associate with RdDM pathway to participate to pathogen defense through regulating some defense genes linked to TEs/repeats (Yu et al., 2013).XXXX here you have a put a sentence on thos article in nature plant cocnering ros1!! AtDML2 and AtDML3 function as genome wide DNA demethylases that remove 5mC marks at sites 3' and 5' of genes in adult cells, but there was no obvious phenotype in the corresponding mutants and gene expression was not significantly affected. 70 In addition, ros1, dml2 or dml3 double or triple Arabidopsis mutants showed little or no developmental alterations, suggesting that DNA demethylases do not have essential functions for development in this species (Penterman et al., 2007;Yu et al., 2013).

Tomato is an important model to study fleshy fruit development and ripening. Some obvious characters associated with fruit development and ripening have been well characterized such as pigment synthesis and degradation, cell wall biosynthesis and disassembling, sugar and organic acids metabolism, hormone biosynthesis and regulation, more specifically ethylene accumulation. Recent studies have shown that the development and ripening of tomato fruit relies on the establishment and maintenance of differential transcription patterns (Alba et al., 2005;Osorio et al., 2011) and complex regulatory pathways that involve both genetic and hormonal controls are operating at these developmental phases (Osorio et al., 2013). Several mutants affecting tomato fruit ripening process or specific fruit characteristic of ripening fruits such as their color have now been characterized. These include the ripening-inhibitor (RIN), non-ripening (NOR), colorless non ripening (CNR) but also never-ripe (Nr), high pigment1 (hp1), high pirment2 (hp2), fruitfull (FUL1 and FUL2), agamous-like1 (AGL1) or the phytoene synthase 1 (PSY1) (Lanahan et al., 1994;[START_REF] Vrebalov | A MADS-box gene necessary for fruit ripening at the tomato ripening-inhibitor (rin) locus[END_REF]Manning et al., 2006;[START_REF] Giovannoni | Fruit ripening mutants yield insights into ripening control[END_REF]Vrebalov et al., 2009;[START_REF] Bemer | The Tomato FRUITFULL Homologs TDR4/FUL1 and MBP7/FUL2 Regulate Ethylene-Independent Aspects of Fruit Ripening[END_REF]. Other mutants include cell wall mutants, such as expansion (Exp1), pg2, Pectin methylesterase (PME), cellulose (Cle1), tomato β-galactosidase (TBG1 and TBG4) [START_REF] Brummell | PRIMARY CELL WALL METABOLISM DURING FRUIT RIPENING[END_REF], Sugar and organic acids mutants, such as 2-oxoglutarate dehydrogenase complex (OGDH) as well as fumarase and malate dehydrogenase (MDH) mutants were also generated [START_REF] Centeno | Malate Plays a Crucial Role in Starch Metabolism, Ripening, and Soluble Solid Content of Tomato Fruit and Affects Postharvest Softening[END_REF]Araújo et al., 2012). Another tomato mutant, GOLDEN2-LIKE (GLK) shows gradient expression of GLK can influence the uneven coloration of green and ripe in fruit. In addition, GLK expression may under regulation of histone modification, suggesting potential function of epigenetic on the fruit ripening process [START_REF] Nogueira | Subchromoplast Sequestration of Carotenoids Affects Regulatory Mechanisms in Tomato Lines Expressing Different Carotenoid Gene Combinations[END_REF].

In recent years, the coordinated changes during tomato development and ripening was analyzed using combined transcriptome, metabolism and proteome characterization (Osorio et al., 2012). However, it appears that a full understanding of tomato fruit development and ripening will not be achieved based only on genetic models. In addition epigenetic regulation, mainly genomic DNA methylation may play a key role in this process (Teyssier et al., 2008;Zhong et al., 2013). However, the study of how fruit development and ripening process is controlled at the epigenetic level is still at its early beginning. Indeed several evidence point out the importance of DNA methylation and chromatin regulation on fleshy fruit development and ripening ripening (reviewed inGallusci et al., 2016). For example, the fruit ripening defect of Cnr mutant is caused by hypermethylation of an upstream region of the CNR promoter (Manning et al., 2006). Zhong et al (2013) also detected that, the promoter region of several genes are demethylated during tomato fruit ripening, suggesting that DNA demethylation may play critical role during this phase of development (Zhong et al., 2013). Indeed we have now shown that active DNA demethylation is critically important for fruit ripening to occur. Phylogenic analysis of DNA demethylases in Arabidopsis and tomato has pointed out that among the four tomato DML genes, SlDML1 and SlDML2 are orthologous to AtROS1, SlDML3 to AtDME (DEMETER), while SlDML4 has no closely related Arabidopsis orthologue (Liu et al., 2015). Tomato DML RNAi plants present fruit ripening defect, likely mediated by inhibition of the expression of key ripening regulator genes RIN, NOR, CNR and carotenoid biosynthesis enzyme PSY1 (Liu et al., 2015). Based on this finding, SlDML2 is considered to be a master Chapter3 71 epigenetic regulator that governs tomato fruit ripening by controlling the DNA methylation level at least at these four genes.

However, the pathways under the regulation of SlDML2 have not been comprehensively identified. With the aim to obtain a more comprehensive view of the roles of active DNA demethylation on tomato fruit development and ripening, we have performed a comparative analysis of the transcriptome and metabolome of WT and DML RNAi fruits at eight fruit development and ripening stages. These analyses was integrated with tomato epigenome determined in WT Ailsa craig plants ( Zhong et al 2013). These analyses reveal that in addition to the four genes (RIN, NOR, CNR, PSY1) previously characterized a large number of metabolites and genes present differential accumulation and expression patterns respectively in DML RNAi transgenic fruits. For example, carotenoid, ethylene biosynthesis and signaling, cell wall synthesis and dissembling, transcription factors, and manu y others are extremely affected in transgenic fruits. These results suggest that several genes, including those playing essential roles for fruit development and ripening might require demethylation for their expression. Here, we present evidence for the first time that active DNA demethylation has very global effects on fruit development and ripening.

I-Fruit Physiology and four DMLs Repression levels in transgenic fruits

To analyze at the molecular and biochemical level the fruits formed by RNAi DML transgenic plants, two independent cultures were performed. For line 8, we used the culture already analyzed in Liu et al (2015). For line 2, a new culture was performed in order to increase the number developmental stages harvested. Interestingly, Line 2 plants from T2 generation showed two distinct phenotypes. Sixteen plants out of the 23 used in this experiment showed fruits with an increased carpel number that will be subsequently referred to "fruits with multiple carpels", whereas 7 plants showed no change in fruit shape or developed fruits smaller than WT (Small fruit). To distinguish between these two fruit phenotypes observed in line 2, fruits with multiple carpels, named line 2Y, were sampled separately from small fruits that were named line 2 X. The same relevant WT control (WT1) was used for both line2Y and line2X. Fruits were harvested at 7 different developmental stages : 20, 30, 35, 39 (equivalent to the WT1 Breaker stage), 46 (equivalent to the WT Red Ripe stage), 55, 70, 85dpa. The samples for line 8 and the relevant WT control (WT2) are described in Liu et al (2015), including an azygous sample at 20 dpa. In this case, fruits were harvested at 5 developmental stages: 20, 35, 39 (equivalent to the WT1 Breaker stage), 55, 70, 85dpa. In total, two independent T2 lines, lines 2 and 8, were used in this study, and for line 2 plants two sublines that differed on fruit size and shape were sampled separately. For each line and subline three individual plants were used as biological replicates for the production of RNA-seq libraries and for GC-MS and NMR analysis.

Fruits from both Line 2Y and Line 2X showed a strong inhibition of the ripening process (Fig 3 .1 A) similar to those previously described for Line 8 and Line 2 (Liu et al., 2015). Indeed, some variations were consistently observed between plants of the same line and subline, as previously documented (Liu et al., 2015) RNA seq data obtained from WT1, WT2, line 2X and Y and line 8 were used to determine the expression level of the 4 tomato SlDMLs gene (Fig 3.1B,p73). Expression patterns in WT were essentially as described in Liu et al (2015). In particular, SlDML2 was the more highly expressed SlDML gene in fruits and is characterized by a sharp increase at the breaker (Br) stage in WT, before decreasing to half of its maximum expression level at 46 dpa, and to almost undetectable levels in fruits at 70 and 85 dpa. In contrast, in transgenic fruits of lines 2 and 8, SlDML2 is knocked down to 50% of WT level during early fruit development and severally repressed at the Br stage. However, SlDML2 mRNA levels increase in overripe fruits to levels higher than WT fruits of the same age. SlDML1 is also repressed by 50% of WT level at 20 and 30 dpa but increased at later stages to levels higher than WT fruits. No major effects were observed on SlDML3 and SlDML4 genes. Similar results are observed in both transgenic lines, consistent with previous conclusion obtained by Q RT-PCR using these transgenic lines. Hence, ripening defects are correlated with the strong repression of SlDML2 during fruit ripening (Liu et al., 2015).

PCA analysis of metabolic compositions allows the separation of WT and transgenic fruits during ripening

To visualize the modifications of WT and DML RNAi fruits metabolic composition through development and ripening, PCA were performed on line 2 and line 8 separately and their respective WT controls. For Line 2, all data including primary metabolites determined by GC-MS and NMR, as well as chlorophylls, carotenoids, lycopene and starch were integrated together. When similar compounds have been analyzed by GC-MS and NMR, only GC-MS result were considered. Altogether, 58 metabolites from GC-MS, 15 from NMR, and chlorophylls, total isoprenoids (including beta-carotene and lycopene) and starch, in total 74 metabolites were considered for line 2 and WT1. For line 8 and WT2 the 64 metabolites obtained by GCMS were used for the PCA analysis.

For WT1 and Line 2, PC1 and PC2 represent 37.1%, 16%, respectively of the total differences in metabolite composition. Similarly for Line 8 and WT2, PC1 represents 30.7% and PC2 19% of the total differences (Fig 3.3,figS3.3,p77,p133). In both cases, a clear separation is observed between early and late developmental stages for both WT and transgenic fruits, which are mainly separated along PC1. WT1 and WT2 from 20dpa to the Br stage were clustered together with transgenic fruits of line 2 and 8 respectively, from 20dpa to 46 dpa (corresponding to Br+7 in WT), indicating that at these stages the changes of metabolites of fruits is very similar in both type of genotypes. At later developmental stages (starting after 46dpa for DML lines, and at Br stage in WT) and older stages up to 85dpa, WT1 and WT2 fruits were all clustered and clearly separated from fruits of line 2 or line 8 respectively of the same age that also clustered together.

When analyzing the compounds responsible for the separation between samples, major differences between Line 2 and WT1 are due to dehydroascorbate, galactose, glucose, Gln, fumarate. Adenosine-like, galactinol, glycerate, carotenoids, xylose as well as malate. Similar results are found for line 8, with the exception of isoprenoids and starches that were not considered for this line. In addition, galactose, raffinose were quite different in line 8 as compared to line 2.

Sugars, organic acids, amino acids, pigments show different accumulation pattern in WT and transgenic fruits

To determine the differences in accumulation patterns between WT and transgenic fruits, K-means clustering was performed using metabolites showing significant differences between WT1 and Line 2Y. A total of 64 compounds were used here (see method). Six clusters were obtained for WT and transgenic fruits that could be ranged in four major accumulation patterns. (i) the abundance of most metabolites in WT1, increased at Br, but almost all these metabolites showed a delayed increase (cluster 5 at 46 dpa) or a delayed and reduced accumulation pattern (cluster 6 at 70dpa) in transgenic line; (ii) the abundance of metabolites in clusters 1 and 2 decreased from Br onward in WT. A similar pattern is also found in the transgenic lines but at later stages at 55dpa or later at 70dpa in transgenic fruits (Fig3.4, p79); (iii) metabolites in Cluster 3 dramatically increased at very late stages (70 and 85 dpa) in WT fruits but the increase does not occur in transgenic fruits; (iv) cluster 4 showed stage specific accumulation pattern, while in transgenic plants almost keep stable level. Compound in each group is indicated in table (Fig 3.4B,p79). The pathway map that shows significantly changed metabolites between WT and transgenic fruits indicates that major differences are observed at ages corresponding to WT fruit ripening (Fig3.5, p80), consistent with the results of the PCA and cluster analyses (Liu et al., 2015). As a conclusion, the general trend is that soluble sugars, amino acids, organic acids and also secondary metabolites, accumulation or degradation is delayed and for some of them remains limited at low levels in transgenic fruits as compared to WT fruit of the same age during the ripening phase (Fig3. 4,Fig 3.5).

Accumulation of sugars

Accumulation kinetics of major soluble sugars were measured using H1 NMR in WT1 and WT2 WVA106 fruits during fruit development and ripening were quite similar to those previously described in Ailsa craig (Carrari et al., 2006)and in WVA106 (Fig 3.2, p 75 and Liu et al, 2015 ).

Glucose and fructose accumulated in a linear manner from 20 to 39 dpa and peaked at the red ripe stage 46dpa, before a slight decline in overripe fruits (55 dpa onward). Cell wall related sugars, such as galactose, guanosine show an accumulation pattern similar to glucose and fructose, in contrast to raffinose, another cell wall related sugar, which showed an opposite trend.

In contrast to what observed in WT1 and WT2 fruits, glucose, fructose and galactose accumulation remains very limited at all stages in DML RNAi fruits of lines 2 (Fig 3.4,Fig S3.1 p79,p131). Consequently, whereas sucrose, declined in WT 1 (cluster 1), it remained abundant even at late stages indicating that this sugar was not efficiently metabolized in transgenic fruits, but this is not the case for sucrose in WT2 and line 8. The accumulation profile of glucose and fructose in DML fruits is similar to the one observed in fruits of the rin, nor and Nr mutants. However, sucrose behaved in the different way as compared to these three mutants that are all characterized by a significant decrease in sucrose content (Osorio et al., 2011).

Accumulation of amino acids

When considering the amino-acids, 21 and 14 were analyzed with GC-MS and NMR respectively, a subset of which presented clearly distinct accumulation patterns in transgenic fruits of both lines as compared to fruits of WT1 and WT2 controls. In WTs, the changes in amino acid content followed essentially two major patterns (1)Glu, Asp,Trp, Ala, Tyr, Gly amount increased during fruit ripening, which located in clustering patterns (i) and (iii).( 2) the abundance of GABA, Ser, Thr, Val, Phe, Ile, β-Ala, Leu decreased from 46 dpa to 85 , although not exactly with the same profile consistent with clustering pattern (ii). In transgenic fruits, these accumulation profiles were changed; with the major differences being observed at fruit ages corresponding to ripe and over ripe WT.

Among the main effects observed, the content in a few amino acids displayed a delayed and limited reduction in transgenic as compared to ripening WT fruits. Thus, Asn, pyroglutamate and Gln remained at high levels in transgenic plants from 55dpa onward, although their content decreased at later developmental stages (70 and 85 dpa). A similar trend was observed for GABA and Val, although in these cases, the differences were transient and occurred between 39 and 55 dpa (Fig 3.5).

In contrast, other amino acid showed a reduced accumulation level in transgenic fruits as compared to WT fruits of the same age. This was observed for Leu, Ile and Ala from 39dpa to 85 dpa (Leu) or later from 46 dpa onward (Ala and Ile). Asp and Glu as two major amino acids, which were also clustered in cluster 5 showed delayed and even higher accumulation in transgenic fruits.

Accumulation of organic acids

82 When considering Organic acids, they show specific behaviors during WT fruit development and ripening. Hence malate, a major TCA intermediates, accumulates to reach the highest level in immature fruits, and starts decreasing at 46 dpa and later stages. Citrate followed an U shaped accumulation kinetics whereas, fumarate remains at rather low level all through fruit development.

Succinate accumulated at very low levels and followed a wave like accumulation kinetic. Finally, 2-oxglutarate peaked at Br+7 in WT. In transgenic fruits, all of these intermediates behaved differently as compared to WT. For example, malate amounts are similar to WT up to the breaker stage, although slightly more abundant in a few plants. In contrast to WT fruits characterized by a sharp decrease in malate content after 46 dpa (6 fold decrease), malate content remains high at 46 dpa before a very progressive decrease from 55 dpa onward. It reached a level similar to WT fruits only after 85 dpa. Considering fumarate, in contrast to WT fruits this compound accumulate in transgenic fruits with the highest content observed at 39 and 46 dpa, before a slight decrease at later developmental stages. Citrate, although the kinetic of accumulation detected using GC-MS and NMR were different, behaved with both methods similarly in transgenic and in WT fruits as previously described (Liu et al., 2015, Sup data Fig S5, p48). Fumarate was slightly more abundant at certain stages in the transgenic lines.

Additional compounds also showed significant differences between line 2 and WT1 at specific fruit developmental stages. For example, organic acids that do not belong to the TCA cycle, including phosphorate, threonate, ethanolamine, nicotinate, galactinol, but also sugar alcohol and sugar phosphate, and octadecanoate, myo-inositol, didn't display clear peaks at the onset of fruit ripening although some of them increased gradually (ethanomamine, galacturonate, threonate, adenosine_like, threitol, guanosine) or inversely decreased (glycerol, myo-insositol).

Accumulation of pigments

Pigments, including chlorophylls, lycopene and total carotenoids were dramatically affected in transgenic fruits. In WT fruits, Chlorophylls showed gradual degradation during development, to reach undetectable levels in red ripe fruit. In transgenic fruits of both line 2 (Fig 3.5 and 8 (fig S3.1), chlorophyll degradation is delayed and chlorophylls were still detected even at 55 dpa. This pattern is similar to the one observed for starch and malate (cluster 1).

Lycopene and total carotenoids are known to accumulation at very high level during tomato fruit rienng (Liu et al., 2015). In WT fruits lycopene was first detected at the breaker stage and reach a maximum level accumulation level at Br+7 (46dpa) and remained highly abundant at later stages in WT fruits. In transgenic fruits, the lycopene accumulation is delayed and dramatically limited. It could hardly be detected at 39 dpa in line 2 plants and 39 in line 8 and its accumulation remainded very limited in both caseq. A similar behaviorwas observed for major sugars (fructose and glucose), and also for galactose which all clustered together (cluster 6).

Network analysis indicates that RNAi DML transgenic fruits display higher network density than WT

To compare the metabolites network in WT and RNAi DML transgenic fruits, we evaluated pairwise correlations of metabolites in each genotype, separately. The same metabolites as those used for clustering analyses in line 2 were also used for pairwise correlation analysis, but only using five developmental stages (35,Br,55,70,85dpa) in order to focus on on fruit ripening.

83

Similarly 50 compounds obtained by GC-MS for WT2 and line 8 were analyzed at the same developmental stages.

Results indicate that 254, 466, 185 pairwise correlations between metabolites could be identified that were unique in WT or in transgenic fruits, and common to both type of fruits, respectively. Similar results were obtained with line 8 (130, 222, 87, pair wise correlation with WT2, in line 8, and both, respectively) (tableS1, provided as additional excel file online).

We subsequently extracted these two types of correlation to determine the corresponding metabolite connections (Fig3. 6, p84; figS3.4, p34, table S1). Obvious examples are pigments and starch that showed more correlated pairs than in WT1. Sugars related to cell wall metabolism, including rhamnose and xylose also had more correlated pairs than in WT (similar to line8/ WT2 analysis). Another cell wall compounds, galactose, behaved in a distinct way. Only 2 common pairs of significant correlation were found in WT and line 2Y (Gln and glucose), but 15 unique pairs were found in WT. This is consistent with the specific accumulation pattern of galactose that do not change along the fruit ripening process in transgenic fruits (FigS3.1, p131). Another striking example is malate, a major intermediate of the TCA cycle. Malate show 9 pairs of significant correlation with other compounds, including positive correlation with citrate, pyroglutamate, galactose in WT1 consistent with the observation that these compounds accumulate in a coordinated way. In contrast, these correlations are not maintained in RNAi DML transgenic fruits, but 28 more pairs were found, for example positive correlation with rhamnose, sucrose. This indicates that primary metabolism as well as carotenoid pathway was affected during fruit ripening in transgenic fruits and suggests that the repression of demethylation affects differentially the accumulation of the different metabolites detected in this study.

III. RNA seq analysis WT and RNAi Transgenic Lines

Previous results have shown that three key fruit ripening regulators (RIN, NOR, CNR) and lycopene biosynthesis gene PSY1 were extremely repressed (RIN, NOR, PSY1) or delayed (CNR) in transgenic fruits (Liu et al., 2015b, Chapter 2). Moreover, the promoter regions of these genes were hypermethylated in RNAi transgenic fruits as compared to WT fruits. In addition, metabolic analyses showed significant differences during fruit ripening between WT and DML RNAi transgenic plants. In order to complete the networks of genes that were differentially expressed in WT and DML transgenic lines and to label out the potential DMLs primary targets, we have characterized transcriptomes using the same tissues as those used for metabolic analysis.

Summary of RNA seq data

RNA seq analysis was performed as described in Zhong et al, (2013). A total of 72 (line 2) and 36 (line 8) samples were analyzed by RNA seq which generated between 3.27 to 14.12 million reads per sample (sampling method see materials and methods). Given the high number of samples, and the quality of the tomato genome assembly, the targeted number of counts was 10 million for all samples. This was shown to be sufficient to determine the main differences between samples but will not allow identifying differences in weakly expressed genes. After filtering 2.57 to 12.25 million reads were obtained between 77.63% and 93.36 %, which could be mapped to the tomato reference genome (Table S2). These analyses were performed in the laboratory of J Giovannoni, using the protocols and bioinformatics pipelines described in Zhong et al (2013).

Differential Gene Expression between WT and transgenic fruits

To identify the differentially expressed genes between WT and transgenic fruits, all DEGs were analyzed by DESeq2. A total of 15,556 genes in WT1 and Line 2Y, 15,556 genes in WT1 and line2X, 14,274 genes in WT2 and line 8, approximately 44.8%, 44.8% and 41.1% respectively of the annotated genes in the tomato genome (Tomato Genome Consortium, 2012), were expressed in at least one sample, The size of the different libraries is shown in FigS3.5 (p135). There was little variation in the total number of genes represented at each stage, similar to other fruit transcriptomic studies (Pattison et al., 2015).

Normalized read counts from independent biological replicates within one line was highly correlated at each stage (R2>0.98) (line2Y compared with line2X), whereas the correlation between line2Y and line8 was lower (for example, R2=0.892 at 55dpa). This suggests variations between lines at the stages analyzed. A higher correlation between adjacent stages was also detected in transgenic lines than in WT meaning that the Chapter3 86 expression pattern of adjacent stages is more similar in transgenic plants as compared to WT fruits (fig3.7A, figS3.6, p87 and p136). Differentially expressed genes (DEGs,Fig3.7,figS3.6,p87 and p136) were identified by pairwise sample comparisons, and those differentially expressed in at least one stage were recorded as DEGs (Method is described as materials and methods). In total, 9,975; 10,095 and 8,390 genes were identified as DEGs in Lines 2Y and 2X versus WT1 and line 8 versus WT2, respectively.

The numbers of up-and down-regulated genes according to fruit stages are shown in Fig. 7B and FigS6B (p83,p130). When comparing the distribution of DEGs at each stage between the different lines, a similar pattern was observed in line 2X, 2Y and line 8, although line 2Y is closer to line 2X as expected. At early stages, from 20 days postanthesis (dpa) until before Breaker (Br) stage, the number of DEGs remained low ranging from 301 to 617 in line2Y, 238 to 486 in line 2X and 38 to 201 in line 8. This indicates that there is little difference between WT and DML RNAi fruits during tomato fruit development. Obviously, there is a sharp increase in DEG number from Br stage and during ripening and later. DEG numbers varies from 3404 to 6759 in line 2Y, 3268 to 7045 in line 2X and 4327 to 5047 in line 8. This clearly indicates that the effect of DML knock down mainly affect the fruit ripening process and has very little impact on early stages of fruit development. Increase in DEG number observed at Br of fruit ripening could be linked to the induction of genes observed in WT fruits at the Br stage (Fig 3.8A,p90). This massive gene induction is not observed in transgenic plants of line 2 and 8. Additionally, many genes are also down regulated in WT fruit at this stage, a phenomenon also not observed with the same intensity in transgenic fruits (see below). It should be noted the number of DEGs is higher when comparing line 8 to WT2 than lines 2 (X and Y) to WT1 at the Br stage. However, as explained above, both cultures were performed independently at two different seasons (line 2 is mainly in spring, while line 8 is in winter). Hence, WT fruits of the same age were more advanced in the line 2 culture than in the line 8. For line 8, WT fruits were at the late Br stage but Line 2 is at early the breaker stage. Comparatively, fewer genes are likely induced at the early breaker stage in WT1 fruits as compared to WT2 fruits at the late breaker stage, the number of DEGs at this stage might be reduced in line 8 versus WT2, as compared to line 2 versus WT2.

For further analysis, DEGs that are common between all lines at selected time points (20, 35, 39, 46, 55, 70 and 85dpa) in all lines (Line 2Y/2X and line 8) were selected. In total, 6212 DEGs satisfied this condition. Additional DEGs that were found in only one line, the list of which is shown in table S3, will not be included in the analysis presented below (Fig3.8B, p90).

To determine the reliability of RNA seq data, five of the DEGs (RIN, NOR, PSY1, ACS4, ZISO) in Line 2Y; eight DEGs (RIN, NOR, CNR, PSY1, ACS2, ACS4, PG2a, ZISO) in line 8 were analyzed at the 8 and 6 stages respectively were checked using QRT-PCR. As shown in Supplemental Figures S3.6C, S3.6D (p136). The RNA seq data were confirmed for the downregulated genes in line 2Y, in line 8. RNA seq data is consistent with qRT-PCR (R2>0.8 in each genotype). In a conclusion, all of these checked DEGs show consistent changes, which confirming the reliability of RNA seq data.

Comparative analysis of transgenic and WT fruits

To assess the dynamics of transcriptional patterns among samples, principal component analysis (PCA) and hierarchical clustering were performed on all the DEGs selected above (Fig 3.9,Fig S3.7,p92 and p137). Both analyses confirmed that most differences in gene expression profiles occurred during the fruit ripening process. The first two principle components explain approximately 68% of the variation at the global transcriptomic level for WT1 and line 2Y/2X (70% for WT2 and line 8, including an azygote line at 20dpa). Before fruit ripening from 20dpa to the Br stage, WT and transgenic fruits were plotted together. The first principal component, which explains 49.3%, separates WT at 46dpa and later ripening stages (55dpa~85dpa) from all other samples; whereas the second principal component (17.7%) (19.8% for WT2 and Line 8) separate WT and transgenic fruits from 20 to 39dpa; from the transgenic fruits at 46dpa and more. Obviously, most of the transcriptomic variance is detected during fruit ripening, as previously described (Liu et al, 2015b).

To discriminate between DEGs, all DEGs were first separated based on the log2FC ratio (Line2Y versus WT1) at each stage (To be clear, here the separation of all DEGs is based on common DEGs were defined above). Once those showed Log2FC<-1 at any stage (among 8 stages that were detected), were considered as downregulated DEGs genes. Those with a Log2FC ration above 1 were considered as upregulated genes in transgenic as compared to WT. This implies that DEGs belonging to the upregulated class are never repressed in transgenic fruit compared with WT. Thus downregulated and upregulated genes were clustered separately.

All DEGs fall into 9 clusters that can be organized in three distinct groups: (i) group 1 corresponding to Clusters 1, 2, 3, represents a total of 3499 genes which show absence or delayed down regulation in transgenic fruits as compared to their repression during WT fruit ripening (ii) group 2 corresponding to clusters 4, 5, represents 1345 genes that show no or delayed induction in contrast to their strong induction observed during WT fruit ripening (iii) group 3 corresponding to clusters 6, 7, 8, 9 represents 1368 genes that show stage specific down regulation during fruit development and ripening in transgenic fruits as compared to WT fruits of the same age (Fig3.10, p93). Number of DEGs in each cluster was listed in table1.

In order to analyze how the global difference of DEGs in three groups, we used Log2FC (2Y/WT1) of all DEGs to plot in PCA again, as in clusters, we found that most genes were overlapped in their own group, indicating the fold change of these genes between WT transgenic fruits occurs on the similar stages. Genes in group 1 and group 2 were separated by those of group 3, which is widely overlapped with group 1 and group2, since the expression of genes in group 3 is either similar to group 1 or group 2, except 39dpa to 55dpa were different with group 1 or group 3, this is the reason why group 3 is overlapped with group 1 and group 2. This result is consistent with the grouping of clusters that show distinct transcript accumulation patterns among the three groups. However as genes in group3 present stage specific repression they might appear similar with those of (A) group 1 correspond to clusters with genes being less expressed in WT than in transgenic at all stages of fruit development (cluster 1-3) (B) group 2 corresponds to DEGs induced at the Br stage in WT and expressed during fruit ripening and at later stages, whereas they are not expressed or lately expressed in transgenic fruits and (cluster 4-5) (C) group 3 correspond to clusters with stage specific differences between WT and transgenic fruits, with clusters 6-9 corresponding to genes induced at Br and expressed during fruit ripening but not at late sages in WT, and induced at very late stages ( after 55 dpa)n cluster 8 to genes induced at late stages ( after 55 dpa) in WT but not in transgenic fruits and Pink, transgenic fruits; Green: WT, black and blue lines are the mean value of calculated using the normalized counts.

A B C

Cluster 5_441 genes Chapter3 93

DEGs distribution within in each cluster

To investigate the distribution of DEGs in biological process, we performed gene enrichment analysis for each group and each cluster, using mefisto software that has ranked genes in 35 MapMan functional categories termed BINs (TableS4, provied as additional excel file online), as indicated in the material and methods [START_REF] Usadel | Extension of the Visualization Tool MapMan to Allow Statistical Analysis of Arrays, Display of Coresponding Genes, and Comparison with Known Responses[END_REF].

DEGs belonging to group 1 (clusters 1, 2, 3 including 920, 2441, 138 DEGs respectively), are in general repressed in WT fruits either during all the ripening process (clusters 1 and 2) or more specifically at the Br stage (cluster 3). However, in transgenic fruits, group 1 DEGs showed distinct expression profiles as compared to WT. DEGs from cluster 1, are induced instead of repressed during fruit ripening. For cluster 2 and 3, DEGs are also down regulated during the ripening of DML RNAi fruit, but their repression level remains limited as compared to WT. Transgenic fruits in cluster 2 showed a slight decrease all along fruit development and ripening, unlike cluster 3, WT presented specific drop at Br stage, causing the separation of cluster 2 and cluster 3 (Fig3.10A, p93).

Gene enrichment shows that Group1 over-represented genes belong to 15 categories (Fig3.11, p95, see table S4). Indeed many genes are unknown, and misc belong to misc. However, the main functional categories correspond to RNA (including RNA processing, transcription and transcription factor), signaling (including sugar and nutrient physiology, receptor kinases) and many cell wall genes.

More interesting, when over-representation were performed on each cluster separately, genes involved in photosystem and cell wall were only enriched in cluster 2. In hormone category, 8 genes responsible for brassinosteroid synthesis and degradation were also found in this cluster. Only histone genes (DNA functional category) were over-represented in cluster3 (Table S4, provided as additional excel file online). Group 2 includes 904, 441 genes in cluster 4 and 5, respectively. In WT fruits the expression of cluster 4 and 5 genes peaked at the Br stage (39dpa), or even later at 46 or 55dpa. In contrast, in transgenic fruits, DEGs from cluster 4 are characterized by a delayed increase in expression that occurs at 70dpa or later, whereas most DEGs in cluster 5 are not induced and remain at the same level throughout fruit development and ripening. In addition, most group2 DEGs are expressed at very low levels in transgenic fruits of both lines 2 and 8. Only 6 functional categories were over-represented in this group (Fig 3.10B,p93). The most abundant subcategory (394 genes) corresponds to genes with unknown function. In addition, 140 genes are related to protein degradation, 48 genes to heat stress, 255 genes to RNA metabolism, including a number of transcription factors, among which the key ripening associated gene RIN (cluster 4) and 7 genes encode receptor kinases. This is consistent with the fruit ripening defect phenotype (see Fig 3.11, p95, and liu et al., 2015b), as genes like RIN are major regulators of fruit ripening. Therefore, huge amount of genes in category of protein degradation, especial ubiquitin was also overrepresented in this group, indicating the normally degradation of proteins during fruit ripening, while the degradation is delayed in transgenic fruits, this is consistent to fruit ripening inhibited fruit phenotype.

When considering clusters enrichment in group 2 separately, we found that all the categories in group 2 (Fig3.11, p95) except signaling were found in cluster 4 and cluster 5, although stress category was not significantly enriched in cluster 5, indicating at least 4 major functional categories in this group, including protein degradation, DNA, RNA and unknown were mainly affected in DML RNAi transgenic fruits (TableS4, provided as additional excel file online).

Group3 which correspond to clusters 6 to 9 is characterized by genes overexpressed in transgenic fruits as compared to WT at specific stages of fruits ripening. In cluster 6 most genes peaked at ripening induction (Br, 39dpa) or at the fully ripe stage(46dpa) of WT fruits, dropped at later stages when fruits were over-ripe, but in transgenic plants, almost all the induction is very limited. Therefore, in transgenic fruits, most genes in this cluster were extremely repressed at 39 to 55dpa, but not at 70-85dpa. This cluster also include some genes were slightly repressed at early stages. DEGs belonging to cluster 7 lately induced in the transgenic fruits (after 70dpa), whereas these genes are highly expressed in WT between 39 (Br) and 55 dpa and drop at later stages when fruits were over-ripe. Therefore, most genes in this cluster appear extremely repressed between 39 to 55dpa, but are more expressed in transgenic than in WT fruits at 70-85dpa. In clusters 8 and 9, gene expression in WT peaked at Br or Br+7dpa and Br+7 or 55dpa respectively. Then their expression level dropped down, however, in transgenic fruits, the induction were delayed even until 55-85dpa.

Most WT genes in cluster 8 were dropped at Br or B7, but induced at later stages, from 55-85dpa. However, in transgenic fruits, these genes kept slightly declined trend from early stages. Chapter3 96 Seven categories were over-represented in this group, including genes related to specific pathway, hormone metabolism, amino acid, lipid metabolism and cell wall.

In cluster 6, genes were over-represented with eight categories. Six DEGs that are considered as hallmarks of the ripening process are found in this cluster. They correspond to the NOR, a NAC transcription factor necessary for ripening induction (Giovannoni 2004), the PSY1 gene that governs carotenoid accumulation [START_REF] Bartley | A tomato gene expressed during fruit ripening encodes an enzyme of the carotenoid biosynthesis pathway[END_REF], the polygalacturonase gene PG2a involved in cell wall softening (Zhong et al., 2013), the ACC oxidase gene ACO3(E8), involved in ethylene synthesis during fruit ripening (Kneissl and Deikman 1996), E4 (Lincoln et al., 1987), and the Zeta-carotene desaturase ZDS gene encoding another critical enzymes of the carotenoid pathway (Fantini et al., 2013). Genes involved in ethylene biosynthesis and signaling are particularly enriched in cluster 6, including ACS2, ACS4 (ACC synthase) and various ETR (ethylene receptors) genes. As well as genes encoding proteins involved in jasmonate synthesis and degradation. This is consistent with the idea that many genes of cluster 6 are tightly related to the fruit ripening process.

Only 3 functional categories are overrepresented in Cluster 7 genes with 95 genes related to RNA metabolisms, including 11 homeobox (HB) transcription factors, 31 to cell whereas 111 DEGS were not assigned. Four functional categories were over-represented in Cluster 8 , in addition to 45 not assigned genes, 10 genes in amino acid metabolism (3 genes involved in glutamate family), 7 genes in ethylene synthesis and degradation (TableS4, provided as additional file on line). Among the 25 DEGs of cluster 9, 7 DEGs are related with ethylene synthesis, degradation and ETR genes were found in this cluster.

DEGs associated with DMR are distributed among all clusters and groups

Among the DEGs we have identified, it is very likely that only part of them will be directly regulated by their DNA methylation level. In order to determine these direct targets, Whole Genome Bisulfite Sequencing has been initiated in collaboration with Pr J Giovannoni's laboratory. However due to technical difficulties, the results are not yet available. For this reason, we have decided to use previous results obtained in Pr J Giovannoni's laboratory that have shown that many genes are demethylated during the ripening of tomato fruits (Zhong et al., 2013). To determine what genes, among the DEGs contain differentially methylated regions (DMRs), DEGs were compared to a list of genes that were shown to contain DMRs within the first 2kb of their promoter region (personal communication from Dr Fei, Boyce Thompson Institute, Cornel NY). These DMRs lists were determined by calculating the average methylation levels on a sliding window of 100bp with 50 bp iteration as described in Zhong et al (2013). It should be noted that this list of genes was obtained by analyzing the development of Ailsa Craig tomato fruits, and we cannot formally rule out that some differences may exist with the WVA106 variety used in our study and Ailsa Craig. However, genes that were shown to contain DMRs in this previous study-RIN, NOR, CNR, PSY1-were also identified has differentially methylated in WVA106 (Liu et al., 2015b), consistent with the idea that DMRs are conserved between both varieties. To identify the DEGs containing DMRs in their promoter regions, the list of common DEGs identified in line 2Y, line 2X, and line 8 and its corresponding WT was crossed with the list of DMRs containing genes (Zhong et al., 2013, Dr Fei, personal communication).

A total of 3,113 DEGs containing one or more DMRs in their promoter region were identified (see Table S9, provided as additional excel file online). DMRs were classified based on two ratios calculated using the DNA methylation percentage. R1 is the ratio between the methylation at 17dpa and breaker stage (42dpa) and R2 at 17 dpa versus breaker+10 (52 dpa). Four main types of situations were found (table 1): (type-a) DEGs with a unique or more DMRs that have both R1 and R2 above 1, this indicates that DNA demethylation occurs at all DMRs during fruit ripening. 2,259 DEGs correspond to this situation; (type-b) DEGs with a unique or more DMRs that have R1 and R2 ratios below 1, consistent with an increase in methylation during fruit ripening at all DMRs. 294 DEGs belong to this class; (type-c) 285 DEGs with more than one DMR but have opposite behaviors, in addition at least one has a type -a behavior and another one with a type-b; (type-d) 294 DEGs with DMR that have the opposite ratios between R1 and R2 at lease in one DMR (See FigS11). Chapter3 98 Surprisingly, DEGs that contain DMRs are found in all three expression groups and almost all clusters. In addition each type of DMR was distributed among the different DEG expression groups (table 1, p91).

In this study, SlDML1 and SlDML2 were suppressed in RNAi DML transgenic plants, especially only SlDML2 was extremely suppressed at breaker stage. Normally, only this gene has the dominant expression during fruit ripening in WT. However, as only DMRs corresponding to a decrease in methylation level during fruit ripening are potential targets for SlDML2 and might therefore be the most relevant in this study (Fig10B, 10C, p89, table1, p95), therefore, further work was focused on genes containing type-a DMRs corresponding to their clusters. Thus, to have the global overview on DEGs with type-a DMRs, gene enrichment were analyzed with over-representation (table 2, p101). DEGs with type-a DMR in group 1 are abundant, involving 12 functional categories: photosynthesis (34 genes), cell wall (52 genes), lipid metabolism (44 genes), amino acid metabolism (11 genes), brassinosteroid (7 genes), C1-metabolism (7 genes), misc (140 genes), RNA (100 genes), kinase (32 genes), signaling (119 genes), transport (97 genes) and 266 no assigned genes.

Those belonging to the expression group 2 range in 4 main functional categories: glycolysis (3 genes), abiotic stresses (22 genes), more specifically heat stress including heat-shock transcription factors, protein degradation (43 genes) and a number of unknown genes (107genes). Concerning group 3, DEGs with type-a DMRs correspond to cell wall degradation (11 genes), lipid metabolism (22 genes), ethylene (14 genes) and UDP glucosyl and glucuronyl transferases (17 genes in misc group) and 112 genes correspond to unknown proteins.

To visualize the distribution of DEGs with DMR among the different DEGs, similar PCA were performed on all DEGs as fig 11A, but this time all DEGs with DMR were labeled with red color (Fig3.12B, p102). Six genes with DMR that were selected (these six genes were far from other genes with DMR, indicating specific difference compare with other DEGs as we can see from table 3 (Fig3.12B,p102;table3,p102). All these six genes contain type-a DMR, except loxC with type-c DMR. Three of these six genes are already known: LOXC, encodes a chloroplast-targeted lipoxygenase isoform responsible for the generation of volatile C6 flavor compounds (Chen et al., 2004). LOXC mRNA amount increases sharply at Br stage in WT. However, this increase is delayed in transgenic fruits. The second gene is LTGP1 encoding a nonspecific lipid transfer protein, a tomato allergen (Le et al., 2006). This gene is highly expressed in WT fruits at early stages until the Br stage, and extremely repressed during fruit ripening. In transgenic fruits, the expression of this gene was extremely repressed at all stages, suggesting that DNA demethylation is necessary for the early expression of LTGP1. AL encodes an acid beta-fructofuranosidase, which is involved in carbohydrate metabolism. AL is highly expressed in style but weakly at stem end of tomato fruit (fruit close the sepal part) during ripening (Nguyen et al., 2014;Zouari et al., 2014).

In this study, this gene is repressed all through the development and ripening process of DML RNAi fruits, while it is strongly induced in WT fruits at the Br stages and further Chapter3 99 increases at Br+7. This indicates that AL may need DNA demethylation for its expression during fruit ripening, as already demonstrated for the NOR or the PSY1 gene (Liu et al., 2015b).

The three other outliners correspond to the uncharacterized genes Solyc01g081250, Solyc06g060410, Solyc09g066150, encoding Glutathione-S-transferase, MORN (Membrane Occupation and Recognition Nexus Domain) repeat protein, Cytochrome P450, respectively. The expression of these three genes peaked at Br+7 or 55dpa in WT, but they are almost totally not expressed at all fruit development and ripening stages in transgenic fruits. This suggests that the expression of these three genes also requires active DNA demethylation during fruit development and ripening.

As a conclusion, all of these six analyzed genes, except loxC containing type-c DMRs, and belong to group 3 or 2, indicating they are potential primarily target of SlDML2.

In the following parts I will detail different metabolic pathway and physiological processes that are critical for fruit ripening and analyze what DEGs between WT and transgenic present potential DMRs. The biosynthesis of the linear C40 lycopene from Geranyl Geranyl Pyrophosphate (GGPP) is one of the most extensively studied metabolic pathways in tomato (Lois et al., 2000;Liu et al., 2015a). Accumulation of lycopene typically occurs during fruit ripening concomitantly to chlorophyll breakdown which result in the typical green to red color change of tomato fruits. All the carotenoid biosynthetic enzymes are located in the plastid, even though the genes are encoded by the nuclear genome. The bottlenecks in carotenoid biosynthesis have been explored by analyzing the transcript level in carotenoid biosynthetic genes and their potential correlation with changes in carotenoid content (for a review see reference (Liu et al., 2015a)). It is well known that a subset of these genes are induced or upregulated at the onset of fruit ripening in WT fruits. They include the genes encoding the 1-deoxy-D-xylulose 5-phosphate synthase (DXS), geranylgeranyl pyrophosphate synthase (GGPPS), phytoene synthase (PSY1), phytoene desaturase (PDS), 15-cis-zeta-carotene isomerase (ZISO), £-carotene desaturase (ZDS), carotene isomerase (CrtlSO). On the contrary, the expression of genes encoding the lycopene ε-cyclase (LCY-E) gene and lycopene ε-cyclase is dramatically repressed at the Br stage of fruit ripening (Lois et al., 2000;Liu et al., 2015a). All these genes (Fig 3.13,FigS3.8,p105,p138) behaved in WVA106 WT1 and WT2 fruits as described in these studies and similarly to previous results obtained on the same variety (Té lef et al., 2006).

An important aspect of the transgenic fruit phenotype is either the absence or the reduced and delayed accumulation of carotenoid during fruit ripening in RNAi DML transgenic fruits (Fig3.2, p75; Fig2.4A in chapter2 p37); (Liu et al., 2015b). We therefore examined the expression profiles of all known genes of the carotenoid pathway as well as those of the genes involved in the 2-C-methyl-erythritol-4-phosphate/1-deoxy-D-xylulose 5-phosphate (MEP/DOXP pathway) that leads to the synthesis of Isopentenyl pyrophosphate, the precursor of all isoprenoids. Plastidic carotenoid synthesis during fruit ripening was shown to initiate from this pathway (Rodrı ǵuez-Concepción and Gruissem 1999).

Eight genes of the MEP/DOXP pathways are differentially regulated between WT and transgenic RNAi DML lines, and one of them, GGPS3 contain putative type-c DMRs in its promoter region (Fig3.13A,3.13C,FigS3.8,p105,p138). Indeed GGPS3 (cluster 7) is not induced in transgenic fruits (log2FC (Line2Y/WT 1) = -1.06; log2FC (Line 8 / WT 2) = -1.60 at 39 dpa) consistent with the idea that demethylation is necessary for the induction of this gene. However, as it promoter region contains two DMRs with opposite behaviors their potential role in the regulation of this genes is unclear. IPI2 is clustered in cluster 2, indicating that this gene is more expressed in transgenic fruits as compared to WT fruits during ripening. However IPI2 contains a type-a DMR in its promoter, also questioning the function of DNA demethylation in this case.

The expression of DXS1 and GGPS2 also increases during WT fruit ripening, but not in DML RNAi transgenic fruits of the same age. As the promoter region of these genes do not contain any DMRs it seems unlikely that they depend on the activity of the DML2 protein for their expression. Thus there is no evidence that genes of the MEP/DOX pathway are directly regulated by methylation. Thirteen of the 29 known genes of the carotenoid biosynthesis pathway are differentially expressed in DML RNAi fruits compared to WT fruits of the same age. Among these genes PSY1, CrtlSO, ZISO and ZDS are clustered in group2. They are induced at the Br (39dpa) and remain expressed at the Br+7 (46dpa) stages in WT, but are not expressed or lately and weakly in all transgenic lines (Fig3. 13B,3.13C,FigS3.8A,3.8C,p105,p138). We have already shown that the PSY1 promoter region contain a Type-a DMR and undergo DNA demethylation during WT fruit ripening but not in transgenic fruits, which correlates with the absence of gene induction (Liu et al., 2015b). Three additional genes, namely, CrtlSO, ZISO, and ZDS also contain a type-a DMR in their promoter, indicating that their expression correlates with demethylation in WT fruits. Thus it is very likely that the DMRs present in the CrtlSO, ZISO, and ZDS promoter region will not be demethylated in the DML RNAi lines thereby impairing their expression.

As previously observed for IPI2, CCD4B and NCED although clustered in group 1 (delayed degradation in transgenic lines) contain a type-a DMR. Two other genes of this pathway do not contain any DMR in their promoter although their regulation is affected in transgenic lines, yet not in a consistent way. CHY1 is repressed at 46dpa in line 2 (log2FC=-2.07), but not in line 8, whereas CHY2 is repressed at 39dpa in line 8 (log2FC=-1.49) but not in line 2.

A number of Transcriptional factors from different families are associated with differentially methylated regions

There are 344 out of a total of the 1845 tomato annotated transcriptional factors (TFs) showed differential expression between fruits of DML RNAi plants of line 2 or 8 and those of WT plants. These TFs include members of AP2/ERF (APETALA 2/ethylene-responsive element binding factor), bHLH (basic helix-loop-helix), bZIP (basic domain-leucine zipper), MYB, WRKY, NAC, MADS and some other families (see tableS5, provied as additional excel file online).

Among those, 177, 84 and 83 genes were clustered in group 1, group 2 and group 3 respectively (tableS5). Some TF families, such as YABBY, GATA, and Nin-like were only found in group1, whereas the E2F, FAR1, NF-YA families were specifically clustered in groups2 and 3 (See tableS5, provide as additional excel file online).

Among the 167 genes clustered in the DEG group 2 and group 3, 81 are associated with a DMR in their promoter region. Sixty five DEGs have a type-a DMR (get demethylated during ripening) and 16 are associated with other types of DMR (type-b, c, d) (Fig 3.14,table S5,p108).

DEGs associated with type-a DMRs belong to various TFs families. 52 are distributed over 14 different TFs families that are represented at least by two members. Thirteen other DEGs belong to 13 additional TF families each represented by a single member. Altogether, this indicated that members of 27 different families of transcriptional factors are potentially directly regulated by active demethylation during fruit ripening.

The most abundant TFs associated with type-a DMRs are members of the HSF (Heat Shock Factor) and of ERF (Ethylene responsive Factor) families (7 and 6 genes in each family, respectively). All members of HSF with type-a DMR are induced at Br or B7 in WT, but were not induced in line 2 or line 8, consistent with their clustering in the DEGs clusters (3 in cluster 4, 2 in cluster 5, 1 in cluster 6, 1 in cluster 7) (Fig 3.14,p108 and Fig 3.10,p93).

The ERF family is involved in ethylene signal transduction. Two of the ERF genes (ERF2, ERF6) are strongly induced at the Br stage and remain expressed during ripening and at later stages (cluster 4 and cluster 6), and two others are transiently expressed during WT ( cluster 5 and 7) fruits ripening ( ERF1 and ERF4). Expression of these 4 genes is either repressed or delayed in the transgenic fruits, in agreement with their association with a type-a DMR. However, the two last ERF are down regulated in WT fruits ripening and appear more expressed in transgenic than in WT fruits (cluster 6). The role of demethylation in this case needs to be determined.

As ethylene synthesis is dramatically delayed and reduced in DML transgenic fruits (Liu et al., 2015b), this may suggest a specific control of this regulatory pathway by DNA demethylation in tomato fruits.

To further access the importance of active DNA demethylation on TFs encoding genes during fruit ripening, TF genes were selected on the following criteria. (i) Firstly, the 20 most

Genes Encoding Cell Wall-Biosynthesis and Modifying Protein are potentially regulated by demethylation

Fruit texture is tensely associated with fruit shelf life and transportability. During fruit ripening, the structure and composition of cell wall polymers are markedly changed, as a result of the expression of genes encoding polygalacturonases, pectin methylesterases and other enzymes involved in cell wall degradation, expansion and extensions [START_REF] Seymour | Regulation of ripening and opportunities for control in tomato and other fruits[END_REF].

We have analyzed the fruit firmness using line 8, as fruits from line 8 have a shape which is similar to the one of WT this allowing a more accurate comparison between the two types of fruits. Results shown in Fig 15D (p108) clearly indicate that transgenic fruits remain firm much longer than WT fruits, suggesting that cell wall metabolism could be affected when DNA demethylation is impaired.

We therefore examined the association between DEGs involved in cell wall metabolism and DMRs. Two hundred fourteen DEGs were identified that are annotated as cell wall related genes according to Mapman categories and reviewed in Seymour et al [START_REF] Seymour | Regulation of ripening and opportunities for control in tomato and other fruits[END_REF]Pattison et al., 2015). Among these cell wall related genes, 157 belong to group1 (30 in cluster 1, 125 in cluster 2 and 2 in cluster 3) and 94 of them contain DMRs of various type in their promoter region (Fig 3 .15A). Many of these genes are expressed during fruit development and their expression declines during WT fruit ripening (Fig3.15B, p112). Therefore their expression is higher in transgenic fruits at stages corresponding to WT fruit ripening and senescence. However, 71 of them are associated with type-a DMRs (table S6, provided as additional excel file online).

Fifty-six additional cell wall related DEGs are in group 2 and 3. 23 of these DEGs are in clusters 6 and correspond to genes down regulated during WT fruit ripening but that do not present significant expression variations in transgenic fruits. All others are in clusters 3, 4 (group 2) and 7 and 9 (group 3) and are not induced in transgenic fruits 39 and 46 dpa, in contrast to their induction during WT fruit ripening or later (Fig3.14B, 3.14C). Twenty-five of these DEGs are associated with type-a DMRs characterized by a decrease in DNA methylation during ripening whereas one has a type-b DMR that become hypermethylated. The remaining 5 genes are associated with typeb, c or d DMRs (Fig3.14A, 3.14C).

As previously noted (see part 2 and 3) for isoprenoid synthesis and Transcription Factors, type-a DMRs are not necessarily associated with genes specifically induced during WT fruit ripening. We found that 9 DEGs from cluster 6 that are normally repressed during WT fruit ripening contain type-a DMRs. In addition, 71 group1 DEGs that are down-regulated during the development and ripening of WT fruits, whereas their expression is maintained or enhanced (cluster 1) are also associated with type-a DMRs.

In contrast, genes from group 2 and 3 (clusters 7 and 9) are characterized by a high expression level at the Br stage and 46 dpa in WT fruits, at a stage when their methylation level is low (table S6). These genes are not induced in the transgenic fruits. As they are associated with type-a DMRs this is most likely due to the lack of demethylation at the DMRs in the transgenic lines, as already shown for PSY1, RIN, NOR and CNR (Liu et al., 2015b;Fig7C). They include known genes encoding the Polygalacturonase A (PG2a), the Beta-xylosidase 4 (XYL1), an Expansin (LeEXP1), the Endoglucanase 1 (Cel2), and the Mannan endo-1 4-beta-mannosidase (MAN4). Additional cell wall related genes contain a type-a DMR but their function has not yet been determined (Fig 3 .15C, p112) Among these genes, the expression of the major fruit polygalacturonase gene, PG2a which normally occurs at the Br and Br+7in WT fruits, was severally delayed and reduced in transgenic fruits (log2 fold difference = -4.53 in line 2Y, log2 fold difference=-7.54 in line 8) (Fig 3 .15D). XYL1 which encodes a β-xylosidase is the most highly affected DEGs the highest repression level being observed at 46 dpa in line 2 (log2 fold difference= -7.71 in line 2Y, log2fold difference= -7.95 in line 8) and 55dpa in line 8 (log2 fold difference= -8.15). This gene is not expressed at early stages of WT fruit development (20-39dpa), but shows a sharp increase in expression level during fruit ripening, which contrast with its reduced expression in the transgenic fruits. A similar observation can be done for the CEL 2 gene which encodes the Endoglucanase 1 and for the EXP1 gene. CEL 2 is also extremely repressed in the transgenic fruits (log2 fold difference = -4.62 at 39dpa in line 2Y, log2 fold difference = -6,58 at 39dpa in line 8). EXP1 present a sharp increase at Br and 46 dpa in WT, whereas the EXP1 mRNA accumulation is delayed and reduced in transgenic fruits (log2 fold difference = -3.05 in line 2Y, log2 fold difference = -3.45).

In addition, six other genes including the CEL1 (Endoglucanase) and the TBG4 (βgalactosidases), genes which are down regulated in the transgenic fruits are associated with other types of DMRs, making unclear the link between active DNA demethylation and their expression.

Finally, some differences were found between line 2 and line 8. Eight DEGs associated with type-a DMR were not consistently found in line 8 and line 2 when compared to WT plants. For example, the PME2.1, PME1.9 genes encoding pectinesterases and GP2 encoding a BURP domain-containing protein (BURP domain is named by four typical members, BNM2, USP, RD22, and PG1β ((Van Son et al., 2009)) were not normally induced in young fruits of line 2 only, but not in line8 (FigS9, p133). A similar situation is observed for the genes encoding the Xyloglucan endotransglucosylase/hydrolase 2 (LeXET2) and the Xyloglucan endotransglucosylase/hydrolase 7 (tXET-B). But interestingly, among these genes with variation, all of them are induced at early developmental stages, except for tXET-B.

As a conclusion there is a clear association between genes important for fruit softening and typ-a DMRs, suggesting that DNA methylation directly control certain aspects of fruit cell wall metabolim.

Genes involved in Ethylene biosynthesis, perception and response

We have shown in Chapter 2 that ethylene synthesis is extremely repressed and delayed in RNAi DML transgenic fruits. Ethylene is only detected after 70 dpa at very low levels both in lines 2 and 8 (Liu et al.;2015b, sup data Fig S6, chapter 2). We therefore examined the expression of all genes involved in ethylene biosynthesis, ethylene perception and response.

SAM1 in cluster 7 and SAM3 in cluster 3 have a high expression during early development, while decrease during fruit ripening. In line 2Y (not in line 8), the expression of SAM1 is slightly lower than in WT at later stages (70, 85dpa), while SAM3 is higher than WT with fruit development and ripening in all genotypes. Among all DEGs in ethylene pathway, only ACS6 in cluster 7 encodes a protein directly involved in ethylene biosynthesis. ACS6 gene expression normally declines during fruit ripening, while in transgenic fruit the decrease is delayed. Differences can be seen between lines because in line 8, ACS6 is not repressed at all stages in contrast to line 2 (Fig 3.16,Fig S10,p115,p140). Three other DEGs encode proteins involved in both ethylene biosynthesis system 1 and system 2. They correspond to ACO1, 3 (cluster 6, group 3) and are not significantly affected during early fruit development although they show a delayed induction in transgenic as compare to WT ripening fruits (Fig 3.16A,FigS 3.10A,p115,p40). ACO4, another gene participating to the ethylene biosynthesis systems 1 and 2, has a very low expression level in WT compared with other ACO genes. It is expressed at higher levels in in transgenic fruits. System 2 specific gene, ACS2 and ACS4, ACO5 (cluster 6, 6, 5, group 2 and 3, respectively) are strongly induced or up-regulated in WT fruits at the breaker stage, reaching a maximum level of expression at 46 dpa (RR stage), before decreasing to a very low level at 55 dpa. Expression of these genes was in general delayed and reduced in transgenic fruits: ACO5 was the most affected gene and was barely expressed in transgenic fruit after 55 dpa, whereas, ACS 2 and 4 were expressed at low levels from 46 or 55 dpa until 85 dpa (Fig 3.16A,FigS 3.10A,p115,p140). These expression patterns are well correlated with the accumulation of ethylene described in these lines (Liu et al., 2015b, FigS6).

We then determined what genes were associated with DMRs. ACO1, 5 and ACS2 contain an identified DMR in their promoter regions, whereas ACS4 does not. However, only ACO1 is associated with a type-a DMR, suggesting that this gene requires demethylation for its expression. Two other genes, ACO5 and ACS2 are associated with type-c DMR and in this case the link between DNA methylation level of the DMRs and gene expression is unknown. Finally the lack of DMRs in the ACS4 and ACO3 promoter region, suggest that these genes are not regulated by demethylation, although they are not or lately induced in the transgenic plants.

Type-a DMR are also found in ACO4 that participate to the ethylene both system 1 and system 2 (Fig 3.16,p115).

Among the genes involved in ethylene perception, only 6 DEGs, ETR2, ETR3, ETR4, ETR5, EBF2 and EIL2, out of the 17 genes that were differentially expressed in fruits in our conditions could be identified. All six genes are induced during the ripening of WT fruits or in overripe fruits (EIL2). The expression pattern of ETR4 was however ambiguous because variable between lines. In line 2Y ETR4 was clustered in cluster 1 (group1) because this gene was not extremely repressed (log2FC=-0.81 at 39dpa and -0.93 at 46dpa). This was not the case in Line 2X (log2FC=-0.85 at 39dpa, Log2FC=-2.14 at 46dpa) and Line 8 (log2FC=-3.07) where ETR4 was extremely repressed. So, considering all lines ETR4 should also be considered as a gene wasn't normally induced in the Chapter3 114 transgenic fruits during fruit ripening. All other genes were clustered in clusters 3 and 4 and are therefore not induced in transgenic fruit. Among these different DEGsonly ETR4 and EBF2 were associated with type-a DMRs. In contrast, ETR2 has a type-b DMR, and ETR5 a type-c in its promoter region, whereas ETR3 and EIL2 lack any DMR.

Forty seven DEGs were detected among the genes encoding the ERF and AP2-EREBP (ERFlike) family which are the transcription factors responsible for ethylene response (Fig 3.16B,fig S3.10,p115 and p140). Most of them were consistently clustered in group1 and only 16 DEGs belonged to group 2 and 3, and were strongly induced during fruit ripening. Among DEGs in group 2 and 3, 6 DEGs were associated with type-a DMR and 2 with type-c DMRs.

It is also worth pointing out, that neither CTR as the downstream of negative regulators of EIN2 involved in ethylene signaling and response, were affected in RNAi DML transgenic fruits.

As a conclusion, even though the expression of several genes in the ethylene pathway but also in ethylene perception and response was impacted in transgenic lines, only a few of them are likely directly regulated by DNA demethylation. In particular, for ethylene biosynthesis, only genes of system 2 seem to be under direct methylation regulation. This suggests both direct and indirect effects of DNA demethylation on the regulation of genes involved in ethylene production and response in tomato fruits.

Other Hormone Biosynthesis and Responses in DML RNAi transgenic fruits

We also analyzed the impact of SlDML2 knock down on hormones other than ethylene. DEGs encoding proteins linked to auxin, brassinosteroid, cytokinin, gibberellin, jasmonate and ABA metabolism and signaling were examined and their association with DMR determined (Fig 3.17,p118 and Sup data Table S7, provided as additional excel file online). In all cases an important number of DEGs were identified although only a few of them were associated with DMRs. Most of the identified DEGs were in group 1 and therefore are more expressed in transgenic than in WT fruits at all stages of fruit development and ripening. Indeed, DEGs from group 2 and group 3 (clusters 7 and 9) were also identified. However most of them were related to ethylene (see Fig 3.16,chapter3,p115) and ABA (Fig 3.17E,p118) synthesis and signal transduction. Hence, most DEGs related to auxin, jasmonate, brassinosteroid are upregulated in transgenic fruits.

Many of the auxin related DEGs are highly expressed at early stages of WT fruit development and decrease during ripening (27 genes in cluster 2 and 3). However, 13 DEGs were upregulated at the Breaker stage or later in WT fruits and repressed in transgenic fruits (group 2 (cluster 4, 5) and 3 (clusters 6, 7, 8)). These include the SAUR3 gene (Solyc09g008170, cluster 6) which is the most highly repressed auxin related DEGs at the Br stage (log2FC=-7.57 of line 2X, log2FC=-6.86 of line 2Y, log2FC=-6.72 of line 8 at 39dpa) and the SlARF18 gene (Solyc01g096070, group 3 cluster 6). Both genes were associated with type-a DMRs, consistent with demethylation being necessary for their expression. Other genes, SAUR5 (Solyc01g096340), SAUR6 (Solyc06g072650), SAUR7 (Solyc07g042490) are in group2 and 3, but were not associated to any DMR.

As previously observed, type-a DMRs were not specifically associated with genes normally induced during WT fruit ripening. Fourteen DEGs belonging to group 1 also contain a type-a DMR (Fig 3 .17A).

Genes involved in jasmonate (JA) biosynthesis and signaling were also affected in transgenic fruits, although their general fold changes weren't as large as those observed for ethylene. Many of the DEGs ( 15) are expressed at early stages of fruit development and repressed during ripening in WT fruits but their down regulation is delayed in transgenic fruits (group 1). Type-a, but also types -b and c DMRs were associated with these DEGs. In addition a few DEGs from group 2 contained type DMRs, whereas others that are induced in overripe WT fruits, but not expressed in WT were associated either with type-a or type -b DMRs.

ABA is produced from the carotenoid pathway. ABA content peaks at the transition to fruit ripening, before the synthesis of ethylene, and then decreases after fruit ripening. Therefore, ABA is also considered as an important factor controlling fleshy fruit ripening (Leng et al., 2014). Consistent with this view, 26 genes out of 55 DEGs involved in ABA pathway are clustered in group 2 (5 in cluster 4, 4 in cluster 5) and 3 (9 in cluster 6, 6 in cluster 7, and 1 in cluster 8), indicating relatively high expression during fruit ripening in WT, while in transgenic fruits, the expression pattern was various. In RNAi DML transgenic fruits, we found that ABA biosynthesis wasn't affected, as 50 DEGs identified are associated with ABA signaling and five in ABA perception. Among ABA perception, only three (Solyc03g007310, Solyc06g050500, Solyc08g082180) are repressed in both line 2 and line 8, while Solyc06g050500, Solyc08g082180 were associated with type-a DMRS, Solyc03g007310 with type-d DMR. In ABA response, we found 15 DEGs were associated with type-a DMRs in group 2 and 3, while 12 DEGs in group 1 were also associated with type-a DMR. This suggests that active DNA demethylation may also regulate the ABA pathway, but excluding ABA biosynthesis. It is well known that brassinosteroids (BRs) are steroid plant hormones essential for plant growth and development. Among all DEGs involved in this pathway only CYP85 (Solyc02g089160) and CYP90C1 (Solyc02g084740) found in cluster 6 and cluster 7 were significantly different in WT and in both line 2 and line 8. These two genes encode cytochrome P450. For some other DEGs in group 2 and 3, the differences between WT and transgenic fruits were not consistently detected. We analyzed the gene encoding CYP85 also known as the Dwarf gene because of its central role in catalyzing multiple C-6 oxydation during BRs biosynthesis (Shimada et al., 2001;Castle et al., 2005). Although this gene was only induced at the fruit ripening transition and ripening stages in WT fruits but not in transgenic one (log2FC=-2.30 in line2X, log2FC=-1.87 in line2Y, log2FC=-3.30 in line8), it was not associated with any DMR. Inversely, nine of the 21 upregulated DEGs belonging to group1, are associated with type-a DMRs (fig 3.17B, p118).

Only 8 DEGs involved in gibberellin (GA) and 8 in cytokine (CK) synthesis and signaling were detected: (Fig 3 .17C, 3.17D, p118). In the GA pathway, as previously observed type-a DMRs were either associated with genes of group 2 and 3 (cluster 6 and 7) (Solyc12g0070430, Solyc07g056670 and Solyc11g072310) but also to DEGs from group 1 (Solyc12g006460) mainly expressed during fruit development, and dramatically dropped during fruit ripening, in transgenic fruits, the decline is slower.

In CK pathway, four DEGs (Solyc12g014190, Solyc08g062820, Solyc04g081290, Solyc01g098400) were found in group 2 and 3, although not always in all transgenic lines (Solyc04g081290, Solyc04g008110 are not affected in line 8). Type-a DMR were found in four of these DEGs, also indicating the possible function of active DNA demethylation during tomato fruit development and ripening.

As a conclusion we have observed that many of the genes involved in various hormone metabolism and signaling are differentially regulated between WT and transgenic fruits. However, contrary to our expectation, type-a DMRs corresponding to region loosing demethylation during fruit ripening, are not systematically associated with the genes induced during WT fruit ripening and repressed in the transgenic fruits of the same age. DMRs were found associated with all patterns of DEGs. Inversely all types of DMRs were also associated with genes of groups 2 and 3.

DMLs may interact with other Epigenetic regulators in tomato fruits

To assess eventual interactions between SlDML2 and genes involved in DNA methylation and histones posttranslational modifications, we selected within the DEGs those related to these processes. DNA methyltransferase were identified based on their homology with the Arabidopsis orthologues and a list of 124 genes involved in histone modifications was used (Aiese Cigliano et al., 2013;[START_REF] Gallusci | DNA methylation and chromatin regulation during fleshy fruit development and ripening[END_REF] Three genes, SlMET1, SlCMT4 and SlDRM6 encoding DNA methyltransferases were differentially expressed in transgenic fruits. SlMET1 is expressed in a rather constant way at developmental stages in WT fruits with a drop at the Br stage. In transgenic fruits almost no expression is detected after 46 dpa. This gene is associated with a type-c DMR indicating it has at least two DMRs with opposite behaviors. The expression of SlDRM6 is similar to SlMET1 in WT, but its expression is almost not detectable in transgenic fruits. However, no DMR was found in the promoter of this gene.

DEGs encoding histone acetyltransferase (HAT), histone deacetylases (HDAC), histone methyltransferases (HMT) and histone demethylases (HMT) were mostly associated with type-a DMRs although in a few cases type-b and c were also found. Thus the three HATs genes, HAG7, HAG10 and HAG13 which are induced at the Br stage and highly expressed during WT fruit ripening, but that present a delayed and reduced expression transgenic fruits are all associated with a type-a DMR (Fig 3.18,p121). Indeed, all genes presenting this expression pattern are not associated with a type a-DMR. Only three of the 7 DEGs encoding HDM have one, one DEG of the 6 encoding HMTs and two of the 4 DEGs encoding HDACs. Inversely type-a DMRs were also associated with genes repressed during WT fruit ripening, as previously described for all the pathways analyzed above (Fig 3.18,p121).

It should be also noted, that seven members of JMJ gene family encoding histone demethylase were identified as DEGs. Almost all of them, except JMJ15 and JMJ13, showed increased expression levels after 46 dpa in WT, at stages corresponding to highly overripe fruits. This may indicate an important function role for this gene when fruits are maintained for a very long time on the plant. These genes were not induced in transgenic fruits. Only JMJ10 (cluster 4) in group 2 was found associated with type-a DMR (decreased DNA methylation during fruit ripening).

Finally considering all DML demethylases, both SlDML1 and SlDML2 was repressed in RNAi DML plants at early stage of fruit development, while only SlDML2 was extremely repressed at the Br stage (Liu et al., 2015b). SlDML3 was also slightly repressed in line 8, but not in line 2, and was not considered as common DEGs here. Interestingly, when we screened these genes for the presence of DMRs the promoter of SlDML2 was associated with two type-a DMRs). Lei et al (2014) have shown that ROS1 can regulate its own DNA methylation levels via an TE (helitron family) in its promoter region. This region can sense DNA methylation levels in Arabidopsis (Lei et al., 2015). In our case, SlDML2 as one of the two ROS1 orthologous gene, may also be self-regulated by sensing its own DNA methylation level in WT generally.

From this study, it was suggested DMLs not only can regulate TF or other genes expression, perhaps it can also regulate genes through these histone modifiers.

V. Conclusion and discussion

In chapter 2 active DNA demethylation was shown to be a necessary trigger for tomato fruit ripening by regulating the expression of genes encoding ripening transcription factors (RIN, CNR and NOR) and rate-limiting enzymes of key biochemical processes (PSY1). We have demonstrated a direct cause and effect relationship between active DNA demethylation and fruit ripening, mediated primarily by the SlDML2 protein. SLDML2 RNAi fruits were unable to ripen following the hyper methylation of the 4 genes cited above. This first study highlighted the importance of active DNA demethylation on tomato fruit ripening (Liu et al., 2015b).

In chapter 3, we wanted to characterize the global consequences of active DNA demethylation inhibition on the fruit ripening process and beyond in overripe stages. To achieve this goal, two independent transgenic lines (line 2 and line 8) and their corresponding WT controls were used for transcriptomic and metabolic analysis. As methylome data from our lines are not yet available at this time, we have used, as a preliminary approach to identify genes that are likely to be under direct methylation control previous data from Zhong et al. (2013), who has analyzed the distribution of DMRs in tomato genes during the tomato fruit ripening process. These DMRs have been identified by analyzing the variations of methylation levels at promoter regions (2kb) during the ripening Ailsa craig in WT fruit.

5.1 Genes likely to undergo demethylation participate to a wide range of physiological processes.

5.1.1-Majour effects are observed during fruit ripening

Analysis of primary metabolites using both H1NMR and LC MS showed that the accumulation patterns of many detected metabolites, including most of primary metabolites, a few secondary metabolites (carotenoids, chlorophylls) were significantly different in transgenic fruits from those observed in WT fruits. Indeed some variability was observed between plants and lines, but in all cases ripening WT fruits (46 dpa) and older fruits (up to 85 dpa) were clearly separated from the transgenic fruits of the same age by PCA analysis. In contrast no separation between WT and transgenic fruits was observed during early phases of fruit development (up to 39dpa). Similar results were obtained when performing PCA analysis using the RNA seq data. This indicates that most of the differences induced by knocking down SlDML2 occur during fruit ripening, and impact both gene expression and metabolites accumulation.

When network analysis was performed on all the metabolites altered during fruit ripening process (35, 39, 55, 70, 85dpa), we found that in both transgenic lines, the density is higher than WT, again verified the difference between WT and transgenic fruits, indicating the potential function of active DNA demethylation on metabolic scale. Indeed multiple aspects of fruit ripening were altered. Phenotypic characterization indicated that fruits did not ripen properly. Among the strongest effects, fruits presented reduced softening (Fig 3 .1A, p73), reduced and delayed carotenoid accumulation together with delayed chlorophyll degradation, and modified accumulation of several primary metabolites. Consistent with this observation, various primary metabolites presented an altered accumulation pattern in transgenic as compared to ripening WT fruits. For example, malate, GABA, pyroglutamate, asparagine, glutamine and glutamate, as well as chlorophylls and starch were much more abundant in transgenic than in WT fruits from 39 dpa to 85 dpa, although no difference was found at early stages. An opposite situation is found for lycopene or alanine.

5.1.2-DML2 Knlck down has complex Effects on primary metabolites accumulation

The accumulation of several amino acids was shifted during fruit ripening (Fig 3.2,Fig S 3.1,3.2,p75,p131,132), also consistent with the overrepresentation of genes involved in amino acid metabolism in DEGs of groups 1 and 3 (cluster 6). In total, 152 genes involved in in this process were identified among the DEGs (Table S8). Noteworthy, 23 of these DEGs are associated type-a DMR (decreased DNA methylation during fruit ripening), some of which are induced during WT fruit ripening such as Solyc08g066240 and Solyc08g066260 that encode enzymes involved in histidine degradation, Solyc08g014130 encoding a leucine specific 2-isopropylmalate synthase, and Solyc09g091470 encoding 3-ketoacyl CoA thiolase 2, involved in branched amino acids metabolism, which is important for volatile synthesis. These 5 genes are strongly induced at Br stage, while their induction was extremely repressed and delayed in both lines 2 and 8. Meanwhile, the corresponding amino acid histidine showed delayed degradation during fruit ripening in transgenic fruits, while it is normally repressed during WT fruit ripening (Fig S3.1,S3.2,p131,p132). Other amino acids, such as branched amino acids were also altered in transgenic fruits. This may indicate links between the synthesis of these amino acids, gene expression and DNA demethylation.

Glutamate is one of the most important compounds determining the taste of tomato fruits [START_REF] Bellisle | Glutamate and the UMAMI taste: sensory, metabolic, nutritional and behavioural considerations. A review of the literature published in the last 10 years[END_REF]. In WT, the accumulation of Glu increased during fruit ripening and peaked at Br (39dpa) or Br+7 (46dpa) , whereas, in transgenic fruits, accumulation of Glu was reduced during ripening, but its content is even higher than in WT in fruits at 70 and 85 dpa. Also, the accumulation of Gln is higher at all stages in transgenic than in WT fruits (Fig 3.1,S3.1,S3.2). It was shown that the increased levels of Glu in ripe fruits is correlated with increased levels of the glutamate synthease (GOGAT: Solyc03g083440, Solyc08g044270). The content of glutamate is consistent with the observation that GOGAT (glutamate synthase, Solyc03g083440, Solyc08g044270), a key enzyme is responsible for Glu synthesis from Gln or 2-oxglutarate is extremely repressed in both line 2 and line 8 at Br and 46 dpa [START_REF] Ikeda | Dynamic Metabolic Regulation by a Chromosome Segment from a Wild Relative During Fruit Development in a Tomato Introgression Line, IL8-3[END_REF]. No DMRs was found associated with the GOGAT gene, suggesting that this gene is not under methylation control. Hence, GOGAT repression might be the result of an indirect effect of SlDML2 knock down.

Considering GABA content in RNAi DML transgenic fruits, there is a progressive degradation during WT fruit ripening, which occurs at a slower rate in RNAi DML transgenic fruits (Fig 3.2,p75). Three genes encoding Glu decarboxylases (GAD), which convert L-Glus into GABA are present in the tomato genome (Solyc03g098240, Solyc11g011920, Solyc01g005000). These three genes were upregulated in transgenic fruits as compared to WT at all stages, a situation already described in the ethylene insensitive mutant ful1/2 mutant, [START_REF] Bemer | The Tomato FRUITFULL Homologs TDR4/FUL1 and MBP7/FUL2 Regulate Ethylene-Independent Aspects of Fruit Ripening[END_REF]. We found that FUL1 is extremely repressed in RNAi DML transgenic fruits during Chapter3 124 fruit ripening and may therefore cause the repression of the GAD genes. Interestingly, FUL1 was associated with type-a DMR (decreased DNA methylation during fruit ripening), and it seems under RIN control [START_REF] Bemer | The Tomato FRUITFULL Homologs TDR4/FUL1 and MBP7/FUL2 Regulate Ethylene-Independent Aspects of Fruit Ripening[END_REF]Zhong et al., 2013) which is also controlled by demethylation (Liu et al., 2015b). This suggests that the pathway from Glu and GABA may be indirectly affected by demethylation through a subset of genes, including transcription factors. Thus, modifications of these amino acids content could be an indirect consequence of the absence of demethylation. However, whether the hypermethylation level of these genes in DML RNAi transgenic fruit is directly responsible for the gradual delayed degradation or synthesis of amino acids during fruit ripening would be an interesting issue for further studies.

5.1.3-Inhibition of carotenoid results from the repression of genes of the carotenoid pathway

When carotenoids content was considered, we found that the accumulation of lycopene was extremely inhibited and limited in transgenic fruits, as seen from fruit phenotypes (Fig 3.1A, Fig 3.2, liu et al., 2015b). This finding is consistent with previous study (chapter 2). RNA seq data revealed that four key genes involved in lycopene biosynthesis are potential primarily targets of SlDML2 (Fig 3.13,p105). Indeed we have previously shown that the PSY1 promoter region is hypermethylated in plants knocked down for SlDML2, and establishing a causal relationship between hypermethylation of PSY1, reduced PSY1 gene expression and limited carotenoid accumulation (Liu et al., 2015b). The results here indicate that three other genes ZISO, ZDS and CrtlSO are also associated with type-a DMRs indicating that they might require demethylation for their expression.

5.1.4-Cell wall

As mentioned previously, transgenic fruits were significantly harder than WT fruits of the same age. Consistent with this phenotype, galactose did not accumulate in transgenic fruits, although this compound is very abundant in ripening WT fruits [START_REF] Eda | Structural and functional analysis of tomato β-galactosidase 4: insight into the substrate specificity of the fruit softening-related enzyme[END_REF]. The function of several genes involved in cell wall metabolism has been determined in tomato fruits. For example, EXP1 was found to have important role on polyuronide depolymerization during fruit ripening. Suppression of this gene expression leads to enhanced fruit firmness and delayed fruit ripening, although the breakdown of structurally hemicelluloses was not altered in this mutant [START_REF] Brummell | Modification of Expansin Protein Abundance in Tomato Fruit Alters Softening and Cell Wall Polymer Metabolism during Ripening[END_REF]Minoia et al., 2016). CEL2 mutant was shown to be associated with fruit abscission but without alteration of fruit softening [START_REF] Flors | Absence of the endo-β-1,4-glucanases Cel1 and Cel2 reduces susceptibility to Botrytis cinerea in tomato[END_REF]. Loss of function of TBG4 which encodes a β-galactosidase (TBG1-7) was associated with alteration of fruit firmness and to a reduced galactose loss.

As explained in part IV, these genes were significantly down regulated in transgenic fruits as compared to ripening WT fruits. This is very likely contributing to the phenotype observed : delayed softening and lack of galactose accumulation. Furthermore, their promoter is associated with type-a DMRs that are demethylated during fruit ripening except for TBG4 associated to type-d DMR. As a conclusion cell wall metabolism might be at least for some genes under direct demethylation control. Chapter3 125

Many genes with impaired regulation in transgenic fruits are not associated with specific DMRs

In this study, there are 6, 212 genes (3,4727 in total) found as common DEGs to lines 2 and 8. We have focused our studies on the common DEGs that represent 17.9% of the tomato genes, indicating a global effect of active DNA demethylation.

They were screened for the presence of DMRs in their promoter region using the results of Zhong et al, (2013). DMRs were classified in subgroup to identify those corresponding to a demethylation process (named type-a DMRs), as these are the most likely to be targeted by demethylases. As summarized in table 2, a total of 3,113 DEGs are associated with DMRs among which 2,295 with type-a DMR (decreased DNA methylation during fruit ripening), 294 with type-b DMRs (increased DNA methylation during fruit ripening), 285 with type-c DMR (have more than two DMRs, one of type-a and one of type-b), and 275 with type-d DMR (DNA methylation changes are not consistent between Br and RR compared with 17dpa). The link between DMRs and gene expression will be discussed in the following section.

Near half of the DEGs (3,099) were not associated with any DMRs. Indeed, we may find additional DEG associated with DMRs when methylome data from the DML lines will be available, but it is very likely that many DEGs will not be associated to any DMRs. This indicates that the impact of SlDML2 knock down on fruit ripening cannot be only due to direct consequences of DNA methylation levels in the promoter regions of genes expression, but also to multiple indirect effects. An example is provided by the GOGAT gene as discussed in glutamate biosynthesis pathway (chapter3 partV-1b) that is extremely repressed in transgenic fruits during fruit ripening, while no DMR was found on this gene. A similar situation if found for many other genes that could contribute to the ripening phenotypeof DML RNAi plants , including genes involved in cell wall metabolism or hormones synthesis and signaling (see chap 3, part IV). For these genes their regulation is unlikely to be directly due to change in their methylation level. However, 167 transcription factors were differentially expressed in DML RNAi transgenic fruits as compared to WT fruits, and 82 of these TFs were associated with type-a DMR (Chap 3,Fig 3.14,p108). Hence, it is possible that some of the genes without DMRs will be regulated by TFs that are under direct demethylation control, as suggested for the FUL1 gene above, generating a cascade reaction leading to very general effects on fruit ripening. In addition to that we have also shown that genes encoding histone modifiers were affected in RNAi DML transgenic fruits. Since the corresponding enzymes can also directly affect gene expression by changing their chromatin state, this may indicate another indirect way, not directly to changes in the methylation status, to regulate DEGs without DMRs. However, we cannot rule out that some of these genes will also require demethylation for their ripening induced expression (or repression). Indeed, comparing the methylation level of the PSY1 gene in WT and DML RNAi lines at 20 dpa suggest that demethylation at this gene starts at early developmental stages, at least before 20 dpa. In WT cytosine methylation in the PSY1 DMRs is below 20% but above 50% in the transgenic lines (Liu et al., 2015B). This is consistent with the observation that both SlDML1 and SlDML2 are repressed in young transgenic fruits. Whether this is a more general phenomenon that affect other genes is not yet known and will await the analysis of the methylome of the DML RNAi transgenic fruit.

Chapter3 126

As a conclusion, this study shows us not all DEGs are associated with differentially methylated regions. Of note, this analysis is based on DMRs previously defined during the ripening process WT Ailsa craig fruits. It is based on the difference in methylation levels found at 17 dap, versus 39 and/or 46 dap at gene promoters (Zhong et al., 2013). We cannot rule out that additional DMRs will be identified, and/or some others will be lost by analyzing the methylome of the fruits knock down for SlDML2. There are several reasons that sustain this idea. (1) Lack of DMRs could be due to demethylation events occurring before 17 dpa. In lines 2 and 8, SlDML2 and SlDML1 are both knocked down at early stages of fruit development and may already target genes involved in fruit ripening at this stage. This is illustrated by comparing the methylation level of the DMRs in the PSY1 promoter region at 20 dpa in transgenic and WT fruits (chapter 2, fig6A, Liu et al., 2015b). It is close to 20% in WT but above 50% at several Cs in transgenic fruits consistent with an early demethylation occurring at this promoter. Hence depending on the methylation level observed at 17 dpa in Ailsa craig, some DMRs might have escaped identification. This may contribute to the important number of DEGs not associated with DMRs in our study. (2) We cannot rule out that part DMR of the DMRs will not maintained in the WVA106 variety as compared to Ailsa craig. Indeed, the 4 genes associated with DMRs analyzed in Liu et al, are maintained between both varieties, but they correspond to very critical genes for fruit ripening. Tang et al (2016) found that only 27% hyper-DMRs in Arabidopsis ros1-4 are also hyper-DMRs in ros1-1, ros1-4 and ros1-1 are in Col-0 and C24 ecotypes as background respectively. This suggests ROS1 targeting is greatly influenced by genetic backgrounds (Tang et al., 2016). Therefore, in this study, we cannot rule out that others DMRs, may be associated to less genes, will present variations between varieties as these Ailsa craig and WVA106 fruits are also different on some as aspects, the most obvious being the size of the fruits.

Answering these questions now requires the analysis of the methylome data of SlDML RNAi plants.

(i) Is DNA methylation level correlated with gene expression in both WT and transgenic fruits? To answer this question it is necessary to performcorrelatative analyses between these two parameters separately for WT and transgenic lines. Again, because of the DMR defined threshold here, correlation analysis between gene expression and methylation level in both WT and transgenic fruits will be very interesting point for further work.

(ii) Considering about half DEGs without DMRs, this may suggest either the expression of these genes were regulated by other transcription factors, these transcription factors were affected by DNA demethylation or these genes were affected by some other regulators, such as histone modifiers. For example, similar phenomenon in TBG4 as mentioned in cell wall pathway.

Demethylation might not be strictly associated with gene induction during fruit ripening.

We initially expected that type-a DMR will be associated with genes induced during WT fruit ripening that were not induced in the transgenic fruits of the same age. However, DMR of types a, b and c are distributed across the 9 clusters of DEGs, and only type-d DMRs are associated to DEGs of cluster 9 (25 DEGs) (Table 1). Chapter3 127 DEGs containing type-a DMRs are the most abundant DEGs in each expression group, consistent with results of Zhong et al (2013) indicating that many genes undergo demethylation during fruit ripening. However, whether demethylation at these DMRs is always associated with induction of gene expression remains to be clarified. This is likely the case for DEGs containing type-a DMR and belonging to the group 2 (clusters 3 and 4) and to the clusters 6-9 of group 3. These DEGs correspond to genes induced during fruit ripening or later stages in WT fruits that are not induced or present a delayed and reduced expression in transgenic fruits. They encode enzymes involved in glycolysis, stress responses, transcription regulation, including transcription factors, protein degradation, cell wall degradation, lipid metabolism, hormone metabolism, misc group, including UDP glucosyl and glucoronyltransferases and a number of unknown genes, indicating that active DNA demethylation may indeed be involved in multiple processes during fruit ripening. Subsequently, we focused on specific pathways, including carotenoid biosynthesis, ethylene pathway, cell wall modification and degradation, ripening factors as well as other transcription factors related to biotic and abiotic stress, and analyzed DEGs involved in other hormones and epigenetic modifiers.

In most pathways analyzed, the expression of some specific genes is likely depending on theDNA methylation level in their promoter region. An example is provided by the carotenoid pathway as discussed above, three genes (ZISO, CrtlSO, ZDS), in addition to PSY1 that may also need active DNA demethylation for their expression. As a conclusion, active DNA demethylation is likely necessary for the expression of selected genes involved in several different pathways during tomato fruit ripening.

However, 1315 DEGs with type-a DMR were also abundant in group 1, especially cluster 2 (895 DEGs, table 1). When gene enrichment was performed in cluster 2, we found genes mainly involved photosynthesis, cell wall degradation, lipid metabolism, C1-metabolism, RNA process, signaling, transport and misc group, as well as some unknown genes. These genes are however not induced during WT fruit ripening, but down regulated at the onset of fruit ripening. In transgenic fruits, repression of these genes was generally slown down (Fig 3.10,table 2,p93,p101). Hence, in this case, decreased DNA demethylation at the DMRs located in the promoter region is not associated with induction but rather to repression of gene expression. The underlying molecular mechanisms are so far unknown. A tempting hypothesis could be that hypermethylation at this sites in transgenic fruits might prevent the binding of proteins necessary to repress these gene expression.

Therefore, it indicates that active DNA demethylation might not be strictly associated with induction of gene expression during fruit ripening. In addition, genes with declined expression pattern may also the direct target of active DNA demethylation. In addition, there are 845 DEGs with other types DMRs (type-b, type-c and type-d), indicating more complex methylation patterns, as some of these DEGs contain more than one DMRs that eventually present opposite behaviors during fruit ripening. In these cases the relation-ship between methylation levels and gene expression remains to be established. Of particular interest are the DMRs corresponding to gain in DNA methylation (type-b and c). As DRM6; that is normally upregulated in WT fruits is downregulated in transgenic lines, these DMRs could correspond to DRM6 targets. The role of increase methylation at these DMRs remains to be determined. In addition to loss of methylation, some DEGs are associated with DMRs that were shown to gain methylation during fruit ripening (Zhong et al, 2013). The function of these DMRs is so far unknown because these DEGs were found in all clusters and were not associated with a specific expression pattern. It is also unclear what mechanisms are responsible for such locus specific increase in DNA methylation. Interestingly the DRM6 gene that was previously shown to be upregulated during tomato fruit ripening is down regulated in the DML RNAi lines. DRM6 encode a DNA methyltransferase a protein family involved in de novo DNA methylation that could therefore contribute to locus specific gain of methylation. Whether active DNA demethylation also controls de novo methylation during fruit ripening will now require further investigation. Similarly the functional analysis of DRM6 in tomato fruits is now required to understand the role of de novo methylation during fruit ripening.

Active DNA methylation: a more general model

Based on these results, active DNA methylation appears as a central point controlling several aspects of the fruit ripening process. In addition, we have shown in chapter 2 that the SlDML2 gene is repressed in nor, Cnr and rin mutant backgrounds although the expression level observed in the pericarp of rin mutant fruitswas significantly higher than in the nor mutant and in the Cnr epimutant. It is therefore possible that the ripening defects observed in the rin, nor and Cnr genetic background is in part mediated by a limited active DNA demethylation, which is consistent with the observation that both the rin and Cnr plants and fruits are hypermethylated [START_REF] Gallusci | DNA methylation and chromatin regulation during fleshy fruit development and ripening[END_REF]. Integrating this idea with the results presented in chapter3 lead to a more general model of the role of active DNA demethylation during tomato fruit ripening, which is presented in Fig 19.

Conclusion

Based on previous study by Liu et al (2015b), the results presented here highlight the central role of active DNA demethylation during tomato fruit ripening. In addition to a general role in the regulation of genes directly involved in several metabolic pathways, it is likely that several transcription factors as well as epigenetic regulators are under direct methylation control. However, we could not establish a district relationship between DNA reduction of DNA methylation and induction of gene expression, as not all DEGs containing a type-a DMRs do not correspond to genes normally induced in WT and repressed in transgenic plants. Some were corresponding to an opposite situation and in a few cases more complex methylation pattern (several DMRs) were also found. Indeed these conclusions are based on methylation analysis obtained in another variety. They might however reflect the situation of WVA106 fruits, although some variations are expectable when the methylome of DML RNAi fruits will be analyzed. Hence the relationship between DNA demethylation and gene expression might be more complex than expected, and not limited to the starting hypothesis of this work: DNA demethylation is an absolute requirement for the expression of critical ripening induced genes. This is indeed clearly the case (Liu et al., 2015b), but the analysis presented here also suggest that DNA demethylation might also be necessary for the repression of several genes as well. Chapter 4_ General Discussion and Further Work

Part I Discussion

In the work presented here, we have demonstrated that active DNA demethylation is the mechanism responsible for the loss in 5mC at the onset of fruit ripening. In DML RNAi transgenic fruits, the induction of four key genes (RIN, NOR, CNR, PSY1) associated with fruit ripening were extremely delayed and limited because of the hypermethylation in their promoter region. It is known that in Arabidopsis DMLs can target genes throughout the genome, although in this case this was not associated to specific phenotypes but rather to the protection of genes against potentially deleterious methylation ( Penterman et al., 2007). Here (Chapter 3) we have identified a number of genes involved in several different metabolic and regulatory pathways that are differentially expressed between WT and DML RNAi lines. In addition a subset of these DEGs was associated with regions that were shown to be differentially methylated in the Ailsa Craig variety during the ripening process (Zhong et al, 2013). This also suggests that SlDML2 is targeted to several different genes during fruit ripening that require demethylation for their expression.

General Discussion

1-Active demethylation may have additional functions beyond gene induction

Surprisingly, we did not find that type-a DMRs are solely associated with genes normally induced during fruit ripening. In addition type-a DMRs were found at genes that are repressed during fruit ripening. In this case, the function of active DNA demethylation remains to be determined, but a tempting hypothesis would be that active DNA demethylation is necessary for the repression of these genes, for example, demethylation on this gene may facilitate the binding of the repressors, which repress this gene expression during fruit ripening. This would be consistent with the observation that all these genes presented a delayed repression during fruit ripening that are associated with specific aspects of the transgenic fruit phenotypes, such as delayed catabolism of chlorophylls or starch. Whether this hypothesis is true will at least require showing that these genes are hypermethylated in the transgenic fruits and that this hypermethylation prevent the binding of factors necessary for repression of these genes. However, this new potential function of active DNA demethylation in fruit ripening has also been integrated in the new model proposed fig [START_REF] Bhutani | DNA Demethylation Dynamics[END_REF].

It should also be noted that so far we have not been able to analyze the methylation level at other genome sites in the transgenic lines. In Teyssier et al (2008) it is shown that the global methylation level fruit pericarp decreases by 30% during tomato fruit ripening. This is unlikely to be solely due to demethylation at specific promoters but also will require the active demethylation of highly methylated genome region such as transposons. Consistent with this idea, Zhong et al (2013) have shown that in addition to promoter demethylation transposons are also demethylated during fruit ripening although only in the CG context. It is so far unknown whether this process is also due to active DNA demethylation mediated by SlDM2, or by dilution of methylation that could be due to endoreduplication associated to a loss of MET1 activity. As explained before, DNA endoreduplication is very limited during fruit ripening, but could still be sufficient to lead to a moderate reduction in DNA methylation in the absence of efficient maintenance methylation Chapter 4 142 mechanisms. The specific loss of CG type of methylation would be consistent with this idea, although it was also shown that Demethylases have a bias toward CG sites.

2-Active DNA demethylation may play a more important role in tomato than in Arabidopsis

As reviewed in chapter 1, Arabidopsis ros1 mutant or triple mutant rdd didn't show obvious phenotype except for abnormal stomatal lineage cell numbers, however, in DML RNAi transgenic tomato, fruit ripening was affected as well as other additional phenotypes were observed in some transgenic lines. These mutant phenotypes indicate that active DNA demethylation may have a more important role in tomato than in Arabidopsis.

On the other side, when considering DEGs percentage in each case, Arabidopsis ros1 mutant was shown that a very limited number of genes are under the control of DMLs (Penterman et al., 2007[START_REF] Lister | Highly Integrated Single-Base Resolution Maps of the Epigenome in Arabidopsis[END_REF], even in triple mutant rdd, only 0.53% genes were differentially expressed [START_REF] Lister | Highly Integrated Single-Base Resolution Maps of the Epigenome in Arabidopsis[END_REF]. Whereas, tomato SlDMLs are likely to have a major role in the regulation of gene expression, and may affect several aspects of tomato plant development. DEGs occupy 41.24% of total genes that were detected reads in DML RNAi transgenic plants. Considering 0.53% DEGs for Arabidopsis only use the average value of floral tissue [START_REF] Lister | Highly Integrated Single-Base Resolution Maps of the Epigenome in Arabidopsis[END_REF], therefore, when we only consider DEGs at breaker stage, DEGs is still occupy 18.47%, which indicates that DEGs number is still larger in tomato than in Arabidopsis, suggesting the stronger effect of active DNA demethylation in tomato compared with Arabidopsis.

When considering the difference of DNA methylation during fruit development and ripening in tomato, 52,095 DMRs were identified, and most of these DMRs are concentrated in regions 5′ upstream of genes (Zhong et al, 2013). This was also the case in Arabidopsis, but this phenomenon appears much more limited as only 179 genes were found differentially methylated in their promoter region and this was not associated with changes in gene expression. This may explain why in tomato, active DNA demethylation can affect gene expression on a large scale, as compared with Arabidopsis. In addition, in Arabidopsis, only 5% of methylated cytosines in the genome and very few transposable elements (TEs), but in tomato and other species, such as maize, there is striking difference as reviewed in chapter 1. In tomato, the overall genome methylation level occupies more than 22% of whole genome, moreover, more than 60% of its genome consists of heavily methylated TEs (Zhong et al., 2013). Similar phenomenon was found in maize and rice (reviewed in [START_REF] Gallusci | DNA methylation and chromatin regulation during fleshy fruit development and ripening[END_REF]. It has been proved the major targets of ROS1 is intergenic regions and transposons, especially transposons are those TEs close to protein coding genes, suggesting the important function of ROS1 to gene expression (Tang et al., 2016). In this case, active DNA demethylation was considered to be more important in tomato than in Arabidopsis via regulating TEs which is related to gene expression.

In addition, the proportion of cytosine context varies also between these species and Arabidopsis, such as CHH context, which is associated with the directly influence of nearby genes expression. Therefore, from this study, we can see active DNA methylation may play more important role in tomato than in Arabidopsis. Our work supports this idea and highlights the critical function of active DNA demethylation in fleshy fruit.

3-Active demethylation maybe also important in other fruits

As we demonstrated in this study, active DNA demethylation is absolutely necessary for tomato fruit ripening via controlling numerous genes expression. Since tomato is the model plant of climacteric fruit, therefore whether demethylation is also necessary in other climacteric fruit as well as other non-climacteric fruit is also interesting question. Interestingly, as reviewed in chapter1, anthocyanin synthesis in apple, pear skin is associated with DNA methylation levels in the promoter of MYB10. In addition, in oil palm, hypomethylation in a TE Karma is associated with the origin of mantled trait [START_REF] Ong-Abdullah | Loss of Karma transposon methylation underlies the mantled somaclonal variant of oil palm[END_REF]. These studies suggest DNA methylation negatively correlate with gene expression in other fruits and also the methylation status on TE is also correlated with important fruit phenotype (Telias et al., BMC Plant Biology, 2011;[START_REF] Wang | The methylation of the PcMYB10 promoter is associated with green-skinned sport in Max Red Bartlett pear[END_REF]. Although there is no any direct evidence of causal and effects about demethylation on other fruits until now, outside of tomato, DNA demethylation may also play essential role in other fruits.

Part II Perspectives 1-Active DNA demethylation may regulate other aspects of tomato plant development

We have shown that the inhibition of fruit ripening in SlDML RNAi lines is correlated with the hypermethylation of key genes controlling fruit ripening (Liu et al., 2015), and most likely of many additional genes that contribute to the fruit ripening process. However, we have also observed in some of the transgenic lines that developmental defects were not limited to fruit ripening. In line 2 and line 1 but also in additional lines (not shown) fruits presented an increased number of carpels that was determined at very early stages during flower formation. Similarly we also observed leaves of modified shapes that had lost the typical indentation of tomato leaves (lines 1, 2 and others). The questions remains so far whether these developmental alterations affecting flowers and leaves observed in the SlDML RNAi lines are also linked to the hypermethylation of specific genes? As a first step, to answer this question, a transcriptomic analysis has been performed by RNA-SEQ on leaves and flower, in order to identify genes which are differentially expressed in WT and transgenic samples (data not shown). Unfortunately, very few genes were found that are differentially regulated in transgenic plants compared to WT tissues, and most were related to stress. Indeed this work has to be further developed. However, it will be necessary to analyze very specific tissues of the meristems, as these developmental defects most likely occur very early. Using stem apices and entire flowers might not allow to identify genes regulated by their methylation events that are involved in these phenotypes as several different tissues with specific epigenetic states were mixed. Tissue dissection will be necessary for that, and collaboration has been initiated with Dr Z Lipman in order to achieve this. Recently, Satgé et al (2016) found that DEMETER plays critical role for Medicago nodule development, there are around 400 DEGs were identified and 474 regions were hypermethylated in MtDME mutant. These suggest the possible wide range functions of demethylation in plants (Satgé et al., 2016).

2-Characterization of the tomato SlDML2 protein

Arabidopsis DMLs proteins have been shown to function as DNA glycosylase-lyases, but the activity of SlDML2 has not been successfully demonstrated yet. However, as pointed out in chapter 2, the full length SlDML2 and its truncated forms are difficult to produce in bacteria. Both the expression and the solubility of these proteins are low in E.coli. It will be very interesting to figure out the optimized condition for this gene expression. To date, only in Arabidopsis was developed a model which help DMLs recognize their targeted size (methylated CGs). DML targeting seems to require additional protein, such as Methyl-CpG-binding domain (MBD) proteins, histone acetyltransferase IDM1 and the alpha-crystallin domain proteins IDM2 and IDM3 [START_REF] Lang | The Methyl-CpG-Binding Protein MBD7 Facilitates Active DNA Demethylation to Limit DNA Hyper-Methylation and Transcriptional Gene Silencing[END_REF]. However, how DMLs recognize their targets in still unknown. The tomato system may provide the tools necessary to decipher the mechanisms of DML targeting. Potential demethylase targets have been identified by comparing gene expression patterns and the association of genes with DMRs. This will be confirmed when the methylome data of the DML RNAi lines will be available. In addition, we have generated lines that overexpress a tagged SlDML2 protein which may now be used for ChIP experiments, aiming at the identification of SlDML2 binding sites in the genomic DNA. In addition, these lines could also be used to identify possible partners for SlDML proteins in tomato fruits.

3-Analyses referring to more global, long-term perspectives

a. Increase DNA demethylation may enhance plant stress response Firstly, the tomato SlDML RNAi plants could be used to study the function of SlDML in pathogens response in tomato. It has been shown that under stress condition, DNA methylation status will change. Moreover, Arabidopsis ros1 or triple mutant rdd increase susceptibility to pathogens due to lack of RdDM-induced DNA demethylation at corresponding defense genes, suggesting the primary function of demethylation under stress (Yu et al., 2013;Le et al., 2014). More recently, [START_REF] Zhang | Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation[END_REF] found the loss of flavor and volatiles of tomato under chilling stress are associated with the hypermethylation at the promoter of major ripening factor, such as RIN, NOR and some volatile synthesis related genes were hypermethylated, suggesting an additional role for DNA demethylation under stress [START_REF] Zhang | Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation[END_REF]. In this study, we found a number of genes related to biotic or abiotic stress were differentially expressed, such as genes in group 2 were enriched with heat shock protein response to heat stress, this is consistent to the potential function of DNA demethylation under stress condition. Therefore, we question, if overexpress SlDML2, whether it is possible to enhance response to pathogens or other stress? In this condition, DML RNAi mutant will be used as negative control. This study will give the hint of active DNA demethylation on stress response in tomato under different stress conditions.

As has been proved in this report, the importance of repressing DNA demethylation genes expression in plants is an efficient method to assess the functions of epigenetic marks in specific developmental process, such as fruit ripening and vegetative development. Furthermore, the research on epigenetic might break out the traditional bottlenecks to prove especially useful for quality improvement in plants such as the domesticated soybean, wheat, etc (Ecker, 2013). In a word, the main outcome of this study is the realization that the identification of epigenetic variation in genes that encode economically important plant traits that might provide an important new resource for creating improved crop varieties. Indeed using tomato DMLs as a way to target specific epigenetic modifications in the tomato genomes (epigenome editing) could provide an innovative way to breeders to create new characteristics following the formation of chosen epialles.

Materials and Methods

Chapter 2

Vector construction and protein purification 1) The construct was inserted into the PET300 expression vector to add a polyhistindine (His6) Tag at the N-terminus of recombinant protein;

2) Expression of recombinant proteins was carried out in E.coli (Rosetta2 strain, DE3) cells;

3) A fresh single transformant colony was inoculated into 10ml of LB medium containing ampicillin 100ug/ml and chloramphenicol (34ug/ml), and incubated at 37°C, overnight; 4) A 2.5ml aliquot of the overnight culture was incubated into 250ml of LB medium containing containing ampicillin 100ug/ml and chloramphenicol (34ug/ml), and incubated at 37°C, 250rpm, until OD600 was 0.1;

5) The culture was placed at 23°C and incubated until OD600 was 0.7, expression was induced by adding isopropyl-1-thio-b-D galactopyranoside (IPTG) to 1mM and incubating for 3h; 6) After induction, cells were collected by centrifugation at 13000g for 30min and the pellet frozen at -80°C;

7) The stored pellet was thawed and resuspended in 3.5ml sonication buffer (SB: 20mM Tris-HCl PH8.0, 500mM NaCl, 20% glycerol, 15mM b-mercaptoethanol, 1% Tween-20) supplemented with 5Mm imidazole. Cells were disrupted by sonication and lysate was clarified by centrifugation.

8) The supernatant was loaded onto a Ni2+-sepharose column (Qiagen) prequilibrated with SB buffer supplemented with 5mM imidazole, followed by 10ml of SB supplemented with 100mM imidazole. Proteins were eluted with a 30ml gradient of imidazole (100mM to 1M) in SB and collected in 0.5ml fractions. An aliquot of each fraction was analyzed by SDS-PAGE and those containing a single band of the overexpressed protein were polled. 9) Protein desalting and concentrated. To clean up the purified recombinant protein, PD-10 desalting kit (GE Healthcare) was used, after that protein was concentrated with centrifugal filter devise (Amicon). Experiments were performed as protocols offered in kit.

Proceed to protein quantification using Bradford assay 10) In microplate using 200ul as a final volume; 11) For the standard curve: Use BSA (Promega 10mg/ml diluted to 1mg/ml), prepare 5 points: 0; 1; 2; 3; 5ug BSA (corresponding to 0, 1, 2, 3, 5 ul 1mg/ml solution), add 100ul Bradford; 12) For the samples: dilute 1/10 th : 4ul + 96ul water + 100ul Bradford; 13) Read the absorbance and calculate the proteins concentrations.

14) To test solubility, analyzing 10ug sonication solution with soluble protein and also pellet on SDS PAGE gel.

Enzyme activity test

15) Double strands preparation (substrates) and reaction 5uM fluorescein-labelled strand 10ul and 10 uM unlabeled 10ul, put 95°C for 5min, then put in room temperature to slowly cool down. The concentration of double substrates is 250fmol/ul. Enzyme reaction, in a total reaction volume of 50ul , containing 20Nm substrates (1pmol), 22.5nM purified protein (7ug/ul), 50mMTris-Hcl (1M), 1mMEDTA, 1mMDT, 0.1mg/ml BSA (10mg/ml), these reaction mixture were incubated at 30°C for 2h. (MSPI was also incubated with reaction mixture instead of recombinant protein as a positive control) 16) Reactions were stopped by adding 20mMEDTA, 0.6% sodium ddecylsulphate (SDS), and 0.5mg/ml proteinase K, and the mixtures were incubated at 37°C for 30min. 17) DNA was extracted with phenol: chloroform: isoamyl alcohol (25:24:1) and ethanol precipitated at -20°C in the presence of 0.3mM Nacl and 16mg/ml glycogen; 18) Samples were resuspendend in 10ml 90% formamide and heated at 95°C for 5min;

19) Reaction products were separated in a 12% denaturing polyacrylamide gel containing 7M urea; 20) Fluorescein-labelled DNA was visualized using the blue fluorescence mode of the FLA-5100 imager.

Solutions used in Chapter 2

Chapter 3 Plant material and Samples collection

All experiments were performed using a cherry tomato variety, Solanum lycopsersicum cv. West Virginia 106 (cv WVA106) that was grown in greenhouse conditions as described on Liu et al (2015).

For line 8, plant samples are those harvested in Liu et al (2015). For line 2 a new culture has been performed in order to obtain a complete developmental series. The experimental plan was designed as explained in chaper 1 (Liu et al., 2015b) to span tomato fruit development and ripening in cv West Virginia 106 (WVA106) and transgenic DML RNAi plants over a period of 85 d from fruit set to account for the strongly delayed ripening phenotype of the transgenic fruits. At stages following mature green, the DML RNAi fruits diverge from the WT, because they are significantly delayed in ripening induction and almost completely ripening. For all analysis, six plants, 3 for line 2X and 3 for line 2Y were used to harvest all fruit samples for metabolomics, transcriptomic and WGBS analysis. Due to dramatic differences of the kinetic of fruit ripening, fruit s from WT and line 2 plants identically staged, which allows comparing changes in the context of a developmental parameter (days postanthesis) that can be precisely measured were manually harvested, dissected and the pericarp was stored at -80°C following . Plants from line 2 and the relevant WT control (WT1), fruits were harvested at [START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF]35,39 (Br),Br+7 (Red Ripe),55 (Br + 16),70 (Br + 31), and 85 (Br + 46) dpa. For all fruit samples, three individual T2 plants were used each being considered as a biological replicate, and for each plant and time point, a minimum of six fruits were processed and stored at -80 °C until used.

Metabolism data analysis

GC-MS Metabolite Analysis

The relative levels of metabolites of (58 identified metabolites in Line 2Y/2X, 64 metabolites in line 8) were determined exactly as described in (Carrari et al., 2006). Each measurement was performed in triplicate using one plant as a biological replicate using 50mg of lyoplylized powder.

1H-NMR Metabolite analysis

Absolute concentration of 34 metabolites for (Line 2Y, 2X and WT1) were performed as described in chapter 2 (Liu et al., 2015). For line 8, results are those described in Chapter 1 (Liu et al., 2015).

Carotenoid analysis and Starch analysis

Carotenoid analysis was done as described in chapter 2 (Liu et al., 2015) ; Starch was determine in line 2 samples and relevant WT control using the enzymatic approach described in [START_REF] Hendriks | ADP-Glucose Pyrophosphorylase Is Activated by Posttranslational Redox-Modification in Response to Light and to Sugars in Leaves of Arabidopsis and Other Plant Species[END_REF]. Experiments were performed in triplicates. identified as differentially expressed when significantly different in at in at least one case. It worth pointed out is, all the genes were considered as differentially expressed genes (DE genes) here only if they fulfill the following croterai: (i) Padj ≤ 0.05 in at least one comparison; (ii) log2FC≥ |±1| (FC= fold change of transgenic and WT) in at least one comparison.

Expression data analysis

Data for linear regression of independent cDNA libraries from the same or different time point was based on genes that were expressed at least one sample, then the normalized data was transformed by log10 (normalized counts+1).

Data for both Principal component analysis and hierarchical clustering was performed using the differentially expressed genes (6212 DEGs) that were common between line 2 and line 8. Normalized data were transformed using log2 (normalized counts+1). Expression Data for all heatmaps and clustering were performed using the spearman method. All data analyses were conducted with software R.

Gene Enrichment

Genes were functionally categorized based on previously defined Mapman bins (35 Categories). Overrepresentation was determined using software mefisto, and P values were adjusted for multiple testing using Berfino correlation, therefore, only the over-representation Padj<0.05 were considered as significant over-represented. (BINs; [START_REF] Usadel | Extension of the Visualization Tool MapMan to Allow Statistical Analysis of Arrays, Display of Coresponding Genes, and Comparison with Known Responses[END_REF]).

Primers used for qRT-PCR in Chapter 3

Solyc

Name Primer Sequence 5'-3'

Solyc12g098710.1 ZISO ZISO-Q-FW ACTCATTGGAGAGCGTGCTT ZISO-Q-RV AGTTCGTGAATCCCAGCAAC Solyc05g050010.2 ACS4 ACS4-Q-FW AGCAATGCAGGGGTTTATTG ACS4-Q-RV CCGAGCAATTGAACGAAGAT Solyc10g080210.1 PG2a PG2a-Q-FW ACAAGTGCAACAAAGGTGGC PG2a-Q-RV TTGCACGTAGCCTCTGATGG Solyc01g095080.2 ACS2 ACS2-Q-FW TGGATGGATTTGCGTCCACT ACS2-Q-RV CCACCCTGGCTCTTGACATT Solyc05g012020.2 RIN RIN-Q-FW AACATCATGGCATTGTGGTG RIN-Q-RV GTGTTGATGGTGCTGCATTT Solyc10g006880.2 NOR NOR-Q-FW AGAGAACGATGCATGGAGGTTTGT NOR-Q-RV ACTGGCTCAGGAAATTGGCAATGG Solyc02g077920.2 CNR CNR-Q-FW GCCAAATCAAGCAATGATGA CNR-Q-RV TCGCAACCATACAGACCATT Solyc10g080210.1 PSY1 PSY1-Q-FW ATCTTTGGTCTTGTACCGCAAA PSY1-Q-RV GGCAGTTTTTGTAGGAGGCACA

Fig 1 .

 1 Fig 1. 1 Genome-wide methylation levels for different cytosine context (CG, CHG, and CHH) in different planant species. ......................................................................................

1 Fig 1 . 2 Fig 1 . 3 NFig 1 . 4 Fig 1 . 5 Fig 1 . 6 Fig 1 . 7 Fig 1 . 8 Fig 1 . 9 Fig 1 . 10 Fig 1 . 11 Fig 1 . 12 Fig 1 . 13 Fig 2 . 1 Fig 2 . 2 Fig 2 . 3 Fig 2 . 4 Fig 2 . 5

 112131415161718191101111121132122232425 Fig 1. 1 Genome-wide methylation levels for different cytosine context (CG, CHG, and CHH) in different planant species. ...................................................................................... Fig 1. 2 Structure of a nucleosome. ............................................................................................. Fig 1.3 N termini and C termini of the core histones and their residue-specific epigenetic modifications at four-nucleosome core histones. ............................................................... Fig 1. 4 Epigenome organization in Arabidopsis and maize. ................................................... Fig 1. 5 Association of DNA cytosine methylation, TE density, small RNA and gene expression in tomato............................................................................................................. Fig 1. 6 Mechanism of RdDM in plant. .................................................................................... Fig 1. 7 Genes with DNA methylation variations during Arabidopsis floral development. .. Fig 1. 8 Active DNA demethylation through direct base excision repair pathway in plants Fig 1. 9 Working model for the IDM1-IDM2-IDL1-MBD7 complex functioning in ROS1 mediated active ................................................................................................................... Fig 1. 10 Phenotypic of epidermal patterning in the ros1 and rdd mutants and and promoter DNA methylation of EPF2 in Arabidopsis. ...................................................................... Fig 1. 11 Natural epimutant of Linaria vulgaris fowers and tomato CNR. ............................. Fig 1. 12 Overview of ripening regulation in tomato fruits. ................................................... Fig 1. 13 Simplified scheme showing ethylene biosynthesis and response ........................... Fig 1. 14 Different types of fruit peel pigment patterns in 'Honeycrisp' apple and Methylation levels in 'Honeycrisp' evaluated using bisulfite sequencing...................... Fig 2. 1 Structures of SlDML protein and its Arabidopsis homologous proteins.. ................ Fig 2. 2 Structures of SlDML2 proteins along with their truncated versions used in this study ............................................................................................................................................. Fig 2. 3 Cloning vector and expression vector used in this study .......................................... Fig 2. 4 SlDML2-full leng, SlDML3-full length and SlDML2-845 expression and purify test........................................................................................................................................Fig 2. 5 Mechanism of DNA demethylase incision assays (ref) and the acitivity test on SlDML2-845, SlDML2-962 and MspI. ............................................................................

Fig 2 . 6 Fig 2 . 7 Fig 3 . 1 Fig 3 . 2 Fig 3 . 3 Fig 3 . 4 Fig 3 . 5 Fig 3 . 6 Fig 3 . 7 Fig 3 . 8 Fig 3 . 9 Fig 3 .Fig 3 . 11 Fig 3 . 13 Fig 3 . 16 .Fig 3 . 17 Fig 3 . 18 Fig3. 19 .Fig 3 .S 1

 262731323334353637383933113133163173181931 Fig 2. 6 Fruit phenotype of azygous and other defects on line 1 and line 2 as well as process of screening T4 generation of line 2 and line 1 ................................................................ Fig 2. 7 Phenotype of RNAi DML transgenic plants lose transgenic ....................................

  . The introduction part is organized into six sections. Part I of chapter I presents general notions about epigenetic marks and how they are distributed along plant genomes. Part II and III ofchapter I focus on DNA methylation and demethylation, including the description of the various components controlling these epigenetic modifications, as well as their biological functions; (II: Mechanism of DNA methylation; III: DNA demethylation in plants); PartIV of chapter I is a brief summary of the importance of epialleles in plants; Part V of Chapter I introduces tomato fruit development nd ripening and related physiological changes; Part VI summarizes the current knowledge of the role of DNA methylation / demethylation during fruit development and ripening when the work presented here was started.

Fig 1 . 1

 11 Fig 1. 1 Genome-wide methylation levels for different cytosine contexts (CG, CHG, and CHH) in different plant species. Cytosine methylation levels in 34 different plant species.Figure A was adapted from Niederhuth et al (2015); Cytosin methylation level and genome size in different species. Figure A and Figure B showed CG methylation level is highest in all the species were measured. Figure B was adapted from Mirouze et al (2014).

Fig 1 . 2

 12 Fig 1. 2 Structure of a nucleosome. The assembly of DNA into a compact structure termed chromatin is essential for packaging the genome into the cell nucleus. Å: angstroms. Figure was adapted from Georgopoulos (2002).

Fig 1 . 3 N

 13 Fig 1.3 N termini and C termini of the core histones and their residue-specific epigenetic modifications at four nucleosome core histones. H2A, H2B, H3 and H4 represent fournucleosome histones. Different shapes with letters represent different histone marks as indicated. Figure referenced from Graff et al (2008)

Fig 1 . 4

 14 Fig 1. 4 Epigenome organization in Arabidopsis and maize. The organization of genes (green) and TEs (pink), the relative abundance of three chromatin modifications, CHG DNA methylation (red), CHH DNA methylation (black), and H3K9me2 methylation (blue). Figure is adapted from Springer et al (2016).

Fig 1 . 5

 15 Fig 1. 5 Association of DNA cytosine methylation, TE density, small RNA and gene expression in tomato. Genes were classified into 5 groups based on their expression level in tomato fruit at breaker (group 5: highest, group 1: lowest). (A) Distribution of miniature inverted transposable elements (MITEs) in the regions 2 kb upstream and downstream of TSS and PAS (bin size = 100 bp). (B) Distribution of 24nt small RNAs. (C) Distribution of CG methylation. (D) Distribution of CWG methylation. (E) Distribution of CCG methylation. (F) Distribution of CHH methylation. TSS: transcription start site; PAS: polyadenylation site. Figure is adapted from Zhong et al (2013).

Fig 1 . 6

 16 Fig 1. 6 Mechanism of RdDM in plants. RNA transcripts are generated from repetitive sequences (transposons and others) by an RNA polymerase known as PolI V. RNA-DEPENDENT RNAPOLYMERASE (RDR) then converts the RNA to double stranded transcripts. These are processed into 24-nucleotide small RNAs (siRNAs) by DICER-LIKE3 (DCL3). These are methylated at their ends by HUAENHANCER1 (HEN1) and the guide strand complementary to the genomic DNA, that will be the target of the RdDM, is incorporated into ARGONAUTE (AGO4). AGO4 is recruited through interactions with PolV and KOWDOMAIN-CONTAINING TRANSCRIPTION FACTOR1 (KTF1). RNA-DIRECTEDDNA METHYLATION1 (RDM1) links AGO4 and DOMAINS REARRANGED METHYLTRANSFERASE2 (DRM2), which catalyzes de novo methylation of DNA. Figure is adapted from Gallusci et al (2016).

Fig 1 . 7

 17 Fig 1. 7 Genes with DNA methylation variations during Arabidopsis floral development.Comparison of genes differentially methylated at one or more sequence contexts and differentially expressed between meristem and early flower. 'Gene Body' and 'Promoter' represent the transcribed region and the 1 kb upstream region of genes, respectively; 'Transcription' represents genes that are differentially expressed. Figure is taken from[START_REF] Yang | Whole-genome DNA methylation patterns and complex associations with gene structure and expression during flower development in Arabidopsis[END_REF]

Fig 1 . 8

 18 Fig 1. 8 Active DNA demethylation through direct base excision repair pathway in plants (Wu and Zhang 2010). Base excision repair (BER) through direct excision of 5-methylcytosine (5meC). Initiation of the BER pathway can be carried out by a glycosylase that directly excises 5meC to generate an abasic (apurinic and apyrimidinic (AP)) site. The DNA backbone is nicked by an AP lyase (or by the glycosylase itself if it is bifunctional). The 3′ sugar group is then cleaved by an AP endonuclease and the resulting single nucleotide gap is filled in with an unmethylated C by an unknown polymerase and ligase. It has been well established in plants that the demeter (DME; also known as repressor of silencing 1 (ROS1)) family of enzymes can carry out the 5meC glycosylase reaction. Figure is adapted from Wu and Zhang (2010).

Fig 1 . 9

 19 Fig 1. 9 Working model for the IDM1-IDM2-IDL1-MBD7 complex functioning in ROS1 mediated active DNA demethylation at some locus in Arabidopsis. MBD7 forms a complex with IDM1, IDM2 and IDL1, and recognizes methylated DNA through methyl-CpG-binding domains. Then IDM1 is recruited to specific loci and acetylates histone H3 at K18 and K23, facilitating active DNA demethylation by ROS1. Figure referenced from Li et al (2015)

Fig 1 . 10

 110 Fig 1. 10 Phenotypic analysis of epidermal patterning in the ros1 and rdd mutants and promoter DNA methylation of EPF2 in Arabidopsis. A. (a-d) Microscopic image of cotyledon adaxial epidermal cells from 3-day-old Col (a), epf2-1 (b), ros1-4 (c) and rdd (d). Small-cellclusters are indicated by brackets. B. Snapshot in the Integrated Genome Browser showing DNA methylation levels of the EPF2 promoter and upstream region in Col, ros1-4 and rdd. Figure is adapted from Yamamuro et al (2014).

Fig 1 .

 1 Fig 1. 11 Natural epimutants of Linaria vulgaris fowers and tomato CNR. A. View of a wildtype Linaria fower compared to a peloric mutant. Floral diagrams of wild-type (top) and peloric (bottom) fowers showing the relative positions of different organs, with identities indicated by colours: blue (dorsal) brown (lateral) yellow (ventral). The WT fower has an axis of dorsoventral asymmetry orientated such that the dorsal (upper or adaxial) part is nearer the stem whereas the ventral (lower or abaxial) part is nearer to the subtending leaf. The peloric fower is radially symmetrical, with all petals resembling the ventral petal of the wild type. The epigenetic change is at the Lcyc locus. B. Revertant sectors occasionally seen on mature CNR fruits. The epigenetic change is at the CNR locus. Figures were adapted from[START_REF] Cubas | An epigenetic mutation responsible for natural variation in floral symmetry[END_REF] andManning et al (2006).

Fig 1 . 12

 112 Fig 1. 12 Overview of ripening regulation in tomato fruits. Transcriptional regulation involved during the ripening process. Figure is adapted from Osorio et al (2013).

Fig 1 .

 1 Fig 1. 13 Simplified scheme showing ethylene biosynthesis and response in tomato. Arrow heads represent positive regulatory interactions, and bar represent negative regulation. Figure comes from Liu et al (2015b).

Fig 1. 14

 14 Fig 1. 14 Different types of fruit peel pigment patterns in 'Honeycrisp' apple and Methylation levels in 'Honeycrisp' evaluated using bisulfite sequencing. Distribution of anthocyanin in apple peels of blushed (A) and striped (B) fruits of 'Honeycrisp', indicating regions classified as red or green stripes; (C). Comparison of percent methylation in two regions (-1007 to -684 and -534 to -184) of the MYB10 promoter (GenBank accession EU518249) between red and green stripes. Figures referenced from Telias et al (2011)(Telias et al., 2011)

Fig 1 . 15

 115 Fig 1. 15 Strategy used for this PhD project to study functional analysis of active DNA demethylation in tomato.

  active DNA demethylation | DNA glycosylase lyase | epigenetic | tomato | fruit ripening

  Author contributions: T.C.H., Y.H., and P.G. designed research; R.L., A.H.-K., L.S., E.T., D.R., A.M.-B., S.H., M.L., J.K., C.W., C.D.-G., N.H.C., M.M., T.C.H., and P.G. performed research; A.H.-K. targeted bisulfite pyrosequencing; R.L., A.H.-K., E.T., D.R., A.M.-B., S.H., T.C.H., J.T., M.B., Y.H., G.B.S., J.J.G., and P.G. analyzed data; and E.T., G.B.S., J.J.G., and P.G. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. Freely available online through the PNAS open access option. Data deposition: Full array datasets of WT (Ailsa craig) and of the rin, nor, and Cnr mutants have been deposited with the Sol Genomics Network and are accessible under the following link: ftp://ftp.solgenomics.net/microarray/, file name rinnorcnr microarrays Liuetal PNAS2015. These array datasets have been used to analyze the expression of the four DML genes in the tomato rin, nor, and Cnr mutants and in WT fruits. The results are shown in Fig. 6B and Dataset S1.

Fig. 1 .

 1 Fig. 1. Differential expression of SlDML genes in tomato organs. Absolute quantification of SlDML1, SlDML2, SlDML3, and SlDML4 mRNA; SlDML4 gene expression is presented in a separate diagram because of its very low expression level. Fruit pericarp is at 5, 10, 20 dpa and at Breaker (BR, 39 dpa), orange (O), and red ripe (RR). Asterisks indicate significant difference [Student's t test (n = 3)] between SlDML2 and all other SlDML genes: *P < 0.05; **P < 0.01; ***P < 0.001. Error bars indicate means ± SD. Ap, stem apex; CF, closed flowers; L, leaves at positions 3, 4, 5, 8, 10, 16, and 20 from apex; OP, open flowers 5, 10, and 20; R, roots; S, stem from whole seedlings.

Fig. 2 .

 2 Fig. 2. Phenotypes of tomato DML RNAi fruits. (A) Fruits (70 dpa) (upper lane) or fruit sections (lower lane) from eight independent representative T0 RNAi plants. (B) Fruits (85 dpa) from T2 plants (left to right); WT plants, line 2 plants (DML2A and DML2B), line 8 plants (DML8A and DML8B), and an azygous plant (AZ). (C) Ripening kinetics of WT (Top), DML8A (Middle), and DML2A (Bottom). (D) WT bicarpel (Upper) DML2B multicarpel fruits (Lower).(E) VIGS experiment on 47-dpa (Br + 5) fruits injected with PVX/SlDML2 [fruits (1) and (3)] or PVX [fruits (2) and (4)] at 12 dpa [fruits (3) and (4)] inside of fruits (1) and (2), respectively. (Scale bars: 1 cm.)

Fig. 3 .Fig. 4 .

 34 Fig. 3. Residual expression of SlDML genes in fruits of transgenic DML RNAi plants. Normalized expression of the SlDML genes (A) in 20-dpa transgenic fruits of plants from line 2 (DML2A and -2B), line 8 (DML8A and -8B), an azygous plant (AZ), and the respective WT1 and WT2 controls (B) in WT2 and DML8A fruits at seven developmental stages. Expression of the SlDML genes was normalized to EF1α and to the corresponding WT fruits at 20 dpa. For each SlDML gene, asterisks indicate significant difference [Student's t test (n = 3)] between transgenic plants and WT controls, respectively, at 20 dpa (A) or at the same age during fruit development (B). *P < 0.05; **P < 0.01; ***P < 0.001). Error bars indicate mean ± SD.

Fig. 5 .

 5 Fig. 5. Expression and demethylation at key genes controlling ripening are inhibited in DML RNAi plants. (A) Expression of the RIN, NOR, CNR, and PSY1 genes in transgenic DML8A and WT fruits normalized to EF1α and to WT fruits at 20 dpa. Asterisks indicate significant difference [Student's t test (n = 3)] between WT and DML8A samples at a given stage: *P < 0.05; **P < 0.01; ***P < 0.001. Error bars indicate means ± SD. (B) McrBC-PCR analysis of selected promoter fragments in fruits of WT, azygous (Azy), and DML8A plants; 1 μg of genomic DNA was digested with McrBC (NEB) during 5h (+);(-) indicates negative control for the digestion reaction that was performed without GTP. In the WT and azygous plants, the part of NOR, RIN, and PSY1 promoter regions analyzed are methylated at 35 dpa (no amplification) but are demethylated at 55 dpa (amplification). In DML8A plants, the three promoter regions behave similarly to WT at 35 dpa but remained methylated at 55 dpa (no amplification in both cases). The pectin-methyl esterase (PME) promoter is used as an unmethylated control, and the CNR promoter fragment used here was found to be sufficiently methylated at all stages for complete digestion by McrBC.

Fig. 6 .

 6 Fig. 6. Bisulfite-sequencing analysis at the NOR, CNR, and PSY1 promoter fragments in WT and transgenic DML RNAi plants. (A) Heat-map representation of DNA methylation at selected NOR, CNR, and PSY1 promoter regions (SI Appendix, Fig. S8) in fruits of control (WT1 and WT2) and transgenic (DML2A, -2B, -8A, and -8B) plants at five (WT and line 8) or four (line 2) developmental stages. For each promoter, two fragments have been analyzed (fragment 1, gray box; fragment 2, black box), the positions of which are shown in SI Appendix, Fig. S8 and Fig. S9. The position of the Cs within each promoter fragment is also shown (number in the columns on the right side), as defined in SI Appendix, Fig. S8. For each promoter, Cs have been clustered considering the two PCR fragments analyzed together. (B) Changes in expression of SlDML genes in fruits of Ailsa Craig (WT) and near-isogenic mutant lines rin, Cnr, and nor, as determined by microarrays analysis. For fruit development, days postanthesis are shown. Mature green is 40 dpa in Ailsa Craig and then Br is 49 dpa. For nonripening mutants, Br onward are 49 dpa + 1-7 d. Asterisks indicate significant difference (variance ratio, F tests) between WT and mutant lines for the SlDML2 gene only to avoid overloading the figure: *P < 0.05; **P < 0.01; ***P < 0.001). Details of expression results and statistical analyses for all four genes are provided in Dataset S1. Error bars indicate means ± SD. (C) Proposed function of DNA demethylation in the control of fruit ripening; SlDML2 is necessary for the active demethylation of the NOR, CNR, RIN, and PSY1 promoter region, thereby allowing these gene expressions. SlDML2 gene expression is reduced in the rin, nor, and Cnr background, suggesting a regulatory loop. There is at this time no evidence of direct regulation of the SlDML2 gene by the RIN, NOR, or CNR protein. SlDML2 may control the expression of additional ripening induced gene, as shown in this study for the PSY1 gene and suggested by the demethylation of several promoters during fruit ripening (20). Arrows indicate activation. Lines indicate repression: black, direct effects; gray, direct or indirect effects.

  Fig. S1

Figure S1 :

 S1 Figure S1: Comparison of DNA Glycosylase Lyase sequences from tomato and from Arabidopsis thaliana. (A) Schematic diagram of domain structures of tomato and Arabidopsis thaliana DNA Glycosylase Lyase proteins. Numbers on the right indicate the number of amino acids in each protein. The positions of the domains are indicated in TableS1. (B) Phylogenetic analysis. An unrooted dendogram was generated using the Maximum Likelihood method in MEGA v.6 based on the JTT model (S 10). Sequences of DNA glycosylase proteins were aligned using Muscle. The numbers at the branching points indicate the percentage of times that each branch topology was found during bootstrap analysis (n=1000). (C) The Helixhairpin-helix -Gly/Pro rich domain (HhH-GPD) domain of tomato DNA Demethylase was aligned with those of Arabidopsis. Red dot indicates the highly conserved Lysine residue necessary for catalytic activity, blue dot shows the conserved aspartic acid residue present in the active site and green dots show the cysteine residues that constitute a [4Fe-4S] cluster[START_REF] Mok | Domain structure of the DEMETER 5-methylcytosine DNA glycosylase[END_REF]. Accession numbers are indicated in TableS1.

  Fig.S2

  Figure S2:(A) RNAi strategy: the sequence encoding part of the Helix-hairpin-helix -Gly/Pro rich domain (HhH-GPD) of SlDML1 (+3897; +4123) was used to generate an RNAi construct in the vector pK7GWIWG2 (I). Alignment with corresponding sequences of SlDML2 (+4252; +4378), SlDML3 (+4191; +4470) and SlDML4 (+3328; +3551) are shown. Sequence homology of SlDML1 with the corresponding domain of SlDML2, SlDML3, and SlDML4 is 90%, 83% and 75% respectively. Nucleotides shown in black correspond to differences between SlDML 2, 3, and 4 and SlDML1. Alignment was performed using the multalin software (http://multalin.toulouse.inra.fr/multalin/multalin.html).

Figure S3 :

 S3 Figure S3: Fruit, flower and leaf phenotypes of transgenic RNAi plants. (A) Phenotype of fruits formed on T2 plants (line 8) obtained after self-pollination of a single T1 parent. Fruits were harvested at 85 dpa. Number refers to individual plants from which fruits were harvested. Fruits representative of each plant are shown although on a single plant, fruit phenotype intensity may vary depending on plant age and position of the fruit.  indicates azygous plants that have lost the transgene after segregation. In this situation fruit ripening reversed to WT.  design plants DMLA and DMLB that were selected for metabolic, gene expression and methylation analysis. ▲ indicate additional plants used as control for carotenoid measurement and or gene expression analysis and or methylation analysis. White bar: 1 cm. Similar ripening phenotypes were obtained in T2 plants of line 2. (B) Typical fruits of plants DML8B, and DML2B are shown along with WT fruits of the same age. Developmental stages are indicated. Plants of line 8 were self-pollinated whereas flowers of plant 2B required to be back crossed with WT pollen to allow fruit development. Fruits of plant DML2B are characterized, in addition to the delayed ripening phenotype by an increased number of locules. (C) Leaf (upper panel) and flowers (lower panel) of WT (left) and transgenic plants of line 2 (right). Leaf lacks indentation and flowers are fasciated. Such flowers need to be hand pollinated and will give fruits with multiple carpels (up to 18 in a few cases). (D) Representative leaf (upper panel) of WT (left) and transgenic T2 plants of line 1 (right). Representative flower (left) and fruit (right) of transgenic T3 plants of line 1 (lower panel).

Figure S4 : 2 , 4 )

 S424 Figure S4: VIGS analysis of SlDML2 function in tomato fruit ripening. (A) Construction of PVX/SlDML2. The specific 5' coding region (1-480) of SlDML2 mRNA was PCR amplified and cloned into the PVX vector to generate PVX/SlDML2. (B) Fruits from Ailsa Craig plants were injected with PVX/SlDML2 (1, 2) or PVX (3, 4) at 14 dpa. Fruits were photographed 2 days after the breaker stage (Br + 2, 43dpa); (2, 4) Inside of fruits 1-3, respectively. Ripening-inhibited sectors in fruits injected with PVX/SlDML2 remain green.(C) SlDML gene expression analysis in ripening (R) and non ripening (NR) sectors of fruits treated with PVX/SlDML2. Values are normalized to EF1a and to the expression of the corresponding gene in the ripening sectors which represent the 100% of expression level. *** indicate significant difference (p<0.005) between R and NR sectors as determined with a student t test (n=3).

Figure S5 :Figure S6 :

 S5S6 Figure S5: characterization of the metabolites content of the transgenic RNAi fruits. (A) PCA was performed with MatLab Software (version 7.4.0) to evaluate the grouping of samples without any knowledge of their group, using the absolute concentration of 31 metabolites determined from 1 H-NMR analysis of WT2 (△) and DML8B (o) [upper panel] and WT1 (△) and DML2A (o) and DML2B (□) [lower panel] tomato pericarp fruit harvested at 20, 35, 39, 55, 70, 85 and 110 dpa. PC1, (33.88% of the global variability) separates WT fruits at 55, 70, 85 [upper and lower panels] and 110 dpa, [upper panel] from all other samples. PC2 (19.15% of the total variability) separates fruit samples of WT1, WT2 and transgenic (DML8B and DML2A, 2B) at 20 dpa from 35dpa and 39dpa, irrespective to their genotype. (B) Sugar (sucrose, glucose, fructose, galactose and rhamnose), (C) organic acids (malic and citric acids) and (D) amino acids (aspartate, asparagine, glutamate, glutamine and GABA) content was determined by quantitative 1 H NMR spectroscopy as previously described (Sup ref S11) using for each stage and plant a minimum of 6 fruits in 3 biological replicates. An ANOVA one way was performed and difference between samples were evaluated using a t student test (n=3). Stars indicate difference between WT and transgenic fruits of the same age (*: p<0.05; **: p<0.01; ***: p<0.001).

Figure S7 :

 S7 Fig. S6

Figure S8 :

 S8 Figure S8: Promoter sequences analyzed using MCR-BC PCR and bisulfite PyrosequencingPromoter sequences of RIN, NOR, PSY1 and CNR genes. Bases are numbered from the ATG. Fragment analyzed using McrBC-PCR (Fig.5) are shown in italic. For the NOR, CNR and PSY1 promoter fragments, sequences analyzed by Bisulfite-pyro-sequencing are underlined and limited either by red primers (PCR fragment 1) or by blue primers (PCR fragment 2). For each fragment analyzed by BS pyro-sequencing cytosines or group of cytosines for which the methylation level has been determined, have been numbered starting from the 5' part of the amplified sequence. ATG is shown.

Figure S9 :

 S9 Figure S9: Gene targeted Bisulfite Pyrosequencing Analysis: Methylation levels of the PSY1 (A), NOR (B), and CNR (C) promoters at the two PCR fragments shown in Fig. S8. Methylation level at 20, 35, 39 (Br), 55 and 85 dpa is shown in WT fruits (upper panels) and in the transgenic RNAi line DML8A (lower panels) at the same stages. Fruit phenotypes are indicated on the right. DNA sequence is depicted as a black line on which are shown the differentially methylated regions (DMR) as determined using McrBC-PCR (red lines, this study), DMRs identified in (20) (black lines) and the position of the RIN BS identified by RIN-ChIP sequencing[START_REF] Zhong | Single-base resolution methylomes of tomato fruit development reveal epigenome modifications associated with ripening[END_REF]. Note the higher methylation level of PSY1 fragment 1 (A; CC8 to C22) at all stages observed in plant DML8A as compared to WT as well as the reduction in methylation at the NOR (B) and CNR (C) fragment 2 during WT fruit ripening but not in fruits of the DML8A plant .

Fig 2 . 1

 21 Fig 2. 1 Structures of SlDML protein and Phlogenetic analysis with Arabidopsis homologous proteins. (A) Schematic diagram of domain structures of SlDML in tomato and its four AtDML paralogs in arabidopsis. (B) Phylogenetic analysis of SlDML and AtDML( Liu et al., 2015).

Fig 2 . 4

 24 Fig 2. 4 SlDML2-full leng, SlDML3-full length and SlDML2-845 expression and purify test. Crude protein of full length SlDML2 and SlDML3 (A), DML2-845 and DML2-962 (B), purified protein DML2-845(C). Wash: pureed protein during protein purification; -: No IPTG induction Finally, only SlDML2-845, DML2-962 could be purified, and the concentration is still low (Fig 2.4). Protein purification was performed using the following method which referenced as Ponferrada-Marí n et al., 2009.

DML2

Fig 2 . 5

 25 Fig 2. 5 Mechanism of DNA demethylase incision assays (figure comes from Gehring et al (2005)) and the acitivity test of SlDML2-845, SlDML2-962 and MspI. No signal was dected on DML2-845 or DML2-962, but signal was found on MSPI (B).

Fig 2 . 6

 26 Fig 2. 6 Fruit phenotype of azygous and other defects on line 1 and line 2 as well as process of screening T4 generation of line 2 and line 1. A. Fruits phenotype of azygous phenotype; B. Other developmental defects of line 1 and line 2; C. Screening T4 generation of line 1 and line 2 with multi-carpels and abnormal flowers.

Fig 2 . 7

 27 Fig 2. 7 All phenotypes of RNAi DML transgenic plants reversed to WT after transgenic segregation. Leaf, flower and fruit (Br+7/46dpa) of WT (A) and transgenic plants of Line 1 after lose transgene on T4 generation (B).

Fig 3 . 1 Fig 3 . 2

 3132 Fig 3. 1 Phenotypes of tomato DML RNAi fruits and DML expression patterns. (A) Fruits from T2 plants (left to right); WT plants, line 2 plants (Line2Y and Line2X). Fruits of Line 2Y have multiple carpels, those for Line 2X are small and have a normal carpel phenotype. (B) Expression level of four DML genes in WT1, WT2 and line 2Y, line 2X, line 8 as determined by RNA seq. Asterisks indicates significant difference between WT and transgenic samples at a given stage: *p<0.05; **p<0.01; ***p<0.001. Error bars indicate biological repetitions of means ±SD.

Fig 3 . 1

 31 Fig 3. 1 Principal component analysis of metabolic profiles of WT1 and line 2 fruits during development and ripening. (A) PCA using primary metabolites determined by H1-NMT, chlorophylls, carotenoids and starch of WT1 (red square), line 2 X (green circle) and line 2Y (blue triangle) at 8developmental stages. Note the clear separation of WT and transgenic fruits from Br (39 dpa) to 85 dpa. (B) Variables plot of metabolites for the first two principal components (PC1 and PC2). Compounds that give large contribution either to PC1, PC2 or both are labeled with red color.

Fig 3 . 4

 34 Fig 3. 4 Clustering of metabolic profiles in WT1 and line 2Y fruits during fruit development, ripening and later stages. (A) Clusters were obtained based on all 64 metabolites measured by LC-MS as described in the methods. The pink line represents the median value in each cluster. Grey lines represent independent metabolites WT is on the left, and Line 2Y on the right. (B) Compounds in each cluster.

Fig 3 . 5

 35 Fig 3. 5 Metabolite changes in WT1 and line2 tomato fruits. The color legend indicates normalized fold changes relative to the mean of WT and line2. 3PGA, 3-phosphoglyceric acid; PEP, phosphoenolpyruvate. Amino acids, sugars, TCA-cycle intermediates, pigments and metabolites without measured with GC-MS or NMR are displayed in blue, green, purple, red, and grey colored font, respectively.

Fig 3 . 6

 36 Fig 3. 6 Metabolite network of correlations in WT fruit and DML2 fruit. These networks represent unique metabolite correlations in WT 1 fruit (A) and unique metabolite correlations in DML2 fruit (B). The Blue edges represent significant positive correlations. Red edges represent significant negative correlations (adjusted p < 0.05). Dot nodes with pink colors represent amino acids; Parallelogram with green color, TCA cycle; Hexagon with green color: organic acids. Octagon with cyan-blue: fatty acids; Round rectangle with grey: others; V with yellow: sugars and sugar related.

Chapter3 87 Fig 3 . 7

 8737 Fig 3. 7 Relationship of tomato fruit pericarp related transcript expression profiles and differentially expressed genes. A. Correlation analysis of RNA seq data between line 2Xand Y at 39 dpa., line 8 and line 2Y at 39dpa, line 2Y at 35 and 39 dpa, and WT1 at 35 and Br stage (39dpa) B. Number of DEGs at each stage between Line 2Y and Line 8 and their respective controls, WT1 and WT2.

Fig 3 . 8

 38 Fig 3. 8 Difference of DEGs numbers at different stages and venne diagram of common DEGs among Line 2Y, Line2X and Line 8. A. Differently expressed genes (DEGs) between line 2Y and WT 1 at 35 and 39 dpa, line 8 and WT 2 at 35 and 39 dpa (Br ) stage. Red dots represent DEG between the two samples analyzed whereas black dots genes not differentially expressed between the two samples compared. Those with -1 < Log2FC < 1 are also represented in red color in this case. B. Venn diagram of DEGs unique and shared between line 2Y, line2X and line8.

  at other stages, thus explaining the partial overlap between group 3 and groups 1 and 2 (Fig 3.12A, p102).

Fig 3 . 9 Fig 3 . 10

 39310 Fig 3. 9 Principal component analysis of RNA seq data and DEGs profiles of WT1 and line 2 fruits during development, ripening and later stages. A. Distributions of genotypes and development stages. Color indicates the different genotypes: red square, WT; blue triangle line2Y and green circle line 2X. For Each stage has been performed in triplicate. B. Heatmap of all common DEGs between WT1 and Line 2Y. Hierarchical Clusters are shown on the left and were obtained by Spearman method.

Fig 3 . 11

 311 Fig 3. 11 Enrichment of DEGs in each group. Gene numbers in each category were overrepresented. (A) Group 1 (cluster 1-3);(B) Group 2(cluster 4-5); (C) Group 3 (cluster 6-9).

Fig 3 .Table 3 . 4 . 2

 3342 Fig 3. 12 PCA of all DE genes in three groups onto the 1/2 subspace with Log2FC of Line2Y/WT. A. Distribution of all common DEGs in three groups (groups were classified in Fig 3.10) B. PCA of DEGs associated with DMRs in three groups. Pink: genes in group1; Blue: genes in group2; Green: genes in group3. Grey: all DE genes. Red: genes with DMR. C. Summary of all DEGs with DMRs in each group.

DFig 3 . 13

 313 Fig 3. 13 Expression of genes of the Carotenoid pathway in RNAi DML transgenic fruit compared to WT. A. DEGs of the MEP/DOPX pathway (A) and DEGs of Carotenoid pathway (B) C. Heatmap of gene expression in A and B. DEGs from groups 2 (cluster 4 and 5) and 3 (cluster 6-9) with DMRs in their promoter are highlighted in red color (repression in RNAi lines). Black arrows represent a route rather than a single metabolic reaction and thus may be composed of multiple reactions.

Fig 3 . 14

 314 Fig 3. 14 DEGs associated with DMR encoding transcription factors that were repressed at least at one stage in transgenic fruit. Heatmap shows the expression of TF families that were clustered in group 2 (cluster 4 and 5) and 3 (cluster 6-9) and contain DMRs; DMR types are indicated.

Fig 3 . 15

 315 Fig 3. 15 Profile of DEGs involved in cell wall metabolism and fruit firmness. A. Distribution of DEGs with DMR related to cell wall metabolism in the three groups DEGs defined in Fig 10; B. Boxplot of average gene expression in both WT and line 2 in groups1, 2 and 3; C. Heatmap showing the expression of genes related to cell wall in group 2 and 3. DE Genes in group 2 and group 3 with different types were labeled; D. Fruit firmness measured on WT 2, azygous and three replicates of line 8.

Fig 3 . 16

 316 Fig 3. 16 Profile of ethylene-related DEGs. Heat maps showing the DEGs in DML RNAi transgenic fruits related to ethylene biosynthesis (A), ethylene perception and signaling (B). Red color represent DEGs in group 2 (cluster 4 and 5) and 3 (cluster 6-9). a, b, c, d represent DMR types as explained in table 1. C. Expression of DEGs involved in ethylene biosynthesis, ACS2, ACO1, 5 were associated with DMRs, no DMR on ACO3 (Fig adapted from Cara and[START_REF] Giovannoni | Molecular biology of ethylene during tomato fruit development and maturation[END_REF] Liu et al., 2015a)

Fig 3 . 17

 317 Fig 3. 17 Profile of hormone related DE genes. A to G, Heat maps showing the DE genes in RNAi DML transgenic fruits that related to Auxin (A), Brassinosteroid (B), Cytokinin (C), Gibberellin (D), ABA (E), Jasmonate (F). Red color represent genes were clustered in group2 and 3. a,b,c,d DEGs with DMR type.

Fig 3 . 18

 318 Fig 3. 18 DEGs corresponding to genes involved in DNA demethylation, DNA methylation, histone modification. Heat maps showing the DEGs between the DML RNAi transgenic fruits of line 2 and the WT1 control that are related to DNA demethylation (DMLs: DNA demethylases) DNA methylation (DMTs: DNA methytransferase) and histone modifications -HAT: histone acetyltransferases; HDACs: histone deacetylases; HDMs: histonedemethylases; HMTs: histone methytransferases). DEGs with DMRs were labeled a, b, c, d depending on the DMR type. Red color represents DEGs in group 2 (cluster 4 and 5) or 3 (cluster 6-9).

Fig3. 19 .

 19 Fig3. 19. Proposed model of fruit ripening regulation. SlDML2 is necessary for the active demethylation of multiple aspects, in addition the previously regulatory loop of NOR, CNR, RIN and PSY1(Liu et al., 2015), The new identified fruit ripening induced genes associated with typea DMR involved in multiple ripening aspects seems under the directly control of active DNA demethylation. Subsets of genes repressed during fruit ripening associated with type-a DMR in thick dash box indicates a question mark. Other differentially expressed genes in thin dashed box are the secondary candidates as SlDML2 targets. Arrows indicate activation. Lines indicate

Fig 3 .S 1

 31 Fig 3.S 1 Characterization of metabolite content in WT1 and in transgenic RNAi fruits Line 2Y/2X. Relative metabolite contents of (A) Soluble sugars,(B) sugar alcohols and sugar phosphates, (C) TCA-cycle intermediates, (D) organic acids , and (E) amino acids, (F) fatty acids (G) Other compounds. For each compound a Turkey test was performed between WT and transgenic fruits. Stars indicate significant difference between WT and transgenic fruits of the same age (*: p<0.05; **: p<0.01; ***: p<0.001). Compounds shown in A, B, C, E were analyzed using GC-MS as in Carrari et al (2006).

Fig 3 .S 2 Fig 3 .S 3

 3233 Fig 3.S 2 Characterization of metabolite content in WT2 and in transgenic RNAi fruits of Line 8. Relative metabolite contents of (A) amino acids, (B) Soluble sugars, (C) TCA-cycle intermediates, (D) organic acids and (E) sugar alcohols and sugar phosphates, (F) fatty acids (G) Other compounds. For each compound a Turkey test was performed between WT and transgenic fruits. Stars indicate significant difference between WT and transgenic fruits of the same age (*: p<0.05; **: p<0.01; ***: p<0.001). Compounds shown in A, B, C, E were analyzed using GC-MS as inCarrari et al (2006)

Fig 3 .S 7 Fig 3 .S 8 Fig 3 .S 9 2 Fig 3 .

 37383923 Fig 3.S 7 Principal component analysis of RNA seq data and DEGs profiles of WT2 and line 8 fruits during development, ripening and later stages. A. Distributions of genotypes and development stages. Color indicates the different genotypes: purple square, WT; green triangle line 8 and cyan circle Azgote-20dpa. Each stage has been performed in triplicate. B. Heatmap of all common DEGs between WT2 and Line 8. Hierarchical Clusters are shown on the left and were obtained by Spearman method.

  Principal component analysis of metabolic profiles of WT2 and line 8 fruits during development and ripening. ................................................................................... 133 Fig 3.S 4 Metabolite network of correlations in WT fruit and DML2 fruit. ........................ 134 Fig 3.S 5 Row counts control in each tissue. ........................................................................ 135 Fig 3.S 6 Relationship of tomato fruit pericarp related transcript expression profiles and differentially expressed genes .......................................................................................... 136 Fig 3.S 7 Principal component analysis of RNA seq data and DEGs profiles of WT2 and line 8 fruits during development, ripening and later stages. .......................................... 137 Fig 3.S 8 Expression of genes of the Carotenoid pathway in RNAi DML transgenic fruit compared to WT. .............................................................................................................. 138 Fig 3.S 9 Profile of DEGs involved in cell wall metabolism and fruit firmess .................... 139

Characterization of metabolite content in WT2 and in transgenic RNAi fruits Line 8................................................................................................................................. VI Fig 3.S 3 Fig 3.S 10 Profile of Ethylene-related DEGs in line 8. ......................................................... 140

Table 1

 1

. DEGs distribuation and DMRs type in each cluster and group. ................... ............95

Table 2. Enrichment of MapMan functional categories (BINs) in the DEGs associated with type-a DMR in group 1, 2 and 3 ...................................................................................... 101 Table 3. DEGs with DMR that labeled with selected genes in Line 2Y ............................... 102 Table 4 Transcription factor with DMR as top expressed genes and RIN target genes with DMR. ................................................................................................................................. 109

  Laboratory of Fruit Biology and Pathology, University of Bordeaux, Institut National de la Recherche Agronomique, CS20032 Villenave d'Ornon, France; Laboratory for Functional Genomics, Fondation Jean Dausset-Centre d'Études du Polymorphisme Humain, F-75010 Paris, France; c Laboratoire de Génomique et Biotechnologie des Fruits, Université de Toulouse, Institut National Polytechnique-École Nationale Supérieure d'Agronomie de Toulouse, F-31326 Castanet-Tolosan, France; d Laboratoire de Génomique et Biotechnologie des Fruits, Institut National de la Recherche Agronomique, F-31326 Castanet-Tolosan, France; e Research Center for Plant RNA Signaling, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou 310036, China; f School of Biosciences, University of Nottingham, Loughborough, Leics LE12 5RD, United Kingdom; g Laboratory for Epigenetics and Environment, Centre National de Génotypage, Commissariat à l'Energie Atomique-Institut de Génomique, 91000 Evry, France; h School of Life Science, University of Warwick, Coventry CV4 7AL, United Kingdom; and i United States Department of Agriculture, Robert W. Holley Center and Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, NY 14853 Edited by Robert L. Fischer, University of California, Berkeley, CA, and approved July 8, 2015 (received for reviewMarch 3, 2015)

a,2 a b

  toulouse.inra.fr/multalin/multalin.html).

	A
		WT 1	2	3	4	5	6	7	WT	8		9	WT	10	11	12	13	WT 14	15	16	17	18	B	WT 20	21 WT 22 A 24 25
		A
		WT 1	2	3	4	5	6	7 WT	8	9	WT	10	11		12	13	WT	14	15	16	17	18	B	WT 20	21 WT 22 A	24	25
	B	dpa		35			39 (Br)		55			70	85			C
		WT
		B
		DML8B
		DML2B
		(B) Residual SlDML gene expression: SlDML gene expression was measured by Real time RT-PCR
		analysis in WT1 and DML2A (line 2) fruits at 20, 35, 55 (Br+16), 70 (Br+31) and 85 (Br+46) dpa. An
		ANOVA was performed and differences with WT1 fruits of the same age were analyzed using a
		student t test (n=3). Stars indicate difference between WT and transgenic fruits of the same age (*:
		p<0.05; **: p<0.01; ***p<0.001). The Br stage (39 dpa) was not analyzed due to a limited number of
		fruits produced by the transgenic plants of line 2 as explained in the methods.

TTATTC 4 TTGTTAAGTTTAAAAATAAAAATGC 5 TAAAAAAATTTTTTAC 6 AATGAAAGAA TATTATAAAAC 7 TAATTAAATCC 8 GTCC 9 AAATTATATC 10 ATAC 11 GTATC 12 GC 13 GAGGATTC 1 4 ATC 15 ATAAATTGAC 16 TAC 17 TAGTC 18 GTCGTATTTGTTGTCTCTATCCGAGTTCAAGATCA ACGATACTATATATAAATACATCGATAGAGACAAGTTGTTGTAAAAAAATTCC 1 AAGTGT GAC 2 AC3TAGGCC 4 AAATTTGTCC 5 AAAGAGTAGCC 6 TAGAAATGCTTTC 7 TTATC 8 TTATTAT C 9 TGTC 10 TGTCG 11 AGTC 12 ATGTC 13 AAACTTC

  14 TGTTGTAAAATTTAATC15 ACTCC16 TAATT CG 17 ATATTTC 18 AAAATCG 19 AGTTTTGC 20 AAATTAAGAAAATTTC 21 ATTGTAGGACG 22 AGT TTCCTC 23 TTTAATTAAATGATTC 24 ATATGAGCG 25 CC 26 ACG 27 AATTC 28 AAC 29 TGAATATC 30 AAATAAAATAC 31 TGAATGATTGATATAGATCTC 32 TTTATATATC 33 TTGTGCAGGATAAAGT

	). ATCTGGTACATAAACTATTGTGCTTATGTAGAATTTGGGGAAGAAACGTCAAGGAATATA -2132 ATGTAAAGTATAGTAGACAATTTATTTTATCGTATACATATTAATAATTATTTTCACGATTC GAATATATATAACCGATAGATCACACAATAATAAATATTAGTGTTGCTCATCGAAAACTCC GATGCACTAATGTTTGCCACTAATTCTTAAGATAGATAACAAACACATCTAAACATTATTA ATTAAGTGTATATATACAACATATTTTAAACTTATTCTATAACTGGATTTCAATTTAAAAAA AATAATGATGTGTCATGTCCCAAAGTTAGTTGCACTCTAAAAAAAGTTAAAAGGTTTTTAA CCAAAAATAACTTCTTGACTATAACAAATTAGAGTTGGAATTAATAATCAAAACATATAAA AATTGATATTTTTAAACAAGTTTTACACCATAATGTAGCAATCCATCCTGTTAGTGATATT GTCTGCTTTAAATCTAGGAATGTACGTCTTTAAAATGCGTCATTAGTGGGTAAGACATGC TTACTTAAAACACGTCATTAATGAATAAGATTTGTTTACTTATATACTCAACATCTCTCATA TATTTTACTGATGTGAAATTAGTTATCTTAAACCGGAATGTCAGTACACTTCATTTGTATC TTTTTTTATATGAGCCATTATCATTTACATGTAAAAGTGCACCTTAAAGCTGGTTAAGCTT ATAAACTATAAATTGTTCATTTTTTCTCGTTTAATAATCAATATCTACTTAACAAGGCCTGT TTAATAGATGATAATAGTTTAAGTAGAAAAATGAAATTGTAACTTTTTTACGACTTTTAACA TTTCAACTATCAGTTAGTAATATGCTCATCCATTACATATTTTAAAGAGAACAAAGAACCA TTAAAAGGTTAAAAACTTATTATAAAGTTAAATATTTTTTCAGTATATATGAAAGGACCTTA CAAGTTACAACTAAATCTTTTGAAAGAAAAGTATCGGTCACTACTAAGTTTTCCAAGAAAA ACAACAACAAAGGAACAATCTTTTTCTACCACAAGGGGATGTGACTATTGATAGAATCCA TTCATTTTAATGGGAGGGCAATTTTTTTTTAAGCGGATTCAAAATATAAAAAAGTAAATAT ACGGACAAAAAAAAATAAGAAAATTTATCAACGTATACATAAGAAAAGTTGCATACTTCCA AATAGACATGATACATAAACATGATCTTTAACTTGACGTCAGTTGGCAACTATATGTGCA CAAGTAGGCACTTAAACTTGTATAAGATTGAACAATTGACACATTCATCCTACAGGCACC CTACATGAAAATTTTGTGTCCTGCGTGGCGTCCTACGTGTATCATGTCATGCATGACATG TGTGGCTACTTGTTCAATTTTATACAAGAGTAAGTGCCTACTTGTGCGCATCCAAAGTTG AGGGTCATAGTTACCGACTGACGTCAAGTTAAGAGTCATGTTTATGTATTATGCCCTCCA GGTAACATAGATTTGAAGAAGCATGGAATGCATGTAGATCTTACTTCTCGTGAAAATGGT TTTCAAATACGAATAGATTAGTCTCGGCTCAAGTAAAACATTTTAAAAGTAAGTACTTAAG ACAAAATAATACAATAATAAAAAAGTTATGATAATATTAAATAATAAAAACTATAGCAAAAT ATAATATATTATCGAAGCAAACATAAATGTCTAATTCAAGCCTCGATAAATGAAAAAAATA ATCTAATTTGAACACCGCAACTTTCTTTTAAATGGGCCCTCCACGACACTAATCTAGATT AATCGAAATAATAAATTCTGAAATACCTCATGATATATAGTAAAACAAAAAAGTCTTTATT CTCTTTTCTTCTTGACTAGGGAACCATTAGATTTTAAAGACATTAAATCTATTACCCTTAC CCTAAGAATAAGAAGATGTAAAGTAGAAGAGAAAACAACCAAAACCATATATATACATAT ATATAATTACATTATATTGTCTTATAACATATAGTCTTTTAAGGAAAAACAAATTTAGAAAA AAATAATATTATTTTACATTTTTTTTCTTCATACAATATG NOR (Solyc10g006880). -2568 TAATTCAAAAGCAAATGAAGGACCATTCAAAAATTGTCCAAGTTAGGGCTACTAATTTTG AAATAGATTCCACTTGCTTTTTTCTTTAATTAGGTAAGTGCAACATCCATAAATATTTTTCA AGATATTTTTCCGTAATTCATTCACAATTTTTTTTAAAAGAATTATTTAGTGTTTACCTGTT TACATTTATATTGAAATTAATTAAATTTAAAATCATAATTAAGAGTGGAGAAATTTCATTTA TCAATAACCTAAATACTTAATTCTCCAATGAAACTAACTATAAGATTTTTCTCCCTAATAAT AGGTTCATTTATTTTAGATTGGTCATGTGAAGGATATGTGTTGAAAC 1 AAATCCC 2 TAAAT TATCGATTAATTATATTGCCTAATTTTCAGTTATCAAGCTCTAATTACATCATTGTCATGTA TTAATCTAATCACCTCTTCAATTTATGCTAATGACGACCTCCACTTCTAATTTAATATTAAC ATATACACTATTTATTTTTCCACTAACGACTAATTTTTTTAATTTTTTTTTGACAATATTTAT ATAGTAATTTCTGCTAAGGTTAATTCTTAGTTTTTATCAACTCATTTTTACTATATATAATTA ATGTCCTTCTCAAAGCCTAATAACGCCCATTTTACGTTAAGTTAAACTGTTAGAATTGAC GAAATTAGGATTAAATTTTAAAAAGAATCTTGAAATATGATTTAAATATATTCACAAAATTA TATCAGAAAAATAAATAAAAAATTTAAAATAAAATTGTGTAAGAAAAAAAGAATTGTTATC GATTTTAAATAAAAAAGAAAAAATAACATATATAAAACGAAAAAAAATATATTTTTCTTAGT GAGTAGATTTATCCACACTAGTAATTGTGTGATTATTGTAACATATTATTCATTAGTCTAG GTACGAATTAATTGACTCGAATATTATCGTCCTAATAAAAAAAATATTCTTAATTTTGTTCT ATTTTTTAATTAGCTTATTCCAAAGTAAAAAAAATCAAAGACATGTTCTTATATTTATGAAC TTCTTAATTAAACATTTATAATTACCACAAGAATCTCAAGACATGTTTATAATTAATAAATT TAGATGTCTGTTTTTCTTTCTAATTAAATTAATATAATTTTACCTTTGATAGCATATATTTAT AATTACCATAGAATTCAAAGCATGTTTACTGTTAGATAAATTTAAATATCTTCTATATTTTC TAAAACCTTTGGCGTCCAATTCGATCAAAGTATGTCCACACAATTCAATACTACAAAAAC TTTCTATATAAAGAGAGATAATAGTCAAAATACATCTGAAATGTTACGTTTTTTGTAAAATT TCTATTTAAATTATCACGTGCTCAATTTTTTTTACCTAAATCATTATCAACTATTTAACAAT ACACATCTCAATTATCAGTTATTTTCTTTTTCTACTTGAATACAGTAATATTTCAGATAAAA AAAGAAAAAGAGAAACAATTGATAATTATATTAACGCGTGATTTGATAAATAATTAATGAG TTTATGTATAAAAAATGAACACCTCATGGTTCAAAAAAAAATCTTGCAAAAATATAATACT CTAGATACTATTTTTTACCATTAAAGTATATATTTCAATATATATATATATATATATATATAT ATATAAACAAAAATATATGTAATGGCATTACTGTAAATTCAGTGTTGCCTTATACCATATA TAAGTAAGTGTGGGGGCTAAATTAACCAACTAAATTCCTTCTTGTTTATCATTTTCTCTCT TCCCAAAAAAAAATCCCAAAATTTAATCATAATACAATTCGAATTTATCAACCTCGTACTA CGTACATATTTTTGTTGGTACGTAAAATACTGAATTCAGGTCAACTCAAACATCGTAAATT GTGATTTCTTTATG PSY1 (Solyc03g031860). -2345 GTTCACAATGTCAAAATCTAAACAACTAAAAACGACGAGGAGTAAGGTTTGCAAC GACGATAACAAGGATTAGGCAACAATTAGAGTTGTGAATTGTGAGTATTAACTAT ACTTTTACTATATTAGGCAGAATTTTTGCACTCAATGAGTAACTTGATTTATTTATT TTTTATTTCGCCCTAAATTATTGGACAAGTCATATATTTGTTTTGAAAACATTCTTT TATTGGCTAAATCGAAAATTGAATCGTTAAAGATCAAAAATCAATAACAAATATCT TATTGGTTTAACATATTTAAAAATAAAAAACCAATAAATCTAACTAATAATATTTAA TACGAAAACGAAATGGACTGACACACATTCCTAAATTTTTGGTCAAAATTTTTTCA TAATTTCCCTAAAATCTAAAATATTAAATATTTGACGGAAACAAAAAATTCACTTTT AATAAATTATTTGAAGGACTAAAACAGTGGAAGAATATATTTAAGAAGCTAATTTG AACCTAGTGCCAAATATAAAGGGACCATTTTTGTCATTTTTCAACTTGAAAATCTA CGTGTCTTAATATAACACCAAAGAATTAATATTTACTGAAAAAATGTAAAAATGAG GATATGGATTCTGAATCACTCAATTCCAATCAGCAAAAATAAAATAAAATAAAATA AAATAAAATTTAAAAAATAATAATAAATGCTATAAAATGACCAAAATGTGTGGAGC AAAAAGTGCAGAAAAAACCAACAAATTGCATTCTCCATTCTTGGAAGTGGCCATT CTTGATTTCTTGAAACAAAGGTTTGTTTCCCTTCACTTCTTGATATGTAAAGTTGC TTC 3 AGTTCTGCGTATATGCCCCTTTTACTCGATTGTCCACGTGTTGGTACCAACTTGCATGCG AATCTTTATAACTTTCTATTGCTTTGCTAGTGTTTTTGTTATATACAGGGGGTGGA
	GTTAGAGGGTAAGTTACGCATTTAGTCGTAACTTAGTCAAACTTCGTAATAATTT
	AGTAAGTTAAAATATATTAGAAATTTTCAGAATTCATAAACTTTAAATTTTAAATTTTG
	ACTTCGCTTTGTGTGACTATACAATTACAGAAATTCAGAGTGGCCATTGTTGAAAGAGA
	GGGTGGAATTTGTGTAAGTTTTGTTTCCTTTC 1

AGTTC 2 TTGATATATAAAGTTGC 3 AATC 4 T TTAAC 5 ATTC 6 TTTGTTCAC 7 TTTC 8 TATAGGTTTGC 9 TAGGTTC 10 GGTTAAATTC 11 AGTAGC 1 2 TTTAGTTTAAACCC 13 TATGC 14 GGAATAGAGAATGTGTAAAC 15 TTTAAACTTC 16 AAATTTT GGCTCC 17 GC 18 ATACG 19 AC 20 TAGC 21 GAC 22 TATATAATAATAGGAATTGAGCACTTGGCTT

	TTGTATATAGCTTCTATGTGTACCAAAATTAGAAAATCAGGCGATTATTATAATCTTGTTG
	ACTAAATATAGAATGCATCCATTACCCCCAAAAAGTGTGATTCCACTGTCATAGGAGGTT
	TTTTTTATTTCATTTTATTTGTGCTTTCAATAATGTAGAGTAGTTTTACAAAGATCCTTTCT
	TTGTGACACATGGTAGGTAATATTGCTGATTTTGTTGTAGTTTTGGGGTTATAAAGTTTCA
	AATTATTTATACTGGAGGGTAGGGGTGGGGGTTGTCTATAATGCAGGTTATGGTTTTAC 1
	GTGAACTC 2 AATAATTATTGTAGATAC

3 TAAGAAATCC 4 ACTC 5 AGTGTTC 6 TTGC 7 GGTGTC 8 TTGC 9 TTTTGATTTC 10 AGC 11 ATC 12 AC 13 TTGTAGTTGATTGTGTTTAGATTATC 14 AC 15 ATTAT TC 16 TGTGGC 17 TGTAAC 18 TGTATCC 19 TTGTTAGTTGC 20 TTTGTTTC 21 TAC 22 AC 23 TGTTGTTT TCCCTC 24 TTTTATACC 25 TATTTTGATATGTTGTACTCGAACGAGGGTCATCGGGGAACA

	ACCTCTTTACCTCCGTGAGGTAGAGCTATGGTCTGTGTCCACTCTACCCTCCCCAGATC
	CCTCTTGTAGGATTTCACTATATTGTAATATTAACTTGAGGTCACTATAGGAGCTCAAA
	AACTTCTAATTTTGAATCAATGTCTGGTTATACTTTTTTTGTCATAACTGTATCTCA
	AATGTGGTGTTTGGTTTATCTCATTTTGCAGAAGTCAAGAAACAGGTTACTCCTG
	TTTGAGTGAGGAAAAGTTGGTTTGCCTGTCTGTGGTCTTTTTATAATCTTTTTCTA
	CAGAAGAGAAAGTGGGTAATTTTGTTTGAGAGTGGAAATATTCTCTAGTGGGAAT
	CTACTAGGAGTAATTTATTTTCTATAAACTAAGTAAAGTTTGGAAGGTGACAAAAA
	GAAAGACAAAAATCTTGGAATTGTTTTAGACAACCAAGGTTTTCTTGCTCAGAAT
	G
	CNR (Solyc02g077920).
	-3526
	TCACAATCACAAGCAGGCAGTGAAACAATTACATCAAGCTCGTTTCATAGATTCTTCATT
	TTGGAATAATAGCTTGTCACAGAGTCTGTTCCTTGTTTCAAATTAGCAATTTCTGCGCAC
	AAATAATAAATCCTCGTCAAATTCGATCTATCAAAACGCTCCTTGTATTCATCCCATACCT
	TCTTCGCAATTGAAGCATAAACTATGCTTGGCATCAAATCAGCTGTAACAGTACTTCCTA
	TCCATGATAACACAATTGCATTAAATTTTTCCCATTACGCTTCTAGGTCTCCTTTAAACTT
	ACTCTTTGTGCAGTTTCCATCCACAAATCCAAGTTTTACTTTGCCTCGCAGTGCTAGTTT
	CATCGATTTGCTCCATAGAGAGTAGTTCTCTGGTCCTGTGAGTTTGATCGGAGTTATTAC
	TAAGTCTGGAGAATCAGAAGCTTAAAGATAGAGAGGATGATGATGATTAATTTTTGTTG
	C 1

AGC 2 TGGAACTTCC 3 ATC 4 TGTAGC 5 AC 6 ATTGTTCTCC 7 TGTC 8 ATTTCC 9 TAAAC 10 TAATT GATTGC 11 GATTAACTC 12 AAATTCC 13 TAAGC T C 14 AGC 15 TGAAGGTGAGATC 16 GCC 17 GCTC 1 8 TGATACC 19 ATGTTAATTTGTAGTTATGTATGTAGAATTTATGGTGAATAAGTTC 20 ACC 21 A

	AGTTCTTCCTCTACTTGCCTATCTCGATAGAAAAATTTTTGATAGGAAAGAAAAAAACTGA
	TCGAAGCGAGAGAGGGAGCAGTAATGAGGAATATACAAATAAGGTCATTTTGGGGAACC
	ATTAAGCTATAAAACAATAATACACACTTATGAATTACCGATATATAATTTAATTTGGAATT
	TCATTCATATGGTTAATAGCAACAGAGTTGTCTTTGTATTAGTGCACTATCAATTTAATAC
	CTAGCTGTGACACTAAAAAGCTAGGTGCCCACAATTATTAAAACAAAAGTGTATCCACCT
	CAAGAAGAAGAAAAAAGGCAAATATGATATAAAACCATTTAACAAAGTCCATATCACAAA
	AATTAGACGGCAAAATCATACACGACTAATTTATAGATTCACTGAACCATGCAATTCTATA
	CCGTTCACTTCCAATAAATAAAACATAATACACTATGTTTAGAGTACAAGACTCTCCTTGC
	TTGAAAAGGACTACCAAGTAGGGGTTACTGCAGTGACTACCAAGTAGGGGTTACTGCAG
	TCATTTGTTAATTCATTTTGAGTAATGTAACTGTGCAAGATAATGATGTTTTTTTTCCTTTT
	TGGTTAACTAAGATAATGATGGATTTAGGTAGATGAATTAGAC 1 ATC 2 TAGTGATAATGG
	AGAGCC 3
	TTGATGAATTTTC 22 TAAGCTGCTACAGAGATATTGGAAGAGAAAAAGAGGATCACTATT
	TCATTGAATCTAAATTGAATTATCTTTTTTTAATCATAATTGATGGCTAGTACTGTTATAGG
	TCCAGCTAACCTACTTCTAGAAAGTTCCATTTTAACTGACCTCATAACAAATTGTAACTAA
	TTTTGTTAGCTACATCACAAATGACACTTACAAGAATAACAGTAATAAGAAACAAGTTATT
	TCAACAGCTATCATTTATTATGTTACCTCATCTTGTATCGTGTTAATCCGTACAGACATAA
	TTAAAATACAAAATAAGAAAATTAGAACTAGAGGCTCTAAACAGGAAATTTCAGGAAGTT
	CCACCTCTGCCTAGCTATATTACATGATTTAAAAGGTATAATACAAGATGAACTCCTTAAA
	ATTATCAGAATACTTTTGTTTAAAAACTCGAATTACCCGTTGTTTCAATTGATGAAGTGTT
	TTAATCTGACACTTCCGGTTCGTTGTTATTCCTATACTAGATTGTTAAGTTAACCACATAT
	TTTTTTAATCACACATTTACCTCAATAAGATATAAAACTTTAAATATTTTCTTCTTGAGGTT
	GATACATATTATTATGAGATGACATATTTATGTGGTTAACTTAATTATGCGATAGACAAAT
	AAAAACACGTGCAAAAGTTCATTCAAAATTTAAAATTTAACGTGACTACTTGGAACATTTT
	ATTAGAAATTTAGGTGTTCAGTTAAAATAAGACTTATTGAAGTATCTAACCAGAATATCCT
	GACAAATTAAGGGACTTATCATGTATTATGCCCTTCAAAAAGATTACTTCTTTATTAATGA
	TGATTAGTTATACTCATAAGTAATAACCTCACTTCTTTTTCAGCCCATGTCCTAACCTTGT
	TTTGTTTTCTTCCAATCATGGAGTCCCTTTGTCATTTGTCTATCAGTTTGTTAGCCTCCCT
	TCACTAATAATTATCCATAACCGGCTAATAAAGTACATTCCATTTAAGTGTAAAAGAAAAA
	TTGAAGAGTTTGCCTATTCTTTCTCACCACGTCCTCCCTAGAAAGTTCTCGTCACGCTTC
	ATTGTCAATTGTCATTCCTTCGACAACAAGGGAATATATAGTTGGAATACTTCTGTCCCA
	TCCATCCTGCCTACACACAAGTTATTCATTCTAACCTGTCTTTGCCTACTAAGATACGTCT

AGTGC 4 AAC 5 AATTGAGC 6 ACTC 7 TAC 8 TGGACC 9 GAC 10 ATGGAC 11 AAC 12 TGAGA GACC 13 AAC 14 TTGC 15 AGTATTATAATAGTGC 16 AAATTATAGTTTAGTC 17 GACTCCCTTC 18 G GAATC 19 TAC 20 TAC 21 ATAAAGAAC 22 TACC 23 ATAAAC 24 TATGTTAGATGGC 25 TATTAC 26 GGA GTTTAAATTAAACTC 27 GAAAATATC 28 AGAAAAAGAAGTAACTTC 29 AACC 30 AATTAC 31 AATG C 32 ATACCC 33 TTATC 34 AC 35 AAGTGAAAAAGAGTAAAC 36 GTGCC 37 AAACTC 38 TTTTGATCCC

	TCC 39 AAAGCTAGAGGAAAAGAGTGAGCAATTCACTACAAACCACTGGCTTTGGTCTAT
	GGTTGACACAACTCCTCGGCTAATTGGTCAAAATATCTTGTGACCACCAACCAGCAAGC
	ACTAAATTGGATGTTCTATCAGCTTCTTTACATCATAAAACAGTGAATACTGAACGCTGA
	GAGGCTAACTGACTGCCCAAAAAAACCTTGACAAAAAGTTAGTGGAGTAACTACCTAGG
	AGTAAATTCAATAGTAGACCTTGAAAAGAACTTTAGCAAAGTCATCATAAATGCTCTTCAC
	GTCTCATGTACTATGTTAAGGAATGGTCACATTTCTCTCTGCATTAAAGCTAGTTCATGTT
	AAAAGTTGAGGCCGGTAGTAGTTTCAACTTTCAATTTAATTCCACCTTTCCTGGCCCACT
	TCTGTACGGAACACCAATCAGAATCTTTAGTTCATCTTAACACCAAAGCATCTCCACTTA
	GACACTTACTAGACTTCACATAGGAGGAAAAATATGGAACTGGTGGTCCTCACACGTAC
	TTACCTTTCTTTTTTTACCTTTGTTCAAGTTTCATACTCTTTTATCTGGCTTCCTCACTCTA
	TTTTGGCCCAATAGGTTCTCCTCACAGGGATG

Table 1 . T4 Plants culture in greenhouse

 1

	Plants	Azygous plants	% azygous plants	Germinated seeds
	Line2-AC11	1	8%	13
	Line2-T6	2	6%	36
	Line1-B7	10	22%	45
	Line 1-D8	3	7%	46

Clusters pigment, starch sugar, sugar- related amino acids TCA organic acids fatty acids others

			sucrose,
	Cluster 1	starch, chlorophylls	raffinose, rhamnose, raffinose,	Leu,Pro, Ser, Val,Thr,bAla, Ile,GABA,Phe	citrate, malate		unkS5.4, UDP_like, unkS2,97
			myoinositol
	Cluster 2		ribulose-5-p	Asn,Gln,His, pryo-Glu	fumarate, succinate	nicotinate	trigonelline, choline, urea
	Cluster 3		galactinol	Gly,Tyr,Ala,
	Cluster 4		glycerol	puterscine	2oxglutarate
	Cluster 5		xylose	Asp,Glu		ethanolamine, threonate, galacturonate	palmitate, octadecan-oate	Calystegine A3,uracil, urate, unkD5,15
	Cluster 6	lycopene, carotenoids	fructose, galactose, glucose, guanosine threitol,	Trp		ascorbate, like d-ascorbate, adenosine_	uridine_like, 3CGA, trans

Table 1 . DEGs distribution and DMRs type in each cluster and group.

 1 DMRs have been classified in four groups based on the methylation ratio R1= methylation at 17dpa/ methylation at 39 dpa, and R2= methylation at 17dpa/ methylation at 46 dpa.

	DMR distribution

Table 2 . Enrichment of MapMan functional categories (BINs) in the DEGs associated with type-a DMR in group 1, 2 and 3.

 2 Contingency gives the numbers of genes (i) from the BIN in the input list (ii) the background (iii) not in the BIN in input list, and (iv) not in the background. P-Values adjusted with Bonferroni.

			DMR			39_Log2	46_Log2F
	Groups Clusters	type	Solyc	Name	FC	C	Pathway	Reference
			c					jasmonate.synthesis-degradation
	3	7		Solyc01g006540	loxC	-6,12	1,69	lipoxygenase	Chen et al., 2004
			a
	3	6		Solyc10g075100	Itpg1	-7,56	-2,29	lipid transfer proteins	Le et al., 2006
			a					major CHO	Nguyen et al., 2014;
	2	5		Solyc03g083910	AI	-6,47	-8,23	metabolism.vacuolar	Zouari et al., 2014
			a					misc.glutathione
	2	5		Solyc01g081250 Unknown1 -3,95	-8,92	transferases
			a					signalling.
	2	5		Solyc06g060410 Unknown2 -4,23	-6,06	phosphinositides
			a
	2	4		Solyc09g066150	P450	-4,98	-7,9	misc.P450

Table 1 . Transcription factor with DMR as top expressed genes and RIN targets with DMR. A.

 1 Genes selected based (i) the 20 most repressed at Br stage in line2Y and line 8; (ii) the 20 most highly expressed in WT fruits at Br stage in group 2 and 3 in both line2 and line8, except Solyc06g069430 that is outside the top 20 in Line 2Y.B. All DE TFs found in transgenic fruits with a RIN Binding Site and DMRs.

	1

of 6 | www.pnas.org/cgi/doi/10.1073/pnas.1503362112 Liu et al.

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of 6 | www.pnas.org/cgi/doi/10.1073/pnas.1503362112 Liu et al.

Acknowledgements I Acknowledgements This work was performed in the Ecophysiology and Functional Genomics of Vine as well as Fruit Pathology and Biology Group at INRA, University of Bordeaux from Sep.2013 to Nov.2016. The project was funded by Fulbring grant, Agence National de Recherche. I was funded by Chinese Scholorship Councile. ACKNOWLEDGMENTS. We thank Marie Mirouze for critical reading of the manuscript and Antoine Daunay and Nicolas Mazaleyrat for technical support in bisulfite pyrosequencing analysis. We acknowledge Syngenta and specifically Dr. Charles Baxter for help with the tomato GeneChip studies and Alex Marshall for help with the array analysis, as well as Cécile Cabasson and Jim Craigon for help in statistical analysis. Metabolomic profiling was performed on the Metabolome Facility of Bordeaux Functional Genomics Center and supported by the French National Infrastructure for Metabolomics and Fluxomics (MetaboHUB) funded by the Agence Nationale de Recherche (ANR, Project ANR-11-INBS-0010). R.L. was the recipient of a grant from the Chinese Scholarship Council and P.G. of a Fulbright grant. G.B.S., T.C.H., and N.H.C. acknowledge financial support from the Biotechnology and Biological Sciences Research Council, UK (Grants BB/F005458/1 and BB/J015598/1), and G.B.S. acknowledges support from the European Cooperation in Science and Technology (COST) Action FA1106. Y.H., J.K., and C.W. were supported by Hangzhou Normal University and the National Natural Science Foundation of China (NFSC, Grant 31370180). M.B. and M.L. received support from the Laboratoire d'Excellence (LABEX) entitled "Towards a Unified theory of biotic Interactions; the roLe of environmental Perturbations" (TULIP, ANR-10-LABX-41) and from the networking activities within the European COST Action FA1106. J.J.G. was supported by National Science Foundation Grant IOS-1322714.

List of Supplementary Tables (provided as additional excel file online)

Table S1. Significent correlations in different WT and lines……………………………....... TabeS2. Reads obtained by RNA seq after clean and mapped percentage for all the genotype and three replicates………………………………………………………………………………….. TableS3. Differentially expressed genes that only found in Line 2 (TableS3_1) or Line 8 (TableS3_2 ) and DEGs that specific differentially expressed at 46dpa (TableS3_3)…………….. TableS6. All differentially expressed cell wall related genes in group 1 and group 2 and 3…. TableS7. All differentially expressed genes of other hormones………………………………. VII TableS8. All differentially expressed genes involved in amino acids and Nitrite metabolism... TableS9. The ratio of all differentially expressed genes with DNA methylation level……......

Chapter 1

Chapter1_General Introduction

DNA methylation in plants

SI Supplementary Tables

Supplementary Table S1: repressed TF genes at 39 dpa in DML RNAi fruits compared to WT were identified; (ii) among these genes, TF genes with the highest counts number at Br stage in WT were further selected.

Six genes were primarily identified under these criteria (Table 4A). Five of these six genes are well-known ripening regulators, including AP2a (APETALA2a), FUL1 (FRUITFULL), RIN (RIPENING INHIBITOR), NOR (NON-RIPENING) and an uncharacterized gene (Solyc06g053960, HSA6b) from HSF family. RIN, NOR, that are both associated with a type-a DMR have been reported to be targeted by active demethylation through SlDML2 (Liu et al., 2015b). Other four novel genes are also associated with a type-a DMR (see table 4A, p109), suggesting that these genes might also be under direct DNA demethylation control during fruit ripening. Zhong et al (2013) have shown that RIN binding sites are preferentially demethylated during fruit ripening (Zhong, et al., 2013). We therefore analyzed all differentially expressed TF genes, those associated both with RIN binding sites and with DMRs. As a result, twenty differentially expressed TFs with different type of DMR were identified (table4, p109), four of them corresponding to genes of known function (table4A, p109), while another 7 genes also associated with type-a DMR belong to group 2 (cluste 4 and 5) and 3 (cluster 6 and 7) suggesting that they are regulated by both the RIN protein and by active demethylation.

Chapter 3_ supplementary figures

PCA analysis of metabolites

All the data used for PCA and heatmap were normalized using the following formula: log2 [(value of each sample+1)/the average of all the samples in transgenic fruits and WT)], they were performed using R software;

Clustering on metabolites

Metabolite clustering were use Multiple Experiment Viewer (MeV 4.9.0), clustering used pearson with median value.

Visual Network Creation

Networks were constructed using Cytoscape software (Cline et al., 2007). Nodes are genes, metabolites, and edges are the significant correlation between the nodes. The layout of the nodes color is based on the positive or negative correlation between two metabolites.

RNA sequencing and Reads mapping

Strand-specific RNA sequencing libraries were prepared as previously described [START_REF] Zhong | High-Throughput Illumina Strand-Specific RNA Sequencing Library Preparation[END_REF]. All sequencing reactions were performed on GAIIx or HiSeq2000 according to the manufacturer's instructions in the core facility of Cornell Weill Medical College.

Strand-specific RNA-Seq reads were first aligned to adaptor, ribosomal RNA and tRNA sequences using Bowtie and allowing two mismatches [START_REF] Langmead | Ultrafast and memory-efficient alignment of short DNA sequences to the human genome[END_REF]. The resulting filtered reads were aligned to the tomato genome using Tophat and allowing one segment mismatch [START_REF] Trapnell | TopHat: discovering splice junctions with RNA-Seq[END_REF]. Methods are as described in Zhong et al., (2013). Experiments were performed in collaboration with Dr N Gapper.

Identification of differentially expressed genes

To clean raw counts (filtered counts), one threshold was set before raw counts were normalized. For each gene at each stage (including 3 biological replicates for each genotype), if one sample row counts was ≤ 50 sample at each stage among all corresponding lines and replicates (eg, 9 samples total of Line 2Y, 2X and WT1 at 20dpa, 6 samples total of Line8 and WT2 at 20dpa), all counts number of this gene was considered as 0 at this stage.

To identify differentially expression genes during fruit development and ripening, the expression data were first normalized by DESeq2 package in R [START_REF] Love | Moderated estimation of fold change and dispersion for RNA-seq data with DESeq2[END_REF]. Differentially expressed genes were identified by pairwise sample comparisons, and the majority of genes were