Lacour Thomas

Babin Marcel

Lavaud Johann

P Kroth

Diversity in xanthophyll cycle pigments content and related non-photochemical quenching (NPQ) among microalgae: implications for growth strategy and ecology

Keywords: Xanthophyll cycle, pigments, microalgae, photoacclimation, non-photochemical quenching, NPQ, diversity, diatoxanthin, zeaxanthin XC, xanthophyll cycle, NPQ, non-photochemical quenching, Dt, diatoxanthin, Dd, diadinoxanthin, Z, zeaxanthin, V, violaxanthin, A, antheraxanthin, LHC, light-harvesting antenna complexes, QE, quenching efficiency, K E , Light saturation parameter for growth, E, Growth irradiance, µ, growth rate, DES, xanthophyll de-epoxidation state, Y 0 , Y-intercept

Xanthophyll cycle-related non-photochemical quenching, which is present in most photoautotrophs, allows dissipating excess light energy. Xanthophyll cycle-related NPQ depends principally on xanthophyll cycle pigments composition and their effective involvement in non-photochemical quenching. Xanthophyll cycle-related NPQ is tightly controlled by environmental conditions in a species/strain specific manner. These features are especially relevant in microalgae living in a complex and highly variable environment. The goal of this study was to perform a comparative assessment of non-photochemical quenching ecophysiologies across microalgal taxa in order to underline specific involvement of non-photochemical quenching in growth adaptations and strategies.

We used both published results and data acquired in our laboratory to understand the relationships between growth conditions (irradiance, temperature and nutrient availability), xanthophyll cycle composition and xanthophyll cycle pigments quenching efficiency in microalgae from various taxa.

We found that in diadinoxanthin-containing species, the xanthophyll cycle pigment pool is controlled by energy pressure in all species. At any given energy pressure, however, the diatoxanthin content is higher in diatoms than in other diadinoxanthin-containing species. XC pigments quenching efficiency is species-specific and decreases with acclimation to higher irradiances. We found a clear link between the natural light environment of species/ecotypes and quenching efficiency amplitude. The presence of diatoxanthin or zeaxanthin at steady state in all species examined at moderate and high irradiances suggests that cells maintain a light-harvesting capacity in excess to cope with potential decrease in light intensity.

INTRODUCTION

What is the xanthophyll cycle (XC)-related non-photochemical quenching (NPQ)?

XC is one of the most important photoprotection mechanisms in photosynthetic organisms [START_REF] Demmig-Adams | Carotenoids and photoprotection in plants: A role for the xanthophyll zeaxanthin[END_REF][START_REF] Masojídek | The xanthophyll cycle in green algae (Chlorophyta): Its role in the photosynthetic apparatus[END_REF][START_REF] Brunet | Can the xanthophyll cycle help extract the essence of the microalgal functional response to a variable light environment?[END_REF][START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF]. XC protects plastids from over-excitation of the photosynthetic pigments and over-reduction of the electron transport chain that may led to the generation of reactive oxygen species (ROS). It thereby prevents potential damages that mainly result from the ROS-generated oxidative stress, the primary target of photodamage being the PsbA (D1) protein of photosystem II (PSII). XC allows the safe dissipation of excess excitation energy as heat in the light-harvesting antenna complexes (LHC) of PSII. Because this process is mirrored by chlorophyll a (Chl a) fluorescence changes, it is commonly evaluated via the so-called non-photochemical quenching of chlorophyll a fluorescence (NPQ; Demmig-Adams et al. 2014). The main part of NPQ that is related to the XC process is called qE, the 'energy dependent quenching' and is the main NPQ component among most eukaryotic photoautotrophic taxa (see [START_REF] Niyogi | Evolution of flexible non-photochemical quenching mechanisms that regulate light harvesting in oxygenic photosynthesis[END_REF][START_REF] Derks | Diverse mechanisms for photoprotection in photosynthesis. Dynamic regulation of photosystem II excitation in response to rapid environmental change[END_REF][START_REF] Goss | Biodiversity of NPQ[END_REF] for further details). Note that although widely distributed, the XC-mediated NPQ is not present in all photosynthetic lineages, and several groups and species have been reported to show no XC-NPQ and/or alternative XC regulation (see for instance the recent reports by [START_REF] Kaňa | Non-photochemical quenching in cryptophyte Alga Rhodomonas salina is located in Chlorophyll a/c antennae[END_REF][START_REF] Cheregi | Presence of state transitions in the cryptophyte alga Guillardia theta[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF][START_REF] Christa | Photoprotection in a monophyletic branch of chlorophyte algae is independent of energydependent quenching (qE)[END_REF][START_REF] Berne | The peculiar NPQ regulation in the stramenopile Phaeomonas sp. challenges the xanthophyll cycle dogma[END_REF], well illustrating the amazingly complex functional biodiversity of the XC-NPQ process [START_REF] Goss | Biodiversity of NPQ[END_REF].

There are two main XC (note that there is also a lutein cycle in plants, see [START_REF] Esteban | Involvement of a second xanthophyll cycle in nonphotochemical quenching of chlorophyll fluorescence: The lutein epoxide story[END_REF]): i) the violaxanthin (V) cycle, found in higher plants, in the green (Chlorophyta) and brown algae (Phaeophyceae) and in the Chromeraceae Chromera velia (member of the Alveolate clade), and ii) the diadinoxanthin (Dd) cycle, found in the main algal classes Bacillariophyceae (denoted as 'diatoms' elsewhere in the text), Xanthophyceae, Haptophyceae, and Dinophyceae (Goss and[START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF]Lepetit 2015). In Dd-containing algae, the V cycle can also be observed depending on species and light conditions (Lohr andWilhelm 1999, Blommaert et al. 2017). The V cycle consists of two de-epoxidation steps in which V is sequentially converted into anteraxanthin (A)

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This article is protected by copyright. All rights reserved and zeaxanthin (Z). The Dd cycle consists of one de-epoxidation step that converts Dd into diatoxanthin (Dt). Z (and A) and Dt interact with antenna complexes to convert the PSII LHC antenna into a heat-dissipating state. The regulation of the XC and mediated NPQ at the molecular level has been the object of intense research in various photosynthetic organisms (see the recent syntheses by [START_REF] Niyogi | Evolution of flexible non-photochemical quenching mechanisms that regulate light harvesting in oxygenic photosynthesis[END_REF], Demmig-Adams et al. 2014[START_REF] Goss | Biodiversity of NPQ[END_REF][START_REF] Magdaong | Photoprotective, excited-state quenching mechanisms in diverse photosynthetic organisms[END_REF][START_REF] Pinnola | Molecular mechanisms involved in plant photoprotection[END_REF]. In microalgae, its peculiarities have been extensively studied in green representatives (Finazzi andMinagawa 2014, Erickson et al. 2015), in the Heterokont diatoms [START_REF] Lepetit | Molecular dynamics of the diatom thylakoid membrane under different light conditions[END_REF][START_REF] Büchel | Fucoxanthin-chlorophyll-proteins and non-photochemical fluorescence quenching of diatoms[END_REF][START_REF] Lavaud | The peculiar features of non-photochemical fluorescence quenching in diatoms and brown algae[END_REF] and Eustigmatophyceae Nannochloropsis sp. [START_REF] Cao | A transthylakoid proton gradient and inhibitors induce a non-photochemical fluorescence quenching in unicellular algae Nannochloropsis sp[END_REF][START_REF] Bína | A two-component nonphotochemical fluorescence quenching in eustigmatophyte algae[END_REF][START_REF] Park | Chlorophyll-carotenoid excitation energy transfer and charge transfer in Nannochloropsis oceanica for the regulation of photosynthesis[END_REF], and in Chromera velia [START_REF] Kotabová | Non-photochemical fluorescence quenching in Chromera velia is enabled by fast violaxanthin de-epoxidation[END_REF][START_REF] Quigg | Photosynthesis in Chromera velia represents a simple system with high efficiency[END_REF][START_REF] Kuthanová Trsková | Antenna proton sensitivity determines photosynthetic light harvesting strategy[END_REF].

The importance of the environment in triggering the XC and related NPQ: stress vs. acclimation.

The accumulation of xanthophyll pigments in response to excessive light intensity was first described in higher plants more than 55 years ago [START_REF] Yamamoto | Studies on the light and dark interconversions of leaf xanthophylls[END_REF]. XC-related energy dissipation is now generally thought to be the result of an imbalance between the energy availability (source) and the demand for photosynthates (sink; Adams et al. 2014). Exposure to more light than can be utilized by the photosynthetic process leads to a relative compensatory increase in XC-mediated NPQ that decreases PSII quantum yield efficiency and thus the amount of energy directed to photochemistry. A) or Dt and the concomitant increase in XC-mediated NPQ was described in response to high irradiance in higher plants [START_REF] Demmig | Photoinhibition and zeaxanthin formation in intact leaves: A possible role of the xanthophyll cycle in the dissipation of excess light energy[END_REF], green algae (Niyogi et al. 1997, Finazzi and[START_REF] Finazzi | Non-photochemical quenching and energy dissipation in plants, algae and cyanobacteria[END_REF], diatoms (Olaizola et al. 1994, Lavaud andGoss 2014) and brown algae (Harker et al. 1999, Lavaud andGoss 2014). It has been also reported in response to other abiotic factors affecting photosynthetic performance and growth such as for instance, low temperature and nutrient availability in higher plants [START_REF] Huner | Energy balance and acclimation to light and cold[END_REF][START_REF] Morales | Thermal energy dissipation in plants under unfavorable soil conditions[END_REF]) and microalgae [START_REF] Wykoff | The regulation of photosynthetic electron transport during nutrient deprivation in Chlamydomonas reinhardtii[END_REF][START_REF] Mock | Long-term temperature acclimation of photosynthesis in steady-state cultures of the polar diatom Fragilariopsis cylindrus[END_REF][START_REF] Allen | Whole-cell response of the pennate diatom Phaeodactylum tricornutum to iron starvation[END_REF][START_REF] Petrou | Photophysiological responses of Fragilariopsis cylindrus (Bacillariophyceae) to nitrogen depletion at two temperatures[END_REF], drought stress in higher plants [START_REF] Morales | Thermal energy dissipation in plants under unfavorable soil conditions[END_REF], desiccation in mosses and lichens [START_REF] Bilger | Non-photochemical quenching and energy dissipation in plants, algae and cyanobacteria[END_REF], as well as in response to a combination of several environmental stresses (i.e., light, temperature and salinity; see for instance in a variety of taxa; Petrou et al. 2011[START_REF] García-Plazaola | Thermal energy dissipation and xanthophyll cycles beyond the Arabidopsis model[END_REF], Verhoeven 2014, Laviale et al.

Accumulation of Z (and

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This article is protected by copyright. All rights reserved 2015). Removal of photosynthetic electron sinks (e.g., young, developing leaves and/or fruits) can also lead to XC-mediated NPQ in plants (Adams et al. 2014).

Light history is also important in determining the level of photoprotective capacity in plants and algae (Raven andGeider 2003, Demmig-Adams and[START_REF] Demmig-Adams | Photoprotection in an ecological context: the remarkable complexity of thermal energy dissipation[END_REF]. In that framework, XCmediated NPQ is a key mechanism in cell response to natural diel light cycle. Several studies have examined how diel changes in XC pigment content and related NPQ allow to optimize photosynthesis under changing natural illumination in land plants [START_REF] Demmig-Adams | Using chlorophyll fluorescence to assess the fraction of absorbed light allocated to thermal dissipation of excess excitation[END_REF], seagrasses [START_REF] Ralph | Operation of the xanthophyll cycle in the seagrass Zostera marina in response to variable irradiance[END_REF], macroalgae [START_REF] Schofield | Photosystem II quantum yields and xanthophyllcycle pigments of the macroalga Sargassum natans (phaeophyceae): Responses under natural sunlight[END_REF][START_REF] Gévaert | Laminaria saccharina photosynthesis measured in situ: photoinhibition and xanthophyll cycle during a tidal cycle[END_REF] and microalgae [START_REF] Masojídek | The xanthophyll cycle in green algae (Chlorophyta): Its role in the photosynthetic apparatus[END_REF][START_REF] Van Leeuwe | Photoacclimation in microphytobenthos and the role of xanthophyll pigments[END_REF], Dimier et al. 2009a[START_REF] Quigg | Photosynthesis in Chromera velia represents a simple system with high efficiency[END_REF][START_REF] Schuback | Diurnal variation in the coupling of photosynthetic electron transport and carbon fixation in iron-limited phytoplankton in the NE subarctic Pacific[END_REF]. Under relatively steady light exposure, high light acclimated cells/organisms have much larger xanthophyll pools (Dd+Dt or Z+A+V), often leading to a greater capacity for XC-mediated NPQ in both plants [START_REF] Demmig-Adams | Modulation of photosynthetic energy conversion efficiency in nature: from seconds to seasons[END_REF]) and algae [START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF][START_REF] Brunet | Pigments and photoacclimation processes[END_REF][START_REF] Lavaud | The peculiar features of non-photochemical fluorescence quenching in diatoms and brown algae[END_REF]. XC pigments and related NPQ induction and relaxation kinetics are also modified by environmental growth conditions related to habitat characteristics. For example, plant leaves acclimated to shade and sunflecks show a minor pre-existing Z pool and a fast onset and relaxation kinetics of XC-mediated NPQ [START_REF] Demmig-Adams | Modulation of photosynthetic energy conversion efficiency in nature: from seconds to seasons[END_REF], Demmig-Adams et al. 2014). On the contrary, plants and trees acclimated to sun and intermittent cold temperatures, or long-term frozen soils, show full Z retention and thus sustained NPQ (sometimes named qZ, see [START_REF] García-Plazaola | Thermal energy dissipation and xanthophyll cycles beyond the Arabidopsis model[END_REF], Demmig-Adams et al. 2014[START_REF] Verhoeven | Sustained energy dissipation in winter evergreens[END_REF][START_REF] Míguez | Activation of photoprotective winter photoinhibition in plants from different environments: a literature compilation and meta-analysis[END_REF]. Similar retention of Z or Dt and related NPQ under different conditions of light and temperature has been reported in several groups of microalgae [START_REF] Perkins | The application of variable chlorophyll fluorescence to microphytobenthic biofilms[END_REF][START_REF] Berne | The peculiar NPQ regulation in the stramenopile Phaeomonas sp. challenges the xanthophyll cycle dogma[END_REF]. For instance, polar diatoms grown at 0°C and high irradiance show a strong retention of Dt and related sustained NPQ [START_REF] Lacour | The role of sustained photoprotective non-photochemical quenching in low temperature and high light acclimation in the bloom-forming Arctic diatom Thalassiosira gravida[END_REF].

In macroalgae, a strong relationship between incident irradiance and XC and related NPQ ability relates to depth: it can be observed among species that colonize different levels of the intertidal/tidal shore continuum [START_REF] Harker | Effects of high light and desiccation on the operation of the xanthophyll cycle in two marine brown algae[END_REF][START_REF] Rodrigues | A smaller and impaired xanthophyll cycle makes the deep sea macroalgae Laminaria abyssalis (phaeophyceae) highly sensitive to daylight when compared with shallow water Laminaria digitata[END_REF][START_REF] Nitschke | Chlorophyll a fluorescence responses of temperate Phaeophyceae under submersion and emersion regimes: a comparison of rapid and steady-state light curves[END_REF], and in surface vs. deep blades of the same giant kelp individual, Macrocystis pyrifera (García-Mendoza and Colombo-Pallotta 2007). In microalgae, light fluctuations inherent to the water column optical features and hydrodynamics influence XC and related NPQ kinetics over time scales from seconds to seasons [START_REF] Brunet | Can the xanthophyll cycle help extract the essence of the microalgal functional response to a variable light environment?[END_REF][START_REF] Brunet | Pigments and photoacclimation processes[END_REF][START_REF] Giovagnetti | The velocity of light intensity increase modulates the photoprotective response in coastal diatoms[END_REF]. The ability to rapidly

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This article is protected by copyright. All rights reserved modulate the XC and related NPQ kinetics and extent as a function of unpredictable light intensity fluctuations is believed to be a key feature of the physiological and metabolic flexibility in microalgae [START_REF] Wilhelm | Light acclimation in diatoms: From phenomenology to mechanisms[END_REF].

Differences between taxa: ecological implications.

The involvement of XC-NPQ in the ecology of photosynthetic organisms has shown growing interest, especially for marine phytoplankton (Lavaud andGoss 2014, Petrou et al. 2016). Comparative ecophysiology including evolutionary biology [START_REF] Niyogi | Evolution of flexible non-photochemical quenching mechanisms that regulate light harvesting in oxygenic photosynthesis[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF][START_REF] Christa | Photoprotection in a monophyletic branch of chlorophyte algae is independent of energydependent quenching (qE)[END_REF][START_REF] Magdaong | Photoprotective, excited-state quenching mechanisms in diverse photosynthetic organisms[END_REF] has strongly helped to better understand the physiological fundamentals of XC and related NPQ, particularly in plants and trees (Adams and Demmig-Adams, 2014). Photoautotrophs show great interspecific differences in XC pigment pool, de-epoxidation state

(DES = Dt/[Dt+Dd] or [Z+A]/[Z+A+V]
) and related NPQ, partially because they experience different in situ growth environments (e.g., typically sun vs. shade acclimation in plants; [START_REF] Demmig-Adams | Modulation of photosynthetic energy conversion efficiency in nature: from seconds to seasons[END_REF]. Species and ecotypes grown under similar conditions retain differences in XC pool size, DES, and effective and potential related NPQ as reported in plants [START_REF] Demmig-Adams | Photoprotection in an ecological context: the remarkable complexity of thermal energy dissipation[END_REF][START_REF] García-Plazaola | Thermal energy dissipation and xanthophyll cycles beyond the Arabidopsis model[END_REF][START_REF] Míguez | Diversity of winter photoinhibitory responses: a case study in co-occurring lichens, mosses, herbs and woody plants from subalpine environments[END_REF], macroalgae [START_REF] Christa | Photoprotection in a monophyletic branch of chlorophyte algae is independent of energydependent quenching (qE)[END_REF], and microalgae [START_REF] Lavaud | Photoprotection capacity differs among diatoms: Possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF][START_REF] Bailleul | An atypical member of the light-harvesting complex stress-related protein family modulates diatom responses to light[END_REF][START_REF] Giovagnetti | Growth and photophysiological responses of two picoplanktonic Minutocellus species, strains RCC967 and RCC703 (Bacillariophyceae)[END_REF][START_REF] Stamenković | Xanthophyll cycle pool size and composition in several Cosmarium strains (Zygnematophyceae, Streptophyta) are related to their geographic distribution patterns[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF]. For example, plant annual species show lower XC-mediated NPQ than evergreens and different kinetics of XC-mediated NPQ induction and relaxation [START_REF] Demmig-Adams | Carotenoids and photoprotection in plants: A role for the xanthophyll zeaxanthin[END_REF]Demmig-Adams 2014, Míguez et al. 2017). In microalgae, it was proposed that the XC-characteristics are influenced by ecological niche adaptation (see the many examples in Lavaud andGoss 2014, Petrou et al. 2016) and growth forms [START_REF] Cartaxana | Physiological versus behavioral photoprotection in intertidal epipelic and epipsammic benthic diatom communities[END_REF][START_REF] Shi | Habitat-specific differences in adaptation to light in freshwater diatoms[END_REF][START_REF] Blommaert | Contrasting NPQ dynamics and xanthophyll cycling in a motile and a non-motile intertidal benthic diatom[END_REF] with no obvious phylogenetic connection [START_REF] Barnett | Growth form defines physiological photoprotective capacity in intertidal benthic diatoms[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF]. Furthermore, the XC and related NPQ characteristics were proposed as an adaptive trait that could explain the geographical/spatial species distribution in land plants adapted to natural sun and shade environments (i.e., desert vs. forest canopy; [START_REF] Demmig-Adams | Characteristics and speciesdependent employment of flexible versus sustained thermal dissipation and photoinhibition[END_REF], 2014), overwintering evergreen trees (i.e. as a function of height distribution; [START_REF] Demmig-Adams | Characteristics and speciesdependent employment of flexible versus sustained thermal dissipation and photoinhibition[END_REF], 2014)), and in macroalgae (as a function of depth distribution; [START_REF] Rodrigues | A smaller and impaired xanthophyll cycle makes the deep sea macroalgae Laminaria abyssalis (phaeophyceae) highly sensitive to daylight when compared with shallow water Laminaria digitata[END_REF][START_REF] Nitschke | Chlorophyll a fluorescence responses of temperate Phaeophyceae under submersion and emersion regimes: a comparison of rapid and steady-state light curves[END_REF]. In microalgae XC and mediated NPQ features were positively related to i) latitude [START_REF] Bailleul | An atypical member of the light-harvesting complex stress-related protein family modulates diatom responses to light[END_REF], Stamenković et al. 2014, Laviale et

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This article is protected by copyright. All rights reserved al. 2015), ii) different marine (lagoon vs. coast vs. open ocean;[START_REF] Dimier | Photoprotection and xanthophyll-cycle activity in three marine diatoms[END_REF], 2009b[START_REF] Lavaud | Photoprotection capacity differs among diatoms: Possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF][START_REF] Six | Contrasting photoacclimation costs in ecotypes of the marine eukaryotic picoplankter Ostreococcus[END_REF]) and freshwater (river vs. lake vs. pool; [START_REF] Stamenković | Xanthophyll cycle pool size and composition in several Cosmarium strains (Zygnematophyceae, Streptophyta) are related to their geographic distribution patterns[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF][START_REF] Shi | Habitat-specific differences in adaptation to light in freshwater diatoms[END_REF]) ecosystems, iii) different habitats of the same ecosystem, i.e. spring to summer shift from ice-covered to ice-free water column in polar systems [START_REF] Petrou | Southern Ocean phytoplankton physiology in a changing climate[END_REF] or different sediment types in estuarine intertidal flats [START_REF] Cartaxana | Physiological versus behavioral photoprotection in intertidal epipelic and epipsammic benthic diatom communities[END_REF], Barnett et al. 2015), iv) as well as the temporal/seasonal succession of phytoplankton [START_REF] Meyer | Xanthophyll cycling in Phaeocystis globosa and Thalassiosira sp.: a possible mechanism for species succession[END_REF][START_REF] Dimier | Photoprotection and xanthophyll-cycle activity in three marine diatoms[END_REF], Petrou and Ralph 2011[START_REF] Polimene | Modelling a light-driven phytoplankton succession[END_REF].

What can control differences in NPQ beyond the XC pigment content? Quenching efficiency (QE).

Beyond the apparently direct NPQ regulation by the XC pigment content (i.e., the more XC pigments, the higher NPQ), the quenching efficiency (QE) of xanthophyll pigments is an important factor for the ability to dissipate excess energy. It can be easily illustrated as the slope of the NPQ vs. Dt or Z+A linear relationship. In plants as well as in algae, different species and clones can show similar XC pool size and DES with a drastically different XC-mediated NPQ (and vice versa; i.e., similar NPQ extent with different XC pigment content), implying strong differences in QE of, presumably, functionally different pools of Dt or Z+A molecules (Lavaud andLepetit 2013, Quaas et al. 2015).

Indeed, XC pigments are not totally and exclusively involved in the NPQ process, which contributes to their apparent global QE, because they have additional photoprotective functions such as, in particular, antioxidants (Esteban and[START_REF] Havaux | Beyond non-photochemical fluorescence quenching: The overlapping antioxidant functions of zeaxanthin and tocopherols[END_REF]García-Plazaola 2014). An apparently loser link between XC content, DES and related NPQ depends on many intracellular variables including the synthesis and function of NPQ regulatory partners other than the XC pigments, and firstly a large diversity of proteins of the light-harvesting system-LHC [START_REF] Büchel | Fucoxanthin-chlorophyll-proteins and non-photochemical fluorescence quenching of diatoms[END_REF][START_REF] Wobbe | Multi-level light capture control in plants and green algae[END_REF]. Specific LHC proteins have been demonstrated to play a crucial role in modulating xanthophylls QE, especially LHCSR in green microalgae [START_REF] Peers | An ancient light-harvesting protein is critical for the regulation of algal photosynthesis[END_REF][START_REF] Erickson | Light stress and photoprotection in Chlamydomonas reinhardtii[END_REF], and LHCX in diatoms [START_REF] Bailleul | An atypical member of the light-harvesting complex stress-related protein family modulates diatom responses to light[END_REF], Lepetit et al. 2017[START_REF] Taddei | Dynamic changes between two LHCX-related energy quenching sites control diatom photoacclimation[END_REF]).

Nevertheless, QE has been considered as a good indicator of the adaptation of a species/strain to a light environment (Lavaud et al. 2007, Goss and[START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF].

Objectives of the study.

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This article is protected by copyright. All rights reserved Although the diversity of molecular mechanisms involved in XC and related NPQ induction and relaxation has been described before for a variety of taxa [START_REF] Goss | Biodiversity of NPQ[END_REF], the diversity of XC pigments and related NPQ responses to environmental conditions (physiodiversity sensu [START_REF] Wilhelm | Physiodiversity -New tools allow physiologist to embrace biodiversity and reconstruct the evolution of 'physiologies'?[END_REF] has not been studied quantitatively. This is especially relevant in microalgae as regards the broad spanning of evolutionary trajectories and ecological niches they have colonized that have generated a highly diversified molecular composition, organization and regulation of LHC antennas dynamics (Büchel 2015, Giovagnetti andRuban 2018).

The goal of our study was to better understand the diversity of the XC-related NPQ across microalgal taxa and its variability among growth conditions, including light, temperature and nutrient availability. We used published results to decipher the relationship between growth conditions, XC pigment content and QE in microalgae. The discussion also considers some of the ecophysiological implications of our findings and it endeavors to answer the following questions: i) How does the growth environment control the XC pigment content? ii) Does the XC pigment content change across taxa under similar growth conditions or similar physiological status? iii) Does Quenching efficiency-QE change among taxa, and does it vary with growth conditions? iv) Does it reveal taxa adaptation to their ecological niche environmental features?

MATERIALS AND METHODS

XC and related NPQ data available in the literature.

Light, temperature and nutrient data.

Additional data were retrieved from previous studies (i.e., works on unialgal cultures) that included measurements of XC pigments at various irradiances and temperatures under nutrient replete labcontrolled conditions. We only selected the studies that included the measurement of growth rate (µ) under several irradiances, allowing the computation of the light saturation parameter for growth (K E , see computation below). It considerably limited the number of qualifying works as most of them measured µ under one or two (typically 'low light' and 'high light') irradiances which is insufficient for a reliable determination of K E . Table S1 in the Supporting Information synthesizes the studies under consideration, the species that were investigated, the growth temperature and the number of

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This article is protected by copyright. All rights reserved incident growth irradiance steps at which µ was measured. In all cases, physiological parameters were determined after some period of acclimation to the growth conditions, i.e. cells were in a fully (photo)acclimated state under balanced growth conditions (i.e., in contrast to a sudden change from their steady-state growth conditions). K E was determined using the following Poisson function with two parameters, µ m and K E , as proposed by [START_REF] Macintyre | Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria[END_REF]: µ = µ m (1-exp[-E/K E ]) where µ is the specific growth rate (d -1 ), µ m is the maximum growth rate, E is the growth irradiance (µmol photons • m -2 • s -1 ) and K E is the light saturation parameter for growth (µmol photons • m -2 • s -1 ). The relationship was fitted to the data by non-linear least-squares.

The data supporting the relationship between nutrient-limited growth and the amount of XC pigments are scarce; they were extracted from two studies: Goericke and Montoya (1998) and [START_REF] Stolte | Genetic and physiological variation in pigment composition of Emiliania huxleyi (Prymnesiophyceae) and the potential use of its pigment ratios as a quantitative physiological marker[END_REF]. Datasets documenting the effect of different growth temperatures are also scarce, and were limited to our own data [START_REF] Lacour | The role of sustained photoprotective non-photochemical quenching in low temperature and high light acclimation in the bloom-forming Arctic diatom Thalassiosira gravida[END_REF]T. Lacour, unpub. data; see Table S1)

Quenching efficiency-QE (NPQ vs. de-epoxidized xanthophyll content relationship).

Our analysis was based on data from previous studies that include simultaneous measurement of NPQ and the de-epoxidized forms of xanthophyll pigments: Dt or Z and A (normalized to the total pool of Chl a); note that only the two main XC were considered. The relationship between NPQ and Dt or Z(+A) is generally linear, at least over a certain range (see for instance, and for a variety of organisms: [START_REF] Brugnoli | Zeaxanthin and non-photochemical quenching in sun and shade leaves of C3 and C4 plants[END_REF], [START_REF] Lavaud | General features of photoprotection by energy dissipation in planktonic diatoms (Bacillariophyceae)[END_REF], Dimier et al. (2009a), [START_REF] Masojídek | The xanthophyll cycle in green algae (Chlorophyta): Its role in the photosynthetic apparatus[END_REF], [START_REF] Stamenković | Xanthophyll cycle pool size and composition in several Cosmarium strains (Zygnematophyceae, Streptophyta) are related to their geographic distribution patterns[END_REF], and [START_REF] Barnett | Growth form defines physiological photoprotective capacity in intertidal benthic diatoms[END_REF]. We computed the slopes and the y-intercepts (Y 0 ) of NPQ vs. Dt or Z(+A) content by fitting the data by linear least-squares. In few cases, when NPQ saturated for high Dt or Z(+A) content (see for instance [START_REF] Lavaud | In diatoms, a transthylakoid proton gradient alone is not sufficient to induce a non-photochemical fluorescence quenching[END_REF], the slope and Y 0 were computed on the initial linear part of the relationship (see an example in Fig. S1 in the Supporting Information). Tables S2 andS3 in the Supporting Information synthesize the studies under consideration, the species that were investigated, the values of the slopes and of Y 0 , the evidence for possible NPQ saturation (only observed in some diatoms, see Table S2), and the number of data points.

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RESULTS AND DISCUSSION

Pigments of the diadinoxanthin (Dd) cycle: effect of growth irradiance (E), temperature and nutrient availability

Irradiance.

We normalized XC pigments (Dd + Dt) to Chl a as it has been done routinely in previous studies. It allows scaling XC pigments to the amount of Chl a, the most abundant photosynthetic pigment, common to all photosynthetic eukaryotes, which is found in LHCs (together with Chl b and c) and in PSI and PSII (constant across eukaryotes). XC cycle pigments normalized by Chl a is therefore a good estimator for the number of XC pigments per photosynthetic electron transport chain. We pooled existing data (see Table S1). (Dd + Dt)/Chl a increased with growth irradiance in all taxa (Fig. 1, A andB). Such an increase has been already discussed before (see [START_REF] Macintyre | Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria[END_REF] and is in agreement with the concept of an increase in the potential for photoprotection, and for XC-mediated NPQ in particular, as acclimation to growth irradiance (E) increases. The relationship between Dd+Dt and E was generally linear although both the slope and y intercept (Y 0 ) were highly variable, especially in taxa other than diatoms (Fig. 1, A andB). Noticeably, Y 0 , which represents the basal amount of XC pigments, was remarkably conserved (8 ± 2 mol Dd+Dt • [100 mol Chl a] -1 ) among diatoms. Dt/Chl a also increased with growth irradiance in all taxa and the slope was highly variable (Fig. 2, A andB). Y 0 was generally  0, as at low irradiance, most of the Dd+Dt pool remains in the form of Dd until reaching an irradiance threshold beyond which Dd starts being de-epoxidized in Dt (see [START_REF] Lavaud | Silencing of the violaxanthin de-epoxidase gene in the diatom Phaeodactylum tricornutum reduces diatoxanthin synthesis and non-photochemical quenching[END_REF].

As previously proposed by [START_REF] Geider | A dynamic regulatory model of phytoplanktonic acclimation to light, nutrients, and temperature[END_REF], photoacclimation of pigments is accomplished through mechanisms that 'integrate' the mean E, species sensitivity for light and other environmental conditions (as, for instance, temperature and nutrients, see below). It is accomplished through the combined effects of reactions down-stream PSII and relative to the photon flux, and therefore the excitation pressure. Microalgae appear to well adapt to the light conditions of their specific habitat, which is reflected in their growth vs. E relationship [START_REF] Edwards | Light and growth in marine phytoplankton: allometric, taxonomic, and environmental variation[END_REF]. For example, open-ocean isolates tend to have a lower light saturation parameter for growth (K E ), implying adaptation to lower average irradiance, than coastal isolates [START_REF] Edwards | Light and growth in marine phytoplankton: allometric, taxonomic, and environmental variation[END_REF][START_REF] Lacour | Growth, Chl a content, photosynthesis, and elemental composition in polar and temperate microalgae[END_REF]. This adaptation was

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This article is protected by copyright. All rights reserved shown to relate, in part, to the ability for XC-mediated NPQ (Strzepek andHarrison 2004, Lavaud et al. 2007). In general, at a given E, the need for photoprotection can be expected to be higher in lowlight adapted species/strains than in high-light adapted ones [START_REF] Raven | Adaptation, acclimation and regulation in algal photosynthesis[END_REF]. However, scaling photoacclimatory biological variables (such as pigments) to E alone is insufficient in comparative studies because of the species-specific variation in K E [START_REF] Macintyre | Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria[END_REF]. Therefore, it was proposed and successfully used [START_REF] Geider | A dynamic model of photoadaptation in phytoplankton[END_REF], 1997[START_REF] Macintyre | Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria[END_REF][START_REF] Lacour | Growth, Chl a content, photosynthesis, and elemental composition in polar and temperate microalgae[END_REF], 2018), to normalize the growth irradiance E to K E to provide a relative scaling of the energy pressure on the photosynthetic apparatus. When analyzed against E/K E , the amount of XC pigments was better conserved among temperate and polar microalgal species (see Table S1) and conditions shows that for all the microalgal species examined here, energy pressure governs photoprotective capacity in a manner which is independent of taxa. From an evolutionary standpoint, such uniform response among Dd-containing microalgal groups and species suggests no distinct general taxonomybased difference in the capacity to synthesize XC pigments. Instead, it appears that species/strainspecific sensitivity to irradiance, which is an adaptive trait that is influenced by ecological niche adaptation [START_REF] Edwards | Light and growth in marine phytoplankton: allometric, taxonomic, and environmental variation[END_REF], is one of the main drivers which determines the XC response to the environment. Recently, [START_REF] Lepetit | High light acclimation in the secondary plastids containing diatom Phaeodactylum tricornutum is triggered by the redox state of the plastoquinone pool[END_REF] highlighted the importance of the redox state of the PQ pool in light acclimation in a diatom. Specifically, they suggested that the level of excitation energy pressure in the plastid and its balance within the photosynthetic electron transport chain governs the XC pigments response to irradiance changes. It is possible that this feature could be extended to all diatoms and even to the Dd-containing algae with secondary plastids. Furthermore, while the relationship between (Dd+Dt)/Chl a vs. E/K E was not significantly different between diatoms (Fig. 1C) and other species (Fig. 1F) (ANCOVA, F 1,130 = 3.86, P>0.05), the slope of the Dt/Chl a vs. E/K E linear regression was 3x higher in diatoms (1.45 vs. 0.47; Fig. 2, C andD). It indicates that for a given level of excitation energy pressure, diatoms synthesize the same amount of Dd+Dt and from this pool they produce, in general, 3 times more Dt than other Dd-containing algae. It suggests that for a given level of energy pressure, all Dd-containing species have a similar potential for XC-mediated NPQ

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This article is protected by copyright. All rights reserved (similar Dd+Dt/Chl a, and aside from other regulatory partners), but diatoms show, in general, higher NPQ at steady state growth irradiance E.

Temperature.

Low temperatures deeply modify the photoacclimation status of cells by affecting differentially the photosynthetic dark and light reactions which generally leads to a decrease in µ m and K E [START_REF] Yoder | Effect of temperature on light-limited growth and chemical composition of Skeletonema costatum (bacillariophyceae)[END_REF][START_REF] Verity | Effects of temperature, irradiance, and daylength on the marine diatom Leptocylindrus danicus Cleve[END_REF], and thus an increase of the excitation pressure on the photosynthetic electron transport chain. The best illustration of this statement in our dataset (see Table S1 As expected, at a given irradiance, T. gravida synthesized higher amounts of Dt+Dd/Chl a and Dt/Chl a vs. E. The corresponding slopes were 1.7x and 2x higher at 0°C than at 5°C, respectively (Fig. 3,A and C; see also [START_REF] Lacour | The role of sustained photoprotective non-photochemical quenching in low temperature and high light acclimation in the bloom-forming Arctic diatom Thalassiosira gravida[END_REF]. Remarkably, when normalized to E/K E , the amounts of XC pigments were very similar in both species independent of the temperature (Figs. 3, B andD, S3).

Nutrients.

Beyond irradiance and temperature, numerous studies have reported that nutrient 'stress' leads to an accumulation of XC pigments [START_REF] Geider | Response of the photosynthetic apparatus of Phaeodactylum tricornutum (Bacillariophyceae) to nitrate, phosphate, or iron starvation[END_REF]. Nutrient stress is a term often used for both limitation and starvation (sensu MacIntyre and Cullen 2005) while they lead to very distinct physiological responses [START_REF] Parkhill | Fluorescence-based maximal quantum yield for PSII as a diagnostic of nutrient stress[END_REF]. For example, [START_REF] Lacour | Neutral lipid and carbohydrate productivities as a response to nitrogen status in Isochrysis sp (T-iso; Haptophyceae) : starvation vs. limitation[END_REF] showed that nutrient starvation enhances triacylglycerol accumulation while nutrient limitation generates the opposite effect. Also, starvation experiments are difficult to compare between each other because they use microalgal cultures that are in unbalanced growth. Hence, in order to examine the XC pigment response to nutrient stress in microalgae, we selected studies that specifically used chemostats to maintain cultures under true nutrient limitation (i.e., balanced growth). For this reason, the only data we could find are from [START_REF] Stolte | Genetic and physiological variation in pigment composition of Emiliania huxleyi (Prymnesiophyceae) and the potential use of its pigment ratios as a quantitative physiological marker[END_REF] and [START_REF] Goericke | Estimating the contribution of microalgal taxa to chlorophyll a in the field--variations of pigment ratios under nutrient-and light-limited growth[END_REF] which deal with Dd-

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This article is protected by copyright. All rights reserved containing microalgae exposed to nitrogen (N) or phosphate (P) limitation (Fig. 4). The species examined, including diatoms and others, show a similar behaviour: (Dt+Dd)/Chl a remained almost unchanged over a large range of nutrient limitation values and increased only when limitation generated a strong decrease (-70-80%) in growth rate (i.e., µ/µ m < 0.2-0.3). This was true for N and for P limitation (but we could find only one species under P limitation).

Under nutrient limitation, cells generally decrease their light harvesting capacity as growth decreases (and as limitation increases), adjusting their ability to capture light to the growth conditions, and thus, preventing an imbalance between excitation energy and the ability to use it via photochemistry and carbon fixation (source vs. sink; [START_REF] Halsey | Physiological optimization underlies growth rate-independent chlorophyll-specific gross and net primary production[END_REF]. Figure 4 shows that under moderate nutrient limitation, most of the species examined (with the exception of Isochrysis galbana) seem to regulate their Chl a content to prevent excitation energy imbalance rather than increasing the size of their XC pigments pool to potentially enhance their capacity for dissipating excessive energy.

It suggests that, when growth is not drastically limited by nutrients, light and temperature appear to be the main environmental drivers of the XC pigment pool size (see Laviale et al. 2015 and references therein).

The only Dt/Chl a data we found were measured in Emiliania huxleyi under N or P limitation by [START_REF] Stolte | Genetic and physiological variation in pigment composition of Emiliania huxleyi (Prymnesiophyceae) and the potential use of its pigment ratios as a quantitative physiological marker[END_REF]. They observed constant Dt/Chl a over a large range of N limitation and a significant increase in Dt/Chl a with increasing P limitation. Although the results from one study cannot be generalized, in E. huxleyi, while the Dd+Dt pool size appears independent from the type of nutrient stress (at least for N and P; Fig. 4), the synthesis of Dt seems to be influenced by the type of limiting nutrient.

Pigments of the violaxanthin (V) cycle: effect of growth irradiance

XC pigments content of the V cycle vs. E data are scarce in plants (4 species, Fig. S4, Table S4 in the Supporting Information), and we could not find any from mosses, lichens, green and brown macroalgae. Therefore, we included in our dataset green microalgae (Chlorophyceae and Prasinophyceae) only (Table S1). Also, we could not find exploitable data in conditions of different temperatures or nutrient limitation, and as growth rates were not measured, K E values were not computable. (V+A+Z)/Chl a, (Z+A)/Chl a and Z/Chl a increased with growth irradiance (Fig. S5 in

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This article is protected by copyright. All rights reserved the Supporting Information) with variable slopes from a species to another (see also in plants in Fig. S4). The Y 0 of the (V+A+Z)/Chl a vs. E linear regression was similar in the species examined (i.e., = 3.6 ± 0.83 mol V+A+Z (100 mol Chl a) -1 ; Fig. S5); a similar value was also found in plants (see Fig. S4). This is ~2x lower than the Y 0 of the (Dd+Dd)/Chl a vs. E relationship. It suggests that i) in Vcontaining microalgae, de-epoxidized xanthophylls do not play such an important role in global photoprotection as in Dd-containing species; and/or ii) they have a lower potential for XC-related NPQ than Dd-containing species, at least when E is low; and/or iii) Z quenching efficiency is higher than the one of Dt (see also below 'Quenching efficiency'). Lower Y 0 may also reveal differences in fast photoprotection strategy. State transitions play an important role in lowering excitation pressure on PSII in green microalgae [START_REF] Finazzi | Non-photochemical quenching and energy dissipation in plants, algae and cyanobacteria[END_REF], which is contrary to, for instance, diatoms. In addition, alternative electron flows appear to be of significant importance in re-routing excess energy in both Chlorophyceae (Chlamydomonas reinhardtii) and Prasinophyceae (Ostreococcus sp.; [START_REF] Cardol | An original adaptation of photosynthesis in the marine green alga Ostreococcus[END_REF][START_REF] Finazzi | Non-photochemical quenching and energy dissipation in plants, algae and cyanobacteria[END_REF][START_REF] Saroussi | Alternative outlets for sustaining photosynthetic electron transport during dark-to-light transitions[END_REF].

Physiological and metabolic distinctions between 'brown' and 'green' counterparts have been listed and discussed before [START_REF] Wilhelm | The regulation of carbon and nutrient assimilation in diatoms is significantly different from green algae[END_REF]) and also tested experimentally in the context of changing light climate [START_REF] Wagner | Balancing the energy flow from captured light to biomass under fluctuating light conditions[END_REF]. Although this later work was based on one green microalga (Chlorella vulgaris) and one diatom (P. tricornutum) species, it clearly showed that, in contrast to constant light, under fluctuating light, the diatom performed better with a much higher conversion efficiency of photosynthetic energy into biomass, in part based on a stronger and more flexible XCrelated NPQ capacity [START_REF] Wagner | Balancing the energy flow from captured light to biomass under fluctuating light conditions[END_REF], Lepetit et al. 2017). Obviously, more studies of this kind are needed that include the diversity of microalgal groups and species-specific response (see for instance Su et al. 2012, Halsey et al. 2013).

Similar to Dd-containing species, in V-containing species, the Y 0 of the linear relationships between Z/Chl a and Z+A/Chl a vs. E were close to 0, illustrating the absence of these quenchers when E was close to 0 µmol photons • m -2 • s -1 in the species examined here.

Quenching efficiency-QE: diversity, influence of irradiance and ecophysiological implications

Although the XC pigment content is informative of light (and/or other growth conditions) acclimation, it is not necessarily a proxy for NPQ-related capacity because de-epoxidized

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This article is protected by copyright. All rights reserved xanthophylls Dt, Z and A can play other photoprotective roles than triggering NPQ (see for instance [START_REF] Havaux | Beyond non-photochemical fluorescence quenching: The overlapping antioxidant functions of zeaxanthin and tocopherols[END_REF]García-Plazaola 2014, Smerilli et al. 2019). XC-mediated NPQ is also determined by the QE of the de-epoxidized xanthophylls. As described above, a linear relationship between the content of de-epoxidized xanthophylls and the concomitant induction of NPQ is generally observed, and the slope of the regression represents the QE of xanthophyll quenchers Dt, or Z and A (Goss and Jakob 2010), i.e., a slope value of 0.5 means that 1 mol of xanthophyll quencher (here normalized to 100 mol Chl a) is needed to trigger 0.5 units of NPQ (see an example in Fig. S1). We thus compiled NPQ vs. Dt and Z (or Z+A) relationship for a number of microalgal species and clones grown under different light conditions (see Tables S2 andS3 and Fig. S6 in the Supporting Information).

Dd-containing species.

QE values were highly variable across planktonic and benthic strains, and even between clones of the diatom Phaeodactylum tricornutum (P. t.2 and P. t.4 strains, see De [START_REF] De Martino | Genetic and phenotypic characterization of Phaeodactylum tricornutum (Bacillariophyceae) accessions[END_REF]) ranging from 0.05 (in a dinoflagellate) to 2.03 (in a diatom-dominated sea-ice community), and with a mean value of 0.54 ± 0.08 mol Chl a • (0.01 mol Dt) -1 (SE, n=32; Table S2). The higher QEs were found in species inhabiting extreme ecosystems: i) intertidal bare mudflats for Opephora sp. and Fragilaria cf. subsalina (slope of 1.13 and 1.28, respectively, Table S2) which are benthic non-motile epipsammon species (i.e., that generally live attached to the particles of intertidal sandy sediments; i.e. exposed to potentially high irradiance and high light fluctuations; [START_REF] Cartaxana | Physiological versus behavioral photoprotection in intertidal epipelic and epipsammic benthic diatom communities[END_REF], Barnett et al. 2015[START_REF] Blommaert | Contrasting NPQ dynamics and xanthophyll cycling in a motile and a non-motile intertidal benthic diatom[END_REF], and ii) sea-ice for a microalgal community dominated by diatoms (Detonula confervacea, slope of 2.03; [START_REF] Katayama | Photoprotective responses of an ice algal community in Saroma-Ko Lagoon, Hokkaido, Japan[END_REF] which are exposed to sub-zero temperatures, very high salinity and potentially moderate irradiances when the snow cover starts to melt in spring. High QEs of ca. 1 (Table S2) were found in diatom strains that are exposed to high light and/or high light fluctuations in their natural habitat, i.e. for instance Phaeodactylum tricornutum (P. t.2 strain, tychoplanktonic, i.e., both planktonic and benthic growth forms, isolated from a supralittoral rock pool, brackish waters), Cylindrotheca fusiformis (tychoplanktonic and coastal species), Ditylum brightwellii (neritic). A similar QE value (ca. 0.90) was reported for species other than diatoms (i.e., Prymnesiophyceae, Bolidophyceae and Dictyochophyceae; see Dimier et al. 2009b for further details). Lower QEs (below 0.5; Table S2), were found in strains adapted to a lower

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This article is protected by copyright. All rights reserved average irradiance and/or to lower light fluctuations such as Skeletonema costatum (planktonic, semienclosed Mediterranean bay), Pelagomonas calceolata (picoplanktonic, Red Sea deep-chlorophyll maximum), and tychoplanktonic species inhabiting estuarine intertidal mudflats (i.e., Brockmanniella brockmanii, Plagiogrammopsis vanheurckii) which are often suspended in turbid waters with high tide or buried in sediments with low tide (see [START_REF] Barnett | Growth form defines physiological photoprotective capacity in intertidal benthic diatoms[END_REF]. Low QEs were also found in benthic motile epipelon (i.e., that generally inhabits intertidal fine muddy sediments) for which photoprotection via XC-NPQ is counterbalanced by behavioural phototactic motility [START_REF] Cartaxana | Physiological versus behavioral photoprotection in intertidal epipelic and epipsammic benthic diatom communities[END_REF], Barnett et al. 2015[START_REF] Blommaert | Contrasting NPQ dynamics and xanthophyll cycling in a motile and a non-motile intertidal benthic diatom[END_REF].

Within the same genus (Thalassiosira sp.) and for the same growth form (i.e., planktonic and marine), QE varied from close to 1 (T. weissflogii and T. rotula) down to 0.19 (T. pseudonana; Table S2). While T. weissflogii and T. rotula originate from coastal estuary and offshore habitats, respectively, characterized by high light fluctuations, T. pseudonana originates from a coastal enclosed bay. Unfortunately, we do not have data for the oceanic species T. oceanica which NPQ is very low (Strzepek andHarrison 2004, Lavaud et al. 2007), i.e., lower than for instance S. costatum (QE of 0.5) and in the same range than benthic epipelon diatoms (mean QE of 0.39; Table S2).

Different QEs could also be found in clones/ecotypes of the same species (P. tricornutum) with the example of the tychoplanktonic P. t.2 and P. t.4 strains. Both strains were respectively isolated from estuarine coastal waters (England Channel coast), and at higher latitudes (Finland Baltic sea coast; De Martino et al. 2007), P. t.4 being thus adapted to lower average irradiances [START_REF] Bailleul | An atypical member of the light-harvesting complex stress-related protein family modulates diatom responses to light[END_REF]). As a result, QE in P. t.4 was 3x lower than the one in P. t.2 when grown under the same low light intensity (0.32 ± 0.08 and 0.96 ± 0.10, respectively; Table S2). At the molecular level, this large difference is due to a lower synthesis of the LHCx1 protein which is involved in XC-mediated NPQ induction [START_REF] Bailleul | An atypical member of the light-harvesting complex stress-related protein family modulates diatom responses to light[END_REF], Lepetit et al. 2017) and which is believed to bind Dd-Dt pigments (Lavaud andGoss 2014, Goss andLepetit 2015). Hence, for the same Dt synthesis in both strains, XC-mediated NPQ, and as a consequence QE, are lower in P.t.4.

The link between the natural light climate of species/ecotypes and QE amplitude was generally supported by our analysis. It strengthens the view (see otherwise discussions by Dimier et al. 2009b, Petrou et al. 2011, Lavaud and Lepetit 2013, Barnett et al. 2015) that Dd-containing growth forms, species and ecotypes adapt their fast light-response to the light climate of their natural habitat, in

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This article is protected by copyright. All rights reserved terms of average irradiance and light fluctuations, through the molecular control of NPQ by Dt synthesis [START_REF] Lepetit | The diatom Phaeodactylum tricornutum adjusts nonphotochemical fluorescence quenching capacity in response to dynamic light via fine-tuned Lhcx and xanthophyll cycle pigment synthesis[END_REF][START_REF] Taddei | Dynamic changes between two LHCX-related energy quenching sites control diatom photoacclimation[END_REF]. [START_REF] Dimier | Photoprotection and xanthophyll-cycle activity in three marine diatoms[END_REF]Dimier et al. ( , 2009b) ) even proposed a classification of Dd-containing microalgae (distributed among pico-, nano-and micro-phytoplankton) in three distinct ecological groups based on their XC properties vs. irradiance and light fluctuations.

Nevertheless, and to be complete, one should note exceptions to this general view with, for instance in the highly diverse and complex consortium of intertidal flat benthic diatoms, low QE values in nonmotile epipsammon species such as Plagiogramma staurophorum (0.26) and relatively high QE values in the tychoplanktonic (Cylindrotheca closterium; 0.59), motile epipsammic (Nitzschia cf. frustulum; 0.80), and epipelic (Seminavis robusta; 0.64) species [START_REF] Barnett | Growth form defines physiological photoprotective capacity in intertidal benthic diatoms[END_REF]. Possibly this is explained by the E growth used in this study and which was on the upper or lower limit of light phenotypic plasticity range for these strains (see for instance the higher range of Es for a lowering of QE in P. tricornutum vs. C. meneghiniana; Table S2).

Also, it was early reported [START_REF] Demers | Rapid light-induced changes in cell fluorescence and in xanthophyll-cycle pigments of Alexandrium excavatum (Dinophyceae) and Thalassiosira pseudonana (Bacillario-phyceae): a photo-protection mechanism[END_REF]) that QE can be modulated as a function of acclimation to E (and likely the light dose), i.e. the same cells acclimated to low or high Es showed different QE values with a ca. 2-5x lower QE for high light acclimated cells of P. tricornutum, S. costatum and C. meneghiniana (Table S2, Fig. 5). This QE difference between low vs. high E is due to a change in the size of the different Dd pools with a larger pool, and consequently a higher Dt proportion, that does not contribute to NPQ under higher E (Schumann et al. 2007, Lavaud andLepetit 2013). Also, the 'saturation' of NPQ vs. Dt relationships was reported in several species (Table S2), i.e., while being high for a range of NPQ and Dt amount, QE suddenly decreases with prolonged exposure to over-saturating irradiances (from ca. 15 to 45 min on, depending on the species; see [START_REF] Blommaert | Contrasting NPQ dynamics and xanthophyll cycling in a motile and a non-motile intertidal benthic diatom[END_REF] for the most recent example). This feature, as well as the lower QE under high light acclimation, have been attributed to the synthesis of additional Dt molecules that do not bind to the LHC system, and therefore do not participate to NPQ [START_REF] Schumann | Investigation of the quenching efficiency of diatoxanthin in cells of Phaeodactylum tricornutum (Bacillariophyceae) with different pool sizes of xanthophyll cycle pigments[END_REF], Lavaud and Lepetit 2013[START_REF] Lavaud | The peculiar features of non-photochemical fluorescence quenching in diatoms and brown algae[END_REF]. It is believed that these additional Dt molecules could participate to the direct scavenging of free radicals and the prevention of lipid peroxidation in thylakoid membranes [START_REF] Lepetit | Evidence for the existence of one antenna-associated, lipid-dissolved and two protein-bound pools of diadinoxanthin cycle pigments in diatoms[END_REF].

Finally, but noteworthy, is the fact that in most species examined Y 0 was close to 0 with no positive intercepts (Table S2). It confirms that in the Dd-containing species, Dt synthesis is mandatory for

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This article is protected by copyright. All rights reserved NPQ induction (see [START_REF] Lavaud | Silencing of the violaxanthin de-epoxidase gene in the diatom Phaeodactylum tricornutum reduces diatoxanthin synthesis and non-photochemical quenching[END_REF]. In three cases, Y 0 was negative meaning that when the photosynthetic system is reoxidized (i.e., after a period of darkness or low light), some Dt molecules remained. It was observed under extreme conditions (Table S2): i) in P. tricornutum grown under over-saturating irradiance (1000 µmol photons • m -2 • s -1 ), and ii) in sea-ice community exposed to extreme environmental stress.

V-containing species.

The relationship between Z (or Z+A) and NPQ was generally linear with a QE for Z and A+Z of 0.32 ± 0.05 mol Chl a • (0.01 mol Z) -1 (SE, n=15) and 0.19 ± 0.03 mol Chl a • (0.01 mol Z+A) -1 (SE, n=15), respectively (Table S3). In general, and although there is only half the data, mean QE in Vcontaining microalgae was ca. half the one of Dd-containing microalgae (Fig. S6B), and with a much lower maximum value (0.64 in Chlorella vulgaris; Table S2). It confirms the generally stronger involvement of de-epoxidized xanthophylls in NPQ in Dd-containing algae, and especially in diatoms [START_REF] Goss | Biodiversity of NPQ[END_REF]. For comparison, in the plants data we found, QE for Z and A+Z was 0.19 ± 0.04 mol Chl a • (0.01 mol Z) -1 (SE, n=3) and 0.39 ± 0.11 mol Chl a • (0.01 mol Z+A) -1 (SE, n=7), respectively (Table S5 in the Supporting Information). The lower QE in V-containing microalgae can be explained by the fact that in many species, a significant portion of NPQ can develop without Z and/or A synthesis (explaining the Y 0 ˃ 0 values observed in several species, Table S3), and for some species only when grown under excess light [START_REF] Finazzi | Non-photochemical quenching and energy dissipation in plants, algae and cyanobacteria[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF][START_REF] Christa | Photoprotection in a monophyletic branch of chlorophyte algae is independent of energydependent quenching (qE)[END_REF]. In fact, in V-containing microalgae, the NPQ mechanism appears very heterogeneous and can be achieved by different processes beyond the XC at the molecular level (reviewed in Finazzi and Minagawa 2014). In the most recent studies (Bonente et al. 2012[START_REF] Lunch | The xanthophyll cycle and NPQ in diverse desert and aquatic green algae[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF], it has been emphasized how V-containing microalgae show a great diversity in XC and NPQ extents, kinetics and relationship, with no obvious reason(s) for such diversity.

Interestingly, the giant kelp Macrocystis pyrifera, which has a V cycle together with a protein composition and spatial organization of its LHC antenna system closer to the diatoms (they both belong to the Stramenopiles; Lavaud andGoss 2014, Goss andLepetit 2015), showed a QE similar to the highest values reported for Dd-containing microalgae (Table S3). Therefore, not only the nature of the XC (i.e., one vs. two de-epoxidation steps) but also the composition and organization of the LHC

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This article is protected by copyright. All rights reserved antenna system determines the efficiency of XC pigments in NPQ as well as its induction kinetics and maintenance over a range of light conditions (see Goss andLepetit 2015, Kuthanová Trsková et al. 2018 for further details).

Studies specifically investigating the link between the natural light climate of species/ecotypes and QE amplitude in V-containing microalgae are scarce. A first study compared two ecotypes of the Prasinophyceae Ostreococcus [START_REF] Six | Contrasting photoacclimation costs in ecotypes of the marine eukaryotic picoplankter Ostreococcus[END_REF], respectively adapted to high irradiance and fluctuating light (Ostreococcus tauri isolated from a South of France lagoon) and to stable low irradiance (Ostreococcus RCC809, isolated from Atlantic Ocean deep-chlorophyll maximum). While NPQ capacity was similar in the two strains, O. tauri showed a higher V de-epoxidation and a lower QE (Table S3). A second study compared four species and ecotypes of the freshwater green microalga Cosmarium sp. (Charophyceae) isolated from different latitudes [START_REF] Stamenković | Xanthophyll cycle pool size and composition in several Cosmarium strains (Zygnematophyceae, Streptophyta) are related to their geographic distribution patterns[END_REF]. All of them displayed very similar QE (Table S3) but C. crenatum (ca. 2x higher) probably due to the fact that in this species, the XC mostly leads to the accumulation of A [START_REF] Stamenković | Xanthophyll cycle pool size and composition in several Cosmarium strains (Zygnematophyceae, Streptophyta) are related to their geographic distribution patterns[END_REF]. No latitudinal adaptation of NPQ-related XC was observed for Cosmarium sp. (in contrast to Ddcontaining microalgae, see [START_REF] Laviale | Response of intertidal benthic microalgal biofilms to a coupled light-temperature stress: evidence for latitudinal adaptation along the Atlantic coast of Southern Europe[END_REF], which might partly be due to the fact that all clones were isolated from similar shallow freshwater habitats exposed to occasional high light exposure.

Obviously two studies are not enough to raise any conclusion on an apparent loser link between QE and adaptation of V-containing microalgae to their light niche. It could be that, XC-related NPQ might not be a major player of their photoadaptive strategy, and QE would not be as good of a fingerprint as it is in Dd-containing microalgae. Therefore, one should look at other relevant processes, such as alternative electron pathways [START_REF] Cardol | An original adaptation of photosynthesis in the marine green alga Ostreococcus[END_REF][START_REF] Saroussi | Alternative outlets for sustaining photosynthetic electron transport during dark-to-light transitions[END_REF]) and the PSII repair cycle [START_REF] Ni | Arctic Micromonas uses protein pools and non-photochemical quenching to cope with temperature restrictions on Photosystem II protein turnover[END_REF], to gain deeper insights on the role of photoprotection in the ecophysiology of V-containing microalgae.

Finally, studies included in our meta-analysis did not allow to state on an effect of growth irradiance on QE (i.e., comparison of QE under several growth Es for a given species; Table S3).

NPQ in a growth and ecophysiological strategy

In order to conceptualize our findings, we related the proportion of absorbed energy that is dissipated as heat (Φ NPQ as calculated by [START_REF] Hendrickson | A simple alternative approach to assessing the fate of absorbed light energy using chlorophyll fluorescence[END_REF]; see Fig. S7 in the Supporting Information)

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This article is protected by copyright. All rights reserved and the growth rate (µ/µ m ) to the energetic pressure during light-acclimated growth (E/K E ) in two diatoms that are known to show very different quenching efficiencies (see Table S2): Cyclotella meneghiniana (low NPQ and QE diatom) and P. tricornutum-P. t.2 strain (high NPQ and QE diatom; Fig. 6). Our model, the construction of which is described in Figure S8 and Appendix S1 in the Supporting Information is based on the relationships between Dt and E/K E (Fig. 2), between QE and E (Fig. 5), and between XC-mediated Φ NPQ and NPQ in diatoms (Fig. S7). We only selected data from these two diatoms, as they were the most complete set that allowed us this modeling procedure.

The fine-tuned NPQ XC-related photoprotection is generally presented as a mechanism limiting photoinhibitory damages during fast and short-term increases in irradiance [START_REF] Demmig-Adams | Nonphotochemical fluorescence quenching in contrasting plant species and environments[END_REF]). As a consequence, under a given and stable light environment (i.e., fixed growth irradiance and E/K E ), one would expect microalgae to modify their photosynthetic machinery in order to exploit in the most optimal manner the actual irradiance (see [START_REF] Geider | Light and temperature dependence of the carbon to chlorophyll a ratio in microalgae and cyanobacteria: implications for physiology and growth of phytoplankton[END_REF][START_REF] Macintyre | Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria[END_REF][START_REF] Raven | Adaptation, acclimation and regulation in algal photosynthesis[END_REF], and thus minimize fast dissipative processes, such as XC-mediated NPQ, which induction could appear futile and even detrimental. In contrast, Figure 6 (and Fig. 2) clearly shows that diatoms acclimated to a given energetic pressure corresponding to a certain growth irradiance still dissipate a significant proportion of the light energy they absorb. With our modeling, at 3K E , i.e., at growth irradiance that nearly saturates growth (corresponding to µ = 0.95 µ m ), diatoms dissipate between 30 % (Φ NPQ = 0.30; low NPQ-QE diatom) and 61% (Φ NPQ = 0.61; high NPQ-QE diatom) of the absorbed light energy at the PSII-associated LHC sites. It means that in conditions of steady-state growth, in a fully photoacclimated state, and despite adjustments of the photosynthetic machinery, diatoms maintain a capacity to absorb light which is higher than their needs and from which a significant (excessive) part of absorbed energy is dissipated as heat via XC-NPQ.

Interestingly, this photoadaptive strategy has first been described in overwintering evergreen plants and trees (Demmig-Adams et al. 2014b). While annuals and deciduous plants lower their Chl a content in response to environmental stresses ('annual growth strategy'), evergreens tend to maintain their Chl a content and induce large NPQ (i.e., qZ; Verhoeven 2014) based on the maintenance of a high Z content ('evergreen growth strategy'). The benefit for maintaining excessive harvesting capacity was proposed to support the relatively prompt resume of C fixation and growth when conditions become favorable for photosynthesis upon spring warming [START_REF] Demmig-Adams | Nonphotochemical fluorescence quenching in contrasting plant species and environments[END_REF].

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This article is protected by copyright. All rights reserved In diatoms, and maybe Dd-containing microalgae, a similar strategy under excess growth irradiance and/or low temperature (Figs. 3,6), would possibly allow to anticipate a decrease in ambient irradiance (and/or increase in temperature), for remaining performant under a wide range of irradiances, and especially well above their K E . The benefits of this strategy are clear if NPQ relaxation is faster (timescale: minute) than the building of the light harvesting machinery (timescale: hours) and also faster or in the same range than the light/temperature fluctuations [START_REF] Macintyre | Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria[END_REF]. We recently reported an extreme of this photoadaptative strategy in a polar diatom [START_REF] Lacour | The role of sustained photoprotective non-photochemical quenching in low temperature and high light acclimation in the bloom-forming Arctic diatom Thalassiosira gravida[END_REF]. It maintains its light harvesting capacity and growth rate at 0°C when grown under an excess irradiance (ca. 50 K E ), and it dissipates most of the absorbed energy via a sustained NPQ triggered by a high and permanent Dt content.

Therefore, instead of disentangling their LHC system to face any prolonged, and potentially unfavorable, change in irradiance and/or temperature, diatoms, and possibly Dd-containing microalgae, maintain their LHC system and tune their photosynthetic efficiency with, at least, XCrelated NPQ. At the molecular level, this is possible because the XC-mediated NPQ process can rapidly modify and maintain the function(s) of the LHC system, i.e., absorption under stable irradiances lower or close to K E , absorption and dissipation for stable irradiances over K E . In such a framework, the modification of the function of the LHC needs to be fast in both ways, i.e. on one hand fast XC-mediated NPQ induction should allow the LHC to rapidly enter and maintain a dissipative state under stable high light conditions, and on the other hand it should be able to rapidly relax to avoid limitation of light absorption and photochemical efficiency upon return to stable more favorable light conditions. This balanced and flexible interplay needs a fine-tuned partnership between many actors (LHC pigments and proteins, regulatory partners of NPQ and XC, etc.) which central node could be the redox state of the plastoquinone-PQ pool [START_REF] Lepetit | High light acclimation in the secondary plastids containing diatom Phaeodactylum tricornutum is triggered by the redox state of the plastoquinone pool[END_REF][START_REF] Wilhelm | Light acclimation in diatoms: From phenomenology to mechanisms[END_REF]. Indeed, the PQ redox state is the cross-road of irradiance/light dose changes and energetic pressure which influences, at different timescales, a feedback and interrelated triggering of the photochemical electron transport rate, the transthylakoïdal pH, the Dd de-epoxidation into Dt, the Dd+Dt pool size and the LHC protein synthesis via the retrograde signaling pathway [START_REF] Lepetit | Light signaling in photosynthetic eukaryotes with 'green' and 'red' chloroplasts[END_REF].

Contrary to light and temperature response, under moderate N limitation (see Fig. 4), Dd-

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This article is protected by copyright. All rights reserved containing microalgae seem to use the 'annual' strategy: they adjust their light-harvesting capacity to their growth capacity [START_REF] Halsey | Physiological optimization underlies growth rate-independent chlorophyll-specific gross and net primary production[END_REF]) so that the need for NPQ is restricted. One possible explanation is based on the N cost of maintaining the LHC system in the 'evergreen' strategy. Indeed, the protein-rich LHC system is very demanding in N, which is, by definition, an unaffordable element under N limitation. This explanation is also in agreement with the fact that nutrient availability is less variable than irradiance and temperature in the natural environment, making the 'evergreen' strategy less efficient, at least for Dd-containing microalgae.

The growth strategy of photoautotrophs depends on the relative benefit/cost balance in a specific environment and/or lifestyle. For planktonic diatoms and microalgae inhabiting a mixed water column, the 'evergreen' strategy could well support its ability to acclimate to the mean irradiance around which the light environment constantly fluctuate. This photoadaptative strategy clearly differs from acclimating to the highest potential irradiance which allows avoiding the harmful effect of light stress but which strongly reduces photosynthetic efficiency under low/moderate light conditions [START_REF] Falkowski | Aquatic photosynthesis[END_REF]. Overall, the hypothesis we propose here (Figs. 6,S8) supports how the diatoms, and possibly the Dd-containing microalgae, can exploit a large range of irradiance changes, coupled with a large range of temperatures (including close to 0°C) and nutrient availability, and over various time scales. This portrait fits well with the ability of diatoms i) to thrive in very different marine ecosystems and habitats, typically coastal vs. open ocean and temperate vs. polar systems (Mock andMedlin 2012, Lacour et al. 2017), and ii) to dominate in habitats with extreme light climate (in terms of high average irradiance and/or high light fluctuations) such as turbulent water columns (i.e., upwelling areas for instance), estuarine intertidal flats, polar sea-ice margins, etc. [START_REF] Lavaud | The peculiar features of non-photochemical fluorescence quenching in diatoms and brown algae[END_REF][START_REF] Lyon | Polar microalgae: New approaches towards understanding adaptations to an extreme and changing environment[END_REF][START_REF] Wilhelm | Light acclimation in diatoms: From phenomenology to mechanisms[END_REF]. The general lightresponse flexibility of diatoms, as well as its diversity (see Table S2; [START_REF] Lepetit | Molecular dynamics of the diatom thylakoid membrane under different light conditions[END_REF][START_REF] Lavaud | The peculiar features of non-photochemical fluorescence quenching in diatoms and brown algae[END_REF][START_REF] Wilhelm | Light acclimation in diatoms: From phenomenology to mechanisms[END_REF], might also well explain, in part, how they (and in general Ddcontaining microalgae) have become essential primary producers of our contemporary oceans [START_REF] Benoiston | The evolution of diatoms and their biogeochemical functions[END_REF][START_REF] Tréguer | Influence of diatom diversity on the ocean biological carbon pump[END_REF].

Future directions

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The molecular regulation of NPQ is complex, it shows a high diversity among autophototrophs, and, although this is a dynamic field of research, it is not yet fully understood [START_REF] Demmig-Adams | Nonphotochemical fluorescence quenching in contrasting plant species and environments[END_REF][START_REF] Goss | Biodiversity of NPQ[END_REF][START_REF] Ruban | Nonphotochemical chlorophyll fluorescence quenching: Mechanism and effectiveness in protecting plants from photodamage[END_REF][START_REF] Wobbe | Multi-level light capture control in plants and green algae[END_REF][START_REF] Magdaong | Photoprotective, excited-state quenching mechanisms in diverse photosynthetic organisms[END_REF][START_REF] Pinnola | Molecular mechanisms involved in plant photoprotection[END_REF]. Various aspects of NPQ regulation were not integrated to this study, especially the induction and relaxation kinetics of XC-related NPQ. They are thought to be an important adaptive trait that could explain, in part, the ecological niche distribution of growth forms and species in the aquatic [START_REF] Dimier | Photoprotection and xanthophyll-cycle activity in three marine diatoms[END_REF](Dimier et al. , 2009b) ) and terrestrial habitats [START_REF] Demmig-Adams | Nonphotochemical fluorescence quenching in contrasting plant species and environments[END_REF]. Obviously, further studies are needed to better understand the respective roles of environment and genetics on XC-related NPQ regulation with a coupled effort in using genetic manipulation, natural biodiversity and field experiments. Thanks to the fact they can now be easily genetically and experimentally manipulated [START_REF] Gruber | Intracellular metabolic pathway distribution in diatoms and tools for genome-enabled experimental diatom research[END_REF][START_REF] Moejes | A systems-wide understanding of photosynthetic acclimation in algae and higher plants[END_REF][START_REF] Tirichine | Recent progress in diatom genomics and epigenomics[END_REF], microalgae have been often used to understand the influence of growth environmental conditions on the functional diversity of XC-related NPQ processes. On the contrary, and as pointed out in our study, investigations of XCrelated NPQ in plants under several light conditions are too few, and often with no quantitative evaluation of the energetic state of the whole organism for a more integrated picture to emerge (see [START_REF] Demmig-Adams | Environmental regulation of intrinsic photosynthetic capacity: an integrated view[END_REF]. More quantitative comparisons of plants and trees adapted and acclimated to different growth conditions are needed to further decipher the diversity of the regulation of XC-related NPQ in multicellular systems (see for instance the recent work by [START_REF] Míguez | Diversity of winter photoinhibitory responses: a case study in co-occurring lichens, mosses, herbs and woody plants from subalpine environments[END_REF].

Studies on NPQ in microalgae have also clearly focused on Dd cycle organisms, and especially on diatoms, at the expense of other groups (Lavaud andGoss 2014, Goss andLepetit 2015), obviously because of their ubiquity, high diversity and major role in the global marine primary production [START_REF] Mock | Chapter seven -Genomics and genetics of diatoms[END_REF][START_REF] Malviya | Insights into global diatom distribution and diversity in the world's ocean[END_REF][START_REF] Benoiston | The evolution of diatoms and their biogeochemical functions[END_REF]. Light-dependent XC pigment content, NPQ and quenching efficiency data in conjunction with growth rate in non-diatom species remain scarce, especially in V-containing and green representatives for which many XC-NPQ studies have been performed using the model organism Chlamydomonas reinhardtii [START_REF] Erickson | Light stress and photoprotection in Chlamydomonas reinhardtii[END_REF][START_REF] Wobbe | Multi-level light capture control in plants and green algae[END_REF]. Nevertheless, recent studies examined the XC-related NPQ in diverse green representatives [START_REF] Lunch | The xanthophyll cycle and NPQ in diverse desert and aquatic green algae[END_REF][START_REF] Stamenković | Xanthophyll cycle pool size and composition in several Cosmarium strains (Zygnematophyceae, Streptophyta) are related to their geographic distribution patterns[END_REF][START_REF] Quaas | Nonphotochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation[END_REF][START_REF] Christa | Photoprotection in a monophyletic branch of chlorophyte algae is independent of energydependent quenching (qE)[END_REF] as well as including new, ecologically relevant, models such as Ostreococcus [START_REF] Finazzi | Non-photochemical quenching and energy dissipation in plants, algae and cyanobacteria[END_REF]. In general, the recent explosion of genome sequencing of many species from different algal

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This article is protected by copyright. All rights reserved groups now allows to better explore at the molecular level the functional diversity of the lightresponse regulation in microalgae [START_REF] Finazzi | Genomic insights into photosynthesis in eukaryotic phytoplankton[END_REF][START_REF] Brodie | The algal revolution[END_REF]. The fact that these species represent a broad diversity of growth forms (planktonic, benthic, tychoplanktonic, etc.) and originate from different ecosystems and habitats (open ocean, coast, estuarine flats, sea-ice, temperate vs. polar system, etc.) will additionally support the study of the XC-related NPQ as a potentially significant functional adaptive trait.

At last, in plants, the improvement of photoprotection in a fluctuating light environment is one of the most promising research path for both enhancing the stress resistance and improving the productivity of future genetically-modified crops [START_REF] Cardona | Enhancing photosynthesis in plants: the light reactions[END_REF], with genetic manipulation of the XC-related NPQ being at the forefront [START_REF] Kromdijk | Improving photosynthesis and crop productivity by accelerating recovery from photoprotection[END_REF][START_REF] Murchie | Safety conscious or living dangerously: what is the 'right' level of plant photoprotection for fitness and productivity?[END_REF]. A better knowledge of the impact of XC-NPQ on metabolism and growth, and its functional diversity in microalgae [START_REF] Goss | Biodiversity of NPQ[END_REF] will likely provide benefit to industrial microalgal production [START_REF] Moejes | A systems-wide understanding of photosynthetic acclimation in algae and higher plants[END_REF] and to the generation of engineered cells for the bioproduction of molecules of interest such as biofuels [START_REF] Hess | Production of chemicals from microalgae lipids -status and perspectives[END_REF][START_REF] Wagner | Towards an understanding of the molecular regulation of carbon allocation in diatoms: the interaction of energy and carbon allocation[END_REF].

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This article is protected by copyright. All rights reserved data point is the mean of 3 independent cultures. In panels A and C, error bars represent standard deviations. Data sources are described in Table S1; the logarithmic scale version of panels B and D can be found in Figure S3, A and B, respectively. m.) were included (see Table S5) for the sake of comparison and a logarithmic scale was used. Data sources are described in Table S2.

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This article is protected by copyright. All rights reserved Table S1: Data sources for the xanthophyll cycle (XC) datasets shown in Figures 1,2, 3, S2, S3 and S5. The selected data include measurements of XC pigments and growth rates of unialgal cultures acclimated to several growth irradiances and one temperature (T, °C). n is the number of distinct irradiances.

Table S2: Data sources for the quenching efficiency (QE) dataset in diadinoxanthin (Dd)-containing species. The selected data included measurements of NPQ and diatoxanthin (Dt) content during short term light treatments of unialgal cultures at different irradiances. E is the growth irradiance, a is the slope of the NPQ vs. Dt relationship, Y 0 is the y-intercept, and n is the number of data points for each species (see the Methods section and Fig. S1).

Table S3: Data sources for the quenching efficiency (QE) dataset in violaxanthin (V)-containing species. The selected data included measurements of NPQ, and zeaxanthin (Z) and antheraxanthin (A) contents during short term light treatments of unialgal cultures at different irradiances (but for Macrocystis pyrifera). E is the growth irradiance, a is the slope of the NPQ vs. Z relationship, Y 0 is the y-intercept, and n is the number of data points for each species.

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This article is protected by copyright. All rights reserved acclimated to 50, 500 and 1000 µmol photons • m -2 • s -1 (Panel A). Linear fits were adjusted on the linear portion of the relationships. The slopes (a) and the Y intercept (Y 0 ) are provided (panels B, C, D). Saturation was observed for cells acclimated at 500 and 1000 µmol photons • m -2 • s -1 (panels C and D). Regressions are shown with 95% confidence and prediction intervals. Data sources are described in Table S1. Note that the E/K E axis is in logarithmic scale. Symbols are the same as in Figures 1 and2. and Z/Chl a (panel C) vs. growth irradiance (E). Data sources are described in Table S1. S1.

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This article is protected by copyright. All rights reserved S2 andS3).

(

  FigS. 1, D-F, 2, C and D; Fig. S2 in the Supporting Information). This was particularly true for Dt/Chl a vs. E/K E relationships within both diatoms and non-diatoms species (Fig. 2, C and D, S2). It

  ; Figs. 3, S3 in the Supporting Information) comes from the response of two diatom polar strains that have contrasted light sensitivity and related niche: Thalassiosira gravida (K E ~12 µmol photons • m -2 • s -1 ) is generally found in low light environments, often underneath the sea-ice floe at the beginning of the Arctic spring bloom, while Chaeotoceros neogracile ((K E = ~35 µmol photons • m -2 • s -1 ) can bloom later in summer and generally at the surface of open waters (i.e., free of sea-ice; Lacour et al. 2017).

Figure 1 :

 1 Figure 1: Diadinoxanthin + Diatoxanthin (Dd + Dt) content for different species and taxa as a function of growth light conditions. (Dd+Dt)/Chlorophyll (Chl a) vs. growth irradiance (E) (panels A, B, C) and vs. growth irradiance normalized to light saturation parameter for growth (K E ; E/K E , panels D, E, F) in diatoms (panels A, D), in other diadinoxanthin-containing microalgae (panels B, E) and in both merged groups (panels C, F). For panels C and F, linear regressions are shown with 95% confidence and prediction intervals, and corresponding R 2 and equations provided. Data sources are described in TableS1; the logarithmic scale version of panel F can be found in FigureS2A. Species abbreviations: T. w. (A), Thalassiosira weissflogii (Actin); T. w. (G), Thalassiosira weissflogii (Grunow);T. g., Thalassiosira gravida; C. n., Chaetoceros neogracilis; S. c., Skeletonema costatum; N. p., Nitzschia palea; F. c., Fragilariopsis cylindrus; E. h., Emiliania huxleyi; H. c., Hymenomonas carterae; A. c., Amphidinium carteri; P. a., Phaeocystis antarctica.

Figure 2 :

 2 Figure 2: Diatoxanthin (Dt) content for different species and taxa as a function of growth light conditions. Dt/ Chlorophyll (Chl a) vs. growth irradiance (E) (panels A, B) and vs. growth irradiance normalized to light saturation parameter for growth (K E ) (E/K E , panels C, D) in diatoms (panels A, C) and in other microalgae (panels B, D). For panels C and D, linear regressions are shown with 95% confidence and prediction intervals, and corresponding R 2 and equations are provided. Data sources are described in Table S1; the logarithmic scale version of panels C and D can be found in Figure. S2, B and C, respectively. Species abbreviations: T. w. (A), Thalassiosira weissflogii (Actin); T. w. (G),Thalassiosira weissflogii (Grunow); T. g.,Thalassiosira gravida; C. n., Chaetoceros neogracile; S. c., Skeletonema costatum; N. p., Nitzschia palea; F. c., Fragilariopsis cylindrus; E. h., Emiliania huxleyi; H. c., Hymenomonas carterae; A. c., Amphidinium carteri; P. a., Phaeocystis antarctica.

Figure 3 :

 3 Figure 3: Effect of temperature on the Diadinoxanthin + Diatoxanthin (Dd + Dt) and Diatoxanthin (Dt) content in species showing different sensitivity to light. (Dd+Dt)/ Chlorophyll (Chl a) (panels A, B) and Dt/ Chlorophyll (Chl a) (panels C, D) vs. growth irradiance (E) (panels A, C) and vs. growth irradiance normalized to (K E ) (E/K E , panels B, D) in the polar diatoms Chaetoceros neogracile and Thalassiosira gravida acclimated at 0°C and 5°C. For panels B and D, linear regressions are shown with 95% confidence and prediction intervals, and corresponding R 2 and equations are provided. Each

Figure 4 :

 4 Figure 4: Diadinoxanthin + Diatoxanthin (Dd + Dt) content in relation to growth under nutrient limitation. Normalized (Dd+Dt)/Chlorophyll (Chl a) vs. µ/µ m in species exposed to various levels ofnutrient limitation (nitrogen-N or phosphate-P). µ/µ m increases as nutrient limitation decreases; when µ/µ m = 1, cultures are replete and growth is optimal. For each species, (Dd+Dt)/Chl a was normalized by its the maximum value. Each data point was generated from a culture acclimated to a given level of nutrient limitation in a chemostat system; see the text for further details. Data were extracted from two studies: Goericke and Montoya (1998) and[START_REF] Stolte | Genetic and physiological variation in pigment composition of Emiliania huxleyi (Prymnesiophyceae) and the potential use of its pigment ratios as a quantitative physiological marker[END_REF].

Figure 5 :

 5 Figure 5: Quenching efficiency (QE) vs. growth irradiance (E) in different species. In both panels, QE is the slope of the NPQ vs. Diatoxanthin (or Zeaxanthin + Antheraxanthin) relationship. Only the species for which QE was reported for several Es are shown. Species abbreviations: C. m., Cyclotella meneghiniana; S. c., Skeletonema costatum; P. t.2 and P. t.4, Phaeodactylum tricornutum strains 2 and 4; A. e., Alexandrium excavatum; diatoms are shown with open symbols and the dinoflagellate A. e. with closed symbols. Note that two plants (grey symbols), Hedera helix (H. h.) and Zea mays (Z.

Figure 6 :

 6 Figure 6: Illustration of potential energy dissipation in diatoms with low and high NPQ ability. Modelled Φ NPQ (proportion of absorbed energy dissipated as heat by NPQ in black) and µ/µ m (in grey) as a function of growth irradiance (E) normalized by the light saturation for growth (E/K E ) in Cyclotella meneghiniana (low NPQ, dotted black line; Lavaud and Lepetit 2013) and Phaeodactylum tricornutum-P. t.2 strain (high NPQ, continuous black line; Lavaud and Lepetit 2013). The computation of Φ NPQ is based on the relationships between E, Diatoxanthin content and NPQ evidenced in this study (see the supplementary material for details and Fig. S8). µ/µ m was modelled as proposed by MacIntyre et al. (2002) (µ/µ m = 1-exp[-E/K E ], see the Methods).

Table S4 :

 S4 Data sources for the xanthophyll cycle (XC) datasets shown in Figure S4. The selected data include measurements of xanthophyll pigments in land plants acclimated to several growth irradiances. n is the number of distinct irradiances. Table S5: Data sources for the quenching efficiency (QE) dataset in land plants. The selected data include measurements of NPQ, Zeaxanthin (Z) and Antheraxanthin (A) contents in land plants during short term light treatments at different irradiances.

Figure S1 :

 S1 Figure S1: Parametrization of the non-photochemical quenching (NPQ) vs. Diatoxanthin (Dt) or Zeaxanthin (Z) + Anteraxanthin (A) relationship as shown in TablesS2 and S3-an example with the diatom Phaeodactylum tricornutum. Relationship between NPQ and Dt in P.tricornutum-P. t.2

Figure S2 :

 S2 Figure S2: Diadinoxanthin + Diatoxanthin (Dd + Dt) and diatoxanthin (Dt) contents for different species and taxa as a function of growth light conditions. (Dd+Dt)/Chlorophyll (Chl a) vs. growth irradiance normalized to the light saturation parameter for growth (E/K E ) in Dd-containing microalgae (panel A). Dt/Chl a vs. E/K E in diatoms (panel B) and in other Dd-containing microalgae (panel C).

Figure S3 :

 S3 Figure S3: Effect of temperature on the Diadinoxanthin + Diatoxanthin (Dd + Dt) content in species showing different sensitivity to light. Dd+Dt/Chl a (panel A) and Dt/Chl a (panel B) vs. growth irradiance normalized to the light saturation parameter for growth (E/K E ) in the polar diatoms Chaetoceros neogracile (circles) and Thalassiosira gravida (triangles) acclimated to 0°C (open symbols) and 5°C (closed symbols). Regressions are shown with 95% confidence and prediction intervals. Each data point is the mean of 3 independent cultures. Note that the E/K E axis is in logarithmic scale. Symbols are the same as in Figure 3.

Figure S4 :

 S4 Figure S4: Zeaxanthin (Z) + antheraxanthin (A) + violaxanthin (V) pigments content in land plants as a function of growth light conditions. (Z+A+V)/Chlorophyll a (Chl a) (panel A), Z+A/Chl a (Panel B)

Figure S5 :

 S5 Figure S5: Zeaxanthin (Z) + antheraxanthin (A) + violaxanthin (V) pigments content in V-containing microalgae as a function of growth light conditions. (Z+A+V)/Chlorophyll a (Chl a) (panel A), Z+A/Chl a (Panel B) and Z/Chl a (panel C) vs. growth irradiance (E). In panels A, B, C, linear regressions are shown and corresponding R 2 and equations are provided. Data sources are described in TableS1.

Figure S6 :

 S6 Figure S6: Quenching efficiency (QE) in different species. In both panels, QE is the slope of the NPQ vs. Diatoxanthin (or Zeaxanthin + Antheraxanthin) relationship. Panel A: Same as Figure 5 including all our dataset (see data sources in TablesS2 and S3). Panel B: Box plot diagram showing

  Panel B: Box plot diagram showing QE in Diadinoxanthin (Dd)-and Violaxanthin (V)-containing species.

Figure S7 :

 S7 Figure S7: Relationship between Φ NPQ (proportion of absorbed energy dissipated as heat by NPQ, see the Methods section) and NPQ in Thalassiosira gravida and Chaetoceros neogracile exposed to various levels of irradiances (from 0 to 2000 µmol photons • m -2 • s -1 ).

Figure S8 :

 S8 Figure S8: Illustration of potential energy dissipation in diatoms with low and high NPQ ability. Quenching efficiency-QE (A) and NPQ (B) vs. growth irradiance normalized to the light saturation parameter for growth (E/K E ) in Cyclotella meneghiniana (low NPQ diatoms) and Phaeodactylum tricornutum-P. t.2 (high NPQ diatoms). µ/µ m was modeled as proposed by MacIntyre et al. (2002) (µ/µ m = 1-exp[-E/K E ], see the Methods section). In panel B, NPQ was modeled from equations 2, 3, 4

Acknowledgments

We thank the joint contribution to the research programs of UMI Takuvik CNRS-Université Laval, ArcticNet (Network Centre of Excellence of Canada), the Canada Excellence Research Chair in Remote Sensing of Canada's New Arctic Frontier, and the Canada Research Chair program. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Accepted Article

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