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Disulfide bond formation on luminal proteins in thylakoids 1240 V. Conclusion 1242 Acknowledgements 1242 References 1242 SUMMARY: Disulfide bonds are post-translational modifications crucial for the structure and function of thousands of proteins. Their formation and isomerization, referred to as oxidative folding, require specific protein machineries found in oxidizing subcellular compartments, namely the endoplasmic reticulum and the associated endomembrane system, the intermembrane space of mitochondria and the thylakoid lumen of chloroplasts. At least one protein component is required for transferring electrons from substrate proteins to an acceptor that is usually molecular oxygen. For oxidation reactions, incoming reduced substrates are oxidized by thiol-oxidoreductase proteins (or domains in case of chimeric proteins), which are usually themselves oxidized by a single thiol oxidase, the enzyme generating disulfide bonds de novo. By contrast, the description of the molecular actors and pathways involved in proofreading and isomerization of misfolded proteins, which require a tightly controlled redox balance, lags behind. Herein we provide a general overview of the knowledge acquired on the systems responsible for oxidative protein folding in photosynthetic organisms, highlighting their particularities compared to other eukaryotes. Current research challenges are discussed including the importance and specificity of these oxidation systems in the context of the existence of reducing systems in the same compartments.

International audience; Land Surface Phenology (LSP) and Leaf Area Index (LAI) are important variables that describe the photosynthetically active phase and capacity of vegetation. Both are derived on the global scale from optical satellite sensors and require robust validation based on in situ sensors at high temporal resolution. This study assesses the PAI Autonomous System from Transmittance Sensors at 57 degrees (PASTiS-57) instrument as a low-cost transmittance sensor for simultaneous monitoring of LSP and LAI in forest ecosystems. In a field experiment, spring leaf flush and autumn senescence in a Dutch beech forest were observed with PASTiS-57 and illumination independent, multi-temporal Terrestrial Laser Scanning (TLS) measurements in five plots. Both time series agreed to less than a day in Start Of Season (SOS) and End Of Season (EOS). LAI magnitude was strongly correlated with a Pearson correlation coefficient of 0.98. PASTiS-57 summer and winter LAI were on average 0.41 m(2)m(-2) and 1.43 m(2)m(-2) lower than TLS. This can be explained by previously reported overestimation of TLS. Additionally, PASTiS-57 was implemented in the Discrete Anisotropic Radiative Transfer (DART) Radiative Transfer Model (RTM) model for sensitivity analysis. This confirmed the robustness of the retrieval with respect to non-structural canopy properties and illumination conditions. Generally, PASTiS-57 fulfilled the CEOS LPV requirement of 20% accuracy in LAI for a wide range of biochemical and illumination conditions for turbid medium canopies. However, canopy non-randomness in discrete tree models led to strong biases. Overall, PASTiS-57 demonstrated the potential of autonomous devices for monitoring of phenology and LAI at daily temporal resolution as required for validation of satellite products that can be derived from ESA Copernicus' optical missions, Sentinel-2 and -3.

The aim of this study was to systematically analyze the potential and limitations of using plant functional trait observations from global databases versus in situ data to improve our understanding of vegetation impacts on ecosystem functional properties (EFPs). Using ecosystem photosynthetic capacity as an example, we first provide an objective approach to derive robust EFP estimates from gross primary productivity (GPP) obtained from eddy covariance flux measurements. Second, we investigate the impact of synchronizing EFPs and plant functional traits in time and space to evaluate their relationships, and the extent to which we can benefit from global plant trait databases to explain the variability of ecosystem photosynthetic capacity. Finally, we identify a set of plant functional traits controlling ecosystem photosynthetic capacity at selected sites. Suitable estimates of the ecosystem photosynthetic capacity can be derived from light response curve of GPP responding to radiation (photosynthetically active radiation or absorbed photosynthetically active radiation). Although the effect of climate is minimized in these calculations, the estimates indicate substantial interannual variation of the photosynthetic capacity, even after removing site-years with confounding factors like disturbance such as fire events. The relationships between foliar nitrogen concentration and ecosystem photosynthetic capacity are tighter when both of the measurements are synchronized in space and time. When using multiple plant traits simultaneously as predictors for ecosystem photosynthetic capacity variation, the combination of leaf carbon to nitrogen ratio with leaf phosphorus content explains the variance of ecosystem photosynthetic capacity best (adjusted R-2 = 0.55). Overall, this study provides an objective approach to identify links between leaf level traits and canopy level processes and highlights the relevance of the dynamic nature of ecosystems. Synchronizing measurements of eddy covariance fluxes and plant traits in time and space is shown to be highly relevant to better understand the importance of intra-and interspecific trait variation on ecosystem functioning.

Plants with lowered activity of enzymes catalyzing the final step of ascorbate synthesis or the equilibrium between reduced and oxidized forms have highly pleiotropic phenotypes suggesting regulatory roles for ascorbate and its oxidized forms. Network analysis of the transcriptome, proteome and key metabolites of RNAi lines for ascorbate oxidase, monodehydroascorbate reductase and galactonolactone dehydrogenase has been carried out in orange fruit pericarp of tomato (Solanum lycopersicum). We show a transcriptional switch-type response with expression profiles in ascorbate oxidase lines being inversed compared to the monodehydroascorbate reductase and galactonolactone dehydrogenase lines. Differentially expressed genes are linked to ribosome biogenesis and translation. The inversion between the transcriptome signatures is not specific to tomato fruit as it is conserved in Arabidopsis. The transcriptome response is not correlated with accumulated proteins which, with the metabolites, are correlated to the activity of the ascorbate redox enzymes. Differentially accumulated proteins include metacaspase, protein disulphide isomerase, chaperone DnaK and carbonic anhydrase and the metabolites chlorogenic acid, dehydroascorbate and alanine. Hub genes are related to signaling, the heat-shock response and ribosome biogenesis. This study in a non-photosynthetic tissue reveals signaling from the ascorbate pool related to the heat-shock response, translation and protein synthesis.

International audience; Because all microclimatic variables change with elevation, it is difficult to compare plant performance and especially photosynthetic capacity at different elevations. Indeed, most previous studies investigated photosynthetic capacity of low- and high-elevation plants using constant temperature, humidity and light but varying CO2 partial pressures (PCO2). * Using gas exchange measurements, we compared here maximum assimilation rates (Amax) at ambient and constant-low-elevation PCO2 for two temperate tree species along an altitudinal gradient (100 to 1600 m) in the Pyrénées mountains.* Significant differences in Amax were observed between the CO2 partial pressure treatments for elevations above 600 m, the between-treatment differences increasing with elevation up to 4 μmol m−2 s−1. We found an increase in Amax with increasing elevation at constant-low-elevation PCO2 but not at ambient PCO2 for both species. Given a 10% change in PCO2, a proportionally higher shift in maximum assimilation rate was found for both species. * Our results showed that high elevation populations had higher photosynthetic capacity and therefore demonstrated that trees coped with extreme environmental conditions by a combination of adaptation (genetic evolution) and of acclimation. Our study also highlighted the importance of using constant CO2 partial pressure to assess plant adaptation at different elevations.; Les conditions microclimatiques étant très variables avec l'altitude, il est difficile de comparer les performances d'une espèce végétale à différentes altitudes, particulièrement la capacité photosynthétique. En effet, la plupart des études antérieures ont estimé le taux maximal d'assimilation à basses et hautes altitudes en maintenant la température, l'humidité de l'air et la lumière constantes mais en laissant varier la pression partielle de CO2 (PCO2). * Afin de comparer le taux maximum d'assimilation (Amax) à pressions partielles de CO2 constantes de basse altitude et variables, nous avons effectué des mesures d'échanges gazeux sur deux espèces d'arbres tempérés le long d'un gradient altitudinal de 1600 m de dénivelé dans les Pyrénées françaises. * La différence entre les deux traitements de PCO2 est significative au-dessus de 600 m d'altitude et atteint un maximum de 4 μmol m−2 s−1. Pour les deux espèces, nous avons mis en évidence une augmentation de Amax avec l'altitude à PCO2 constantes mais pas à PCO2 ambiantes. Pour une modification de PCO2 de 10 %, le changement du taux maximum d'assimilation est proportionnellement supérieur chez les deux espèces. * Nos résultats montrent que les populations de hautes altitudes possèdent une capacité photosynthétique supérieure, démontrant que les arbres font face aux conditions environnementales extrêmes grâce à des adaptations génétiques ou des acclimatations. Notre étude souligne ainsi l'importance de fixer la PCO2 pour comparer l'adaptation des plantes à différentes altitudes.

Les objectifs de ce travail de thèse étaient : (i) identifier les principaux compromis et covariations d’un ensemble de traits foliaires relatifs à l’acquisition du carbone et (ii) caractériser la variabilité de ces traits en réponse à l’éclairement (plasticité phénotypique) et la diversité interspécifique de cette plasticité chez des espèces de forêt tropicale humide. Les mesures ont été réalisées sur des semis de 13 espèces d’arbres élevés en conditions contrôlées dans 3 traitements d’éclairements relatifs distincts. Une analyse coût-bénéfice des traits du bilan de carbone foliaire a été centrée sur les coûts de construction du métamère (CCmetm), le temps de retour sur investissement (PBT) et la mesure des durées de vie des feuilles (LLS). Une forte diversité interspécifique a été observée pour l’ensemble des traits étudiés. Les espèces se répartissent le long d’un axe opposant durée de vie des feuilles et LMA (masse surfacique) d’un côté, aux capacités photosynthétiques (Asat), PNUE (Asat/N), respiration (Rd) et teneurs en azote (Nm) de l’autre. Ces résultats sont en adéquation avec le schéma universel d’acquisition des ressources proposé par Wright et al. (2004). Les relations entre LLS et PBT sont faibles et l’ensemble des espèces amortissent très largement leur CCmetm. De manière générale, le classement des espèces est maintenu d’un traitement à l’autre et, à l’exception des coûts de construction, seuls de faibles effets d’interaction ont été observés entre espèces et traitements. Le calcul d’un indice de plasticité a également permis de montrer qu’en dépit d’une certaine diversité interspécifique de la plasticité phénotypique, aucune espèce n’était globalement plus « plastique » que les autres sur l’ensemble des traits considérés. Enfin, si les espèces pionnières se distinguent nettement par leurs attributs, leur degré de plasticité n’est pas différent de celui des espèces de sous-bois., The aim of this research were (i) identify the main trade-off and covariations of a group of leaf traits related to carbon assimilation, and (ii) assess the irradiance-elicited plasticity, and test whether this plasticity differs among species of tropical rain forest. Measurements were made with saplings from 13 species growing under three levels of irradiance, provided by shading nets, in an open green-house. A cost benefit analysis was undertaken to quantify carbon balance of leaves metamers. Construction costs of metamers (CCmetm), payback time of the investment of carbon into leaf and metamer structure (PBT), and leaf life span (LLS) were recorded on the saplings. A large inter-specific diversity was recorded for all the traits, the species are scattered along a principal component axis opposing on one hand LSS and leaf mass-to-area ratio (LMA), and on the other hand, photosynthetic capacity, photosynthetic nitrogen use efficiency (PNUE), respiration (Rd) and leaf nitrogen content (N). These results are in agreement with the concept of “leaf economics spectrum” suggested by Wright et al. (2004). The relationship between LLS and PBT were very loose, which shows that all species fully cover the construction costs, even under very low irradiance. Species ranking was not modified by irradiance whatever the trait, and, except for specific construction costs, only very weak interactions were found between species and irradiance. The computation of a plasticity index allowed to demonstrate that despite some inter-specific diversity of the values taken by the index for some traits, there was no consistent difference among species, and none of them appeared consistently more plastic than the others. Even if the two pioneer species analysed here differed largely from the others, from the point of view of trait values, they displayed similar levels of plasticity.