6533b855fe1ef96bd12b060d

RESEARCH PRODUCT

Effet d'une carence en soufre combinée à un stress hydrique chez le pois protéagineux : Etude des mécanismes moléculaires mis en jeu dans les organes puits et source au cours de la phase reproductive

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Pea (Pisum sativum L.) is a grain legume crop that produces seeds rich in proteins for food and feed and, thanks to its symbiosis with nitrogen-fixing bacteria, enriches the soil with nitrogen. The wider development of pea cultivation is therefore a major agroecological challenge. Water stress combined with sulfur deficiencies in soils (S is a macroelement necessary for plant defense reactions) are two abiotic stresses that interact in the current context of climate change. However, the molecular mechanisms underlying pea adaptation to water stress and their modulation by sulfur nutrition remain to be elucidated. The objectives of this thesis were, first, to describe the impact of an interaction between these two abiotic stresses, water stress and sulfur deficiency, during the reproductive phase on the yield and quality of pea seeds and, second, to characterize using -omics approaches the underlying molecular mechanisms by focusing on developing seeds and leaves, sources of nutrients for developing seeds.Thus, pea plants (cv. ‘Caméor’) deprived of sulfate two weeks before flowering were subjected to a period of nine days of moderate water stress from the beginning of flowering. Each stress was also applied individually in parallel with a non-stressed condition. The analysis of mature plants showed a synergistic effect of the two single stresses on yield and yield components. On the other hand, the protein composition of the seed, characterized by the 7S/11S globulin ratio, was less affected in response to the double stress than in response to sulfur deficiency alone, and did not vary in response to water stress. These results show that water stress mitigated the negative effect of sulfur deficiency on seed protein composition. Similar results were obtained for the seed nitrogen/sulfur ratio (correlated to the 7S/11S ratio), suggesting that it is a good indicator of seed protein composition in pea.In order to determine the mechanisms by which seeds and leaves adapt their metabolism under these multiple stress conditions, developing seeds and leaves of the first two reproductive nodes were collected prior to the application of water stress, during the combined stress period, and during re-watering. These tissues were subjected to omics analyses (proteomics, transcriptomics, ionomics, metabolomics) offering a global view of the response of seeds and leaves to the single and double stresses. The analysis of seeds revealed a mitigated effect of sulfur deficiency combined with water stress on the seed transcriptome and proteome compared to sulfur deficiency alone. The responses of seeds to the single or combined stresses involved a few proteins but these were involved in the removal of reactive oxygen species or in the maintenance of the redox balance. In leaves, transcriptional reprogramming in response to the double stress occurred at the first and last developmental stages studied. This reprogramming involves genes with roles in post-translational modification and protein transport processes. Changes in the leaf proteome occurred at the end of the double stress and during re-watering, highlighting proteins that play a key role in detoxification processes, including metal accumulation.This new knowledge has allowed the identification of candidate proteins for controlling the mechanisms of seed development or detoxification of cells during abiotic stress. They offer prospects for improving and stabilizing pea yields and seed nutritional quality.