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Compréhension de la capacité d’une plante de Pois à récupérer entermes de croissance et d’acquisition d’azote après un stress hydrique : étudesécophysiologique et moléculaire

Abstract : Pea (Pisum sativum L.) has the unique ability to fix atmospheric dinitrogen (N2) via a symbiosis with soil bacteria in root nodules. Although this specificity makes this crop particularly interesting in the context of agroecological transition, symbiotic nitrogen fixation is particularly sensitive to abiotic stresses such as water deficit, which contributes to the yield instability of this protein crop and reduces its interest for farmers. Yield stability depends both on plant's ability to tolerate stress and on its ability to recover after stress. However, the mechanisms involved during the recovery period have been for now poorly explored. It is, therefore, essential to identify traits of plants maximizing pea resilience to water deficit, in order to propose new ideotypes that are better adapted to environmental conditions of fluctuating water or nutrient availabilities.The main objectives of this study were: i) to identify the ecophysiological processes involved during the recovery period following a water deficit, considering in particular plant growth and plant nitrogen acquisition, and ii) to determine the underlying molecular processes within roots and nodules.During a first experiment in controlled conditions (4PMI Platform, Dijon, France), the dynamics of recovery of two pea genotypes were analyzed in detail after imposing plants before their flowering to a water deficit of two weeks. While one of the genotypes, (Kayanne), was able to maintain its yield under these conditions, yield of the other one (Puget) was decreased by water deficit. We have used both a) a whole-plant approach (using an ecophysiological framework focused on carbon, nitrogen and water fluxes in the plant) and b) so-called "omics" approaches (metabolomics, transcriptomics, and phytohormone assays) concerning root and nodule compartments. This analysis was completed by a second one where 13C and 15N2 isotopic labeling experiment allowed us to precisely measure carbon and nitrogen fluxes in the soil-plant-atmosphere continuum.Our analyses revealed that the two genotypes studied had contrasting resilience abilities, partly explained by different recovery strategies during the re-watering period, and particularly implying processes which were related to nitrogen nutrition. We have demonstrated that during the recovery period Kayanne was able to quickly and strictly re-adjust the formation of nodules to its growth needs, allowing this genotype to fully recover from the 2-week water deficit period. On the other hand, in Puget, the initiation of new nodules after water deficit was delayed compared to control plants, but numerous additional nodules developed. We hypothesized that the associated larger energy cost, which occurred to the detriment of growth, would finally negatively impact Puget’s yield.This difference in the dynamics of the root system response to re-watering was comforted by the molecular analysis performed in root and nodule compartments. The "omics" analysis also highlighted differences in antioxidant and osmoprotective responses between the two genotypes that could help to explain the delay observed for the recovery of the two genotypes.Altogether these results give new insights for the understanding of the regulatory mechanisms underlying the recovery of pea plant after a water deficit. Next step will consist in a statistical integration of the multi-scaled data (ecophysiological, hormonal, metabolomic and transcriptomic data), which should make it possible to identify the main regulators involved in recovery, for breeding strategies leading to the selection of pea ideotypes better suited to fluctuating water conditions.
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Mégane Couchoud. Compréhension de la capacité d’une plante de Pois à récupérer entermes de croissance et d’acquisition d’azote après un stress hydrique : étudesécophysiologique et moléculaire. Sciences agricoles. Université Bourgogne Franche-Comté, 2020. Français. ⟨NNT : 2020UBFCK007⟩. ⟨tel-02940058⟩

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