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Universidad Pública de Navarra (2017)

Drought stress responses in Medicago truncatula and Glycine max : system biology approaches

Seminario Huárriz, Amaia

Titre : Drought stress responses in Medicago truncatula and Glycine max : system biology approaches

Auteur : Seminario Huárriz, Amaia

Université de soutenance : Universidad Pública de Navarra

Grade : Tesis doctoral / Doktoretza tesia 2017

Résumé
After cereals, legumes are crops of great economic importance. However, legume plants are very sensitive to abiotic stresses, being drought one of the most harmful stress in terms of crop production. The general aim of the present work is to gain further insights into two legume species (Medicago truncatula and Glycine max) drought responses at the shoot and root level by using a combination of physiological, morphological, transcriptomic and metabolomic approaches. Ascorbic acid (AsA) is one of the most abundant water-soluble antioxidant compound present in plant tissues involved in plant enzymatic and non-enzymatic detoxification mechanisms. Nevertheless, little is known on the regulation of this antioxidant biosynthesis pathway under drought stress. In chapter 1, through a combination of molecular and physiological approaches, we observed that AsA biosynthesis was severely affected by drought in soybean plants. These analyses showed that drought triggered multiple control points regulating AsA biosynthesis at the GDP-D-mannose pyrophosphorylase and GDPD-mannose 3´, 5´-epimerase level of soybean plants. In parallel, these responses were also observed in the model legume M. truncatula. In chapter 2, work presented here showed the tight link between above- and belowground organs in M. truncatula plants and the fact that, under drought stress conditions, adult plants prioritized root growth over leaf development. Actually, different analyses showed responses which suggest a passive survival strategy for leaves coexisting with an active engagement of the root in drought-stressed plants. New non-destructive and non-toxic protocols are needed to simulate drought conditions to better characterize plant responses under controlled conditions. To that end, in chapter 3, a new simple, efficient and reproducible method is presented to simulate in vitro drought stress conditions in M. truncatula seedlings grown on plates containing different agar concentrations. After validating of this method, it was observed that roots, rather than shoots, play a key role in plant adaptation to stress conditions. The relative simplicity of the method allows for its large-scale application in studies such as population screening for drought resistance traits in a variety of plants. Additionally, in chapter 4 we applied this method in combination with physiological, transcriptomic and metabolomic analyses in one of the most important parts of the root, the absorption zone, responsible for absorbing water and nutrients thus allowing the plant growth. Results led us to conclude that plants exhibited fast molecular responses under drought conditions ; the metabolism of lipids, hormones, cell wall and secondary metabolism were some of the pathways most severely affected. To sum up, work presented here provides new insights into the understanding of legume responses to water-limiting conditions and contributes towards elucidating water stress signals and gene networks controlling the response of legume plants to drought.

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