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RESEARCH PRODUCT

Etude de la régulation du facteur de transcription ATB2 chez Medicago truncatula

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Rapport de stage de Master 2 Spécialité Biologie Intégrative des Interactions Plantes, Microbes, Environnement BAP GEAPSI; Master; Climatic changes since more than a century combined with the urge for better crop yields due to a huge demographic growth and coupled with the need for a more sustainable agriculture led to a number of stresses for plants. Understanding them and their effect on growth, seed quality and seed production of plants is one of the most important agronomical issues of our time. We have chosen to study legumes because they are a major lipid and protein source, as both food and feed, and for their unique ability to absorb the atmospheric nitrogen via a symbiosis with Rhizobium bacteria, whereby they can store more protein in their seeds than other crops. They also can establish an endosymbiosis with some soil fungi which improves water and mineral absorption. Legumes are hence interesting research subjects. We worked on the legume model plant, Medicago truncatula, a diploid, autogamous organism which can produce a large number of seeds in a short period of time and is phylogenetically close to the main legume crops in Europe. We focused on the b-ZIP gene family which codes for regulatory factors controlling the plant metabolism under stress conditions and more specifically on the ATB2 gene. ATB2 expression is not yet known in M. truncatula but it is repressed by high sucrose concentrations and it activates the amino acid metabolism in Arabidopsis thaliana whereby it is a critical intermediary between the Carbon and Nitrogen metabolisms in stress conditions. Being very close to the A. thaliana gene AtATB2, MtATB2 could have the same functions. Thus, the main goals of this study were to study the spatiotemporal expression of MtATB2 during the development of the seed (through in situ Hybridization and pATB2-GUS transgenic plants), to start the functional analysis of this gene with Tnt1 insertion mutants, and to test its induction in abiotic stress conditions like water stress. Contamination problems delayed the transformation experiments, which could not be completed during my training’s timeframe. HIS experiments showed that ATB2 is expressed, in the seed, only in the seed coat and specifically in the outer layer of the Hilum area. Its expression is, throughout the development, stable and constant. MtATB2 is also overexpressed in water stress conditions, unlike AtATB2. The Tnt-mutants likely are Knock-Out mutants for ATB2 because its expression is 90-fold lower than in the wild type. In parallel, we studied the expression of possible ATB2 target genes and showed that one gene called ASN1 had an expression 90-fold lower than the wild type. Their affiliation is, thus, probable but not yet proven. Expression of the other putative target genes did not change significantly. All these results suggest that MtATB2 is an important gene for seed development, and possibly an intermediary between Carbon and Nitrogen pathways, like AtATB2. However, the way it works is probably slightly different from AtATB2.