Analyse génétique et moléculaire de l'immunité des hydathodes et du système vasculaire des Brassicacées
Le résumé fourni par la source
Hydathodes were first characterized at the end of the XIXth century by Anton de Bary, a Prussian botanist, surgeon and microbiologist. Since, theses organs are studied sporadically, even if they are present on leaves of most vascular plants. Localized at the leaf serration tips, hydathodes are the sites of guttation. They are composed of pores in the epidermis and of a peculiar parenchyma connected to the vasculature. Hydathodes are thus a link between leaf xylem vessels and the outside world. Surprisingly, only a handful of pathogens can penetrate the plant this way. Xanthomonas campestris pathovar campestris (Xcc), causal agent of black rot of Brassica is one of them. Xcc represent a threat to agriculture, because it can infect many Brassica crops, such as cabbage, cauliflower, turnip, mustard or radish. Xcc virulence factors are well studied, but not much is known about plant immunity inside hydathodes, even if they are the first contact point between Xcc and the plant. During this PhD project, I studied hydathode transcriptomic and guttation fluid metabolomics characteristics. I also established the genetic bases of cauliflower hydathode post-invasive immunity, by comparing hydathodes responses to an Xcc virulent or avirulent strain, during the early stages of infection. In the second part of the project, I set up a method to screen immune defect in many Arabidopsis thaliana mutants in response to Xcc infection. This method will be a future asset for my host team. I also used it to start the screen of a collection of A. thaliana mutants. I identified more than fifty lines with a modified susceptibility to Xcc. Last, I delved into the link between number of hydathodes, water status of tissues and Xcc infectious strategy. This work brings original results and a protocol that will help us to better understand hydathodes biology as plant organs as well as their role during plant-pathogen interactions.
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