Résumé
Xanthomonas campestris pv. campestris is a vascular phytopathogenic bacterium which is the causal agent of black rot of Brassicaceae such as cabbage or the model plant Arabidopsis thaliana. Its virulence relies on a type III secretion system which injects virulence proteins (also called effectors) directly inside the plant cell. The xopAC gene encodes a type III effector which is Xanthomonas campestris-specific and responsible for the avirulence of Xcc on the Columbia-0 ecotype of A. thaliana when Xcc is directly inoculated in the leaf central vein. The XopAC protein has a N-terminal LRR domain (Leucine Rich Repeat) and a C-terminal Fic domain (Filamentation Induced by CAMP). The LRR is probably involved in an interaction with a plant ligand. The Fic domain is probably involved in the post-translational modification of protein targets by adenylylation (adding of AMP moiety) on a threonine or tyrosine residue. We have shown that both domains are essential for the avirulence function of the XopAC protein on the Col-0 ecotype. Strategies to dissect the XopAC protein function will be presented as well as efforts which are made to identify plant targets of xopAC in order to understand genetic basis of the immune response which occurs in the vascular system of the Col-0 ecotype against Xcc. (Résumé d'auteur)