CYCLIC (1,2)-GLUCAN FROM XANTHOMONAS CAMPESTRIS CAMPESTRIS SUPPRESSES ARABIDOPSIS THALIANA IMMUNITY BY MODULATING FLAGELLIN INDUCED DEFENSE

LAILA TOUM; VERÓNICA DE PINO; GUSTAVO GUDESBLAT; ADRIAN VOJNOV

Maastricht

Congreso; FEMS Microbiology Congress; 2015

Federation of European Microbiological Societies

BackgroundPlants are constantly exposed to microbes, such as bacteria, fungi or viruses. However, disease is not the rule, and most plants are resistant to most microbes. To be successful, a pathogen must overcome constitutive defenses or suppress induced defenses. Our group previously demonstrated that cyclic-(1,2)-glucan (CG), a polysaccharide synthesized by Xanthomonas campestris pv.campestris, suppresses the accumulation of callose deposition, as well as the local and systemic expression of PR1, a defense-related gene associated with salicylic acid (SA) responses (The Plant Cell. 2007: 2077-2089).ObjectivesTo gain knowledge about the mechanism of CG in plants, we proposed to determine how CG suppresses flg22-induced plant defense and if CG is capable of bounding to a membrane receptor in Arabidopsis thaliana. MethodsFlagellin, the most important constituent of bacterial flagella, is an important elicitor of the immune response, activating plant defense. We performed bacterial infection assays with flagellin (flg22) and purified CG to see if CG is capable of impair flg22-induced defense. Additionally, we performed binding assays with Arabidopsis membranes and labeled 14C-CG. ConclusionsWe observed that CG suppresses partially the immunity elicited by flg22 in Arabidopsis thaliana. In addition, CG downregulates WRKY22, WRKY33 and MPK3 expression, early defense genes induced by this elicitor. The radiolabeled glucan, 14C-CG, bound specifically to wild-type plant extracts, suggesting the existence of direct interaction between CG and an still unknown Arabidopsis receptor. The present results shed light on the mechanism by which Xcc CG hijacks, at least partially, plant immune response.