Cyclic-(1,2)-glucan from Xanthomonas campestris campestris suppresses Arabidopsis thaliana immunity by modulating flagellin induced defense

LAILA TOUM; VERÓNICA DE PINO; GUSTAVO E. GUDESBLAT; ADRIÁN A. VOJNOV

Foz do Iguaçú

Congreso; 11th International Plant Molecular Biology Congress; 2015

IPMB

Plants are constantly exposed to microbes, such as bacteria, fungi or viruses. However, diseaseis not the rule, and most plants are resistant to most microbes. To be successful, a pathogenmust overcome constitutive defenses or suppress induced defenses. Our group previouslydemonstrated that cyclic-(1,2)-glucan (CG), a polysaccharide synthesized by Xanthomonascampestris pv.campestris (Xcc), suppresses the accumulation of callose deposition, as well asthe local and systemic expression of PR1, a defense-related gene associated with salicylic acid(SA) responses (The Plant Cell. 2007: 2077-2089). Flagellin (flg22), the most importantconstituent of bacterial flagella, is an important elicitor of the immune response, activatingplant defense. To gain knowledge about the mechanism of CG in plants, we proposed todetermine how CG suppresses flg22-induced plant defense and if CG is capable of bounding to amembrane receptor in Arabidopsis thaliana. We performed bacterial infection assays with flg22and purified CG to see if CG is capable of impair flg22-induced defense. Additionally, weperformed binding assays with Arabidopsis membranes and labeled 14C-CG. We observed thatCG suppresses partially the immunity elicited by flg22 in Arabidopsis thaliana. In addition, CGdownregulates WRKY22, WRKY33 and MPK3 expression, early defense genes induced by thiselicitor. The radiolabeled glucan, 14C-CG, bound specifically to wild-type plant extracts,suggesting the existence of direct interaction between CG and a still unknown Arabidopsisreceptor. The present results shed light on the mechanism by which Xcc CG hijacks, at leastpartially, plant immune response.