The functional and structural characterization ofXanthomonas campestrispv.campestriscore effector XopP revealed a new kinase activity

Abstract

SummaryThe exocyst complex subunit protein Exo70B1 plays a crucial role in a variety of cell mechanisms including immune responses against pathogens. The calcium dependent kinase 5 (CPK5) ofArapidopsis thaliana, phosphorylatesAtExo70B1 upon functional disruption. We previously reported that, theXanthomonas campestrispv.campestiseffector XopP, compromises Exo70B1 and bypasses the host’s hypersensitive response (HR), in a way that is still unclear.Herein we designed an experimental approach based on biophysical, biochemical and molecular assays, based on structural and functional predictions, as well as, utilizing Aplhafold and DALI online servers respectively, in order to characterize thein vivo XccXopP function.The interaction betweenAtExo70B1 andXccXopP is very stable in high temperatures, while theAtExo70B1 appeared to be phosphorylated atXccXopP expressing transgenicArabidopsis.XccXopP reveals similarities with known mammalian kinases, and phosphorylatesAtExo70B1 at Ser107, Ser111, Ser248, Thr309 and Thr364. Furthermore,XccXopP protectsAtExo70B1 from AtCPK5 phosphorylation.Together these findings show that,XccXopP is an effector, which not only functions as a novel serine/threonine kinase upon its host’s protein targetAtExo70B1, but also protects the latter from the innate AtCPK5 phosphorylation, to bypass the host’s immune responses.