The host exocyst complex is targeted by a conserved bacterial type III effector protein that promotes virulence

ABSTRACT For most Gram-negative bacteria, pathogenicity largely depends on the type-III secretion system that delivers virulence effectors into eukaryotic cells. The subcellular targets for the majority of these effectors remain unknown. Here, we show that Xanthomonas campestris , the causal agent of black rot disease, delivers the highly conserved effector XopP that interacts with host’s EXO70 protein. EXO70 is an essential component of the exocyst complex with a role in plant immunity. The XopP/EXO70 interaction is specific and inhibits exocyst-dependent exocytosis without activating a specific plant NLR receptor that guards EXO70. In this way, Xanthomonas efficiently inhibits the host’s PAMP-triggered immunity (PTI) by blocking exocytosis of PR1, callose deposition and the FLS2 immunity-receptor translocation to the plasma membrane, promoting successful infection.