The Type III Effector XopL(Xcc) in Xanthomonas campestris pv. campestris Targets the Proton Pump Interactor 1 and Suppresses Innate Immunity in Arabidopsis.

Xanthomonas campestris pathovar campestris (Xcc) is a significant phytopathogen causing black rot disease in crucifers. Xcc injects a variety of type III effectors (T3Es) into the host cell to assist infection or propagation. A number of T3Es inhibit plant immunity, but the biochemical basis for a vast majority of them remains unknown. Previous research has revealed that the evolutionarily conserved XopL-family effector XopL(Xcc) inhibits plant immunity, although the underlying mechanisms remain incompletely elucidated. In this study, we identified proton pump interactor (PPI1) as a specific virulence target of XopL(Xcc) in Arabidopsis. Notably, the C-terminus of PPI1 and the Leucine-rich repeat (LRR) domains of XopL(Xcc) are pivotal for facilitating this interaction. Our findings indicate that PPI1 plays a role in the immune response of Arabidopsis to Xcc. These results propose a model in which XopL(Xcc) binds to PPI1, disrupting the early defense responses activated in Arabidopsis during Xcc infection and providing valuable insights into potential strategies for regulating plasma membrane (PM) H(+)-ATPase activity during infection. These novel insights enhance our understanding of the pathogenic mechanisms of T3Es and contribute to the development of effective strategies for controlling bacterial diseases.