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.