P-179 - Vesicle cargo profiling to uncover HopM1-mediated apoplast water imbalance and immune suppression in Arabidopsis

Bacterial type III effector proteins play a critical role in mediating plant-pathogen interactions. In Pseudomonas syringae, the highly conserved HopM1 and AvrE effectors promote virulence by inducing “water-soaked” apoplastic lesions to support bacterial proliferation in leaves. HopM1 interacts and/or degrades several HopM1-interacting (MIN) Arabidopsis proteins, including MIN7, an ARF-GEF that regulates the vesicle trafficking pathway. Co-IP experiments revealed that MIN7 is in a complex with a tetratricopeptide repeat protein named HYPERSENSITIVE TO LATRUNCULIN B1 (HLB1).  Both MIN7 and HLB1 localized to the trans-Golgi network/early endosome and their T-DNA mutants partially phenocopied the apoplastic water- and immune-modulating phenotypes of HopM1. Additionally, cad1^S205F, a point mutant of the CONSTITUTIVELY ACTIVATED CELL DEATH (CAD1) gene, initially identified from a genetic screen for dysbiosis in our lab, also partially phenocopied the phenotypes of HopM1. As the MIN7-HLB1-containing complex plays a role in both apoplastic water content homeostasis and immune signalling, our research aims to identify the cargo of MIN7/HLB1-associated vesicles. This will contribute to the fundamental knowledge of the poorly dissected plant endogenous mechanism of maintaining a proper apoplastic water content through a MIN7-HLB1-CAD1 genetic framework and of how pathogens disrupt this mechanism to promote infection.