pv. Effector HopAU1 Interacts with Calcium-Sensing Receptor to Activate Plant Immunity.

Kiwifruit canker, caused by pv. (), is a destructive pathogen that globally threatens the kiwifruit industry. Understanding the molecular mechanism of plant-pathogen interaction can accelerate applying resistance breeding and controlling plant diseases. All known effectors secreted by pathogens play an important role in plant-pathogen interaction. However, the effectors in and their function mechanism remain largely unclear. Here, we successfully identified a T3SS effector HopAU1 which had no virulence contribution to , but could, however, induce cell death and activate a series of immune responses by agroinfiltration in , including elevated transcripts of immune-related genes, accumulation of reactive oxygen species (ROS), and callose deposition. We found that HopAU1 interacted with a calcium sensing receptor in (NbCaS) as well as its close homologue in kiwifruit (AcCaS). More importantly, silencing by RNAi in greatly attenuated HopAU1-triggered cell death, suggesting CaS is a crucial component for HopAU1 detection. Further researches showed that overexpression of in significantly enhanced plant resistance against and , indicating that serves as a promising resistance-related gene for disease resistance breeding. We concluded that HopAU1 is an immune elicitor that targets CaS to trigger plant immunity.