The HY5-NPR1 Module Governs Light-dependent Virulence of AvrPtoB

Light is essential for plant development, yet its influence on pathogen virulence and host immunity remains poorly understood. Here, we showed that the type III effector AvrPtoB from Pseudomonas syringae pv. tomato DC3000 exhibited virulence exclusively under light conditions, but this effect was completely abolished in darkness. This light-dependent regulation was controlled by transcription factor HY5, a central regulator of photomorphogenesis. AvrPtoB directly interacts with HY5 in the nucleus, facilitating its ubiquitination and subsequent degradation. Genetic disruption of HY5 completely eliminated AvrPtoB-induced susceptibility and compromised plant immunity under light. HY5 enhanced plant immunity by binding to promoters of defense-related genes, activating their expression, and stabilizing NPR1 by inhibiting NPR3-mediated degradation. The light-dependent virulence of AvrPtoB and HY5-mediated immunity were both dependent on NPR1. Our findings elucidate a previously uncharacterized mechanism through which light modulates bacterial virulence and plant immunity via the HY5-NPR1 module, providing new paradigm for understanding light-pathogen-host interactions. Total RNA was extracted from leaves of 3-week-old Arabidopsis infiltrated with DC3000 at 0 or 24 hours post infiltration using TRIzol® Reagent