Delicate tuning of H2O2 by salicylic acid, catalase 2, and AtSAP5 incites plant immunity

Abstract

Salicylic acid (SA) triggers plant immunity through redox state changes, initially oxidizing and then reducing. SA binds and inhibits the H2O2-scavenging enzyme catalase 2 (CAT2), promoting an initial oxidative state. However, a reduced state is crucial for a robust immune response. In Arabidopsis, the SA-induced A20/AN1 zinc finger protein, AtSAP5, competes with SA for CAT2 binding, maintaining CAT2 activity. This reduces H2O2 levels and prevents CAT2 degradation through inhibition of H2O2-induced autophagy formation, which forms a positive feedback loop to CAT2 accumulation. Consequently, cells shift to a more reduced state, activating immune responses. Our findings reveal a nuanced regulatory mechanism through which H2O2 levels are controlled by SA with cross-kingdom conserved proteins AtSAP5 and CAT2, managing redox states and plant immunity.