The A rabidopsis oligopeptidases TOP 1 and TOP 2 are salicylic acid targets that modulate SA ‐mediated signaling and the immune response

Summary Salicylic acid ( SA ) is a small phenolic molecule with hormonal properties, and is an essential component of the immune response. SA exerts its functions by interacting with protein targets; however, the specific cellular components modulated by SA and critical for immune signal transduction are largely unknown. To uncover cellular activities targeted by SA , we probed Arabidopsis protein microarrays with a functional analog of SA. We demonstrate that thimet oligopeptidases ( TOP s) constitute a class of SA ‐binding enzymes. Biochemical evidence demonstrated that SA interacts with TOP s and inhibits their peptidase activities to various degrees both in vitro and in plant extracts. Functional characterization of mutants with altered TOP expression indicated that TOP 1 and TOP 2 mediate SA ‐dependent signaling and are necessary for the immune response to avirulent pathogens. Our results support a model whereby TOP 1 and TOP 2 act in separate pathways to modulate SA ‐mediated cellular processes.