Roles of Plant Hormones in Plant Resistance and Susceptibility to Pathogens

Abstract

Plants and animals trigger an innate immune response upon perception of pathogen-associated molecular patterns (PAMPs) such as flagellin. In Arabidopsis, flagellin perception elevates resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), although the molecular mechanisms involved remain elusive. A flagellin-derived peptide transiently enhances the accumulation of a plant microRNA that directs degradation of mRNA for TIR1, an F-box auxin receptor. The resulting repression of auxin signaling effectively restricts Pst DC3000 growth, implicating this previously unsuspected miRNA-mediated switch in bacterial disease resistance. These data suggest that elevation of auxin levels constitute a bacterial pathogenicity strategy that is suppressed during the innate immune response to PAMPs. In a separate work, we showed that DELLA proteins, which are normally associated with gibberellin responses, play a role in the balance between salicylic acid and jasmonic acid-mediated defense signaling pathways. DELLA loss-of-function mutants show reduced growth inhibition in response to flg22, enhanced susceptibility to necrotrophic pathogens, and enhanced resistance to Pst DC3000.