RsmA3 modulates RpoS through the RetS-Gac-Rsm signalling pathway in response to H O stress in the phytopathogen Pseudomonas syringae.

Reactive oxygen species are a fatal challenge to the plant pathogenic bacterium Pseudomonas syringae. In this study, we reveal that the global regulatory protein RsmA3 from the RetS-Gac/Rsm signalling pathway modulates RpoS in the early-log growth phase in the P. syringae wild-type strain MB03, thereby regulating oxidative tolerance to H O and ultimately affecting pathogenicity to the host plant. Following increased H O by external addition or endogenous induction by menadione, the resistance of the mutant strain ΔretS to H O is significantly enhanced due to rapid increases in the transcription of Rsm-related non-coding small RNAs (nc sRNAs), a sigma factor RpoS, and H O -detoxifying enzymes. Moreover, the ΔretS mutant is significantly less pathogenic in cucumber leaves. Seven Rsm-related nc sRNAs (namely, rsmZ, rsmY and rsmX ) show functional redundancy in the RetS-Gac-Rsm signalling pathway. External addition of H O stimulates increases in the transcription of both rsmY and rsmZ. Thus, we propose a regulatory model of the RetS-Gac-Rsm signalling pathway in P. syringae MB03 for the regulation of H O tolerance and phytopathogenicity in the host plant.