Inoculation of ACC deaminase producing endophytic bacteria down-regulates ethylene induced PR-signaling in red pepper (Capsicum annum L.) under salt stress.

Pathogenesis related (PR) signaling plays multiple roles in plant development under abiotic and biotic stress conditions and is regulated by a plethora of plant physiological as well as external factors. Here, our study was conducted to evaluate the role of an ACC deaminase producing endophytic bacteria in regulating ethylene mediated PR signaling in red pepper plants under salt stress. We also evaluated the efficiency of the bacteria in down-regulating the PR signaling for efficient colonization and persistence in the plant endosphere. We used a characteristic endophyte, Methylobacterium oryzae CBMB20 and it's ACC deaminase knockdown mutant (acdS - ). The wild type M. oryzae CBMB20 was able to decrease ethylene emission by 23% compared to the non-inoculated and acdS - M. oryzae CBMB20 inoculated plants under salt stress. The increase in ethylene emission resulted in enhanced hydrogen peroxide concentration, phenylalanine ammonia lyase activity, β-1,3 glucanase activity, and expression profiles of WRKY, CaPR1 and CaPTI1 genes that are typical salt stress and PR signaling factors. Furthermore, the inoculation of both the bacterial strains had shown induction of PR signaling under normal conditions during the initial inoculation period. However, wild type M. oryzae CBMB20 was able to down-regulate the ethylene mediated PR signaling under salt stress and enhance plant growth and stress tolerance. Collectively, ACC deaminase producing endophytic bacteria down-regulate the salt stress mediated PR signaling in plants by regulating the stress ethylene emission levels and this suggests a new paradigm in efficient colonization and persistence of ACC deamianse producing endophytic bacteria for better plant growth and productivity.