CaASR1 promotes salicylic acid- but represses jasmonic acid-dependent signaling to enhance the resistance of Capsicum annuum to bacterial wilt by modulating CabZIP63.

Abstract

CabZIP63 acts positively in the resistance of pepper (Capsicum annuum) to bacterial wilt caused by Ralstonia solanacearum or tolerance to high-temperature/high-humidity stress, but it is unclear how CabZIP63 achieves its functional specificity against R. solanacearum. Here, CaASR1, an abscisic acid-, stress-, and ripening-inducible protein of C. annuum, was functionally characterized in modulating the functional specificity of CabZIP63 during the defense response of pepper to R. solanacearum. In pepper plants inoculated with R. solanacearum, CaASR1 was up-regulated before 24 h post-inoculation but down-regulated thereafter, and was down-regulated by high-temperature/high-humidity stress. Data from gene silencing and transient overexpression experiments indicated that CaASR1 acts as a positive regulator in the immunity of pepper against R. solanacearum and a negative regulator of thermotolerance. Pull-down combined with mass spectrometry revealed that CaASR1 interacted with CabZIP63 upon R. solanacearum infection; the interaction was confirmed by microscale thermophoresis and bimolecular fluorescence complementation assays.CaASR1 silencing upon R. solanacearum inoculation repressed CabZIP63-mediated transcription from the promoters of the salicylic acid (SA)-dependent CaPR1 and CaNPR1, but derepressed transcription of CaHSP24 and the jasmonic acid (JA)-dependent CaDEF1. Our findings suggest that CaASR1 acts as a positive regulator of the defense response of pepper to R. solanacearum by interacting with CabZIP63, enabling it to promote SA-dependent but repress JA-dependent immunity and thermotolerance during the early stages of infection.