CabZIP53 is targeted by CaWRKY40 and act as positive regulator in pepper defense against Ralstonia solanacearum and thermotolerance

Abstract

Broad range transcriptional changes after pathogen invasion decide immune responses to these invaders. The responses of Capsicum annuum plants to bacterial pathogen Ralstonia solanacearum and high-temperature-high-humidity (HTHH) conditions are coordinated by different transcription factors. However, the basic molecular mechanism is not clear. The functions of different Capsicum annuum bZIP transcription factors (TFs) in plant defense are obscured in spite of their great importance in responses to biotic stress. In present study, we functionally characterized a nucleus localized bZIP TF, CabZIP53, for its involvement in pepper defense to Ralstonia solanacearum inoculation (RSI) and HTHH. CabZIP53 is transcriptionally induced in pepper plants by RSI or HTHH. Loss of function studies by Virus-induced gene silencing (VIGS) of CabZIP53 showed significantly impaired pepper basal defense against RSI, increased pathogen growth, decreased HTHH tolerance and hampered expression of immunity- and thermotolerance-associated marker genes such as CaHIR1, CaPR1, CaNPR1, CaABR1, CabZIP63 and CaHSP24 respectively. Similarly, transient overexpression of CabZIP53 mediated by Agrobacterium cells harbouring 35S::CabZIP53-HA in pepper leaves induced hypersensitive response (HR)-like mimic cell death, H2O2 accretion and up-regulated the immunity/thermotoelrance associated marker genes as well as CaWRKY6 CaWRKY40, CabZIP63 and CaCDPK15. qRT-PCR analysis revealed that CabZIP53 makes a positive feed back loop with CaWRKY40. In parallel, we determined that CabZIP53 was regulated directly by CaWRKY40 but indirectly by CaWRKY6. On the whole, our results suggest that CabZIP53 positively regulates plant immunity to RSI and tolerance against HTHH by means of transcriptional networks and positive feedback loops involving CaWRKY40.