| CaWRKY40 is previously known as a positive regulator in the response of pepper(Capsicum annuum) to Ralstonia solanacearum inoculation (RSI) or high temperature-high humidity (HTHH), but the underlying mechanism remains elusive. Herein, we report that CabZIP63, a pepper bZIP family member, participates in this process by regulating the expression of CaWRKY40. CabZIP63 was found to localize in the nuclei by subcellular localization assay, be up-regulated by RSI or HTHH, bind to promoters of both CabZIP63 (pCabZIP63) and CaWRKY40 (pCaWRKY40) by Chromatin Immunoprecipitation (ChIP), and activate pCabZIP63-and pCaWRKY40-driven β-glucuronidase (GUS) expression in a C- or G-box-dependent manner. Silencing of CabZIP63 by virus-induced gene silencing (VIGS) in pepper plants significantly attenuated their resistance to RSI and tolerance to HTHH, accompanied by down-regulation of immunity-or thermotolerance-associated CaPR1, CaNPR1, CaDEF1. and CaHSP24. Hypersensitive response-mediated cell death and expression of the tested immunity-and thermotolerance-associated marker genes were induced by transient overexpression (TOE) of CabZIP63 in pepper leaves, but decreased by that of CabZIP63-SRDX. Additionally, binding of CabZIP63 to pCaWRKY40 was up-regulated by RSI or HTHH, and the transcript level of CaWRKY40 and binding of CaWRKY40 to the promoters of CaPR1, CaNPR1, CaDEFl and CaHSP24 were up-regulated by TOE of CabZIP63 in pepper leaves. On the other hand, CabZIP63 was also up-regulated transcriptionally by TOE of CaWRKY40 in pepper leaves. The data suggest collectively that CabZIP63 directly or indirectly regulates the expression of CaWRKY40 at both the transcriptional and post-transcriptional level, forming a positive feedback loop with CaWRKY40 during pepper’s response to RSI or HTHH. Altogether, our data will help to elucidate the underlying mechanism of crosstalk between pepper’s response to RSI and HTHH. |
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