A conserved double-W box in the promoter of CaWRKY40 mediates autoregulation during response to pathogen attack and heat stress in pepper

CaWRKY40 was previously found to be transcriptionally up-regulated by Ralstonia solanacearum inoculation (RSI) or heat stress (HS), but the underlying mechanism remains unknown. Herein, we report that a double-W box-element (DWE) in the promoter of CaWRKY40 is critical for these responses. The upstream W box unit WI of this composite element is crucial for preferential binding by CaWRKY40 and responsiveness to RSI or HS. DWE-driven CaWRKY40 can be transcriptionally and nonspecifically regulated by itself and by CaWRKY58 and CaWRKY27. The DWE was also found in the promoters of CaWRKY40 orthologs, including AtWRKY40, VvWRKY40, GmWRKY40, CplWRKY40, SaWRKY40, SpWRKY40, NtWRKY40, and NaWRKY40. DWE (AtWRKY40) was analogous to DWE (CaWRKY40) by responding to RSI or HS and AtWRKY40 expression. These data suggest that a conserved response of plants to pathogen infection or HS is probably mediated by binding of the DWE by WRKY40.

Automated summary

The study reveals that the DWE element in the promoter of CaWRKY40 is critical for responses to Ralstonia solanacearum inoculation or heat stress, with preferential binding by CaWRKY40 and regulation by CaWRKY58 and CaWRKY27. Additionally, the presence of DWE in orthologous promoters of other WRKY40 genes indicates a conserved response mechanism to pathogen infection or heat stress mediated by WRKY40 binding to DWE.