Rapeseed WRKY53 regulates pattern-triggered immunity (PTI) through modulating the transcription of salicylic acid biosynthetic genes

Plants have developed a few major immunity systems to combat extraneous pathogens. These systems include pattern-triggered immunity (namely PTI, basal resistance), effector-triggered immunity (called ETI) and systemic acquired resistance (called SAR). Quite a few members of WRKY transcription factor family are famous for their roles in regulating plant immunity through transcriptional reprogramming in Arabidopsis and other plants. Among these, AtWRKY53 plays a pivotal role in leaf senescence and also positively regulate basal resistance against the bacterial pathogen Pseudomonas syringae. However, the mechanism through which WRKY53 mediates this basal resistance remains elusive. Furthermore, the function of WRKY53 in rapeseed plants during Pst DC3000 infection is not yet known. In the current work, the induction of BnaWRKY53 by salicylic acid (SA) led us to hypothesize that BnaWRKY53 might regulate basal resistance through modulation of SA-related pathways. We further identified that BnaWRKY53 not only enhances the resistance of plants towards P. syringae but also regulates SA biosynthetic genes such as IsoChorismate Synthase1 (ICS1) and avrPphB Susceptible 3 (PBS3), which were confirmed by both in vitro EMSA and in vivo ChIP-qPCR assays. Moreover, the production of SA strengthens this response by promoting more transcription of BnaWRKY53 to positively feedback the function of BnaWRKY53. In addition, BnaWRKY53 is suppressed when P. syringae carrying the AvrRpt2 gene, an avirulent strain, is inoculated. Collectively, our results indicate that BnaWRKY53 functions in PTI but might be suppressed by the effector AvrRpt2. This study has not only uncovered the mechanism of WRKY53 in regulating defense response but also provides an alternative for breeding elite cultivar.