CsWRKY40 enhances citrus resistance to Asian citrus psyllid by promoting CsUGT89B1-mediated quercetin-3-O-glucoside biosynthesis.

The Asian citrus psyllid (Diaphorina citri, ACP) is the primary vector of citrus Huanglongbing (HLB), the most devastating disease affecting the citrus industry. The effective management of ACP is crucial for preventing the spread of HLB. An environmentally friendly approach to pest control is the genetic enhancement of plants for improved insect resistance. WRKY transcription factors are known to play vital roles in plant defense against herbivores; however, their specific function in citrus resistance to ACP remains unexplored. This study demonstrated that the ACP-induced expression of CsWRKY40 plays a positive role in enhancing citrus resistance to ACP infestation. This was confirmed through both stable overexpression and virus-induced gene silencing (VIGS) assays in lemon plants (Citrus limon). Metabolomic analysis revealed that the overexpression of CsWRKY40 substantially affected flavonoids, particularly flavonol glycosides. Notably, the quercetin-3-O-glucoside content in CsWRKY40-overexpressing plants was significantly higher than in wild-type (WT) plants after ACP infestation, as confirmed by LC-MS analysis. Furthermore, the study revealed that CsWRKY40 directly binds to and activates the CsUGT89B1 promoter, driving the accumulation of the defense-related metabolite quercetin-3-O-glucoside, thereby enhancing resistance to ACP. Finally, CsERF1B was identified as a direct upstream transcriptional activator of CsWRKY40, which contributed to citrus resistance to ACP by activating the CsWRKY40-mediated defense pathway. These findings provide novel insights into the molecular mechanisms underlying CsWRKY40-mediated citrus defense against ACP and offer potential genetic targets for improving strategies to manage ACP and HLB in citrus cultivation.