The Transcription Factors HbWRKY29 and HbPTI5 cooperatively enhance rubber tree resistance to powdery mildew

Powdery mildew, caused by Erysiphe quercicola, is a major foliar disease that severely reduces the productivity of rubber tree (Hevea brasiliensis). Despite its economic importance, the transcriptional regulatory mechanisms underlying resistance to this pathogen remain unclear. In this study, two key transcription factors, HbWRKY29 and HbPTI5, were identified as cooperative regulators of defence responses against E. quercicola. Both HbWRKY29, a WRKY-family member, and HbPTI5, an AP2/ERF-type transcription factor, were rapidly induced during the early stages of infection. Yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and luciferase complementation imaging (LCI) assays confirmed that HbWRKY29 physically interacts with HbPTI5 in the nucleus. HbWRKY29 also binds a W-box element in the HbPTI5 promoter, activating its transcription and forming a positive feedback loop to amplify immune signalling. Co-expression of these two factors induced hypersensitive response (HR)-like cell death and H₂O₂ accumulation, enhancing resistance to E. quercicola, whereas silencing either gene compromised defence responses. Furthermore, HbPTI5 acts as a transcriptional activator of HbTLP1, a thaumatin-like protein belonging to the PR5 family with antifungal activity. Overexpression of HbTLP1 enhanced resistance to powdery mildew, while silencing this gene weakened immunity. Collectively, these findings reveal a WRKY-ERF transcriptional cascade in rubber tree, which integrates rapid HR activation with sustained antifungal defence. This study provides new insights into the molecular mechanisms of rubber tree immunity, identifying potential targets for breeding disease-resistant cultivars.