WRKY Transcription Factor 9 Is a Positive Regulator in Responding to Root Rot Pathogen .

(Burk) F.H. Chen is a rare and valuable Chinese herb, but root rot mainly caused by severely affects the yield and quality of herbal materials. In this study, we isolated 30 WRKY transcription factors (TFs), which were divided into three groups (I, II, and III) on the basis of a phylogenetic analysis. The expression levels of 10 genes, including , in roots increased in response to a methyl jasmonate (MeJA) treatment and the following infection. Additionally, PnWRKY9 was functionally characterized. The PnWRKY9 protein was localized to the nucleus. The overexpression of in tobacco () considerably increased the resistance to , whereas an RNAi-mediated decrease in the expression level in leaves increased the susceptibility to . The RNA sequencing and hormone content analyses of -overexpression tobacco revealed that PnWRKY9 and the jasmonic acid (JA) signaling pathway synergistically enhance disease resistance. The PnWRKY9 recombinant protein was observed to bind specifically to the W-box sequence in the promoter of a JA-responsive and resistance-related defensin gene (). A yeast one-hybrid assay indicated that PnWRKY9 can activate the transcription of . Furthermore, a co-expression assay in tobacco using β-glucuronidase (GUS) as a reporter further verified that PnWRKY9 positively regulates expression. Overall, in this study, we identified WRKY TFs and demonstrated that PnWRKY9 positively affects plant defenses against the root rot pathogen. The data presented herein provide researchers with fundamental information regarding the regulatory mechanism mediating the coordinated activities of WRKY TFs and the JA signaling pathway in responses to the root rot pathogen.