Chrysanthemum white rust disease, which is caused by the fungus Puccinia horiana Henn., severely reduces the ornamental quality and yield chrysanthemum. WRKY
transcription factors function in the
disease-resistance response in a variety of plants; however, it is unclear whether members of this family improve resistance to white rust disease in chrysanthemum. In this study, using PCR, we isolated a WRKY15 homologous gene, CmWRKY15-1, from the resistant chrysanthemum cultivar C029. Real-time quantitative PCR (RT-qPCR) revealed that CmWRKY15-1 exhibited differential expression patterns between the immune cultivar C029 and the susceptible cultivar Jinba upon P. horiana
infection. In addition,
salicylic acid (SA) treatment strongly induced CmWRKY15-1 expression. Overexpression of CmWRKY15-1 in the chrysanthemum-susceptible cultivar Jinba increased tolerance to P. horiana
infection. Conversely, silencing CmWRKY15-1 via RNA interference (RNAi) in C029 increased sensitivity to P. horiana
infection. We also determined that P. horiana
infection increased both the endogenous SA content and the expression of
salicylic acid biosynthesis genes in CmWRKY15-1-overexpressing plants, whereas CmWRKY15-1 RNAi plants exhibited the opposite effects under the same conditions. Finally, the transcript levels of pathogenesis-related (PR) genes involved in the SA pathway were positively associated with CmWRKY15-1 expression levels. Our results demonstrated that CmWRKY15-1 plays an important role in the resistance of chrysanthemum to P. horiana by influencing SA signaling.