CmWRKY15-1 Promotes Resistance to Chrysanthemum White Rust by Regulating CmNPR1 Expression
Ge Gao, Ruibing Jin, Di Liu, Xin Zhang, Xiaomei Sun, Pengfang Zhu, Hongyu Mao
Abstract
Chrysanthemum white rust (CWR), a disease caused by the fungus Puccinia horiana Henn., seriously impairs the production and ornamental value of chrysanthemums. We previously isolated the disease-resistance gene CmWRKY15-1 from the chrysanthemum and generated CmWRKY15-1 transgenic plants. Here, we determined that CmWRKY15-1 -overexpressing lines of the susceptible cultivar ‘Jinba’ show higher defensive enzyme activity and lower H 2 O 2 levels than a wild type after inoculation with P. horiana , indicating that CmWRKY15-1 positively regulates plant responses to P. horiana . To further explore the mechanism underlying this effect, we performed RNA sequencing using the leaves of wild-type and CmWRKY15-1 -RNA interference lines of the resistant cultivar ‘C029’ after treatment with P. horiana . We identified seven differentially expressed genes in the salicylic acid (SA) pathway, including CmNPR1 ( Non-expressor of pathogenesis-related genes 1 ), encoding an important regulator of this pathway. We isolated the CmNPR1 promoter by hiTAIL-PCR and predicted that it contains pathogen-induced W-box elements. The promoter region of CmNPR1 was activated by P. horiana in a β-glucuronidase activity assay. Yeast one-hybrid assays showed that CmWRKY15-1 binds to the CmNPR1 promoter region to regulate its expression. Finally, we confirmed the interaction between CmWRKY15-1 and CmNPR1 in a bimolecular fluorescence complementation assay. We propose that CmWRKY15-1 interacts with CmNPR1 to activate the expression of downstream pathogenesis-related genes that enhance resistance to P. horiana through the SA pathway. These findings shed light on the mechanism underlying resistance to CWR.