AUTHOR=Gao Ge , Jin Ruibing , Liu Di , Zhang Xin , Sun Xiaomei , Zhu Pengfang , Mao Hongyu 

TITLE=CmWRKY15-1 Promotes Resistance to Chrysanthemum White Rust by Regulating CmNPR1 Expression

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.865607

DOI=10.3389/fpls.2022.865607

ISSN=1664-462X

ABSTRACT=<p>Chrysanthemum white rust (CWR), a disease caused by the fungus <italic>Puccinia horiana</italic> Henn., seriously impairs the production and ornamental value of chrysanthemums. We previously isolated the disease-resistance gene <italic>CmWRKY15-1</italic> from the chrysanthemum and generated <italic>CmWRKY15-1</italic> transgenic plants. Here, we determined that <italic>CmWRKY15-1</italic>-overexpressing lines of the susceptible cultivar ‘Jinba’ show higher defensive enzyme activity and lower H<sub>2</sub>O<sub>2</sub> levels than a wild type after inoculation with <italic>P. horiana</italic>, indicating that <italic>CmWRKY15-1</italic> positively regulates plant responses to <italic>P. horiana</italic>. To further explore the mechanism underlying this effect, we performed RNA sequencing using the leaves of wild-type and <italic>CmWRKY15-1</italic>-RNA interference lines of the resistant cultivar ‘C029’ after treatment with <italic>P. horiana</italic>. We identified seven differentially expressed genes in the salicylic acid (SA) pathway, including <italic>CmNPR1</italic> (<italic>Non-expressor of pathogenesis-related genes 1</italic>), encoding an important regulator of this pathway. We isolated the <italic>CmNPR1</italic> promoter by hiTAIL-PCR and predicted that it contains pathogen-induced W-box elements. The promoter region of <italic>CmNPR1</italic> was activated by <italic>P. horiana</italic> in a β-glucuronidase activity assay. Yeast one-hybrid assays showed that CmWRKY15-1 binds to the <italic>CmNPR1</italic> 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 <italic>P. horiana</italic> through the SA pathway. These findings shed light on the mechanism underlying resistance to CWR.</p>