ZmWRKY79 positively regulates maize phytoalexin biosynthetic gene expression and is involved in stress response

Maize (Zea mays) accumulates maize terpenoid phytoalexins (MTPs), kauralexins and zealexins in response to various elicitations. Although the key biosynthetic genes for these have been characterized, the regulatory mechanism remains unclear. Through co-correlation analysis, a transcription factor (TF), ZmWRKY79, was identified as highly correlated with expression of MTP biosynthetic genes. Gene expression analysis indicated that ZmWRKY79 was induced by Fusarium graminearum infection, phytohormone treatment, and multiple stresses. Overexpression of ZmWRKY79 in maize protoplasts increased expression of genes involved in MTP biosynthesis, jasmonic acid and ethylene pathways, and scavenging of reactive oxygen species (ROS). Subsequent transient RNAi in maize protoplast compromised the induction of MTP biosynthetic genes by jasmonic acid and ethylene combined treatment. Such regulation was further demonstrated to be dependent on a W-box or WLE cis-element. Transient overexpression of ZmWRKY79 in tobacco conferred resistance against Rhizoctonia solani infection through reducing ROS production. Our results indicate that MTP biosynthesis is regulated by the common transcription factor ZmWRKY79, which plays a broad role as a potential master regulator in stress response through involvement in phytohormone metabolism or signaling and ROS scavenging.