TcWRKY75 participates in pyrethrin biosynthesis by positively regulating the expression of TcCHS, TcAOC, and TcGLIP in Tanacetum cinerariifolium

Pyrethrin, a combination of six esters, is a well-known kind of natural insecticide extracted primarily from the flowers of Tanacetum cinerariifolium. Yet the regulatory network of the pyrethrin biosynthetic pathway remains unclear. In this study TcWRKY75 was cloned. This gene exhibited an expression pattern similar to that of some genes in the pyrethrin biosynthesis pathway at different stages of flower development. Transient overexpression of TcWRKY75 in T. cinerariifolium significantly increased its pyrethrin content; conversely, transient silencing of TcWRKY75 decreased its pyrethrin content. Further, in the TcWRKY75-overexpressing transgenic hairy-root lines, the expression levels of TcCHS and TcAOC were both significantly upregulated. Follow-up investigation revealed that the protein encoded by TcWRKY75 positively regulated the expression of TcCHS, TcGLIP, and TcAOC by directly binding to the W-box in their promoters. These results demonstrate that TcWRKY75 functions as a positive regulator in the pyrethrin biosynthesis pathway.