MnWRKY22 Mediates Tissue-Specific Resveratrol Biosynthesis through Coordinated Regulation of the Stilbene Synthase Gene Cluster in Mulberry

Resveratrol, a pharmaceutically significant stilbenoid accumulates in mulberry roots. To elucidate the molecular mechanism underlying this tissue-specific biosynthesis, we systematically analyzed the stilbene synthase (STS) gene family in mulberry. Our investigation revealed that nine out of ten MnSTS genes form tandem repeats in a single genomic cluster. Co-expression clustering and phylogenetic analysis implied that these genes undergo purifying selection, resulting in highly consistent co-expression patterns across tissues, with particularly specific high expression in roots and calli. Subsequent weighted gene co-expression network analysis (WGCNA) identified the transcription factor (TF) MnWRKY22 as a key regulatory candidate. Functional validation confirmed that MnWRKY22 is specifically expressed in roots and calli and directly binds to W-box elements in all MnSTS promoters, thereby activating their transcription. Suppression of MnWRKY22 expression significantly reduced both MnSTS transcript levels and resveratrol accumulation, while its overexpression enhanced MnSTS expression and resveratrol production. Notably, overexpression of MnWRKY22 in leaves ectopically activated otherwise silent MnSTSs, enabling de novo resveratrol synthesis. This study reveals the coordinated evolutionary characteristics of the MnSTS gene family and establishes MnWRKY22 as a unified regulator of tissue-specific resveratrol accumulation in mulberry. These findings provide a foundation for enhancing resveratrol production through metabolic engineering approaches.