HmWER-like modulates branch-specific anthocyanin flux and floral pigmentation in Hydrangea macrophylla.

Anthocyanins are key flavonoid metabolites determining floral pigmentation, and their biosynthesis is tightly regulated through coordinated transcriptional and metabolic processes. Although R2R3-MYB transcription factors are well recognized as central regulators of anthocyanin biosynthesis, the roles of WER-like MYB members in anthocyanin metabolism remain largely unknown. In this study, we identified and functionally characterized HmWER-like, a WER/MYB114-like R2R3-MYB transcription factor from Hydrangea macrophylla, and investigated its role in anthocyanin metabolism and floral pigmentation. HmWER-like exhibited preferential expression during early floral development and was predominantly localized to the nucleus. Correlation analysis during hydrangea flower development revealed that HmWER-like expression was negatively associated with several late anthocyanin biosynthetic genes and anthocyanin accumulation. In contrast, heterologous overexpression of HmWER-like in tobacco resulted in visibly lighter flowers despite a significant increase in total anthocyanin content. Metabolomic profiling further revealed pronounced changes in anthocyanin composition, characterized by increased accumulation of cyanidin-derived anthocyanins together with reduced levels of delphinidin-derived anthocyanins. Transcriptomic profiling revealed extensive transcriptional reprogramming affecting flavonoid biosynthesis, hormone signaling, and stress-responsive pathways. Integrated transcriptomic and metabolomic analyses uncovered coordinated changes in gene expression and metabolite accumulation. Yeast one-hybrid assays further demonstrated that HmWER-like associates with the HmDFR promoter. Collectively, these findings suggest that HmWER-like as a non-canonical MYB regulator of anthocyanin metabolism through coordinated transcriptional regulation and branch-specific redistribution of anthocyanin metabolic flux, thereby modulating anthocyanin composition and floral pigmentation. This study expands the functional repertoire of WER-like MYB transcription factors and provides new insights into the regulatory mechanisms underlying flower coloration in ornamental plants.