The VvBZR1-VvHY5 Module Integrates Brassinosteroid and Light Signaling to Regulate Anthocyanin Biosynthesis in Grape

While both brassinosteroid (BR) and light are known to promote anthocyanin synthesis in grape berries, the mechanism underlying their synergistic action remains elusive. Here, we demonstrated a synergistic relationship between the BR and light signaling pathways in promoting anthocyanin accumulation and identify VvBZR1 and VvHY5 as key components of this regulatory network. Our physiological and molecular data showed that VvBZR1 and VvHY5 activate key genes in anthocyanin biosynthesis, such as VvCHS1 and VvUFGT. Furthermore, overexpression of VvBZR1 or VvHY5 increased anthocyanin content in both grape calli and Arabidopsis stems, and this effect was synergistically enhanced by combined light and 24-Epibrassinolide (EBR) treatment. Mechanistically, VvBZR1 binds to the E-box element in the VvUFGT promoter to activate its transcription, while VvHY5 binds to the G-box element in the VvCHS1 promoter. Yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and co-immunoprecipitation (Co-IP) assays confirmed that VvBZR1 and VvHY5 interact both in vivo and in vitro. Notably, a dual-luciferase (LUC) assay revealed that VvBZR1 and VvHY5 direct interaction reciprocally enhances their transcriptional activation capabilities. In summary, our findings establish the VvBZR1-VvHY5 module as a critical positive regulator that integrates BR and light signaling to promote anthocyanin synthesis in grape.