Effect of brassinosteroids on grape berry ripening by coordinating transcriptomic and metabolic analysis

Brassinosteroids (BRs) are essential for the regulation of plant growth, development, and stress responses. However, a comprehensive understanding of the transcriptional regulatory network governed by BRs that orchestrates grape berry ripening remains limited. Herein, the application of exogenous epibrassinolide (EBR) increased endogenous BRs content while down-regulating the expression of BRs biosynthetic genes, indicating feedback transcriptional regulation of BRs biosynthesis. EBR treatment accelerated coloring and enhanced anthocyanin accumulation, which was closely associated with the up-regulation of anthocyanin biosynthetic genes. In addition, EBR significantly increased water-soluble pectin (WSP) content and concurrently reduced protopectin and cellulose levels, resulting in berry softening. The study also delved into the intricate cross-talks between BRs and other plant growth regulators, for instance, ethylene, abscisic acid (ABA), auxin, and cytokinin. Moreover, transient overexpression of <italic>VvDWF4</italic> (CYP90B1 steroid 22-alpha-hydroxylase) in strawberry increased BRs content, leading to anthocyanin accumulation and fruit softening. These findings provide compelling evidence that the pre-véraison application of BRs provide an effective strategy for enhancing grape berry quality.