Anthocyanin biosynthesis in eggplant (Solanum melongena L.) is highly light-dependent, and insufficient light severely impairs fruit coloration, which restricts the development of the eggplant industry. SmMYB75 is a key positive regulator of anthocyanin biosynthesis, but its regulatory partners remain unclear. In this study, seven SmYABBY genes were identified from the eggplant genome, all containing conserved zinc finger and YABBY domains. Expression analysis showed that SmYABBY1 was predominantly expressed in fruit peel and significantly induced by light, with a peak at 4 h after light exposure. The yeast two-hybrid and bimolecular fluorescence complementation assays indicated that SmYABBY1 interacts with SmMYB75 and the light signaling regulator SmCOP1 in the nucleus. The heterologous overexpression of SmYABBY1 in Arabidopsis enhanced anthocyanin accumulation and upregulated the expression of anthocyanin structural genes. Transient co-expression in tobacco leaves further demonstrated that SmYABBY1 synergistically enhances SmMYB75-mediated anthocyanin biosynthesis. The yeast one-hybrid and Dual-LUC assays revealed that SmYABBY1 does not directly bind to the promoters of SmMYB75, SmDFR, and SmANS but indirectly promotes their transcriptional activity. Our results illustrate that SmYABBY1 acts as a transcriptional co-activator, interacting with SmMYB75 to promote anthocyanin accumulation, while SmCOP1 is involved in this regulatory process. This study provides a molecular basis for improving eggplant coloration under suboptimal light conditions.
Shi et al. (2026) studied this question.