The B-box (BBX) gene family plays a vital role in plant growth, development, and stress responses. This study aimed to characterize the SmBBX gene family in eggplant (Solanum melongena L.), addressing the lack of systematic bioinformatics and functional studies in this species. A total of 33 SmBBX genes were identified through genome-wide analysis. These genes were phylogenetically grouped into five major clades, with shared domain structures, motifs, and genomic architectures among clade members. The gene duplication analysis revealed segmental duplication as the primary mechanism underlying the expansion of SmBBX proteins in eggplant. Additionally, expression profiling across diverse tissues and abiotic stress conditions, combined with the construction of protein–protein interaction networks and luciferase complementation assay, provided valuable insights into the functional roles of SmBBX genes. SmBBX21-2 and SmBBX22 were identified as the key regulators of anthocyanin biosynthesis, activating the expression of SmCHS and SmDFR promoters. Functional validation via heterologous and homologous overexpression demonstrated that SmBBX22 promoted anthocyanin accumulation by upregulating the expression of structural genes (SmCHS, SmF3H, SmF3′5′H, SmDFR, and SmANS) and transcription factors (SmTT8 and SmHY5) important for anthocyanin biosynthesis. Furthermore, the integration of DNA affinity purification sequencing and RNA-seq data revealed the direct transcriptional targets of SmBBX22, including genes involved in secondary metabolism, hormone signaling, and developmental regulation. This highlighted the role of SmBBX22 in phenylpropanoid and flavonoid biosynthesis. This study lays the foundation for understanding the functional roles of BBX genes in eggplant and provides new directions for future research in plant metabolism and stress adaptation.

Anthocyanin is abundant in a few vegetables, including eggplant. It protects plants from abiotic stress and benefits human health, making the research of anthocyanin biosynthesis increasingly important. Flowering time is an important reference for judging reproduction and adaptability, which can guide plant production. In this study, SmbHLH13 from eggplant was identified. Yeast one-hybrid and dual-luciferase assays showed that SmbHLH13 binded and activated the expression of structural genes SmCHS and SmF3H in anthocyanin biosynthesis and it also was bound to the promoter of the key gene SmFT in flowering. Furthermore, genetic transformation of Arabidopsis revealed that overexpression of SmbHLH13 enhanced anthocyanin accumulation and delayed flowering. These results demonstrated that SmbHLH13 might promote anthocyanin accumulation through positive regulation of SmCHS and SmF3H. Moreover, SmbHLH13 might have a role in delaying eggplant flowering.