The Bax inhibitor-1 (BI-1) gene family, which is required for plant growth, development, and stress tolerance, remains largely unexplored in cauliflower. In this study, we identified and characterized cauliflower BI-1 family genes. On the basis of aligned homologous sequences and collinearity with Arabidopsis genes, we identified nine cauliflower BI-1 genes, which encoded proteins that varied regarding length, molecular weight, isoelectric point, and subcellular localization (i.e., Golgi apparatus, plasma membrane, cell membrane, and chloroplast). Phylogenetic analyses detected evolutionary conservation and divergence among these genes. Ten structural motifs were identified, with Motif 5 crucial for inhibiting apoptosis. According to the cis-regulatory elements in their promoters, these genes likely influence hormone signaling and stress responses. Expression profiles among tissues highlighted the diversity in the functions of these genes, which were significantly expressed in the silique and root. Focusing on BobBIL4, we investigated its role in brassinosteroid (BR)-mediated root development and salt stress tolerance. BobBIL4 expression levels increased in response to BR and salt treatments. The functional characterization of this gene in Arabidopsis revealed it enhances root growth and salinity tolerance. These findings provide insights into BI-1 gene functions in cauliflower, while also highlighting the potential utility of BobBIL4 for improving crop stress resistance.
