Genome-Wide Characterization of B-Box Gene Family in Salvia miltiorrhiza

B-box (BBX) is a type of zinc finger transcription factor that contains a B-box domain. BBX transcription factors play important roles in plant photomorphogenesis, signal transduction, as well as abiotic and biological stress responses. However, the BBX gene family of Salvia miltiorrhiza has not been systematically investigated to date. For this study, based on the genomic data of Salvia miltiorrhiza, 27 SmBBXs genes were identified and clustered into five evolutionary branches according to phylogenetic analysis. The promoter analysis suggested that SmBBXs may be involved in the regulation of the light responses, hormones, stress signals, and tissue-specific development. Based on the transcriptome data, the expression patterns of SmBBXs under different abiotic stresses and plant hormones were analyzed. The results revealed that the expressions of the SmBBXs genes varied under different conditions and may play essential roles in growth and development. The transient expression analysis implied that SmBBX1, SmBBX4, SmBBX9, SmBBX20, and SmBBX27 were in the nucleus. A transcriptional activation assay showed SmBBX1, SmBBX4, SmBBX20, and SmBBX24 had transactivation activities, while SmBBX27 had none. These results provided a basis for further research on the role of SmBBXs in the development of Salvia miltiorrhiza.