GmBBM7 promotes callus and root growth during somatic embryogenesis of soybean (Glycine max)

The BABY BOOM (BBM) subfamily of the AP2/ERF transcription factor family is the main regulator of totipotency in plant cells and plays an important role in regulating cell proliferation and plant growth and development. Previously, we identified GmBBM7, a key gene of the soybean BBM gene subfamily (GmBBM family). In this study, we aimed to analyze its molecular characteristics and role in somatic embryogenesis in soybean. First, we identified 17 members of GmBBM family. Phylogenetic and collinear analyses revealed that the GmBBM family genes mainly exhibited a strong genetic relationship with the those of PvBBM family, the BBM family of common bean (Phaseolus vulgaris). Analysis of the promoters revealed that GmBBM family genes were mainly regulated by plant hormones. The expression of GmBBM7 varied in various tissues of soybean. Particularly, it was higher in the roots, immature embryos, grains and callus. Subcellular localization analysis indicated that GmBBM7 encodes a nuclear protein. Furthermore, overexpressed GmBBM7 could significantly enhance callus formation by regulating the levels of gibberellin A1, A3 and A7; abscisic acid; and salicylic acid and could promote root growth and development. In summary, GmBBM7 is an important regulatory gene for somatic embryogenesis and root elongation in soybean. GmBBM7 overexpression in soybean could increase the callus formation rate and density through hormonal pathways and could increase root growth. This study provided theoretical basis for efficient breeding of soybean via gene editing, transgenic and other techniques.