The GmbHLH13-GmCHS7 module positively regulates isoflavones accumulation in soybean (Glycine max. L)

Isoflavonoids are widely regarded as phytoalexins and plant estrogens, with applications in plant defense and human healthcare. However, the mechanism of soy isoflavone synthesis remains unclear. In this study, we identified a gene from Glycine max, designated as basic helix-loop-helix 13 (GmbHLH13), which is a member of the bHLH transcription factor family. Overexpression of GmbHLH13 significantly enhanced the accumulation of isoflavonoids in soybean seeds. A combined analysis of the transcriptome and metabolome showed that GmbHLH13 enhanced the expression of multiple genes in the phenylpropanoid metabolism pathway, leading to increased production of downstream metabolites. We established that GmbHLH13 interacted with GmMYB12B2 and GmWD40-7 to form a MYB-bHLH-WD40 (MBW) complex that binded directly to the promoter region of GmCHS7, further increasing GmCHS7 expression. In addition, GmbHLH13 alone or complexed with GmMYB12B2 or GmWD40-7, positively regulated GmCHS7 expression, however, the effect was lower than that of the MBW complex. The findings of this study provide a valuable genetic breeding resource and gene for improving soybean varieties with high isoflavone content.