Isolation and characterization of GmMYBJ3, an R2R3-MYB transcription factor that affects isoflavonoids biosynthesis in soybean

Isoflavonoids are secondary metabolites that play a variety of roles in plant-microbe interactions and plant defenses against abiotic stresses. Here we report a new MYB transcription factor (TF) gene, GmMYBJ3, that is involved in the isoflavonoids biosynthesis. The GmMYBJ3 gene is 1,002 bp long and encodes a protein of 333 amino acids. Amino acid sequence analysis showed that GmMYBJ3 is a typical R2R3 MYB TF. Yeast expression experiment demonstrated that GmMYBJ3 has its transcription activity in the nucleus and is transiently expressed in onion epidermal cells. The GmMYBJ3 gene was transformed into soybean and the expression activity of the GmMYBJ3 gene was significantly positively correlated with total isoflavonoid accumulation in soybean. Transient expression assays indicated that GmMYBJ3 can activate CHS8 expression. Furthermore, we analyzed the expressions of several genes known involved in the isoflavonoid biosynthesis, including CHS8, CHI1A, PAL1, IFS2 and F3H, in the GmMYBJ3 transgenic plants. The results showed that the expression levels of CHS8 and CHI1A were significantly increased in the transgenic plants compared to wild-type plants, but those of PAL1, IFS2 and F3H remained similar between the transgenic and wild-type plants. These results suggest that GmMYBJ3 participates in the isoflavonoid biosynthesis through regulation of CHS8 and CHI1A in soybean.