Two CYP93A enzymes play a dual role in isoflavonoid biosynthesis in Glycine max L.

Abstract

Glycine max L. is rich in isoflavonoids with diverse biological activities. However, isoflavonoid biosynthetic pathway is not fully elucidated in soybean. In the present study, we investigated characteristics of all the thirteen CYP93 subfamily members, and found GmCYP93A1, GmCYP93A2, and GmCYP93A3 are closely clustered, preferentially expressed in roots, and highly inducible by elicitor. When expressed in yeast, GmCYP93A1 was active towards liquiritigenin, naringenin, and 3,9-dihydroxyptercarpan, GmCYP93A2 towards 3,9-dihydroxyptercarpan with strict substrate specificity, whereas GmCYP93A3 did not show any activity towards all the tested substrates. Both GmCYP93A1 and GmCYP93A2 could catalyze 3,9-dihydroxyptercarpan into daidzein and glycinol, with both hydroxylation and aryl migration activity. Site-directed mutagenesis assays revealed that mutation in Thr446 to Ser446 in heme-binding domain increased the enzyme activity of GmCYP93A1 towards 3,9-dihydroxyptercarpan, which highlights its key amino acid residues as shown with its molecular docking with 3,9-dihydroxyptercarpan and HEM. Overexpression of GmCYP93A1 and GmCYP93A2 in the soybean hairy roots reduced the content of daidzein, whereas knockdown of these two genes increased genistein content, indicating changes in expression level of GmCYP93A1 and GmCYP93A2 altered isoflavonoid flux in soybean. Our studies on the activity of GmCYP93A1 and GmCYP93A2 enriched diverse functions of CYP93 subfamily in soybean isoflavonoid pathway, which is valuable for further understanding and bioengineering of isoflavonoid pathway in soybean.