Small auxin-up RNA promotes GmMYB176 gene transcription to modulate seed isoflavone accumulation in soybean

Introduction Isoflavones possess significant health benefits, including anti-inflammatory, anti-cancer, and antioxidant properties. Soybean ( Glycine max (L.) Merr) is an effective natural source of isoflavones for humans. Thus, it is important to breed soybean varieties with enhanced isoflavone content and to elucidate the secondary metabolic pathways involved. Small auxin-up RNA (SAUR) genes constitute the largest family responsive to auxin, however, few studies have addressed their roles in soybean flavonoid metabolism. Methods In this study, flavonoid-targeted metabolites were measured in GmSAUR:GmSAUR transgenic soybeans. Chromatin immunoprecipitation sequencing (ChIP-seq) was performed to identify potential target genes regulated by GmSAUR. Additionally, RNA‑Seq was performed to identify downstream genes regulated by 35S: GmMYB176 , including GmC4H, GmIF7MaT, GmCYP450 84A1‑like , and GmCYP450 84A1 . Results The transgenic soybeans exhibited higher contents of daidzin and genistin compared to controls. ChIP-seq revealed that GmSAUR binds to the promoter region of GmMYB176 , thereby promoting the expression of downstream genes including cinnamate 4-hydroxylase ( GmC4H ), isoflavone 7-O-beta-glucoside 6′′-O-malonyltransferase ( GmIF7MaT ), cytochrome P450 84A1-like ( GmCYP450 84A1-like ), and cytochrome P450 84A1 ( GmCYP450 84A1 ). This regulatory cascade ultimately led to increased accumulation of soybean isoflavones. Discussion These findings indicate that the GmSAUR gene facilitates soybean isoflavone biosynthesis by modulating the expression of GmMYB176 , providing new insights into the genetic improvement of isoflavone content in soybean.