Targeted expression of Glycine max isoflavone synthase enhances daidzein and genistein content in soybean.

Isoflavonoids are key secondary metabolites in leguminous plants that play essential roles in plant physiology and provide significant health benefits to humans. In the isoflavone biosynthetic pathway, isoflavone synthase (IFS) catalyzes the conversion of naringenin and liquiritigenin into the bioactive isoflavones genistein and daidzein. This study aimed to enhance genistein and daidzein accumulation in soybean seeds through genetic engineering. Agrobacterium tumefaciens strain EHA105 harboring the binary vector pCAMBIA1301 containing GmIFS under the control of a seed-specific promoter (Gmβ-conglycinin) was used to transform modified half-seed explants of soybean cv. JS335. Hygromycin-B-resistant plants were regenerated, hardened, and confirmed by histochemical GUS assay. Molecular analysis by PCR validated the presence of the GmIFS transgene, yielding a 700 bp amplicon. Biochemical analysis revealed that seeds of T₀ transgenic plants showed a 1.53-fold increase in total phenolic content and a 3.67-fold increase in flavonoid content compared to non-transformed controls. Antioxidant assays demonstrated significantly higher DPPH radical-scavenging activity and ferric-reducing antioxidant power (FRAP) in GmIFS-overexpressing plants. HPLC analysis further indicated that transgenic seeds accumulated, on average, 4.07-fold higher daidzein and 1.75-fold higher genistein levels relative to control plants. qRT-PCR analysis showed significantly elevated GmIFS expression in immature cotyledons, mature cotyledons, and seeds of transgenic plants. Overall, these results demonstrate that GmIFS overexpression effectively enhances isoflavone production in soybean seeds, highlighting the potential of metabolic engineering of biosynthetic pathway genes to improve nutritional quality.