GmFNSII-controlled soybean flavone metabolism responds to abiotic stresses and regulates plant salt tolerance

Flavones, a major group of flavonoids in most plant tissues, play multiple roles in plant-environment interactions. In our study, the expression of the two soybean flavone synthase genes, GmFNSII-1 and GmFNSII-2, was significantly increased by methyl jasmonate (MeJA), glucose, mannitol and NaCl treatment, which were also found to increase flavone aglycone accumulation in Glycine max (L.) Merrill. In the GmFNSII-1 promoter, a specific CGTCA motif in the region (-979 bp to-806 bp) involved in the MeJA response was identified. Promoter deletion analysis of GmFNSII-2 revealed the presence of osmotic-responsive (-1,143 bp to-767 bp) and glucose-repressive sequence elements (-767 bp to-475 bp), which strongly supported the hypothesis that glucose induces soybean flavone production by acting as both an osmotic factor and a sugar signaling molecule simultaneously. Silencing of the GmFNSII gene clearly reduced the production of flavone aglycones (apigenin, luteolin and 7,4′- dihydroxyflavone) in hairy roots. The GmFNSII-RNAi (RNA interference) roots that had a reduced level of flavones accompanied by more malondialdehyde and H ₂O₂ accumulation were more sensitive to salt stress compared with those of the control, and we concluded that flavones, as antioxidants, are associated with salt tolerance.