Analysis of flavonoids and characterization of the OsFNS gene involved in flavone biosynthesis in rice

The major flavonoids in rice leaves were analyzed via LC-MS/MS after their total flavonoid extracts were hydrolyzed. The most abundant flavones were apigenin, luteolin, and tricetin. Of these, tricetin was methylated at its 3' and 5'-hydroxyl group to form tricin, which was probably O-glycosylated. Both 3'-O-methylated luteolin and luteolin were found in the C-glycosylated form while apigenin was C-glycosylated. We also cloned and characterized OsFNS, which catalyzes the reaction from flavanone (naringenin) to flavone (apigenin). Analysis of the reaction product with recombinant OsFNS showed that it indeed converts naringenin to apigenin.