Flavanone 3β-Hydroxylases from Rice: Key Enzymes for Favonol and Anthocyanin Biosynthesis

Flavanone 3β-hydroxylases (F3H) are key enzymes in the synthesis of flavonol and anthocyanin. In this study, three F3H cDNAs from Oryza sativa (OsF3H-1~3) were cloned by RT-PCR and expressed in E. coli as gluthatione S-transferase (GST) fusion proteins. The purified recombinant OsF3Hs used flavanone, narin- genin and eriodictyol as substrates. The reaction products with naringen and eriodictyol were determined by nuclear magnetic resonance spectroscopy to be dihydrokaempferol and taxifolin, respectively. OsF3H-1 had the highest enzymatic activity whereas the overall expression of OsF3E1-2 was highest in all tissues except seeds. Flavanone 3β-hydroxylase could be a useful target for flavonoid metabolic engineering in rice.