MOLECULAR AND FUNCTIONAL ANALYSIS OF THE FLAVANONE-3-HYDROXYLASE (F3H) GENE IN WELSH ONION (ALLIUM FISTULOSUM L.)

Secondary metabolites contribute to the biological activities and medicinal attributes of plants. Flavonoids are major metabolites in Allium fistulosum. Flavanone-3-hydroxylase is a key enzyme in the flavonoid biosynthesis pathway. However, the molecular basis of F3H in A. fistulosum is still unknown. In the present study, F3H was cloned from A. fistulosum and named AfF3H; this gene contains 1269 bp and encodes 368 amino acids. Subcellular localization results showed that AfF3H was located in the cytosol. The catalytic activity analysis of the AfF3H recombinant protein showed that the protein catalyses the formation of dihydroquercetin and dihydrokaempferol from eriodyctiol and naringenin. Furthermore, the expression of AfF3H was specific and closely related to flavonoid content. The increased expression of F3H was induced by cold stress. Simultaneously, the content of total flavonoids in Welsh onion also increased with the expression of AfF3H. These results showed that cold stress induced the expression of AfF3H and increased the metabolic flux of flavonoids. The results of this study suggest that AfF3Hplays an essential role in flavonoid biosynthesis in A. fistulosum.