Sequential O-methylation of tricetin by a single gene product in wheat☆

Abstract Flavonoid compounds are ubiquitous in nature. They constitute an important part of the human diet and act as active principles of many medicinal plants. Their O -methylation increases their lipophilicity and hence, their compartmentation and functional diversity. We have isolated and characterized a full-length flavonoid O -methyltransferase cDNA ( TaOMT2 ) from a wheat leaf cDNA library. The recombinant TaOMT2 protein was purified to near homogeneity and tested for its substrate preference against a number of phenolic compounds. Enzyme assays and kinetic analyses indicate that TaOMT2 exhibits a pronounced preference for the flavone, tricetin and gives rise to three methylated enzyme reaction products that were identified by TLC, HPLC and ESI-MS/MS as its mono-, di- and trimethyl ether derivatives. The sequential order of tricetin methylation by TaOMT2 is envisaged to proceed via its 3′-mono- → 3′,5′-di- → 3′,4′,5′-trimethyl ether derivatives. To our knowledge, this is the first report of a gene product that catalyzes three sequential O -methylations of a flavonoid substrate.