Characterization of Two O-Methyltransferase-like Genes in Barley and Maize ∗

Tricin (3 � ,5 � -dimethoxy-5,7,4 � -trihydroxyflavone) is a characteristic flavone constituent of cereal grain plants that is credited for a variety of potential health benefits to humans. We have characterized the flavone-specific O-methyltransferase genes of barley (Hordem vulgare L., Gramineae), HvOMT1, and maize (Zea mays L., Gramineae), ZmOMT1, whose gene products use the flavone tricetin (5,7,3 � ,4 � ,5 � -pentahydroxyflavone) as the preferred substrate and give rise to its 3 � ,5 � -dimethyl derivative, tricin, as the major product. The fact that homologous enzymes catalyze the same reaction also in wheat and rice suggests the existence in cereal grain plants of a flavone-specific O-methyltransferase multigene family. The natural occurrence of tricin in most monocot species implies the widespread occurrence of this gene family. The pharmacological significance of tricin as a naturally occurring constituent with a potential use as a nutraceutical, and the application of metabolic engineering methods to obtain tricin-enriched cereal grain products, are discussed.