Characterization of TwoO.-Methyltransferase-like Genes in Barley and Maize

Abstract

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.

Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

“…PMT has been shown in rice (Withers et al, 2012), brachypodium (Petrik et al, 2014), and maize (Marita et al, 2014). The flavone biosynthesis pathway is shown according to Zhou et al (2008), Corté s-Cruz et al (2003, and Lam et al (2014Lam et al ( , 2015. The enzymes involved in the metabolic route via F2H toward apigenin and luteolin conjugates has been described in rice, wheat, and buckwheat (Fagopyrum esculentum;Brazier-Hicks et al, 2009;Du et al, 2010).…”

“…In addition, HCT of sorghum (Sorghum bicolor) has been studied via in vitro activity assays (Walker et al, 2013). The FOMT involved in the conversion of luteolin and selgin into chrysoeriol and tricin, respectively, in maize is described by Zhou et al (2008) and is identical to the COMT involved in the conversion of 5-hydroxyconiferaldehyde to sinapaldehyde described by Collazo et al (1992), Vignols et al (1995), andPiquemal et al (2002). Question marks indicate biosynthetic steps that are questionable; the reaction from p-coumaric acid toward caffeic acid via a C3H/C4H complex has so far only been shown by in vitro tests using poplar enzymes .…”

Tricin—a potential multifunctional nutraceutical

“…Phylogenetic analysis indicates that a number of flavone OMT homologous genes occur in most cereal plants, such as barley, rice, maize and sorghum, as well as in ryegrass and sugarcane, indicating a plant flavone OMT gene superfamily (Zhou et al 2006b). Flavone OMT genes are often mis-annotated as caffeic acid/5-hydroxyferulic acid 3/5-OMTs (COMTs), possibly because of their high amino acid sequence similarity/identity to COMTs as well as the structural similarity between the phenylpropanoid moiety and the flavonoid-B-ring with its 3-C side chain (Zhou et al 2008(Zhou et al , 2009.…”

Structure-function relationships of wheat flavone O-methyltransferase: Homology modeling and site-directed mutagenesis

“…In fact, alignment of their amino acid sequences shows that the putative residues involved in substrate binding and catalysis are strictly conserved [13]. Several members of this OMT family have previously been mis-annotated as caffeic acid/5-hydroxyferulic acid 3/5-OMTs (COMTs), possibly because of their high amino acid sequence similarity/identity to flavonoid OMTs and the structural analogy between their phenylpropanoid moiety and the flavonoid B-ring with its 3-C side chain (Fig.…”