Publications

• Naringenin 7-O-methyltransferase involved in the biosynthesis of the flavanone phytoalexin sakuranetin from rice (Oryza sativa L.).

  Rakwal R., Agrawal G.K., Yonekura M., Kodama O.

  An inducible S-adenosyl-L-methionine:naringenin 7-O-methyltransferase (NOMT) catalyzing the methylation of naringenin to sakuranetin, a major rice phytoalexin was purified approximately 985-fold from ultraviolet (UV)-irradiated rice leaves. The enzyme is not found in healthy tissues and was purifi ... >> More

  An inducible S-adenosyl-L-methionine:naringenin 7-O-methyltransferase (NOMT) catalyzing the methylation of naringenin to sakuranetin, a major rice phytoalexin was purified approximately 985-fold from ultraviolet (UV)-irradiated rice leaves. The enzyme is not found in healthy tissues and was purified to a nearly homogeneous preparation in one step using adenosine-agarose affinity chromatography, with 1 g rice leaves (UV-irradiated) as starting material. Gel filtration chromatography resulted in an almost pure enzyme, as evidenced by a major band migrating to a position corresponding to a molecular mass of approximately 41 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified NOMT was strongly inhibited by Mn(2+), Ni(2+), Cu(2+), Zn(2+), Hg(2+), and Cd(2+), and to a low degree by Co(2+), Mg(2+), Ba(2+), Ca(2+) and ethylenediamine tetraacetic acid. The amino acid sequence of a NOMT cyanogen bromide (CNBr)-cleavage peptide was highly homologous to that of a caffeic acid 3-O-methyltransferase from maize, and about 70% of the amino acid sequence was obtained after sequencing the peptides generated by CNBr and/or formic acid hydrolysis. NOMT was also shown to be induced in a time-dependent manner, and purified from rice leaves treated with jasmonic acid and copper chloride. << Less

  Plant Sci. 155:213-221(2000) [PubMed] [EuropePMC]

• A set of regioselective O-methyltransferases gives rise to the complex pattern of methoxylated flavones in sweet basil.

  Berim A., Hyatt D.C., Gang D.R.

  Polymethoxylated flavonoids occur in a number of plant families, including the Lamiaceae. To date, the metabolic pathways giving rise to the diversity of these compounds have not been studied. Analysis of our expressed sequence tag database for four sweet basil (Ocimum basilicum) lines afforded id ... >> More

  Polymethoxylated flavonoids occur in a number of plant families, including the Lamiaceae. To date, the metabolic pathways giving rise to the diversity of these compounds have not been studied. Analysis of our expressed sequence tag database for four sweet basil (Ocimum basilicum) lines afforded identification of candidate flavonoid O-methyltransferase genes. Recombinant proteins displayed distinct substrate preferences and product specificities that can account for all detected 7-/6-/4'-methylated, 8-unsubstituted flavones. Their biochemical specialization revealed only certain metabolic routes to be highly favorable and therefore likely in vivo. Flavonoid O-methyltransferases catalyzing 4'- and 6-O-methylations shared high identity (approximately 90%), indicating that subtle sequence changes led to functional differentiation. Structure homology modeling suggested the involvement of several amino acid residues in defining the proteins' stringent regioselectivities. The roles of these individual residues were confirmed by site-directed mutagenesis, revealing two discrete mechanisms as a basis for the switch between 6- and 4'-O-methylation of two different substrates. These findings delineate major pathways in a large segment of the flavone metabolic network and provide a foundation for its further elucidation. << Less

  Plant Physiol. 160:1052-1069(2012) [PubMed] [EuropePMC]

  This publication is cited by 14 other entries.

• Bio-fermentation of modified flavonoids: an example of in vivo diversification of secondary metabolites.

  Willits M.G., Giovanni M., Prata R.T.N., Kramer C.M., De Luca V., Steffens J.C., Graser G.

  A bio-fermentation technique was used for the in vivo diversification of flavonoid structures based on expression in Escherichia coli of six O-methyltransferases (OMTs) from Mentha x piperita and one O-glucosyltransferase (GT) each from Arabidopsis thaliana and Allium cepa. Enzymes were shown to b ... >> More

  A bio-fermentation technique was used for the in vivo diversification of flavonoid structures based on expression in Escherichia coli of six O-methyltransferases (OMTs) from Mentha x piperita and one O-glucosyltransferase (GT) each from Arabidopsis thaliana and Allium cepa. Enzymes were shown to be regio-specific in in vitro experiments and modified a broad range of flavonoid substrates at various positions. Using the flavonol quercetin as a model substrate, we show that the product spectrum produced with the in vivo approach is identical to that found in vitro. Additionally, using mixed cultures of E. coli expressing different classes of modifying genes (OMTs and GTs), the production of polymethylated flavonoid glucosides was observed. This report demonstrates the potential to increase the structural diversity of plant secondary metabolites using a multi-enzyme, bio-fermentation approach. << Less

  Phytochemistry 65:31-41(2004) [PubMed] [EuropePMC]

  This publication is cited by 23 other entries.

• Purification and identification of naringenin 7-o-methyltransferase, a key enzyme in biosynthesis of flavonoid phytoalexin sakuranetin in rice.

  Shimizu T., Lin F., Hasegawa M., Okada K., Nojiri H., Yamane H.

  Sakuranetin, the major flavonoid phytoalexin in rice, is induced by ultraviolet (UV) irradiation, CuCl(2) treatment, jasmonic acid treatment, and infection by phytopathogens. It was recently demonstrated that sakuranetin has anti-inflammatory activity, anti-mutagenic activity, anti-pathogenic acti ... >> More

  Sakuranetin, the major flavonoid phytoalexin in rice, is induced by ultraviolet (UV) irradiation, CuCl(2) treatment, jasmonic acid treatment, and infection by phytopathogens. It was recently demonstrated that sakuranetin has anti-inflammatory activity, anti-mutagenic activity, anti-pathogenic activities against Helicobacter pylori, Leishmania, and Trypanosoma and contributes to the maintenance of glucose homeostasis in animals. Thus, sakuranetin is a useful compound as a plant antibiotic and a potential pharmaceutical agent. Sakuranetin is biosynthesized from naringenin by naringenin 7-O-methyltransferase (NOMT). In previous research, rice NOMT (OsNOMT) was purified to apparent homogeneity from UV-treated wild-type rice leaves, but the purified protein, named OsCOMT1, exhibited caffeic acid O-methyltransferase (COMT) activity and not NOMT activity. In this study, we found that OsCOMT1 does not contribute to sakuranetin production in rice in vivo, and we purified OsNOMT using the oscomt1 mutant. A crude protein preparation from UV-treated oscomt1 leaves was subjected to three sequential purification steps, resulting in a 400-fold purification from the crude enzyme preparation. Using SDS-PAGE, the purest enzyme preparation showed a minor band at an apparent molecular mass of 40 kDa. Two O-methyltransferase-like proteins, encoded by Os04g0175900 and Os12g0240900, were identified from the 40-kDa band by MALDI-TOF/TOF analysis. Recombinant Os12g0240900 protein showed NOMT activity, but the recombinant Os04g0175900 protein did not. Os12g0240900 expression was induced by jasmonic acid treatment in rice leaves prior to sakuranetin accumulation, and the Os12g0240900 protein showed reasonable kinetic properties to OsNOMT. On the basis of these results, we conclude that Os12g0240900 encodes an OsNOMT. << Less

  J. Biol. Chem. 287:19315-19325(2012) [PubMed] [EuropePMC]