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Flavonoid 3'-O-methyltransferase from rice: cDNA cloning, characterization and functional expression
Bong-Gyu Kim1, Youngshim Lee, Hor-Gil Hur
1Bio/Molecular Informatics Center, Department of Molecular Biotechnology, Konkuk University, 1 Hwayang-dong, Kwangjin-gu, Seoul 143-701, Republic of Korea.
Phytochemistry
|January 18, 2006
Summary
Rice O-methyltransferase 9 (ROMT-9) specifically methylates the 3'-hydroxyl group of flavonoids. This enzyme converts quercetin and other 3'-hydroxy flavonoids into their methoxy derivatives, impacting plant secondary metabolism.
Area of Science:
- Plant biochemistry
- Enzymology
- Molecular biology
Background:
- Plant O-methyltransferases (OMTs) catalyze the methylation of secondary metabolites, including phenylpropanoids and flavonoids.
- Understanding OMTs is crucial for elucidating plant metabolic pathways and their products.
Purpose of the Study:
- To clone and characterize a novel rice O-methyltransferase, ROMT-9.
- To investigate the substrate specificity of ROMT-9 towards various flavonoid compounds.
Main Methods:
- Cloning of ROMT-9 from rice using reverse transcriptase polymerase chain reaction (RT-PCR).
- Expression of recombinant ROMT-9 in Escherichia coli and purification via affinity chromatography.
- Enzymatic assays using S-adenosyl-l-methionine and flavonoid substrates (eriodictyol, luteolin, quercetin, taxifolin).
- Analysis of reaction products using TLC, HPLC, HPLC/MS, and NMR spectroscopy.
Main Results:
- ROMT-9 showed 73% identity to caffeic acid OMTs from maize and Triticum aestivum.
- ROMT-9 specifically transferred a methyl group to the 3 ahydroxyl group of quercetin, forming its methoxy derivative.
- The enzyme effectively converted eriodictyol, luteolin, quercetin, and taxifolin into their corresponding 3 ahydroxymethoxy derivatives.
Conclusions:
- ROMT-9 is a rice O-methyltransferase with strict specificity for the 3 ahydroxyl group of flavonoids.
- This finding contributes to the understanding of flavonoid biosynthesis and modification in plants.
