Stress responses in alfalfa (Medicago sativa L). XXII. cDNA cloning and characterization of an elicitor-inducible isoflavone 7-O-methyltransferase

Stress responses in alfalfa (Medicago sativa L). XXII. cDNA cloning and characterization of an... Medicarpin, the major phytoalexin in alfalfa, is synthesized via the isoflavonoid branch of phenylpropanoid metabolism. The methyl group at the 9 position of medicarpin is generally accepted to arise via the methylation of the 4′ position (B-ring) of daidzein. Surprisingly, the isoflavone-O-methyltransferase (IOMT), which is induced along with other enzymes involved in medicarpin biosynthesis, methylates the A-ring 7-hydroxyl group of daidzein in vitro, a reaction that probably does not occur in vivo. Utilizing internal amino acid sequence information from purified alfalfa IOMT, we have isolated three full-length IOMT cDNA clones. A search of the protein databases revealed sequence similarities to O-methyltransferases from various sources. The highest match (50.5% identity) was found between IOMT8 and 6a-hydroxymaackiain 3-O-methyltransferase from Pisum sativum. The molecular weight of alfalfa IOMT expressed in Escherichia coli was similar to that of purified IOMT from alfalfa cell cultures (41 kDa by SDS-PAGE). The recombinant enzyme catalyzed the O-methylation of A-ring hydroxyl group(s) of isoflavones, and could also methylate the pterocarpan (+) 6a-hydroxymaackiain. Alfalfa contains multiple IOMT genes, and closely related sequences are present in the genomes of chickpea and cowpea, species that also produce B-ring methylated isoflavonoids in vivo. Northern blot analysis indicated that IOMT transcripts are rapidly induced following elicitation, prior to the increase in IOMT activity and medicarpin accumulation. The possible role of the isoflavone 7-OMT in the synthesis of formononetin in vivo is discussed. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Plant Molecular Biology Springer Journals

Stress responses in alfalfa (Medicago sativa L). XXII. cDNA cloning and characterization of an elicitor-inducible isoflavone 7-O-methyltransferase

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Publisher
Kluwer Academic Publishers
Copyright
Copyright © 1998 by Kluwer Academic Publishers
Subject
Life Sciences; Biochemistry, general; Plant Sciences; Plant Pathology
ISSN
0167-4412
eISSN
1573-5028
D.O.I.
10.1023/A:1005938121453
Publisher site
See Article on Publisher Site

Abstract

Medicarpin, the major phytoalexin in alfalfa, is synthesized via the isoflavonoid branch of phenylpropanoid metabolism. The methyl group at the 9 position of medicarpin is generally accepted to arise via the methylation of the 4′ position (B-ring) of daidzein. Surprisingly, the isoflavone-O-methyltransferase (IOMT), which is induced along with other enzymes involved in medicarpin biosynthesis, methylates the A-ring 7-hydroxyl group of daidzein in vitro, a reaction that probably does not occur in vivo. Utilizing internal amino acid sequence information from purified alfalfa IOMT, we have isolated three full-length IOMT cDNA clones. A search of the protein databases revealed sequence similarities to O-methyltransferases from various sources. The highest match (50.5% identity) was found between IOMT8 and 6a-hydroxymaackiain 3-O-methyltransferase from Pisum sativum. The molecular weight of alfalfa IOMT expressed in Escherichia coli was similar to that of purified IOMT from alfalfa cell cultures (41 kDa by SDS-PAGE). The recombinant enzyme catalyzed the O-methylation of A-ring hydroxyl group(s) of isoflavones, and could also methylate the pterocarpan (+) 6a-hydroxymaackiain. Alfalfa contains multiple IOMT genes, and closely related sequences are present in the genomes of chickpea and cowpea, species that also produce B-ring methylated isoflavonoids in vivo. Northern blot analysis indicated that IOMT transcripts are rapidly induced following elicitation, prior to the increase in IOMT activity and medicarpin accumulation. The possible role of the isoflavone 7-OMT in the synthesis of formononetin in vivo is discussed.

Journal

Plant Molecular BiologySpringer Journals

Published: Oct 6, 2004

References

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