Publications

• Identification, purification, and characterization of S-adenosyl-L-methionine: isoliquiritigenin 2'-O-methyltransferase from alfalfa (Medicago sativa L.).

  Maxwell C.A., Edwards R., Dixon R.A.

  An O-methyltransferase (OMT) which methylates the 2'-hydroxyl of isoliquiritigenin (2',4,4'-trihydroxychalcone) was identified in alfalfa (Medicago sativa L.) seedlings and cell cultures. The OMT activity increased during early stages of seedling development and was predominantly located in roots. ... >> More

  An O-methyltransferase (OMT) which methylates the 2'-hydroxyl of isoliquiritigenin (2',4,4'-trihydroxychalcone) was identified in alfalfa (Medicago sativa L.) seedlings and cell cultures. The OMT activity increased during early stages of seedling development and was predominantly located in roots. Treatment of alfalfa cell cultures with an elicitor from yeast resulted in a fivefold increase in chalcone OMT activity, whereas treatment of seedlings with CuCl2 caused a reduction in activity. The chalcone OMT was purified to near homogeneity from elicited alfalfa cell cultures. Only one form of the enzyme was found. It consisted of an active monomer of subunit Mr 43,000 which could be photoaffinity labeled with S-adenosyl-L-[methyl-3H]methionine. The purified OMT had a pH optimum of 9.0, pI of 4.7, and was highly specific for the 2'-hydroxyl of 2',4,4'-trihydroxychalcone, with essentially no activity toward narigenin chalcone, caffeic acid, or daidzein. Kinetic analysis indicated a sequential bi bi mechanism with Km values of 2.2 and 17.7 microM for 2',4,4'-trihydroxychalcone and S-adenosyl-L-methionine, respectively. S-Adenosyl-L-homocysteine was a potent inhibitor. The chalcone OMT represents the third distinct OMT isolated from alfalfa cell cultures. << Less

  Arch. Biochem. Biophys. 293:158-166(1992) [PubMed] [EuropePMC]

• Enzymic O-methylation of isoliquiritigenin and licodione in alfalfa and licorice cultures.

  Ichimura M., Furuno T., Takahashi T., Dixon R.A., Ayabe S.

  S-Adenosyl-L-methionine (SAM): isoliquiritigenin (2',4,4'-trihydroxychalcone) 2'-O-methyltransferase (CHMT) of alfalfa (Medicago sativa) catalyses the formation of 4,4'-dihydroxy-2'-methoxychalcone, which is the most potent inducer of nodulation-genes of Rhizobium meliloti, the symbiont of alfalfa ... >> More

  S-Adenosyl-L-methionine (SAM): isoliquiritigenin (2',4,4'-trihydroxychalcone) 2'-O-methyltransferase (CHMT) of alfalfa (Medicago sativa) catalyses the formation of 4,4'-dihydroxy-2'-methoxychalcone, which is the most potent inducer of nodulation-genes of Rhizobium meliloti, the symbiont of alfalfa which forms nitrogen-fixing nodules. SAM: licodione 2'-O-methyltransferase (LMT) is involved in the biosynthesis of a retrochalcone in cultured licorice (Glycyrrhiza echinata) cells and has been shown to be induced as a defence response of the cells. Because licodione exists in an equilibrium mixture of tautomeric 2',4,4',beta-tetrahydroxychalcone (major) and 1-(2,4-dihydroxyphenyl)-3-(4-hydroxyphenyl)-1,3-propanedione (minor), the apparent mode of action of both enzymes is very similar. In this study, cultured alfalfa cells were shown to exhibit rapid and transient increases in the extractable activities of both CHMT and LMT after treatment with yeast extract (YE). Treatment of solution-cultured alfalfa seedlings with YE also resulted in a similar induction of both CHMT and LMT activities in the roots, but no activity was detected in the shoots. These activities were attributed to a single gene product, the CHMT protein, as extracts of Escherichia coli transformed with the CHMT cDNA exhibited both CHMT and LMT activities. In contrast, in G. echinata cells, LMT was induced after YE treatment, but no CHMT activity was observed. It is concluded that alfalfa CHMT and licorice LMT are distinct enzymes, the former displaying the wider substrate specificity. << Less

  Phytochemistry 44:991-995(1997) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Molecular characterization and expression of alfalfa isoliquiritigenin 2'-O-methyltransferase, an enzyme specifically involved in the biosynthesis of an inducer of Rhizobium meliloti nodulation genes.

  Maxwell C.A., Harrison M.J., Dixon R.A.

  A cDNA clone encoding an O-methyltransferase (OMT) from alfalfa has been isolated, which methylates the 2'-hydroxyl of isoliquiritigenin (2',4,4'-trihydroxychalcone) to form 4,4'-dihydroxy-2'-methoxychalcone, the most potent of the nod-gene-inducing flavonoid derivatives released from alfalfa root ... >> More

  A cDNA clone encoding an O-methyltransferase (OMT) from alfalfa has been isolated, which methylates the 2'-hydroxyl of isoliquiritigenin (2',4,4'-trihydroxychalcone) to form 4,4'-dihydroxy-2'-methoxychalcone, the most potent of the nod-gene-inducing flavonoid derivatives released from alfalfa roots. The cDNA clone was identified on the basis of N-terminal sequence identity to purified S-adenosyl-L-methionine:isoliquiritigenin 2'-O-methyltransferase (chalcone OMT) and expression of enzymatically active chalcone OMT protein in Escherichia coli. The deduced amino acid sequence showed significant similarities to other OMTs. Chalcone OMT is encoded by a small gene family in alfalfa and related sequences are present in other legumes. The chalcone OMT gene is expressed primarily in alfalfa roots; transcript levels were highest during the first 2 weeks of development. The OMT transcript was also detected, to a much lesser extent, in root nodules. In contrast, chalcone isomerase (CHI), although expressed at high levels in roots, was found in all plant organs and had a somewhat different developmental expression pattern. Chalcone OMT transcripts were localized primarily to epidermal and cortical cells starting 1.5-2.0 mm behind the root tip, whereas CHI transcripts were present at approximately equal levels in epidermal, cortical and vascular tissues, both at the root tip and throughout the root. Chalcone OMT transcripts were elicitor-inducible in alfalfa cell suspension cultures, although only low levels of methoxychalcone accumulated. The implications of these results for plant-microorganism interactions are discussed. << Less

  Plant J. 4:971-981(1993) [PubMed] [EuropePMC]

• Structures of two natural product methyltransferases reveal the basis for substrate specificity in plant O-methyltransferases.

  Zubieta C., He X.-Z., Dixon R.A., Noel J.P.

  Chalcone O-methyltransferase (ChOMT) and isoflavone O-methyltransferase (IOMT) are S-adenosyl-l-methionine (SAM) dependent plant natural product methyltransferases involved in secondary metabolism in Medicago sativa (alfalfa). Here we report the crystal structure of ChOMT in complex with the produ ... >> More

  Chalcone O-methyltransferase (ChOMT) and isoflavone O-methyltransferase (IOMT) are S-adenosyl-l-methionine (SAM) dependent plant natural product methyltransferases involved in secondary metabolism in Medicago sativa (alfalfa). Here we report the crystal structure of ChOMT in complex with the product S-adenosyl-l-homocysteine and the substrate isoliquiritigenin (4,2',4'-trihydroxychalcone) refined to 1.8 A as well as the crystal structure of IOMT in complex with the products S-adenosyl-l-homocysteine and isoformononetin (4'-hydroxy-7-methoxyisoflavone) refined to 1.4 A. These two OMTs constitute the first plant methyltransferases to be structurally characterized and reveal a novel oligomerization domain and the molecular determinants for substrate selection. As such, this work provides a structural basis for understanding the substrate specificity of the diverse family of plant OMTs and facilitates the engineering of novel activities in this extensive class of natural product biosynthetic enzymes. << Less

  Nat. Struct. Biol. 8:271-279(2001) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.