TY - JOUR

T1 - A flavonoid 7-O-methyltransferase is expressed in barely leaves in response to pathogen attack

AU - Christensen, Anders B.

AU - Gregersen, Per L.

AU - Olsen, Carl E.

AU - Collinge, David B.

PY - 1998/1/1

Y1 - 1998/1/1

N2 - We have shown previously that transcripts corresponding to the cDNA clone pBH72-F1, with similarities to O-methyltransferases (OMT), accumulated in barley leaves in response to attack by the pathogenic fungus Blumeria graminis (Plant Mol Biol 26 (1994) 1797). To investigate the accumulation pattern in the defence response and the organ localization of the pBH72-F1-encoded polypeptide (F1-OMT), an antiserum was raised against Escherichia coli expressed F1-OMT. The 43 kDa protein was absent in normal leaves but accumulated strongly in response to pathogen attack. The F1-OMT protein accumulated faster in barely lines inoculated with an avirulent B. graminis isolates compared to a virulent isolate. Additionally, F1-OMT related proteins were detected in developing kernels. F1-OMT was expressed as a functional enzyme in E. coli and the substrate specificity was investigated. The enzyme exhibited OMT activity towards flavonoid aglycones with the highest activity against apigenin (4',5,7-trihydroxyflavone). In contrast, caffeic acid did not serve a substrate for F1-OMT. The product of F1-OMT was analyzed by HPLC and GC-MS and found to be genkwanin (4',5-dihydroxy-7-methoxyflavone). Initial velocity data were best represented by a sequential bi-bi mechanism, and kinetic parameters of K(SAM) = 10.9 μM, K(apigenin) = 4.6 μM and a specific activity of 0.45 μkat/g were obtained. Barley F1-OMT, apigenin 7-O-methyltransferase, is suggested to be involved in the production of a methylated flavonoid phytoalexin.

AB - We have shown previously that transcripts corresponding to the cDNA clone pBH72-F1, with similarities to O-methyltransferases (OMT), accumulated in barley leaves in response to attack by the pathogenic fungus Blumeria graminis (Plant Mol Biol 26 (1994) 1797). To investigate the accumulation pattern in the defence response and the organ localization of the pBH72-F1-encoded polypeptide (F1-OMT), an antiserum was raised against Escherichia coli expressed F1-OMT. The 43 kDa protein was absent in normal leaves but accumulated strongly in response to pathogen attack. The F1-OMT protein accumulated faster in barely lines inoculated with an avirulent B. graminis isolates compared to a virulent isolate. Additionally, F1-OMT related proteins were detected in developing kernels. F1-OMT was expressed as a functional enzyme in E. coli and the substrate specificity was investigated. The enzyme exhibited OMT activity towards flavonoid aglycones with the highest activity against apigenin (4',5,7-trihydroxyflavone). In contrast, caffeic acid did not serve a substrate for F1-OMT. The product of F1-OMT was analyzed by HPLC and GC-MS and found to be genkwanin (4',5-dihydroxy-7-methoxyflavone). Initial velocity data were best represented by a sequential bi-bi mechanism, and kinetic parameters of K(SAM) = 10.9 μM, K(apigenin) = 4.6 μM and a specific activity of 0.45 μkat/g were obtained. Barley F1-OMT, apigenin 7-O-methyltransferase, is suggested to be involved in the production of a methylated flavonoid phytoalexin.

KW - Blumeria graminis (syn. Erysiphe graminis)

KW - Defence response

KW - Flavonoid 7-O-methyltransferase

KW - Hordeum vulgare

KW - Phytoalexin

UR - http://www.scopus.com/inward/record.url?scp=0031907592&partnerID=8YFLogxK

U2 - 10.1023/A:1005985609313

DO - 10.1023/A:1005985609313

M3 - Journal article

C2 - 9484434

AN - SCOPUS:0031907592

VL - 36

SP - 219

EP - 227

JO - Plant Molecular Biology

JF - Plant Molecular Biology

SN - 0167-4412

IS - 2

ER -