Plant Molecular Biology 26: 1797-1806, 1994. © 1994 Kluwer Academic Publishers. Printed in Belgium. 1797 A putative O-methyltransferase from barley is induced by fungal pathogens and UV light Per L. Gregersen, Anders B. Christensen, Jens Sommer-Knudsen 1 and David B. Collinge* Section for Plant Pathology, Department of Plant Biology, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871-Frederiksberg C, Copenhagen, Denmark (*author for correspondence)," 1Present address: Plant Cell Biology Research Centre, University of Melbourne, Parkville, Victoria 3052, Australia Received 5 September 1994; accepted 9 September 1994 Key words:Hordeum vulgare,Erysiphegraminis, defence response, O-methyltransferase, phenylpropanoid metabolism Abstract A cDNA clone, pBH72-F1 (F1), was isolated from a cDNA library prepared from barley leaves 72 h after inoculation with Erysiphe graminis f.sp. hordei. The 1388 bp nucleotide sequence of pBH72-F1 contains an open reading frame encoding a 42.3 kDa polypeptide of 390 amino acids which shows se- quence similarity to O-methyltransferases (OMTs) from different plant species; the highest identity (41 ~o) was observed with a putative OMT expressed in roots of maize. A phylogenetic analysis shows that the barley and maize sequences are distinctly different from the ortho-diphenol-OMTs involved in lignin formation. A putative S-adenosyl-L-methionine-binding motif (KELVDDSITN) determined for a rab- bit protein-carboxyl OMT is partially conserved in the encoded amino acid sequence. Genomic Southern blot hybridization shows that pBH72-F1 probably represents a single copy gene. The F1 clone corre- sponds to a gene transcript exhibiting a relatively late accumulation in mildew-infected barley leaves compared to other pathogen-induced transcripts, such as transcripts encoding PR proteins, a peroxi- dase, and transcripts homologous to a maize caffeic acid OMT. No transcript was detected in plants exhibiting papilla resistance at time points when resistance is thought to be manifested. The atypical transcript accumulation pattern for F1 was also observed after infection by other pathogens and after UV-light treatment. Introduction Transmethylation of intermediates plays an im- portant role in the biosynthesis of the diverse secondary metabolites produced by plants, and involves the class of enzymes called methyltrans- ferases, many of which use S-adenosyl-L-me- thionine (SAM) as the methyl donor [22]. In The nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number X77467.