Functional expression of an Arabidopsis cDNA clone encoding a flavonol 3 '-O-methyltransferase and characterization of the gene product

We report that the cDNA clone (Accession No. U70424), previously isolated f rom Arabidopsis thaliana as encoding a caffeic acid/5-hydroxyferulic acid O -methyltransferase (OMT) (1), has now been overexpressed in Escherichia col i BL21 and its recombinant protein identified as a novel flavonol 3'-OMT. I t is, therefore, renamed AtOMT1. This cDNA clone has previously been identi fied on the basis of its 88% amino acid sequence similarity and 80% identit y to the aspen bispecific lignin OMT (2), the type member of the group invo lved in lignin biosynthesis, Our data indicate that this novel GRIT uses th e flavonol quercetin as: the preferred substrate, but neither of the hydrox ycinnamic acids, caffeic or 5-hydroxyferulic, to any significant extent. Th is indicates that the high sequence similarity/identity of AtOMT1 to that o f the aspen lignin GRIT (2) is not sufficient to assign the function of thi s gene product, (C) 2000 Academic Press.