Biosynthesis of the major scent components 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene by novel rose O-methyltransferases.

In Chinese rose species and in many modern varieties, two methylated phenolic derivatives, 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene, are major scent components. We show that cell-free extracts of rose petals catalyse the synthesis of 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene by methylation of precursor molecules. An expressed sequence tag approach was used to identify four highly similar O-methyltransferase sequences expressed specifically in petals and anthers. Thin layer chromatography analysis showed that the activities of these enzymes with different substrates and the proportions of reaction products produced closely mimicked those observed using cell-free petal extracts, indicating that orcinol O-methyltransferases are responsible for the biosynthesis of 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene from un-methylated precursors in this organ.