The O ‐methyltransferase gene M do OMT 1 is required for biosynthesis of methylated phenylpropenes in ripe apple fruit

Summary Phenylpropenes, such as eugenol and trans ‐anethole, are important aromatic compounds that determine flavour and aroma in many herbs and spices. Some apple varieties produce fruit with a highly desirable spicy/aromatic flavour that has been attributed to the production of estragole, a methylated phenylpropene. To elucidate the molecular basis for estragole production and its contribution to ripe apple flavour and aroma we characterised a segregating population from a Royal Gala ( RG , estragole producer) × Granny Smith ( GS , non‐producer) apple cross. Two quantitative trait loci ( QTL s; accounting for 9.2 and 24.8% of the variation) on linkage group ( LG ) 1 and LG 2 were identified that co‐located with seven candidate genes for phenylpropene O ‐methyltransferases ( Mdo OMT 1–7 ). Of these genes, only expression of Mdo OMT 1 on LG 1 increased strongly with ethylene and could be correlated with increasing estragole production in ripening RG fruit. Transient over‐expression in tobacco showed that Mdo OMT 1 utilised a range of phenylpropene substrates and catalysed the conversion of chavicol to estragole. Royal Gala carried two alleles ( Mdo OMT 1a , Mdo OMT 1b ) whilst GS appeared to be homozygous for Mdo OMT 1b . Mdo OMT 1a showed a higher affinity and catalytic efficiency towards chavicol than Mdo OMT 1b, which could account for the phenotypic variation at the LG 1 QTL . Multiple transgenic RG lines with reduced Mdo OMT 1 expression produced lower levels of methylated phenylpropenes, including estragole and methyleugenol. Differences in fruit aroma could be perceived in these fruit, compared with controls, by sensory analysis. Together these results indicate that Mdo OMT 1 is required for the production of methylated phenylpropenes in apple and that phenylpropenes including estragole may contribute to ripe apple fruit aroma.