The New Zealand Institute for Plant and Food Research Limited (PFR), Private Bag 92169, Auckland, 1142, New Zealand.
Plant and Food Research Limited (PFR), Private Bag 11600, Palmerston North, 4442, New Zealand.
Plant J. 2015 Jun;82(6):937-950. doi: 10.1111/tpj.12861. Epub 2015 May 20.
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 (QTLs; accounting for 9.2 and 24.8% of the variation) on linkage group (LG) 1 and LG2 were identified that co-located with seven candidate genes for phenylpropene O-methyltransferases (MdoOMT1-7). Of these genes, only expression of MdoOMT1 on LG1 increased strongly with ethylene and could be correlated with increasing estragole production in ripening RG fruit. Transient over-expression in tobacco showed that MdoOMT1 utilised a range of phenylpropene substrates and catalysed the conversion of chavicol to estragole. Royal Gala carried two alleles (MdoOMT1a, MdoOMT1b) whilst GS appeared to be homozygous for MdoOMT1b. MdoOMT1a showed a higher affinity and catalytic efficiency towards chavicol than MdoOMT1b, which could account for the phenotypic variation at the LG1 QTL. Multiple transgenic RG lines with reduced MdoOMT1 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 MdoOMT1 is required for the production of methylated phenylpropenes in apple and that phenylpropenes including estragole may contribute to ripe apple fruit aroma.
苯丙烯类，如丁香酚和反式茴香脑，是许多草药和香料中决定风味和香气的重要芳香化合物。一些苹果品种生产的果实具有非常理想的辛辣/芳香风味，这归因于甲基苯丙烯烯醇的产生，一种甲基化的苯丙烯。为了阐明 estragole 产生的分子基础及其对成熟苹果风味和香气的贡献，我们对皇家 Gala（RG，estragole 产生者）× Granny Smith（GS，非产生者）苹果杂交种的分离群体进行了表征。在 LG1 和 LG2 上鉴定出两个数量性状位点（QTL；占 9.2%和 24.8%的变异），与 7 个苯丙烯 O-甲基转移酶（MdoOMT1-7）候选基因共定位。在这些基因中，只有 LG1 上的 MdoOMT1 表达随着乙烯的增加而强烈增加，并且可以与 RG 果实成熟过程中 estragole 产量的增加相关。在烟草中的瞬时过表达表明，MdoOMT1 利用一系列苯丙烯底物，并催化 chavicol 转化为 estragole。皇家 Gala 携带两个等位基因（MdoOMT1a，MdoOMT1b），而 GS 似乎为 MdoOMT1b 的纯合子。MdoOMT1a 对 chavicol 的亲和力和催化效率均高于 MdoOMT1b，这可以解释 LG1 QTL 的表型变异。具有降低的 MdoOMT1 表达的多个转基因 RG 系产生的甲基化苯丙烯，包括 estragole 和 methyleugenol 的水平较低。与对照相比，这些果实的果实香气差异可以通过感官分析来感知。这些结果表明，MdoOMT1 是苹果中甲基化苯丙烯产生所必需的，并且包括 estragole 在内的苯丙烯可能有助于成熟苹果果实的香气。
