Horticultural Sciences, University of Florida, Gainesville, Florida 32611, USA.
Institute of Plant Breeding, Genetics and Genomics, University of Georgia, Athens, Georgia 30602, USA.
Plant Physiol. 2023 Jan 2;191(1):110-124. doi: 10.1093/plphys/kiac509.
Methyl salicylate imparts a potent flavor and aroma described as medicinal and wintergreen that is undesirable in tomato (Solanum lycopersicum) fruit. Plants control the quantities of methyl salicylate through a variety of biosynthetic pathways, including the methylation of salicylic acid to form methyl salicylate and subsequent glycosylation to prevent methyl salicylate emission. Here, we identified a subclade of tomato methyl esterases, SALICYLIC ACID METHYL ESTERASE1-4, responsible for demethylation of methyl salicylate to form salicylic acid in fruits. This family was identified by proximity to a highly significant methyl salicylate genome-wide association study locus on chromosome 2. Genetic mapping studies in a biparental population confirmed a major methyl salicylate locus on chromosome 2. Fruits from SlMES1 knockout lines emitted significantly (P < 0,05, t test) higher amounts of methyl salicylate than wild-type fruits. Double and triple mutants of SlMES2, SlMES3, and SlMES4 emitted even more methyl salicylate than SlMES1 single knockouts-but not at statistically distinguishable levels-compared to the single mutant. Heterologously expressed SlMES1 and SlMES3 acted on methyl salicylate in vitro, with SlMES1 having a higher affinity for methyl salicylate than SlMES3. The SlMES locus has undergone major rearrangement, as demonstrated by genome structure analysis in the parents of the biparental population. Analysis of accessions that produce high or low levels of methyl salicylate showed that SlMES1 and SlMES3 genes expressed the highest in the low methyl salicylate lines. None of the MES genes were appreciably expressed in the high methyl salicylate-producing lines. We concluded that the SlMES gene family encodes tomato methyl esterases that convert methyl salicylate to salicylic acid in ripe tomato fruit. Their ability to decrease methyl salicylate levels by conversion to salicylic acid is an attractive breeding target to lower the level of a negative contributor to flavor.
水杨酸甲酯赋予番茄（Solanum lycopersicum）果实强烈的风味和香气，被描述为药用和冬青味，这是不理想的。植物通过多种生物合成途径控制水杨酸甲酯的数量，包括将水杨酸甲基化形成水杨酸甲酯，然后糖基化以防止水杨酸甲酯的释放。在这里，我们鉴定了一个番茄甲酯酶亚家族，即水杨酸甲酯酶 1-4，负责将甲基水杨酸甲酯脱甲基形成果实中的水杨酸。这个家族是通过与染色体 2 上一个高度显著的水杨酸甲酯全基因组关联研究位点的接近程度来鉴定的。在双亲群体中的遗传作图研究证实了染色体 2 上存在一个主要的水杨酸甲酯位点。SlMES1 敲除系的果实比野生型果实释放出显著（P<0.05，t 检验）更高量的水杨酸甲酯。SlMES2、SlMES3 和 SlMES4 的双突变体和三突变体比 SlMES1 单突变体释放出更多的水杨酸甲酯，但与单突变体相比，没有达到统计学上可区分的水平。异源表达的 SlMES1 和 SlMES3 在体外作用于水杨酸甲酯，SlMES1 对水杨酸甲酯的亲和力高于 SlMES3。SlMES 基因座经历了重大重排，这可以通过双亲群体中亲本的基因组结构分析来证明。对产生高或低水平水杨酸甲酯的品种进行分析表明，SlMES1 和 SlMES3 基因在低水杨酸甲酯系中表达最高。在高水杨酸甲酯产生系中，没有一个 MES 基因被明显表达。我们得出结论，SlMES 基因家族编码番茄甲酯酶，在成熟的番茄果实中，将水杨酸甲酯转化为水杨酸。它们将水杨酸甲酯转化为水杨酸以降低其水平的能力是一个有吸引力的育种目标，可以降低风味的一个负面贡献物的水平。
