Plant Molecular and Cellular Biology Program, Horticultural Sciences, University of Florida, Gainesville, FL 32611-0690, USA.
Plant J. 2010 Apr 1;62(1):113-23. doi: 10.1111/j.1365-313X.2010.04128.x. Epub 2010 Jan 7.
Methyl salicylate (MeSA) is a volatile plant secondary metabolite that is an important contributor to taste and scent of many fruits and flowers. It is synthesized from salicylic acid (SA), a phytohormone that contributes to plant pathogen defense. MeSA is synthesized by members of a family of O-methyltransferases. In order to elaborate the mechanism of MeSA synthesis in tomato, we screened a set of O-methyltransferases for activity against multiple substrates. An enzyme that specifically catalyzes methylation of SA, SlSAMT, as well as enzymes that act upon jasmonic acid and indole-3-acetic acid were identified. Analyses of transgenic over- and under-producing lines validated the function of SlSAMT in vivo. The SlSAMT gene was mapped to a position near the bottom of chromosome 9. Analysis of MeSA emissions from an introgression population derived from a cross with Solanum pennellii revealed a quantitative trait locus (QTL) linked to higher fruit methyl salicylate emissions. The higher MeSA emissions associate with significantly higher SpSAMT expression, consistent with SAMT gene expression being rate limiting for ripening-associated MeSA emissions. Transgenic plants that constitutively over-produce MeSA exhibited only slightly delayed symptom development following infection with the disease-causing bacterial pathogen, Xanthomonas campestris pv. vesicatoria (Xcv). Unexpectedly, pathogen-challenged leaves accumulated significantly higher levels of SA as well as glycosylated forms of SA and MeSA, indicating a disruption in control of the SA-related metabolite pool. Taken together, the results indicate that SlSAMT is critical for methyl salicylate synthesis and methyl salicylate, in turn, likely has an important role in controlling SA synthesis.
水杨酸甲酯（MeSA）是一种挥发性植物次生代谢物，是许多水果和花卉味道和气味的重要贡献者。它是由水杨酸（SA）合成的，SA 是一种植物激素，有助于植物抵御病原体。MeSA 是由一系列 O-甲基转移酶家族成员合成的。为了详细阐述番茄中 MeSA 合成的机制，我们筛选了一组针对多种底物具有活性的 O-甲基转移酶。鉴定出一种特异性催化 SA 甲基化的酶 SlSAMT，以及作用于茉莉酸和吲哚-3-乙酸的酶。过表达和低表达转基因系的分析验证了 SlSAMT 在体内的功能。SlSAMT 基因定位于染色体 9 的底部附近。对来自与 Solanum pennellii 杂交的导入系的 MeSA 排放分析揭示了与更高果实甲基水杨酸排放相关的数量性状位点（QTL）。更高的 MeSA 排放与 SpSAMT 表达的显著增加相关，这与 SAMT 基因表达是与成熟相关的 MeSA 排放的限速步骤一致。组成型过量产生 MeSA 的转基因植物在感染致病细菌病原体黄单胞菌 pv.vesicatoria（Xcv）后，仅表现出稍晚的症状发展。出乎意料的是，受病原体挑战的叶片积累了显著更高水平的 SA 以及 SA 和 MeSA 的糖基化形式，表明 SA 相关代谢物池的控制受到干扰。综上所述，结果表明 SlSAMT 对甲基水杨酸合成至关重要，而甲基水杨酸可能反过来在控制 SA 合成中发挥重要作用。
