Kroymann J, Textor S, Tokuhisa J G, Falk K L, Bartram S, Gershenzon J, Mitchell-Olds T
Department of Genetics and Evolution, Max Planck Institute for Chemical Ecology, Carl-Zeiss-Promenade 10, 07745 Jena, Germany.
Plant Physiol. 2001 Nov;127(3):1077-88.
Arabidopsis and other Brassicaceae produce an enormous diversity of aliphatic glucosinolates, a group of methionine (Met)-derived plant secondary compounds containing a beta-thio-glucose moiety, a sulfonated oxime, and a variable side chain. We fine-scale mapped GSL-ELONG, a locus controlling variation in the side-chain length of aliphatic glucosinolates. Within this locus, a polymorphic gene was identified that determines whether Met is extended predominantly by either one or by two methylene groups to produce aliphatic glucosinolates with either three- or four-carbon side chains. Two allelic mutants deficient in four-carbon side-chain glucosinolates were shown to contain independent missense mutations within this gene. In cell-free enzyme assays, a heterologously expressed cDNA from this locus was capable of condensing 2-oxo-4-methylthiobutanoic acid with acetyl-coenzyme A, the initial reaction in Met chain elongation. The gene methylthioalkylmalate synthase1 (MAM1) is a member of a gene family sharing approximately 60% amino acid sequence similarity with 2-isopropylmalate synthase, an enzyme of leucine biosynthesis that condenses 2-oxo-3-methylbutanoate with acetyl-coenzyme A.
拟南芥和其他十字花科植物能产生种类繁多的脂肪族硫代葡萄糖苷，这是一类由甲硫氨酸（Met）衍生而来的植物次生化合物，含有一个β-硫代葡萄糖部分、一个磺化肟和一个可变侧链。我们对GSL-ELONG进行了精细定位，该基因座控制脂肪族硫代葡萄糖苷侧链长度的变异。在这个基因座内，鉴定出一个多态性基因，它决定了Met主要是通过一个还是两个亚甲基进行延伸，从而产生具有三碳或四碳侧链的脂肪族硫代葡萄糖苷。两个缺乏四碳侧链硫代葡萄糖苷的等位基因突变体被证明在该基因内含有独立的错义突变。在无细胞酶分析中，来自该基因座的一个异源表达cDNA能够将2-氧代-4-甲基硫代丁酸与乙酰辅酶A缩合，这是Met链延伸的起始反应。甲硫基烷基苹果酸合酶1（MAM1）基因是一个基因家族的成员，该家族与亮氨酸生物合成中的一种酶2-异丙基苹果酸合酶具有约60%的氨基酸序列相似性，2-异丙基苹果酸合酶能将2-氧代-3-甲基丁酸与乙酰辅酶A缩合。
