Glucosinolates are anionic thioglucosides that have become one of the most frequently studied groups of defensive metabolites in plants. When tissue damage occurs, the thioglucoside linkage is hydrolyzed by enzymes known as myrosinases, resulting in the formation of a variety of products that are active against herbivores and pathogens. In an effort to learn more about the molecular genetic and biochemical regulation of glucosinolate hydrolysis product formation, we analyzed leaf samples of 122 Arabidopsis ecotypes. A distinct polymorphism was observed with all ecotypes producing primarily isothiocyanates or primarily nitriles. The ecotypes Columbia (Col) and Landsberg erecta (Ler) differed in their hydrolysis products; therefore, the Col × Ler recombinant inbred lines were used for mapping the genes controlling this polymorphism. The major quantitative trait locus (QTL) affecting nitrile versus isothiocyanate formation was found very close to a gene encoding a homolog of a Brassica napus epithiospecifier protein (ESP), which causes the formation of epithionitriles instead of isothiocyanates during glucosinolate hydrolysis in the seeds of certain Brassicaceae. The heterologously expressed Arabidopsis ESP was able to convert glucosinolates both to epithionitriles and to simple nitriles in the presence of myrosinase, and thus it was more versatile than previously described ESPs. The role of ESP in plant defense is uncertain, because the generalist herbivore Trichoplusia ni (the cabbage looper) was found to feed more readily on nitrile-producing than on isothiocyanate-producing Arabidopsis. However, isothiocyanates are frequently used as recognition cues by specialist herbivores, and so the formation of nitriles instead of isothiocyanates may allow Arabidopsis to be less apparent to specialists.
硫代
葡萄糖苷是阴离子
硫代
葡萄糖苷,已成为植物防御代谢物中最常被研究的类别之一。当组织受损时,
硫代
葡萄糖苷键会被一种名为芥子酶的酶
水解,从而形成多种对食草动物和病原体具有活性的产物。为了进一步了解
硫代
葡萄糖苷
水解产物形成的分子遗传和生化调控,我们对122种拟南芥生态型的叶片样本进行了分析。我们发现,所有生态型都表现出明显的多态性,它们主要产生异
硫氰酸酯或腈。哥伦比亚(Col)和兰茨贝格直立(Ler)生态型的
水解产物不同,因此,我们使用Col×Ler
重组自交系来绘制控制这种多态性的
基因。我们发现,影响腈和异
硫氰酸酯形成的主要数量性状位点(QTL)非常接近编码油菜素
内酯类同源蛋白(E
SP)的
基因,在某些十字花科植物的种子中,该蛋白在
硫代
葡萄糖苷
水解过程中会导致形成表
硫腈而不是异
硫氰酸酯。异源表达的拟南芥E
SP能够在芥子酶的作用下将
硫代
葡萄糖苷转化为表
硫腈和简单腈,因此它比之前描述的E
SP更具通用性。