Arabidopsis Myrosinase Genes AtTGG4 and AtTGG5 Are Root-Tip Specific and Contribute to Auxin Biosynthesis and Root-Growth Regulation.
Arabidopsis Myrosinase Genes AtTGG4 and AtTGG5 Are Root-Tip Specific and Contribute to Auxin Biosynthesis and Root-Growth Regulation.
复制标题
拟南芥黑芥子酶基因 AtTGG4 和 AtTGG5 具有根尖特异性，有助于生长素生物合成和根生长调节
DOI：
10.3390/ijms17060892
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发表时间：
2016-06-07
影响因子：
5.6
通讯作者：
Zhang J
中科院分区：
文献类型：
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作者：
Fu L;Wang M;Han B;Tan D;Sun X;Zhang J
植物黑氨酸酶（β-巯基葡萄糖苷葡萄糖水解酶）分为两个亚类，Myr I和Myr II。在十字花科植物中，Myr - 1的生物学功能被认为是对病虫害的主要生化防御。然而，Myr II的生物学功能仍然不清楚。我们研究了两个Myr II成员基因AtTGG4和AtTGG5在拟南芥中的功能。RT-PCR结果显示，这两个基因在根中均有特异性表达。gus分析结果表明，两种基因均在根尖表达，但存在差异：AtTGG4在根尖伸长区表达，而AtTGG5在整个根尖表达。此外，在根中未观察到在地上器官中产生和储存Myr I黑素酶的黑素细胞，并且在特定区域的所有细胞中均有AtTGG4和AtTGG5的表达。在F2代和F3代中，通过T-DNA插入系tgg4E8和tgg5E12的异花授粉，获得纯合子双突变系tgg4tgg5。对突变体根系黑子酶活性分析表明，AtTGG4和AtTGG5具有加性效应，分别贡献了野生型Col-0根中35%和65%的黑子酶活性，tgg4和tgg5的黑子酶活性受到严重抑制。在Murashiege & Skoog （MS）培养基或水分充足的土壤中生长时，coll -0的根最短，tgg4tgg5的根最长，tgg4E8和tgg5E12的根长度居中。而在水分过多的土壤中生长时，Col-0的根最长，tgg4和tgg5的根最短。这些结果表明，AtTGG4和AtTGG5调控了根的生长，并在抗洪能力中发挥作用。将生长素指示基因DR5::GUS通过异花授粉导入tgg4tgg5。DR5::GUS在F1、F2和F3代幼苗中的表达模式表明，AtTGG4和AtTGG5参与了根系生长素的生物合成。提出的机制是，吲哚硫代葡萄糖苷通过AtTGG4和AtTGG5转运到根尖，通过色氨酸依赖途径转化为吲哚-3-乙腈（IAN）， IAN最终通过根尖的腈酶转化为吲哚-3-乙酸（IAA）。这一机制保证了IAA在根尖正确的细胞中生物合成，从而形成正确的生长素梯度，促进根的健康发育。
Plant myrosinases (β-thioglucoside glucohydrolases) are classified into two subclasses, Myr I and Myr II. The biological function of Myr I has been characterized as a major biochemical defense against insect pests and pathogens in cruciferous plants. However, the biological function of Myr II remains obscure. We studied the function of two Myr II member genes AtTGG4 and AtTGG5 in Arabidopsis. RT-PCR showed that both genes were specifically expressed in roots. GUS-assay revealed that both genes were expressed in the root-tip but with difference: AtTGG4 was expressed in the elongation zone of the root-tip, while AtTGG5 was expressed in the whole root-tip. Moreover, myrosin cells that produce and store the Myr I myrosinases in aboveground organs were not observed in roots, and AtTGG4 and AtTGG5 were expressed in all cells of the specific region. A homozygous double mutant line tgg4tgg5 was obtained through cross-pollination between two T-DNA insertion lines, tgg4E8 and tgg5E12, by PCR-screening in the F2 and F3 generations. Analysis of myrosinase activity in roots of mutants revealed that AtTGG4 and AtTGG5 had additive effects and contributed 35% and 65% myrosinase activity in roots of the wild type Col-0, respectively, and myrosinase activity in tgg4tgg5 was severely repressed. When grown in Murashiege & Skoog (MS) medium or in soil with sufficient water, Col-0 had the shortest roots, and tgg4tgg5 had the longest roots, while tgg4E8 and tgg5E12 had intermediate root lengths. In contrast, when grown in soil with excessive water, Col-0 had the longest roots, and tgg4tgg5 had the shortest roots. These results suggested that AtTGG4 and AtTGG5 regulated root growth and had a role in flood tolerance. The auxin-indicator gene DR5::GUS was then introduced into tgg4tgg5 by cross-pollination. DR5::GUS expression patterns in seedlings of F1, F2, and F3 generations indicated that AtTGG4 and AtTGG5 contributed to auxin biosynthesis in roots. The proposed mechanism is that indolic glucosinolate is transported to the root-tip and converted to indole-3-acetonitrile (IAN) in the tryptophan-dependent pathways by AtTGG4 and AtTGG5, and IAN is finally converted to indole-3-acetic acid (IAA) by nitrilases in the root-tip. This mechanism guarantees the biosynthesis of IAA in correct cells of the root-tip and, thus, a correct auxin gradient is formed for healthy development of roots.