Perry Jason, Dai Xinhua, Zhao Yunde
Section of Cell and Developmental Biology, Division of Biological Sciences, University of California San Diego, La Jolla, CAa 92093-0116, USA.
Plant Physiol. 2005 Nov;139(3):1284-90. doi: 10.1104/pp.105.068700. Epub 2005 Oct 21.
Auxin-resistant mutants have been useful for dissecting the mechanisms that underlie auxin-mediated biological processes. Here we report the isolation and molecular characterization of a novel auxin-resistant mutant in Arabidopsis (Arabidopsis thaliana). Like known mutated AUX/IAA transcription factors, the mutant described here displayed dominant resistance to exogenously supplied auxins (sirtinol, 2,4-dichlorophenoxyacetic acid, indole-3-acetic acid) and a host of pleiotropic phenotypes, including apical hook deformation, defects in lateral root development, reduced stature, and homozygous lethality. This mutant showed the same sensitivity to the ethylene precursor 1-aminocyclopropane carboxylic acid as wild-type plants, and retained the ability to induce IAA19 expression in response to exogenously supplied indole-3-acetic acid. To our surprise, these phenotypes were not caused by a mutation in an AUX/IAA gene, but rather a mutation in a tRNA(ala) gene in which the anticodon was found changed from CGC to CAC. Such a change results in a tRNA that is charged with alanine but recognizes the second most highly used valine codon in Arabidopsis. Therefore, the observed phenotypes are likely the composite of stochastic mutations of many proteins, including downstream effectors.
生长素抗性突变体对于剖析生长素介导的生物学过程的潜在机制很有用。在此，我们报告了拟南芥（Arabidopsis thaliana）中一个新型生长素抗性突变体的分离和分子特征。与已知的突变AUX/IAA转录因子一样，这里描述的突变体对外源供应的生长素（西曲瑞克、2,4-二氯苯氧乙酸、吲哚-3-乙酸）表现出显性抗性以及一系列多效性表型，包括顶端弯钩变形、侧根发育缺陷、植株矮小和纯合致死性。该突变体对乙烯前体1-氨基环丙烷羧酸的敏感性与野生型植物相同，并保留了对外源供应的吲哚-3-乙酸作出反应诱导IAA19表达的能力。令我们惊讶的是，这些表型并非由AUX/IAA基因的突变引起，而是由一个tRNA(ala)基因的突变导致，其中反密码子从CGC变为CAC。这样的变化导致一种tRNA，它携带丙氨酸但识别拟南芥中第二常用的缬氨酸密码子。因此，观察到的表型可能是许多蛋白质（包括下游效应器）随机突变的综合结果。
