Molecular Genetics of Amino Acid Biosynthesis in Arabidopsis

我们研究的目的是确定利用拟南芥的植物特有的氨基酸生物合成特征。我们提出了一种分子遗传学方法，通过分离色氨酸需要突变体来解剖色氨酸途径。这一途径在植物中特别重要，因为它在生长素、类黄酮、木质素前体和其他酚类化合物的生物合成中起着重要作用。我们已经分离出的一个突变体的荧光将被用作遗传标记，以获得更多的色氨酸突变体，并了解色氨酸生物合成与激素IAA产生的关系。作为补充，我们将克隆编码色氨酸生物合成酶的基因。其中一个已经克隆的基因色氨酸合成酶的完整序列将被确定。克隆基因作为探针将揭示调控机制、激素控制和细胞内定位。我们对谷氨酸合成酶（GOGAT）的分析将为氨基酸代谢与光合作用之间的关系提供关键信息。我们对HMG辅酶a还原酶的分析也应该提供有关类固醇生物合成方面的重要见解，这对植物来说是新颖的。以克隆的还原酶基因为探针，我们将能够确定激素（赤霉素和脱落酸）对该酶的调节作用。从拟南芥中分离出色氨酸营养不良分子是植物中氨基酸营养不良的首次证明。这一突破为植物基因调控和代谢开辟了一个前所未有的研究领域。

The goal of our studies is to determine the features of amino acid biosynthesis unique to plants using Arabidopsis thaliana. We propose a molecular genetic approach to the dissection of the tryptophan pathway by isolating tryptophan- requiring mutants. This pathway is of particular importance in plants because of its role in the biosynthesis of auxin, flavanoids, lignin precursor and other phenolic compounds. The fluorescence of one of the mutants we have already isolated will be used as a genetic marker to obtain more Trp mutants and to understand the relationship of tryptophan biosynthesis to the production of the hormone IAA. As a complementary approach, we will clone the genes encoding the tryptophan biosynthetic enzymes. The complete sequence of one of these genes, the tryptophan synthetase, which has already been cloned will be determined. The cloned genes used as probes will reveal mechanisms of regulation, hormonal control, and intracellular localization. Our analysis of the glutamate synthase (GOGAT) should provide key information about the relationship between amino acid metabolism and photosynthesis. Our analysis of the HMG CoA reductase should also provide important insights concerning the aspects of steroid biosynthesis that are novel to plants. With the cloned reductase gene as a probe we will able to determine the effects of hormones (gibberilins and abcissic acid) on the regulation of this enzyme. The isolation of a tryptophan auxotroph of Arabidopsis thaliana was of the first demonstrations of amino acid auxotrophy in plants. Such a breakthrough opens up an area of inquiry into plant gene regulation and metabolism which has not been previously possible.