REGULATION OF AMINO ACID BIOSYNTHESIS GENES IN PLANTS

植物氨基酸生物合成基因的调控

基本信息

批准号：
6695673
负责人：
Gloria CORUZZI
金额：
$ 2.43万
依托单位：
NEW YORK UNIVERSITY
依托单位国家：
美国
项目类别：
财政年份：
1983
资助国家：
美国
起止时间：
1983-12-01 至 2004-02-29
项目状态：
已结题

项目摘要

The overall goal of our research is to gain a molecular understanding of the regulatory processes that control the assimilation of inorganic nitrogen in plants. This process plays a central role in the regulation of plant growth and development. Using molecular-genetic approaches in Arabidopsis, we identified isoenzymes of GS, GOGAT and GDH that control the assimilation of inorganic-N into Glu/Gln, key amino acids used to transport nitrogen within and between cells. Our studies indicate that expression of these genes is regulated by the metabolic status of the plant. For example, transcriptional induction of GS by light, can be mimicked by sucrose in the absence of light. Moreover, sucrose induction of GS expression can be antagonized by amino acids, which results in repression of GS activity. This led us to hypothesize that plants have a mechanism to sense internal levels of amino acids. This would allow a plant to turn off assimilation of inorganic-N when internal levels of amino acid are high. Testing this hypothesis, defining it mechanistically, and identifying components thereof, is the focus of this renewal. Towards this goal, we have begun to characterize amino acid sensing/signaling components in Arabidopsis using molecular-genetic, cell biological, and biochemical approaches. Our reverse genetic studies are driven by the hypothesis that amino acid sensing is primitive and conserved in evolution. In support of this, the repression of GS expression by amino acids in plants is mechanistically reminiscent of the Ntr system in E. coli. Moreover, we identified a plant homologue of an Ntr component, PII, and showed using PII transgenic plants that PII appears to play a role in C:N sensing in chloroplasts an in GS regulation, as it does in Ntr. The amino acid products of N-assimilation are exported from chloroplasts and transported to other cells, and we have evidence that Glu, the prinicple intermediate, may serve as an extracellular signal . In support of this, we identified putative sensors of extracellular Glu, plant homologues of animal glutamate receptors (iGluRs). We showed plant GluRs function as ligand-gated ion channels, and studies of GLR transgenic plants indicate they may play a role in light signal transduction, reminiscent of their counterparts in the retina and brain. These findings suggest iGluRs are derived from a primitive amino acid signaling mechanism that existed before plants and animals diverged. We propose to exploit this evolutionary conservation and test whether Arabidopsis (or GLR mutants we isolate) can be used in a bioassay for drugs to treat GluR-related diseases in humans. We will also use forward genetic approaches to isolate amino acid sensing/signaling mutants in Arabidopsis which may identify components of these evolutionarily conserved amino acid signaling pathways or novel pathways.

我们研究的总体目标是对控制植物中无机氮的调控过程有分子的理解。该过程在调节植物生长和发育中起着核心作用。使用拟南芥中的分子遗传学方法，我们确定了GS，GOGAT和GDH的同工酶，以控制无机-N的同化为GLU/GLN，这是用于在细胞内部和细胞之间运输氮的关键氨基酸。我们的研究表明，这些基因的表达受植物的代谢状态调节。例如，在没有光的情况下，蔗糖可以模仿通过光对GS的转录诱导。此外，氨基酸可以拮抗GS表达的蔗糖诱导，从而导致GS活性抑制。这使我们假设植物具有感知内部氨基酸水平的机制。当氨基酸的内部水平高时，这将使植物可以关闭无机-N的同化。检验该假设，从机械上定义它并识别其组成部分，是该续约的重点。为了实现这一目标，我们已经开始使用分子遗传学，细胞生物学和生化方法来表征拟南芥中氨基酸传感/信号传导成分。我们的反向遗传研究是由氨基酸传感在进化中是原始且保守的假设所驱动的。为此，氨基酸在植物中对GS表达的抑制在机械上让人联想到大肠杆菌中的NTR系统。此外，我们确定了NTR成分PII的植物同源物，并使用PII转基因植物显示了PII似乎在GS调节中在叶绿体中的C：N传感中起作用，就像在NTR中一样。 N-综合的氨基酸产物从叶绿体中输出并运输到其他细胞，我们有证据表明，Prinicple中间体Glu可以用作细胞外信号。为了支持这一点，我们确定了细胞外GLU，动物谷氨酸受体（Iglurs）的植物同源物的推定传感器。我们表现出植物gl的功能作为配体门控离子通道，对GLR转基因植物的研究表明，它们可能在光信号转导中发挥作用，让人联想到视网膜和大脑中的对应物。这些发现表明，iGlurs源自在植物和动物差异之前存在的原始氨基酸信号传导机制。我们建议利用这种进化保护，并测试拟南芥（或我们分离的GLR突变体）是否可以在生物测定中用于治疗人类中与GLUR相关疾病的药物。我们还将使用正向遗传方法分离拟南芥中的氨基酸传感/信号传导突变体，这些突变体可以识别这些进化保守的氨基酸信号通路或新途径的成分。