Regulation of Sulfate Assimilation in Plants

硫酸盐同化是无机硫酸盐（SO42-）为合成半胱氨酸而被还原的途径。半胱氨酸是一种具有多种功能的重要氨基酸。本文主要介绍了其作为植物中重要抗氧化剂谷胱甘肽前体的作用。APS还原酶从5-腺苷酸硫酸盐（APS）中产生亚硫酸盐（SO32-），催化硫酸盐同化的重要步骤。实验证明，APS还原酶是被氧化激活的。提出的假设是APS还原酶在氧化应激条件下调节谷胱甘肽合成中起关键作用。因此，它可能是植物对氧化胁迫反应的重要组成部分。在提出的工作中，将通过探索APS还原酶调控的机制和生理作用来验证项目假设。APS还原酶基因已从几种不同的植物中克隆出来。每一种都将被研究受氧化条件调节的能力。据认为，APS还原酶的调控机制依赖于蛋白中两个可形成二硫键的半胱氨酸残基。将分析酶的半胱氨酸残基的状态。最后，我们还将研究通过在转基因植物中表达细菌同源物来绕过APS还原酶步骤的生理效应。这项工作将为植物对氧化应激反应的一个重要方面提供新的见解，即谷胱甘肽合成的调节机制。APS还原酶是由氧化应激条件激活的一小群酶之一。该系统的新颖性及其与氧化应激的联系是进一步研究APS还原酶的重要原因。

Sulfate assimilation is the pathway by which inorganic sulfate (SO42-) is reduced for cysteine synthesis. Cysteine is an important amino acid with many different functions. This proposal focuses on its role as the precursor of glutathione an important antioxidant in plants.The enzyme APS reductase, which produces sulfite (SO32-) from 5-adenylylsulfate (APS), catalyzes an essential step in sulfate assimilation. Experimental evidence has been obtained that APS reductase is activated by oxidation. The proposal hypothesis is that APS reductase plays a key role in regulation of glutathione synthesis under conditions of oxidative stress. Therefore, it may be an important component in the plant response to oxidative stress.In the work proposed the project hypothesis will be tested by exploring the mechanism and physiological effect of APS reductase regulation. APS reductase genes have been cloned from several different plant species. Each will be studied for the ability to be regulated by oxidative conditions. It is believed that the mechanism of APS reductase regulation relies on two cysteine residues in the protein that can form a disulfide bond. The state of the cysteine residues of the enzyme will be analyzed. Finally, the physiological effect of bypassing the APS reductase step by expressing bacterial homologs in transgenic plants will also be studied.This work will provide new insight into an important facet of plant response to oxidative stress, the mechanism for regulation of glutathione synthesis. APS reductase is one of a small group of enzymes that are activated by oxidative stress conditions. The novelty of this system and the connection with oxidative stress are compelling reasons for further study of APS reductase.