Metal Homeostasis and Tolerance in Plant Chloroplasts - The Role of PAA1 and AtCUTA

所有生物都必须调节金属的体内平衡，包括金属的摄取、运输、储存和分配。本研究的目的是深入了解植物，特别是叶绿体中重金属稳态调节的基本机制。叶绿体是光合作用的场所，而光合作用是驱动地球上所有生命的过程。这个复杂的过程涉及一系列酶和色素，其中许多需要特定的重金属离子作为辅助因子，例如铜、铁、镁、锰和锌。尽管这些金属是光合作用机制以及细胞中其他酶的必要组成部分，但当它们过量存在时是有毒的。因此，叶绿体铜稳态对植物健康和生产力至关重要。本项目重点研究拟南芥的两个基因PAA1和AtCUTA，这两个基因都被认为与金属稳态有关。从假定的叶绿体输入序列的存在判断，这两个基因产物被预测在叶绿体中起作用。基于与从其他来源克隆的基因的相似性，Paa1蛋白可能参与铜转运，AtCutA蛋白参与铜耐受性的调节。本项目对这些蛋白质的定位和功能的假设进行了分析。这两个基因的mRNA水平将根据组织分布、发育阶段和环境条件（如金属毒性或金属缺乏）进行分析。由基因编码的蛋白质在细胞内的位置将被确定。为了研究这些基因在体内的功能，皮隆博士将分析有T-DNA插入的植物品系和过度表达这些基因的植物品系。他们将研究金属稳态和光合装置的组装。最后，确定编码蛋白的金属结合特性和金属特异性。该项目的结果将为重金属在叶绿体中的稳态机制提供急需的基础知识，这是一个尚未开发的研究领域。此外，这项工作可能导致策略的发展，以操纵金属耐受性和积累在植物。反过来，这可以用来增加作物产量和植物的营养价值，或者帮助清理金属污染的地方。

All organisms must regulate metal homeostasis, which involves metaluptake, transport, storage, and distribution. The goal of this research isto gain insight into the basic mechanisms by which heavy metal homeostasisis regulated in plants, particularly in the chloroplast. The chloroplast isthe location of photosynthesis, the process that drives all life on earth.This complex process involves a set of enzymes and pigments, many of whichrequire specific heavy metal ions as cofactors, e.g. copper, iron,magnesium, manganese, and zinc. Although these metals are necessarycomponents of the photosynthetic machinery - as well as of other enzymes inthe cell - they are toxic when present in excess. Therefore,chloroplast copper homeostasis is vital for plant heath and productivity.This project focuses on two Arabidopsis thaliana genes, PAA1 and AtCUTA,both thought to be involved in metal homeostasis. Judged from the presenceof putative chloroplast import sequences, both gene products are predictedto be functional in the chloroplast. Based on similarities with genescloned from other sources, Paa1 protein is likely involved in coppertransport, and AtCutA protein in the regulation of copper tolerance. Thesehypotheses regarding the location and functions of these proteins areanalyzed in this project. The mRNA levels of both genes will beanalyzed with respect to tissue distribution, developmental stage, andenvironmental conditions such as metal toxicity or metal deficiency. Theintracellular location of the proteins encoded by the genes will bedetermined. To investigate the functions of the genes in vivo, Dr.Pilon will analyze plant linesthat have T-DNA insertions and plant lines that overexpress the genes. They will be studied with respect to metal homeostasis and assembly of the photosynthetic apparatus. Finally, the metal binding properties and metal specificity of the encoded proteins will be determined. The results from this project will provide much-needed fundamental knowledge aboutheavy metal homeostasis mechanisms in chloroplasts, a largely unexplored field of research. In addition, this work may lead to the development of strategies to manipulate metal tolerance and accumulation inplants. This, in turn, may be used to increase crop yields and nutritionalvalue of plants, or to help clean up metal-contaminated sites.