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

Colorado State University, Fort Collins CO

Investigators

Abstract

All organisms must regulate metal homeostasis, which involves metal uptake, transport, storage, and distribution. The goal of this research is to gain insight into the basic mechanisms by which heavy metal homeostasis is regulated in plants, particularly in the chloroplast. The chloroplast is the location of photosynthesis, the process that drives all life on earth. This complex process involves a set of enzymes and pigments, many of which require specific heavy metal ions as cofactors, e.g. copper, iron, magnesium, manganese, and zinc. Although these metals are necessary components of the photosynthetic machinery - as well as of other enzymes in the 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 presence of putative chloroplast import sequences, both gene products are predicted to be functional in the chloroplast. Based on similarities with genes cloned from other sources, Paa1 protein is likely involved in copper transport, and AtCutA protein in the regulation of copper tolerance. These hypotheses regarding the location and functions of these proteins are analyzed in this project. The mRNA levels of both genes will be analyzed with respect to tissue distribution, developmental stage, and environmental conditions such as metal toxicity or metal deficiency. The intracellular location of the proteins encoded by the genes will be determined. To investigate the functions of the genes in vivo, Dr.Pilon will analyze plant lines that 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 about heavy 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 in plants. This, in turn, may be used to increase crop yields and nutritional value of plants, or to help clean up metal-contaminated sites.