Genome-Wide Hunt For Metal Hyperaccumulation Genes

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01297747David E. SaltThe overall objective of this project is to identify genes involved in metal hyperaccumulation in metal-hyperaccumulating plants. These unique plant species are able to accumulate between 0.1 and 3% of their shoot dry biomass as Cd, Ni, Se or Zn depending on the species. Such characteristics could be invaluable in current efforts to use plants to clean metal-contaminated sites (phytoremediation). The known metal hyperaccumulators are not well suited for phytoremediation because of their small size and slow growth. However, they are a unique source of genes for metal hyperaccumulation. Over 25% of the known hyperaccumulator species are members of the Brassicaceae family, and as such they are related to Arabidopsis thaliana. By investigating the molecular genetics of metal hyperaccumulation in species related to A. thaliana, the investigators will utilize the technical and genetic resources developed during the Arabidopsis genome project, harnessing powerful functional genomics technologies to dissect metal hyperaccumulation at the genetic level. Metal hyperaccumulators in the Brassicaceae will be collected from around the world, and genes important in hyperaccumulation will be identified using three complementary approaches. Seed from approximately 40 accessions of over 20 different species of hyperaccumulators in the Brassicaceae family will be collected from North America, France, Germany, Austria, Italy, Greece and Turkey. Accessions of metal hyperaccumulators found to be amenable to T-DNA insertional mutagenesis will be identified and over 100,000 genetic lines will be generated. In a forward genetic approach, these lines will be screened for mutants exhibiting metal-sensitivity and loss of metal-hyperaccumulation. T-DNA tagged genes from these mutants will be isolated, and their role in metal hyperaccumulation determined. In a reverse genetic approach, genomic DNA pools will be generated from these lines and screened by PCR to identify lines containing T-DNA insertions in genes already known or suspected to be involved in metal hyperaccumulation. The A. thaliana genome sequence will provide a rich source of candidate genes for this reverse genetic approach. In a third approach, cDNA expression libraries will be created in E. coli and yeast from hyperaccumulating species and screened for genes conferring heavy-metal resistance and sensitivity. Taken together these approaches will provide a comprehensive framework for the identification of genes involved in metal hyperaccumulation in plants. The set of genes identified in this project will provide a valuable resource for the future development of plants ideally suited for the phytoremediation of metal polluted sites. This project was funded through the Joint Program on Phytoremediation, co-sponsored by the Environmental Protection Agency, the National Science Foundation, the Office of Naval Research, and the Strategic Environmental Research and Development Program.