Soils and waters with high levels of toxic heavy metals such as cadmium, arsenic, lead and mercury are detrimental to human and environmental health. These 4 metal(loid)s are among the Superfund's top 7 priority hazardous substances. Recent research and applications indicate that uptake of heavy metals into plants via the root system and accumulation of heavy metals in plant shoots could provide a cost effective approach for toxic metal removal and remediation of heavy metal-laden soils and waters. However many genes, mechanisms and pathways that function in heavy metal over-accumulation in plants remain to be identified and characterized. Phytochelatins are major heavy metal and metalloid chelating and detoxifying thiolate peptides in plants. In recent research we have made advances at understanding mechanisms that contribute to heavy metal detoxification and transport in plants, including isolation of phytochelatin synthase genes, characterization of mechanisms for root to shoot transfer of cadmium, isolation of heavy metal accumulation Arabidopsis mutants, development of a novel microarray-based rapid mutant cloning approach and microarray-based identification of putative transporter genes that may contribute to heavy metal transport. The investigators will test the hypotheses that, phytochelatins affect long distance root to leaf vascular transport of toxic metals; characterization of new toxic metal accumulation mutants will lead to identification of rate-limiting steps that function in plant heavy metal accumulation; and heavy metal sensing and signal transduction mechanisms in plants are important for plant heavy metal resistance and accumulation. To test these hypotheses, the proposed project will, in Specific Aims 1 and 2, characterize novel physiological and molecular mechanisms of root to shoot transport of heavy metals and phytochelatins using physiological, genomic, biochemical and membrane transport analyses. By pursuing a new high-throughput screening approach in collaborative research, the investigators have identified Arabidopsis mutants that affect the accumulation of toxic metals in leaves.
In Specific Aim 3, a newly developed genomic microarray-based rapid mutant mapping and cloning approach will be used to isolate selected heavy metal accumulation mutant genes and characterize the underlying mechanisms.
Specific Aim 4 will be to characterize heavy metal biosensing and transduction mechanisms in plants using a luciferase reporter screen. Trials with contaminated soils from Superfund sites will be pursued in collaboration with Edenspace Corp (in Specific Aim 5), to assess the feasibility of monitoring bioavailable heavy metals and of hyperaccumulating heavy metals and metalloids into plant roots and shoots using transgenic and mutant plants generated in this research.
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