Phytochelatin synthase & resistance to heavy metals

土壤和沃茨中含有大量有毒金属，如镉（Cd）、砷（As）、铅（Pb）和汞（Hg），对人类和环境健康有害。这四种金属是超级基金的前五名优先危险物质。研究表明，植物通过根系吸收重金属可以为土壤和沃茨中有毒金属的去除和修复提供一种有效且经济的方法。植物螯合素是植物和真菌中主要的重金属螯合和解毒巯基肽，能与重金属Cd、Zn、Pb、Hg形成络合物并解毒，最近的研究还发现对As也有解毒作用。植物螯合素合成酶（PCS）产生植物螯合素，因此作为植物中的主要催化金属解毒机制起作用。然而，尚未鉴定出编码植物螯合素脱氢酶的基因。我们最近在植物和真菌中克隆了一个新的植物螯合素合成酶基因家族（PCS）。PCS cDNA在S.酿酒酵母显着提高抗镉。破坏S. pombe和拟南芥产生增加的重金属敏感性。重组PCS蛋白在体外合成植物螯合素。我们将测试的假设，压力信号通路有助于PCS的诱导和解毒，PCS基因的转基因表达，可以与其他金属相互作用的机制，提高重金属的超积累和植物的清除。为了验证这些假设，我们将：（I）表征诱导PCS表达的信号传导机制。(II)研究了PCS在芥菜中的表达和定位，芥菜是研究重金属生物介导的主要植物之一。(III)追求转基因过表达的植物PCS与相关的金属解毒机制，以测试增强的重金属耐受性和积累和（IV）提供选定的转基因株系Phytotech公司，包括在超级基金网站的田间试验。(V)在拟南芥和镉诱导的微阵列分析中进行新的遗传激活标记筛选，以确定参与植物重金属积累的新基因和途径。这些研究的结果可以发挥核心作用，在未来的植物修复策略的重金属吸收和生物去除重金属污染的土壤和沃茨的发展。

Soils and waters with high levels of toxic metals such as cadmium (Cd), arsenic (As), lead (Pb) and mercury (Hg) are detrimental to human and environmental health. These four metals are among the Superfund;'s top five priority hazardous substances. Studies suggest that uptake of heavy metals into plant via the root system could provide a potent and cost effective approach for toxic metal removal and remediation of soils and waters. In plants and fungi, phytochelatins are major heavy metal chelating and detoxifying thiolate peptides, that form complexes with and detoxify heavy metals, including Cd, Zn, Pb, Hg and based on recent research also As. The enzyme phytochelatin synthase (PCS) produces phytochelatin, thus functioning as a major catalytic metal detoxification mechanisms in plants. However genes encoding phytochelatin synthases, had not yet been identified. We have recently cloned a new gene family (PCS) encoding phytochelatin synthases in plants and fungi. Expression of PCS cDNAs in S. cerevisiae dramatically enhance resistance to cadmium. Disruption of the PCS genes in S. pombe and Arabidopsis thaliana produces increased heavy metal sensitivity. Recombinant PCS proteins synthesize phytochelatins in vitro. We will test the hypotheses that stress-signaling pathways contribute to PCS induction and detoxification and that transgenic expression of PCS genes can, together with other metal-interacting mechanisms, enhance heavy metal hyper-accumulation and removal by plants. To test these hypotheses we will: (I) Characterize signaling mechanisms that induce PCS expression. (II) Characterize PCS expression and localization in Brassica juncea, which is one of the major plant species being studied for heavy metal biomediation. (III) Pursue transgenic over-expression in plants of PCS together with associated metal detoxification mechanisms to test for enhanced heavy metal tolerance and accumulation and (IV) provide selected transgenic lines to Phytotech Inc to include in field trials on super fund sites. (V) Pursue novel genetic activation-tagging screens in Arabidopsis and Cd-induced microarray analyses to identify new genes and pathways involved in heavy metal accumulation in plants. Results from these studies could play a central role in the development of future phytoremediation strategies for heavy metal uptake and biological removal of heavy metals form contaminated soils and waters.