Phytochelatin synthase & resistance to heavy metals

土壤和水体中镉(Cd)、砷(As)、铅(Pb2+)和汞(Hg2+)等有毒金属含量较高，对人类和环境健康有害。这四种金属都在超级基金之列；S的五大重点危险物质。研究表明，通过植物根系吸收重金属可以为土壤和水体中有毒金属的去除和修复提供一种有效且经济有效的方法。在植物和真菌中，植物络合素是主要的重金属螯合和解毒硫代多肽，与Cd、Zn、Pb、Hg等重金属形成络合物并解毒，最近的研究也表明它也是一种重金属。植物络合素合成酶(PCS)产生植物络合素，是植物体内金属解毒的主要催化机制。然而，编码植物络合蛋白合成酶的基因还没有被鉴定。我们最近克隆了一个新的基因家族(PCS)，编码植物和真菌中的植物络合蛋白合成酶。PCS cDNAs在酿酒酵母中的表达显著增强了其对镉的抗性。破坏S.pombe和拟南芥中的PCS基因会增加对重金属的敏感性。重组PCS蛋白在体外合成植物螯合素。我们将验证这样的假设，即胁迫信号通路有助于PCS的诱导和解毒，以及PCS基因的转基因表达与其他金属相互作用机制可以促进植物对重金属的超积累和清除。为了检验这些假设，我们将：(I)描述诱导PCS表达的信号机制。(Ii)研究PCS在芥菜型油菜中的表达和定位，芥菜型油菜是目前正在研究的重金属生物修复的主要植物之一。(Iii)寻求转基因植物在PCS植物中的过度表达以及相关的金属解毒机制，以测试增强的重金属耐受性和积累，以及(Iv)向Phytotech Inc.提供选定的转基因株系，以包括在超级基金网站的田间试验中。(V)在拟南芥中进行新的遗传激活标记筛选和镉诱导的微阵列分析，以确定与植物中重金属积累有关的新基因和新途径。这些研究的结果可能在今后制定植物修复策略以吸收重金属并从受污染的土壤和水中生物去除重金属方面发挥核心作用。

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.