Clemens S, Kim E J, Neumann D, Schroeder J I
Department of Biology and Center for Molecular Genetics, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA.
EMBO J. 1999 Jun 15;18(12):3325-33. doi: 10.1093/emboj/18.12.3325.
Phytochelatins play major roles in metal detoxification in plants and fungi. However, genes encoding phytochelatin synthases have not yet been identified. By screening for plant genes mediating metal tolerance we identified a wheat cDNA, TaPCS1, whose expression in Saccharomyces cerevisiae results in a dramatic increase in cadmium tolerance. TaPCS1 encodes a protein of approximately 55 kDa with no similarity to proteins of known function. We identified homologs of this new gene family from Arabidopsis thaliana, Schizosaccharomyces pombe, and interestingly also Caenorhabditis elegans. The Arabidopsis and S.pombe genes were also demonstrated to confer substantial increases in metal tolerance in yeast. PCS-expressing cells accumulate more Cd2+ than controls. PCS expression mediates Cd2+ tolerance even in yeast mutants that are either deficient in vacuolar acidification or impaired in vacuolar biogenesis. PCS-induced metal resistance is lost upon exposure to an inhibitor of glutathione biosynthesis, a process necessary for phytochelatin formation. Schizosaccharomyces pombe cells disrupted in the PCS gene exhibit hypersensitivity to Cd2+ and Cu2+ and are unable to synthesize phytochelatins upon Cd2+ exposure as determined by HPLC analysis. Saccharomyces cerevisiae cells expressing PCS produce phytochelatins. Moreover, the recombinant purified S.pombe PCS protein displays phytochelatin synthase activity. These data demonstrate that PCS genes encode phytochelatin synthases and mediate metal detoxification in eukaryotes.
植物螯合肽在植物和真菌的金属解毒过程中发挥着重要作用。然而，编码植物螯合肽合酶的基因尚未被鉴定出来。通过筛选介导金属耐受性的植物基因，我们鉴定出一个小麦cDNA，TaPCS1，其在酿酒酵母中的表达导致镉耐受性显著增加。TaPCS1编码一种约55 kDa的蛋白质，与已知功能的蛋白质没有相似性。我们从拟南芥、粟酒裂殖酵母中鉴定出了这个新基因家族的同源物，有趣的是，在秀丽隐杆线虫中也发现了同源物。拟南芥和粟酒裂殖酵母的基因也被证明能使酵母中的金属耐受性大幅提高。表达PCS的细胞比对照细胞积累更多的Cd2+。即使在液泡酸化缺陷或液泡生物发生受损的酵母突变体中，PCS表达也能介导Cd2+耐受性。暴露于谷胱甘肽生物合成抑制剂后，PCS诱导的金属抗性丧失，而谷胱甘肽生物合成是植物螯合肽形成所必需的过程。通过HPLC分析确定，粟酒裂殖酵母中PCS基因被破坏的细胞对Cd2+和Cu2+表现出超敏感性，并且在暴露于Cd2+时无法合成植物螯合肽。表达PCS的酿酒酵母细胞产生植物螯合肽。此外，重组纯化的粟酒裂殖酵母PCS蛋白表现出植物螯合肽合酶活性。这些数据表明，PCS基因编码植物螯合肽合酶并介导真核生物中的金属解毒。
