title: Overexpression of Arabidopsis phytochelatin synthase paradoxically leads to hypersensitivity to cadmium stress.
abstract: Phytochelatin (PC) plays an important role in heavy metal detoxification in plants and other living organisms. Therefore, we overexpressed an Arabidopsis PC synthase (AtPCS1) in transgenic Arabidopsis with the goal of increasing PC synthesis, metal accumulation, and metal tolerance in these plants. Transgenic Arabidopsis plants were selected, designated pcs lines, and analyzed for tolerance to cadmium (Cd). Transgenic pcs lines showed 12- to 25-fold higher accumulation of AtPCS1 mRNA, and production of PCs increased by 1.3- to 2.1-fold under 85 microM CdCl(2) stress for 3 d when compared with wild-type plants. Cd tolerance was assessed by measuring root length of plants grown on agar medium containing 50 or 85 microM CdCl(2). Pcs lines paradoxically showed hypersensitivity to Cd stress. This hypersensitivity was also observed for zinc (Zn) but not for copper (Cu). The overexpressed AtPCS1 protein itself was not responsible for Cd hypersensitivity as transgenic cad1-3 mutants overexpressing AtPCS1 to similar levels as those of pcs lines were not hypersensitive to Cd. Pcs lines were more sensitive to Cd than a PC-deficient Arabidopsis mutant, cad1-3, grown under low glutathione (GSH) levels. Cd hypersensitivity of pcs lines disappeared under increased GSH levels supplemented in the medium. Therefore, Cd hypersensitivity in pcs lines seems due to the toxicity of PCs as they existed at supraoptimal levels when compared with GSH levels.
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, Illinois 61801.
authors.forename: Sangman
authors.initials: S
authors.lastname: Lee
authors.forename: Jae S
authors.initials: JS
authors.lastname: Moon
authors.forename: Tae-Seok
authors.initials: TS
authors.lastname: Ko
authors.forename: David
authors.initials: D
authors.lastname: Petros
authors.forename: Peter B
authors.initials: PB
authors.lastname: Goldsbrough
authors.forename: Schuyler S
authors.initials: SS
authors.lastname: Korban
mesh_terms: D019881:Aminoacyltransferases / Q000235:genetics* / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D019256:Cadmium Chloride / Q000494:pharmacology*; D002712:Chlorides / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005981:Glutathione Synthase / Q000378:metabolism; D007113:Immunity, Innate / Q000187:drug effects; D018517:Plant Roots / Q000187:drug effects; D030821:Plants, Genetically Modified; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D029681:Arabidopsis Proteins; D002712:Chlorides; D017967:Zinc Compounds; D003300:Copper; C016837:zinc chloride; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase; D005981:Glutathione Synthase; D019256:Cadmium Chloride; C029892:cupric chloride