title: Characterization of three distinct metallothionein genes of the Ag-hyperaccumulating ectomycorrhizal fungus Amanita strobiliformis.
abstract: Mechanisms evolved in eukaryotes to handle heavy metals involve cytosolic, metal-binding metallothioneins (MTs). We have previously documented that the sequestration of silver (Ag) in the Ag-hyperaccumulating Amanita strobiliformis is dominated by 34-amino-acid (AA) AsMT1a, 1b, and 1c isoforms. Here we show that in addition to AsMT1a, 1b, and 1c isogenes, the fungus has two other MT genes: AsMT2 encoding a 34-AA AsMT2 similar to MTs known from other species, but unrelated to AsMT1s; AsMT3 coding for a 62-AA AsMT3 that shares substantial identity with as-yet-uncharacterized conserved peptides predicted in agaricomycetes. Transcription of AsMT1s and AsMT3 in the A. strobiliformis mycelium was specifically inducible by treatments with Ag or copper (Cu) and zinc (Zn) or cadmium (Cd), respectively; AsMT2 showed a moderate upregulation in the presence of Cd. Expression of AsMTs in the metal-sensitive Saccharomyces cerevisiae revealed that all AsMTs confer increased Cd tolerance (AsMT3 proved the most effective) and that, unlike AsMT1 and AsMT2, AsMT3 can protect the yeasts against Zn toxicity. The highest level of Cu tolerance was observed with yeasts expressing AsMT1a. Our data indicate that A. strobiliformis can specifically employ different MT genes for functions in the cellular handling of Ag and Cu (AsMT1s) and Zn (AsMT3).
authors.affiliation: Department of Biochemistry and Microbiology, University of Chemistry and Technology, Prague, Technická 3, CZ-166 28 Prague, Czech Republic.
authors.forename: Kateřina
authors.initials: K
authors.lastname: Hložková
authors.affiliation: Department of Biochemistry and Microbiology, University of Chemistry and Technology, Prague, Technická 3, CZ-166 28 Prague, Czech Republic.
authors.forename: Michaela
authors.initials: M
authors.lastname: Matěnová
authors.affiliation: Department of Biochemistry and Microbiology, University of Chemistry and Technology, Prague, Technická 3, CZ-166 28 Prague, Czech Republic.
authors.forename: Petra
authors.initials: P
authors.lastname: Žáčková
authors.affiliation: Institute of Molecular Genetics, v.v.i., Academy of Sciences of the Czech Republic, Vídeňská 1083, CZ-142 20 Prague 4, Czech Republic.
authors.forename: Hynek
authors.initials: H
authors.lastname: Strnad
authors.affiliation: Institute of Microbiology, v.v.i., Academy of Sciences of the Czech Republic, Vídeňská 1083, CZ-142 20 Prague 4, Czech Republic.
authors.forename: Hana
authors.initials: H
authors.lastname: Hršelová
authors.affiliation: Institute of Molecular Genetics, v.v.i., Academy of Sciences of the Czech Republic, Vídeňská 1083, CZ-142 20 Prague 4, Czech Republic.
authors.forename: Miluše
authors.initials: M
authors.lastname: Hroudová
authors.affiliation: Department of Biochemistry and Microbiology, University of Chemistry and Technology, Prague, Technická 3, CZ-166 28 Prague, Czech Republic. Electronic address: pavel.kotrba@vscht.cz.
authors.forename: Pavel
authors.initials: P
authors.lastname: Kotrba
mesh_terms: D000545:Amanita / Q000235:genetics* / Q000378:metabolism*; D003300:Copper / Q000378:metabolism; D004361:Drug Tolerance; D020869:Gene Expression Profiling; D008668:Metallothionein / Q000235:genetics* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012834:Silver / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D015032:Zinc / Q000378:metabolism
chemical_list: D012834:Silver; D003300:Copper; D008668:Metallothionein; D015032:Zinc
keywords: Ectomycorrhizal fungi; Gene expression; Metal binding; Metallothionein