title: AtIREG2 encodes a tonoplast transport protein involved in iron-dependent nickel detoxification in Arabidopsis thaliana roots.
abstract: Iron acquisition in Arabidopsis depends mainly on AtIRT1, a Fe2+ transporter in the plasma membrane of root cells. However, substrate specificity of AtIRT1 is low, leading to an excess accumulation of other transition metals in iron-deficient plants. In the present study we describe AtIREG2 as a nickel transporter at the vacuolar membrane that counterbalances the low substrate specificity of AtIRT1 and possibly other iron transport systems in iron-deficient root cells. AtIREG2 is co-regulated with AtIRT1 by the transcription factor FRU/FIT1, encodes a membrane protein, which has 10 putative transmembrane domains and shares homology with vertebrate Fe2+ exporters. Heterologous expression of AtIREG2 in various yeast mutants, however, did not demonstrate an iron transport function. Instead, expression in wild-type and nickel-sensitive cot1 yeast cells conferred enhanced tolerance to elevated concentrations of nickel at acidic pH. A role in vacuolar substrate transport was further supported by localization of AtIREG2-GFP fusion proteins to the tonoplast in Arabidopsis suspension cells and root cells of intact plants. Transgenic plants overexpressing AtIREG2 showed an increased tolerance to elevated concentrations of nickel, whereas T-DNA insertion lines lacking AtIREG2 expression were more sensitive to nickel, particularly under iron deficiency, and accumulated less nickel in roots. We therefore propose a role of AtIREG2 in vacuolar loading of nickel under iron deficiency and thus identify it as a novel component in the iron deficiency stress response.
authors.affiliation: Institut für Pflanzenernährung, Universität Hohenheim, 70593 Stuttgart, Germany.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Schaaf
authors.forename: Annegret
authors.initials: A
authors.lastname: Honsbein
authors.forename: Anderson R
authors.initials: AR
authors.lastname: Meda
authors.forename: Silvia
authors.initials: S
authors.lastname: Kirchner
authors.forename: Daniel
authors.initials: D
authors.lastname: Wipf
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D008954:Models, Biological; D009532:Nickel / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry; D018517:Plant Roots / Q000378:metabolism*; D030821:Plants, Genetically Modified; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D005656:Fungal Proteins; C514010:IREG2 protein, Arabidopsis; D010940:Plant Proteins; D049452:Green Fluorescent Proteins; D009532:Nickel; D007501:Iron