AtIREG2 Encodes a Tonoplast Transport Protein Involved in Iron-dependent Nickel Detoxification in Arabidopsis thaliana Roots

• Published in: The Journal of biological chemistry 2006-09, Vol.281 (35), p.25532-25540
• Main Authors: Schaaf, Gabriel, Honsbein, Annegret, Meda, Anderson R., Kirchner, Silvia, Wipf, Daniel, von Wirén, Nicolaus
• Format: Article
• Language: English
• Subjects: Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Biological Transport; Cation Transport Proteins - chemistry; Cation Transport Proteins - genetics; Fungal Proteins - chemistry; Gene Expression Regulation; Green Fluorescent Proteins - metabolism; Hydrogen-Ion Concentration; Iron - metabolism; Models, Biological; Nickel - metabolism; Plant Proteins - chemistry; Plant Roots - metabolism; Plants, Genetically Modified; Substrate Specificity
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M601062200

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.