Plant Physiology Preview
Published on February 2, 2007; 10.1104/pp.106.092015
OPEN ACCESS ARTICLE
Received October 26, 2006
Accepted January 28, 2007
A Novel Major Facilitator Superfamily Protein at the Tonoplast Influences Zn Tolerance and Accumulation in Arabidopsis
Michael J. Haydon and Christopher S. Cobbett *
Department of Genetics, The University of Melbourne, Parkville, Australia 3010
* Corresponding author; email: ccobbett{at}unimelb.edu.au.
Zinc (Zn) is an essential micronutrient required by all cells but is toxic in excess. We have identified three allelic Zn-sensitive mutants of Arabidopsis thaliana. The gene, designated ZINC-INDUCED FACILITATOR1 (ZIF1), encodes a member of the Major Facilitator Superfamily (MFS) of membrane proteins which are found in all organisms and transport a wide range of small, organic molecules. Shoots of zif1 mutants showed increased accumulation of Zn, but not other metal ions. In combination with mutations affecting shoot to root Zn translocation, zif1 hma2 hma4 triple mutants accumulated less Zn than the wild type but remain Zn-sensitive, suggesting that the zif1 Zn-sensitive phenotype is due to altered Zn distribution. zif1 mutants were also more sensitive to cadmium but less sensitive to nickel. ProZIF1-GUS fusions were expressed throughout the plant, with strongest expression in young tissues, and predominantly in the vasculature in older tissues. ZIF1 expression was highly induced by Zn and, to a lesser extent, by manganese. A ZIF1-GFP fusion protein localised to the tonoplast in transgenic plants. MTP1 has been identified as a tonoplast Zn transporter and a zif1-1 mtp1-1 double mutant was more sensitive to Zn than either of the single mutants suggesting ZIF1 influences a distinct mechanism of Zn homeostasis. Over-expression of ZIF1 conferred increased Zn tolerance and inter-veinal leaf chlorosis in some transgenic lines in which ZIF1 expression was high. We propose that ZIF1 is involved in a novel mechanism of Zn sequestration, possibly by transport of a Zn ligand or Zn-ligand complex into vacuoles.
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