Plant and Cell Physiology Advance Access originally published online on March 7, 2005
Plant and Cell Physiology 2005 46(5):762-774; doi:10.1093/pcp/pci081
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A Putative Function for the Arabidopsis Fe–Phytosiderophore Transporter Homolog AtYSL2 in Fe and Zn Homeostasis
1 Institut für Pflanzenernährung, Universität Hohenheim, D-70593 Stuttgart, Germany
2 Biochimie et Physiologie Moléculaire des Plantes, Centre National de la Recherche Scientifique (Unité Mixte de Recherche 5004)/Institut National de la Recherche Agronomique/Agro-M/Université Montpellier II, 2 place Viala, F-34060 Montpellier cedex 1, France
3 ZMBP-Pflanzenphysiologie, Universität Tübingen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany
5 Corresponding author: E-mail, vonwiren{at}uni-hohenheim.de; Fax, +49-711-459-3295.
Although Arabidopsis thaliana does not produce phytosiderophores (PS) under Fe deficiency, it contains eight homologs of the metal–PS/metal–nicotianamine (NA) transporter ZmYS1 from maize. This study aimed to investigate whether one of the closest Arabidopsis homologs to ZmYS1, AtYSL2, is involved in metal–chelate transport. Northern analysis revealed high expression levels of AtYSL2 in Fe-sufficient or Fe-resupplied roots, while under Fe deficiency transcript levels decreased. Quantitative real-time polymerase chain reaction (PCR) and analysis of transgenic plants expressing an AtYSL2 promoter::ß-glucuronidase gene further allowed the detection of down-regulated AtYSL2 gene expression under Zn and Fe deficiency. In contrast to ZmYS1, AtYSL2 did not mediate metal–PS or metal–NA transport in yeast mutants defective in Cu or Fe uptake, nor did AtYSL2 mediate Fe(II)–NA-, Fe(III)–NA- or Ni(II)–NA-inducible currents when assayed by two-electrode voltage clamp in Xenopus oocytes. Moreover, truncation of the N-terminus to remove putative phosphorylation sites that might trigger autoinhibition did not confer functionality to AtYSL2. A direct growth comparison of yeast cells transformed with AtYSL2 in two different yeast expression vectors showed that transformation with empty pFL61 repressed growth even under non-limiting Fe supply. We therefore conclude that the yeast complementation assay previously employed does not allow the identification of AtYSL2 as an Fe–NA transporter. Transgenic plants expressing an AtYSL2 promoter::ß-glucuronidase gene showed expression in root endodermis and pericycle cells facing the meta-xylem tubes. Taken together, our investigations support an involvement of AtYSL2 in Fe and Zn homeostasis, although functionality or substrate specificity are likely to differ between AtYSL2 and ZmYS1.
4 These authors contributed equally to this work.
(Received June 11, 2004; Accepted February 25, 2005
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