title: A putative function for the arabidopsis Fe-Phytosiderophore transporter homolog AtYSL2 in Fe and Zn homeostasis.
abstract: 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::beta-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::beta-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.
authors.affiliation: Institut für Pflanzenernährung, Universität Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Schaaf
authors.forename: Adam
authors.initials: A
authors.lastname: Schikora
authors.forename: Jennifer
authors.initials: J
authors.lastname: Häberle
authors.forename: Grégory
authors.initials: G
authors.lastname: Vert
authors.forename: Uwe
authors.initials: U
authors.lastname: Ludewig
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Briat
authors.forename: Catherine
authors.initials: C
authors.lastname: Curie
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D005260:Female; D005293:Ferritins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D007501:Iron / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D013045:Species Specificity; D014982:Xenopus laevis; D015003:Yeasts / Q000235:genetics / Q000378:metabolism; D003313:Zea mays / Q000235:genetics / Q000378:metabolism; D015032:Zinc / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D007502:Iron Chelating Agents; D026901:Membrane Transport Proteins; D010940:Plant Proteins; C504141:YSL2 protein, Arabidopsis; C058550:phytosiderin; C419784:yellow stripe1 protein, Zea mays; D005293:Ferritins; D007501:Iron; D015032:Zinc