A putative function for the Arabidopsis Fe-phytosiderophore transporter homolog AtYSL2 in Fe and Zn homeostasis

• Published in: Plant and cell physiology 2005-05, Vol.46 (5), p.762-774
• Main Authors: Schaaf, G.(Universitaet Hohenheim, Stuttgart (Germany)), Schikora, A, Haeberle, J, Vert, G, Ludewig, U, Briat, J.F, Curie, C, Wiren, N.V
• Format: Article
• Language: English
• Subjects: 2′-deoxy-mugineic acid; Animals; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; ARABIDOPSIS THALIANA; Carrier Proteins - metabolism; Cation Transport Proteins - genetics; Cation Transport Proteins - metabolism; CINC; DMA; Evolution, Molecular; Female; FER; Ferritins - metabolism; Gene Expression Regulation, Plant - genetics; GFP; green fluorescent protein; GUS; HIERRO; HOMEOSTASIE; HOMEOSTASIS; IRON; Iron - metabolism; Iron Chelating Agents - metabolism; iron transport; Life Sciences; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; Molecular Sequence Data; NAAT; NAS; nicotianamine; nicotianamine amino-transferase; nicotianamine synthase; Oocytes; open reading frame; ORF; Phylogeny; phytosiderophore; Plant Proteins - genetics; Plant Proteins - metabolism; PLANTAS TRANSGENICAS; PLANTE TRANSGENIQUE; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Promoter Regions, Genetic - genetics; SIDEROFOROS; SIDEROPHORE; SIDEROPHORES; Species Specificity; strategy II; TMD; TRANSGENIC PLANTS; transmembrane-spanning domain; Vegetal Biology; Xenopus laevis; Xenopus oocytes; yeast complementation; Yeasts - genetics; Yeasts - metabolism; Zea mays - genetics; Zea mays - metabolism; ZINC; Zinc - metabolism; β-glucuronidase
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pci081

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 Fesufficient 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-xyleum 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.