title: AtDUR3 encodes a new type of high-affinity urea/H+ symporter in Arabidopsis.
abstract: Urea is the major nitrogen form supplied as fertilizer in agricultural plant production but also an important nitrogen metabolite in plants. We report the cloning and functional characterization of AtDUR3, a high-affinity urea transporter in plants. AtDUR3 contains 14 putative transmembrane-spanning domains and represents an individual member in Arabidopsis that belongs to a superfamily of sodium-solute symporters. Heterologous expression in urea uptake-defective yeast as well as two-electrode voltage clamp and uptake studies using (14)C-labeled urea in AtDUR3-expressing oocytes demonstrated that AtDUR3 mediates urea transport. In both heterologous systems, urea transport was stimulated at low pH. In oocytes, inward currents indicated that urea is cotransported with protons. By contrast, a supply of Na(+) ions could not stimulate urea transport. Transport of (14)C-labeled urea by AtDUR3 in oocytes exhibited saturation kinetics with a K(m) of approximately 3 micro M. AtDUR3 was expressed in shoots and roots and upregulated during early germination and under nitrogen deficiency in roots. We propose a role of AtDUR3 in urea uptake by plant cells at low external urea concentrations.
authors.affiliation: Institut für Pflanzenernährung, Universität Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Lai-Hua
authors.initials: LH
authors.lastname: Liu
authors.forename: Uwe
authors.initials: U
authors.lastname: Ludewig
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002478:Cells, Cultured; D005260:Female; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D010802:Phylogeny; D017494:Proton Pumps / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D027981:Symporters / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D014508:Urea / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D029681:Arabidopsis Proteins; D002250:Carbon Radioisotopes; C474639:DUR3 protein, Arabidopsis; D007473:Ion Channels; D017494:Proton Pumps; D027981:Symporters; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D014508:Urea; D009584:Nitrogen