First published online February 21, 2003; 10.1105/tpc.007120
The Plant Cell, Vol. 15, 790-800,
March 2003, Copyright © 2003,
American Society of Plant Biologists
AtDUR3 Encodes a New Type of High-Affinity Urea/H+ Symporter in Arabidopsis
Lai-Hua Liua,
Uwe Ludewigb,
Wolf B. Frommerb and
Nicolaus von Wirén1,a
a Institut für Pflanzenernährung, Universität Hohenheim, D-70593 Stuttgart, Germany
b Zentrum für Molekularbiologie der Pflanzen, Pflanzenphysiologie, Universität Tübingen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany
1 To whom correspondence should be addressed. E-mail vonwiren{at}uni-hohenheim.de; fax 49-711-4592344
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 14C-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 14C-labeled urea by AtDUR3 in oocytes exhibited saturation kinetics with a Km of  3 µM. 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.
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