Plant Cell Advance Online Publication
Published on February 21, 2003; 10.1105/tpc.007120
Received September 3, 2002
Accepted December 19, 2002
AtDUR3 Encodes a New Type of High-Affinity Urea/H+ Symporter in Arabidopsis
Lai-Hua Liu 1, Uwe Ludewig 2, Wolf B. Frommer 2, and Nicolaus von Wirén 1*
1
Institut für Pflanzenernährung, Universität Hohenheim, D-70593 Stuttgart,
Germany
2
Zentrum für Molekularbiologie der Pflanzen, Pflanzenphysiologie, Universität
Tübingen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany
* To whom correspondence should be addressed. E-mail: vonwiren{at}uni-hohenheim.de.
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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