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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Physiological and Transcriptomic Aspects of Urea Uptake and Assimilation in Arabidopsis Plants^1,[W]

INRA, Jean-Pierre Bourgin Institute, Unité de Nutrition Azotée des Plantes, F–78000 Versailles, France (P.M., M.L., C.M., F.D.-V.); INRA, Unité Mixte de Recherche en Génomique Végétale, F–91057 Evry, France (F.B., J.-P.R.); and BiotechMarine BP 65, 22260 Pontrieux, France (X.B.)

Urea is the major nitrogen (N) form supplied as fertilizer in agriculture, but it is also an important N metabolite in plants. Urea transport and assimilation were investigated in Arabidopsis (Arabidopsis thaliana). Uptake studies using ¹⁵N-labeled urea demonstrated the capacity of Arabidopsis to absorb urea and that the urea uptake was regulated by the initial N status of the plants. Urea uptake was stimulated by urea but was reduced by the presence of ammonium nitrate in the growth medium. N deficiency in plants did not affect urea uptake. Urea exerted a repressive effect on nitrate influx, whereas urea enhanced ammonium uptake. The use of [¹⁵N]urea and [¹⁵N]ammonium tracers allowed us to show that urea and ammonium assimilation pathways were similar. Finally, urea uptake was less efficient than nitrate uptake, and urea grown-plants presented signs of N starvation. We also report the first analysis, to our knowledge, of Arabidopsis gene expression profiling in response to urea. Our transcriptomic approach revealed that nitrate and ammonium transporters were transcriptionally regulated by urea as well as key enzymes of the glutamine synthetase-glutamate synthase pathway. AtDUR3, a high-affinity urea transporter in Arabidopsis, was strongly up-regulated by urea. Moreover, our transcriptomic data suggest that other genes are also involved in urea influx.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Françoise Daniel-Vedele (vedele{at}versailles.inra.fr).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.119339

^* Corresponding author; e-mail vedele{at}versailles.inra.fr.

Received March 18, 2008; accepted May 16, 2008; published May 28, 2008.