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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Systemic Signaling of the Plant Nitrogen Status Triggers Specific Transcriptome Responses Depending on the Nitrogen Source in Medicago truncatula^1,[W]

Biochimie et Physiologie Moléculaire des Plantes, UMR 5004, INRA-CNRS-Sup Agro-UM2, Institut de Biologie Intégrative des Plantes, F–34060 Montpellier, France (S.R., P.T., A.G., M.L.); Unité de Génétique et Ecophysiologie des Légumineuses, UMR INRA, BP 86510, F–21065 Dijon, France (S.F., C.J., C.S.); Unité de Recherche en Génomique Végétale, UMR INRA 1165–CNRS 8114–UEVE, F–91057 Evry, France (S.B., M.L.M.-M.); Max-Planck-Institut für Molekulare Pflanzenphysiologie, 14476 Potsdam-Golm, Germany (M.J.v.d.M., K.K., A.R.F., M.U.); Laboratoire des Interactions Plantes Micro-organismes, UMR INRA/CNRS 441/2594, F–31326 Castanet Tolosan, France (J.G.); and UMR AgroParisTech/INRA MIA 518, F–75231 Paris, France (M.L.M.-M.)

Legumes can acquire nitrogen (N) from NO₃^–, NH₄⁺, and N₂ (through symbiosis with Rhizobium bacteria); however, the mechanisms by which uptake and assimilation of these N forms are coordinately regulated to match the N demand of the plant are currently unknown. Here, we find by use of the split-root approach in Medicago truncatula plants that NO₃^– uptake, NH₄⁺ uptake, and N₂ fixation are under general control by systemic signaling of plant N status. Indeed, irrespective of the nature of the N source, N acquisition by one side of the root system is repressed by high N supply to the other side. Transcriptome analysis facilitated the identification of over 3,000 genes that were regulated by systemic signaling of the plant N status. However, detailed scrutiny of the data revealed that the observation of differential gene expression was highly dependent on the N source. Localized N starvation results, in the unstarved roots of the same plant, in a strong compensatory up-regulation of NO₃^– uptake but not of either NH₄⁺ uptake or N₂ fixation. This indicates that the three N acquisition pathways do not always respond similarly to a change in plant N status. When taken together, these data indicate that although systemic signals of N status control root N acquisition, the regulatory gene networks targeted by these signals, as well as the functional response of the N acquisition systems, are predominantly determined by the nature of the N source.

² Present address: Department of Biology, New York University, 100 Washington Square East, New York, NY 10003.

³ Present address: The Samuel Roberts Noble Foundation, Ardmore, OK 73401.

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: Marc Lepetit (lepetit{at}supagro.inra.fr).

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

www.plantphysiol.org/cgi/doi/10.1104/pp.107.115667

^* Corresponding author; e-mail lepetit{at}supagro.inra.fr.

Received January 7, 2008; accepted February 13, 2008; published February 20, 2008.

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