Regulation of the high-affinity NO3- uptake system by NRT1.1-mediated NO3- demand signaling in Arabidopsis.
The NRT2.1 gene of Arabidopsis thaliana encodes a major component of the root high-affinity NO(3)(-) transport system (HATS) that plays a crucial role in NO(3)(-) uptake by the plant. Although NRT2.1 was known to be induced by NO(3)(-) and feedback repressed by reduced nitrogen (N) metabolites, NRT2.1 is surprisingly up-regulated when NO(3)(-) concentration decreases to a low level (<0.5 mm) in media containing a high concentration of NH(4)(+) or Gln (>or=1 mm). The NRT3.1 gene, encoding another key component of the HATS, displays the same response pattern. This revealed that both NRT2.1 and NRT3.1 are coordinately down-regulated by high external NO(3)(-) availability through a mechanism independent from that involving N metabolites. We show here that repression of both genes by high NO(3)(-) is specifically mediated by the NRT1.1 NO(3)(-) transporter. This mechanism warrants that either NRT1.1 or NRT2.1 is active in taking up NO(3)(-) in the presence of a reduced N source. Under low NO(3)(-)/high NH(4)(+) provision, NRT1.1-mediated repression of NRT2.1/NRT3.1 is relieved, which allows reactivation of the HATS. Analysis of atnrt2.1 mutants showed that this constitutes a crucial adaptive response against NH(4)(+) toxicity because NO(3)(-) taken up by the HATS in this situation prevents the detrimental effects of pure NH(4)(+) nutrition. It is thus hypothesized that NRT1.1-mediated regulation of NRT2.1/NRT3.1 is a mechanism aiming to satisfy a specific NO(3)(-) demand of the plant in relation to the various specific roles that NO(3)(-) plays, in addition to being a N source. A new model is proposed for regulation of the HATS, involving both feedback repression by N metabolites and NRT1.1-mediated repression by high NO(3)(-).
Krouk
Gabriel
G
Biochimie et Physiologie Moléculaire des Plantes, Unité Mixte de Recherche 5004, Agro-M, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Montpellier, France.
Tillard
Pascal
P
Gojon
Alain
A
D000641:Ammonia / Q000378:metabolism / Q000494:pharmacology; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D015854:Up-Regulation
D000641:Ammonia; D027321:Anion Transport Proteins; D029681:Arabidopsis Proteins; D009566:Nitrates; D010940:Plant Proteins; D012333:RNA, Messenger; C477335:NRT2.1 protein, Arabidopsis; C101492:NRT1.1 protein, Arabidopsis; C510574:NRT3.1 protein, Arabidopsis