title: Characterization of a dual-affinity nitrate transporter MtNRT1.3 in the model legume Medicago truncatula.
abstract: Primary root growth in the absence or presence of exogenous NO(3)(-) was studied by a quantitative genetic approach in a recombinant inbred line (RIL) population of Medicago truncatula. A quantitative trait locus (QTL) on chromosome 5 appeared to be particularly relevant because it was seen in both N-free medium (LOD score 5.7; R(2)=13.7) and medium supplied with NO(3)(-) (LOD score, 9.5; R(2)=21.1) which indicates that it would be independent of the general nutritional status. Due to its localization exactly at the peak of this QTL, the putative NRT1-NO(3)(-) transporter (Medtr5g093170.1), closely related to Arabidopsis AtNRT1.3, a putative low-affinity nitrate transporter, appeared to be a significant candidate involved in the control of primary root growth and NO(3)(-) sensing. Functional characterization in Xenopus oocytes using both electrophysiological and (15)NO(3)(-) uptake approaches showed that Medtr5g093170.1, named MtNRT1.3, encodes a dual-affinity NO(3)(-) transporter similar to the AtNRT1.1 'transceptor' in Arabidopsis. MtNRT1.3 expression is developmentally regulated in roots, with increasing expression after completion of germination in N-free medium. In contrast to members of the NRT1 superfamily characterized so far, MtNRT1.3 is environmentally up-regulated by the absence of NO(3)(-) and down-regulated by the addition of the ion to the roots. Split-root experiments showed that the increased expression stimulated by the absence of NO(3)(-) was not the result of a systemic signalling of plant N status. The results suggest that MtNRT1.3 is involved in the response to N limitation, which increases the ability of the plant to acquire NO(3)(-) under N-limiting conditions.
authors.affiliation: University of Angers, UMR-1191 Physiologie Moléculaire des Semences, IFR 149 Quasav, 2 Boulevard Lavoisier, 49045 Angers cedex 01, France.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Morère-Le Paven
authors.forename: Laure
authors.initials: L
authors.lastname: Viau
authors.forename: Alain
authors.initials: A
authors.lastname: Hamon
authors.forename: Céline
authors.initials: C
authors.lastname: Vandecasteele
authors.forename: Anthoni
authors.initials: A
authors.lastname: Pellizzaro
authors.forename: Céline
authors.initials: C
authors.lastname: Bourdin
authors.forename: Carole
authors.initials: C
authors.lastname: Laffont
authors.forename: Bruno
authors.initials: B
authors.lastname: Lapied
authors.forename: Marc
authors.initials: M
authors.lastname: Lepetit
authors.forename: Florian
authors.initials: F
authors.lastname: Frugier
authors.forename: Christian
authors.initials: C
authors.lastname: Legros
authors.forename: Anis M
authors.initials: AM
authors.lastname: Limami
mesh_terms: D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D046913:Medicago truncatula / Q000235:genetics / Q000378:metabolism*; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism*
chemical_list: D027321:Anion Transport Proteins; D000091285:Nitrate Transporters; D009566:Nitrates; D010940:Plant Proteins