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.

Prochlorococcus can use the Pro1404 transporter to take up glucose at nanomolar concentrations in the Atlantic Ocean

“…Thus, we will refer to Pro1404 as a dual affinity transporter. To our knowledge, only two other transporters, a potassium and a nitrate transporter from plants, have been shown to be dual-affinity transporters with a biphasic kinetics by the use of an ectopic expression approach similar to the one shown here (21)(22)(23). In the case of the nitrate transporter, the alternation from the high-affinity to the lowaffinity mode and vice-versa is controlled by phosphorylation (24).…”

Nitrate transporters: an overview in legumes

“…A quantitative genetic approach allowed us to identify a major QTL involved in the control of M. truncatula radicle elongation in post-germination phase in both N-free medium and medium supplied with 5 mM nitrate. The MtNPF6.8 gene, which coincided with the peak of the QTL, appeared to be a significant candidate involved in the control of primary root growth and nitrate-sensing (Morère-Le Paven et al 2011). Further experiments using npf6.8 mutants indicated that MtNPF6.8 has the hallmarks of a nitrate sensor (Fig.…”

“…In this species, nitrate has an inhibitory effect on primary root growth at low and high concentrations in two different ecotypes, A17 and R108 (Yendrek et al 2010;Morère-Le Paven et al 2011;Pellizzaro et al 2014). A quantitative genetic approach allowed us to identify a major QTL involved in the control of M. truncatula radicle elongation in post-germination phase in both N-free medium and medium supplied with 5 mM nitrate.…”

Proteomic Analysis of the Soybean Symbiosome Identifies New Symbiotic Proteins*

“…AtNPF6.3 (AtNTR1.1, CHL1), one of 53 proteins in the NPF of Arabidopsis, can transport nitrate (99) and auxin (100) as can the M. truncatula homolog MtNRT1.3 (101,102). In this context, indole acetic acid uptake by isolated soybean symbiosomes as reported (103) may be relevant.…”