The Arabidopsis root stele transporter NPF2.3 contributes to nitrate translocation to shoots under salt stress

Christelle Taochy, Isabelle Gaillard, Emilie Ipotesi, Ronald Oomen, Nathalie Leonhardt, Sabine Zimmermann, Jean-Benoît Peltier, Wojciech Szponarski, Thierry Simonneau, Hervé Sentenac, Rémy Gibrat, Jean-Christophe Boyer

In most plants, NO3 (-) constitutes the major source of nitrogen and its assimilation is mainly achieved in shoots. Furthermore, recent reports have revealed that reduction of NO3 (-) translocation from roots to shoots is involved in plant acclimation to abiotic stress. NPF2.3, a member of the NAXT (NitrAte eXcretion Transporter) subgroup of the NRT1/PTR family (NPF) from Arabidopsis, is expressed in root pericycle cells, where it is targeted to the plasma membrane. Transport assays on NPF2.3-enriched Lactococcus lactis membranes showed that this protein is endowed with NO3 (-) transport activity, displaying a strong selectivity for NO3 (-) against Cl(-) . In response to salt stress, NO3 (-) translocation to shoots is reduced, at least in part because expression of the root stele NO3 (-) transporter NPF7.3 is decreased. In contrast, NPF2.3 expression was maintained in these conditions. A loss-of-function mutation in NPF2.3 resulted in decreased root-to-shoot NO3 (-) translocation and reduced shoot NO3 (-) content in plants grown under salt stress. Also, the mutant displayed impaired shoot biomass production when plants were grown under mild salt stress. These mutant phenotypes were dependent on the presence of Na(+) in the external medium. Our data indicate that NPF2.3 is a constitutively expressed transporter whose relative contribution to NO3 (-) translocation to the shoots is quantitatively and physiologically significant under salinity. This article is protected by copyright. All rights reserved.