Résumé
Nitrogen (N) is the mineral nutrient required in the highest amount in plants, leading to massive use of N fertilizers in agriculture and resulting in pollution problems. It is thus essential to find ways to improve Nitrogen Use Efficiency (NUE) and design biotechnological or breeding strategies for a better N fertilizer use. Since nitrate (NO3-) is the primary N source in agricultural soils, root NO3- transporters are important targets that have been the purpose of intensive studies. Elucidation of the signalling pathways involved in the regulation of root NO3- uptake has led to the identification of several molecular elements regulating both root transporters and root system architecture. The latter determines the volume of soil explored by the plant. The multiple root NO3- uptake systems and the molecular signalling pathways involved in their regulation are detailed and discussed in an effort to discriminate how these elements contribute to the regulation of root architecture and/or root NO3- uptake. Furthermore, recent reports are discussed to illustrate how NO3- transporter genes can be used as molecular tools for improving NUE in crops.