Acts as a dual component transporter with NTR2.1, NRT2.2 and NRT2.3. Required for high-affinity nitrate transport. Involved in the regulation of NRT2.1, NRT2.2 and NRT2.3 expression, and in both, HATS (high-affinity transport system) and LATS (low-affinity transport system) activities in plant roots. Imports nitrate with high affinity when expressed with NTR2.1, NTR2.2 or NTR2.3 in a heterologous system (Xenopus oocytes). Heterotetramer composed of two NRT2.1, NRT2.2 or NRT2.3 and two NAR2.1 (By similarity). Interacts with NRT2.1, NRT2.2 and isoform 1 of NRT2.3. Expressed in epidermal cells of primary and lateral roots, root-shoot junction zone, vascular tissues of adventitious root primordia, stems and coleoptiles of germinating seeds. Circadian-regulation with a peak in the middle of the morning. Induced by nitrate and sucrose in roots. Down-regulated by asparagine and aspartate in roots. Plants silencing NAR2.1 have decreased nitrate uptake in roots under both high and low nitrate conditions. Belongs to the NAR2 family.