Involved in nitrate transport, but does not seem to be able to mediate transport by its own. Acts as a dual component transporter with NTR3.1. Acts as a repressor of lateral root initiation under high sucrose/low nitrate conditions. Monomer. Heterotetramer composed of two NRT2.1 and two NRT3.1. Interacts with NRT3.1. Root cortical and epidermal cells. Not expressed in new lateral root Primordia. Detected in shoots. Up-regulated at transcript level by light and sucrose, and transiently by nitrate, but no changes at protein level. Down-regulated by ammonium, amino acids and N-metabolites resulting from nitrate reduction. Induced by sudden N starvation and by growth on low nitrate concentration. Circadian-regulation. Expression increases during the light phase and decreases during the dark phase. Might be subject to partial proteolysis at the C-terminus. Impaired in the high-affinity nitrate transport. Reduced growth on low-nitrate media. Reduced nitrate uptake and increased lateral root initiation. Belongs to the major facilitator superfamily. Nitrate/nitrite porter (TC 2.A.1.8) family.