Revisiting the functional properties of NPF6.3/NRT1.1/CHL1 in xenopus oocytes

The functional characterization of NPF6.3/NRT1.1 has revealed interesting transport properties: the transport of nitrate and auxin, a dual-affinity transport behavior for nitrate depending on external nitrate concentration and the eletrogenicity of the nitrate transport. However, some of these properties remained controversial and were challenged here. We used a combination of uptake experiments using 15N-labelled nitrate and two-electrode voltage-clamp on xenopus oocytes expressing WT and mutant proteins. In our experimental conditions in xenopus oocytes, we could not show NPF6.3/NRT1.1 electrogenicity and only low-affinity transport properties were recorded. Moreover, further functional characterization of a NPF6.3/NRT1.1 point mutant, P492L, allowed us to hypothesize that NPF6.3/NRT1.1 is regulated by internal nitrate concentration and that the internal perception site involves the P492 residue.