Participation of Relevant Nitrate Transporters on Cl- Homeostasis in Plants

Active anion transporters of higher plants involved in root Cl¿ uptake remain unknown. Given the strong dynamic interaction between NO3¿ and Cl¿ homeostasis, we have addressed in this work the hypothesis that plasma membrane transporters involved in root NO3¿ uptake are also involved in the regulation of Cl¿ homeostasis in higher plants. With this aim, the involvement of the Arabidopsis thaliana NO3¿ transporters AtNRT2.1, AtNRT2.2 and AtNPF6.3, as well as the regulatory protein AtNRT 3.1, in the uptake and accumulation of NO3¿ and Cl¿ has been studied here under conditions of both high and low NO3¿/Cl¿ availability. We have identified AtNPF6.3 and AtNRT3.1 as NO3¿ transporters that are also involved in the regulation of root Cl¿ uptake under low NO3¿ availability. We present also evidence showing that reduction of NO3¿ transport in A. thaliana lines mutated in any of the previous plasma membrane proteins gives rise to increased plant Cl¿ accumulation. We propose that these phenomena respond to compensatory mechanisms aimed regulating Cl¿ homeostasis to improve nitrogen-use efficiency under conditions of deficient NO3¿ uptake.