Nitrate is an essential macronutrient for plant growth. In addition it has signaling functions triggering specific adaptations in metabolism and root development. In A. thaliana, the transporter NRT2.1 is known to have a central role for root nitrate uptake and it could also play a role in signaling for root development in response to nitrate. Previous work initiated by both partners started to draw a complex picture for NRT2.1 post-translational regulations involving phosphorylation of N- and C-terminus at a total of five different sites, interaction with partner proteins, and cleavage of the C-terminal part. The goal of this project is now to build on the strong complementarity of skills between the German and the French partners and combined proteomics approaches with biochemistry, genetic and plant physiology to decipher these complex regulatory mechanisms. Specifically, the project aims at (i) understanding the dynamics of protein-protein interactions of NRT2.1 depending on its modification status, (ii) identification of further regulatory proteins (kinases, phosphatases) acting on NRT2.1, (iii) deciphering the mechanisms of NRT2.1 C-terminal proteolysis as an additional regulatory mechanism. The project will provide novel and valuable insights into the regulation of root nitrate uptake and/or nitrate sensing, which has a strategic importance to improve plants nitrogen use efficiency.