Plant nitrogen nutrition: sensing and signaling

•Root nitrate sensing is affected by rhizosphere pH and water availability.•Nitrate transporters are involved in sensing cellular pH changes.•Root derived small mobile peptides act as long-distance N signaling.•Shoot derived HY5 acts as a mobile signal coordinating C/N balance.

In response to external fluctuations of nitrogen (N) supplies, plants can activate complex regulatory networks for optimizing N uptake and utilization. In this review, we highlight novel N-responsive sensors, transporters, and signaling molecules recently identified in the dicot Arabidopsis and the monocot rice, and discuss their potential roles in N sensing and signaling. Furthermore, over the last couple of years, N sensing has been shown to be affected by multiple external factors, which act as local signals to trigger systemic signaling coordinated by long-distance mobile signals. Understanding of this complex regulatory network provides a foundation for the development of novel strategies to increase the root N acquisition efficiency under varying N conditions for crop production.