N uptake and signaling pathway in plants. Plants uptake nitrate (NO3−) through NRT transporters. NRT1.1 is dual affinity nitrate transporter, whose affinity is changed by phosphorylation through CIPK23 and CBL1/9. In addition to nitrate uptake, NRT1.1 generates calcium (Ca2+) signaling through Phospholipase c (PLC). Ca2+ induces CPK-dependent phosphorylation of NLP6/7 transcription factors, leading to nuclear accumulation of NLP6/7. HBI also accelerates nuclear accumulation of NLP6/7 by reducing cellular reactive oxygen species (ROS) level. Nuclear localized NLP6/7 interact with NRG2 and TCP20 to activate expression of N-responsive genes. NLP2, ANR1, and TGA1/4 act as positive regulator for N-responsive genes. In contrast, LBDs, NIGT1, and IWS1 negatively regulate expression of N-responsive genes. NRT2.1 is a high affinity nitrate transporter, and phosphorylation inactivates NRT2.1 under high N conditions. NRT2.1 phosphorylation was removed by CEPD-induced phosphatase (CEPH) under N starvation condition, activating NRT2.1 dependent nitrate uptake. Ammonium transporter 1;1 (AMT1;1) is responsible for ammonium (NH4+) uptake. AMT1;1 is inactivated by phosphorylation through CIPK23 and ACTPK1 under high NH4+ conditions to inhibit toxic accumulation of NH4+ in cells. The figure was created with Biorender.com.
