Major transcription factor families involved in nitrogen stress adaptation in plants

Abstract Nitrate (NO3−) is the major inorganic N form in aerobic soils and also a potent signal that regulates plant growth and metabolism. Current understanding of the N and NO3− signaling in the model plant(s) is huge, owing to the development of molecular tools and sequencing technology. Primary nitrate response (PNR) refers to the rapid (within minutes) activation of nitrate-specific genes (NR, NiR, G6PDH, HRS1) without additional protein synthesis and is regulated by CHL1, calcium-dependent kinases (CPKs), CBLs, CIPKs, phosphatases, and transcription factors like NLPs, NRG2, SPL9, etc. The second component is N starvation response (NSR), which includes slow activation of high-affinity nitrate transporters belonging to the NRT2 family (NRT2.4, NRT2.5) in response to N starvation. Some of the important genes that are reported to regulate NSR are LBD36, 37, CBL7, miR169, NFYA, HRS1, and HHOs. The accumulated knowledge on the molecular aspects of N signaling can be exploited for enhancing NUE and N stress adaptation in crop plants.