Advances in the study of calcium signaling-mediated nitrate signaling in plants

Nitrate is not only the main nitrogen source in plants, but also an extremely important signaling molecule. Nitrate signaling integrates and coordinates the expression of a wide range of genes, metabolic pathways, and ultimately, plant growth and development. Calcium signaling is involved in the primary nitrate response pathway. However, how calcium signaling mediates nitrate sensing and signaling from the extracellular space to the cytoplasm and nucleus is much less understood. In this review, we describe how cyclic nucleotide-gated channel 15-nitrate transceptor 1.1 (CNGC15-NRT1.1), calcineurin B-like protein (CBL), CBL-interacting protein kinases (CIPKs), calcium-dependent protein kinases (CPKs), and phospholipase C (PLC) act as key players and the potential backbone of the nitrate-signaling pathway, from the plasma membrane to the nucleus. We also discuss future directions for studying how calcium signaling interconnects the upstream nitrate sensor complex with downstream multiple sensors of the nitrate-signaling pathway to complete nutrient-growth regulatory networks.