Sodium-Induced Calcium Signaling in Plants Under Salinity Stress

Global climate change is posing serious threat to agricultural productivity worldwide. Therefore, ensuring global food security in the light of current and future scenarios of global climate change is among the major challenging issues. Climate change induces the rate, frequency, and intensity of several biotic and abiotic stresses. Soil salinization is one of the major abiotic stresses and it is predicted to increase by 10% annually under the climate change effects. Owing to their sessile nature, plants evolved with a variety of defense mechanisms to tolerate various salinity levels. It has been reported that a variety of sensors, channels, transporters, and signaling molecules work together in plants to detect and respond to salinity stress accordingly. The majority of these are based on a sodium-induced increment of cytosolic calcium concentration, it’s sensing, and signaling mechanisms. The precise mechanism of sodium uptake and transport-mediated calcium signaling is one of the responsible mechanisms for the establishment of salinity tolerance in plants. Non-selective cation channels (NSCCs), potassium transporters (KT), and high-affinity potassium transporters (HKT) families are involved in primary sodium influx into the plant’s roots. Whereas the sodium proton exchangers (NHX) and salt overly sensitive families (SOS) are involved in the sodium sequestration within cells and its cytosolic homeostasis. MOCA1 (Monocation-induced Ca2+ Increases 1) and OSCA1 (osmo-sensory calcium antiporter1) are plasma membrane channels involved in calcium signaling. The activity of MOCA1 is triggered by sodium-induced ionic stress whereas OSCA1 is stimulated by osmotic stress caused by high sodium concentration. The KEA1/2 and KEA3 (plastidial K+ exchange antiporters) are found on the chloroplast membrane and also function as an osmosensory element, responsible for cytosolic calcium spikes, triggered via osmotic imbalances under salinity stress. The plasma membrane receptor-like kinase FERONIA (FER) also participates in salt-triggered calcium spikes in order to protect cell wall structure throughout stress. Overall, plants activate sodium transporters and channels in order to maintain ionic homeostasis and response to salt stress via establishing the salt overly sensitive (SOS) pathway through calcium signaling, which is one of the important defense strategies under salinity stress. The calcium signaling mechanism under sodium-imposed salinity stress will be summarised in this chapter, which might be a useful strategy for developing salt-tolerant cultivars and achieving the goal of sustainable agricultural yield.