Calcium's multifaceted functions: From nutrient to secondary messenger during stress
Jaspreet Kour, Kanika Khanna, Arun Dev Singh, Shalini Dhiman, Tamanna Bhardwaj, Kamini Devi, Neerja Sharma, Puja Ohri, Renu Bhardwaj
Abstract
An essential macronutrient for plants, calcium (Ca2+) is needed for a variety of functions both under normal and stressful situations. It displays characteristics of a structural component and acts as a secondary messenger during several physiological processes. It behaves as a signaling molecule while under stress. It manifests a variety of symptoms, such as weakening the cell wall, at lower concentrations or in insufficient situations, demonstrating its significant significance at peak levels. Calcium is taken up by roots through a variety of channels or proteins that are positioned on the plasma membrane. These channels are divided into three categories based on their electrophysiological properties: voltage-independent channels (VICs), hyperpolarization-activated channels (HACCs), and depolarization-activated channels (DACCs). Protein channels allow it to enter the cytosol, where it is then exported towards the apoplast or xylem by Ca2+/H+ antiporters or Ca2+-ATPases. In addition to these, Ca2+ also functions as a secondary messenger throughout physiological, stress-related, and developmental events. The interaction of pumps and influx exporters/channels, also known as calcium signatures, is what causes the signal to be produced. The primary decoding proteins for reactions are calmodulins (CaM), calmodulin-like proteins (CMLs), calcineurin B-like proteins (CBLs), CBL-interacting protein kinases (CIPKs), and calcium-dependent protein kinases (CDPKs/CPKs). After the signals have been processed, transporters, transcription factors, and channels then transmit them into outputs, which lead to the shutting of stomata and gene expression. Ca2+ homeostasis is also preserved during signaling by several transporting components that control the outflow and import of Ca2+, respectively. These transporters include Ca2+-ATPases, Ca2+/H+ exchangers, Mechanosensitive channels (MSLs), Cyclic nucleotide-gated channels (CNGCs), Two Pore Channels (TPCs), Glutamate-like Receptor channels (GLRs), and Ca2+/cation exchangers (CCXs). Due to their sessile nature, plants have been subjected to a range of environmental challenges, including nutrient deficit, metal stress, temperature stress and drought. To investigate the many roles that calcium plays, this review has gone into detail about the various processes via which Ca2+ has been studied to play a part throughout these stresses.