Calcium Signaling Network in Plants

I thank Dr. Renu Tuteja for critical reading and corrections on the article. This work was partially supported by the grants from the Department of Biotechnology (DBT), Department of Science and Technology (DST) and Defence Research and Development Organisation (DRDO), Government of India. I apologize if some references could not be cited due to space constraint. AbSTrAcT Calcium ion (Ca2+) is one of the very important ubiquitous intracellular second messenger molecules involved in many signal transduction pathways in plants. The cytosolic free Ca2+ concentration ([Ca]cyt) have been found to increased in response to many physiological stimuli such as light, touch, pathogenic elicitor, plant hormones and abiotic stresses including high salinity, cold and drought. This Ca2+ spikes normally result from two opposing reactions, Ca2+ influx through channels or Ca2+ efflux through pumps. The removal of Ca2+ from the cytosol against its electrochemical gradient to either the apoplast or to intracellular organelles requires energized ‘active’ transport. Ca2+‐ATPases and H+/Ca2+ antiporters are the key proteins catalyzing this movement. The increased level of Ca2+ is recognised by some Ca2+‐sensors or calcium‐binding proteins, which can activate many calcium dependent protein kinases. These kinases regulate the function of many genes including stress responsive genes, resulted in the phenotypic response of stress tolerance. Calcium signaling is also involved in the regulation of cell cycle progression in response to abiotic stress. The regulation of gene expression by cellular calcium is also crucial for plant defense against various stresses. However, the number of genes known to respond to specific transient calcium signals is limited. This review article describes several aspects of calcium signaling such as Ca2+ requiremant and its role in plants, Ca2+ transporters, Ca2+‐ATPases, H+/ Ca2+‐antiporter, Ca2+‐signature, Ca2+‐memory and various Ca2+‐binding proteins (with and without EF hand).