Calcium Homeostasis: Role of CAXs Transporters in Plant Signaling
نویسندگان
چکیده
Calcium is an essential macronutrient as well as an ubiquitous second messenger, playing a pivotal role in plant growth and development. The neutral cytosolic pH, acidic apoplastic and vacuolar pH is maintained by synergistic action of different channels/transporters in plant cells. In the cytosol, a submicro-molar range of calcium is maintained for efficient biochemical and physiological functioning including calcium-mediated signal transduction. A concerted interplay of channels/transporters, mediating influx and efflux of ions across membranes, tightly regulates the concentration of calcium in the cytosol by sequestering extra calcium into vacuole. For calcium homeostasis, the pre-requisite is to balance and maintain high calcium level in cytoplasm during signaling events and subsequently counterbalanced after the removal of the signal. Hence, the major mechanism in plant cell for calcium homeostasis is redistribution of calcium and other cation in exchange for the H generated by various H pumps and antiporters. Calcium/cation antiporter (CaCA) superfamily consist of five families, one of them is CAX multigene family (H/cation exchangers). In last two decades, several studies have been reported involving discovery of biochemical, physiological and molecular characterization of CAX family members extensively. CAX proteins are mainly constituted in vacuolar membrane and responsible for maintaining low cytosolic Ca and/or other cations against their concentration gradient in cells. CAX family play an important role in calcium signaling, ion compartmentalization, sequestering of essential and heavy metal ions in vacuole. CAXs could be agriculturally important to increase the calcium content in edible part of plant and sequester heavy metals from polluted soil. In this review, we are primarily elaborating the functional aspect of CAX protein family in calcium homeostasis and stress mediated signaling in plants. _____________________________________________________________________________________________________________
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