Molecular Cloning and Comparative In silico Analysis of Calmodulin Genes from Cereals and Millets for Understanding the Mechanism of Differential Calcium Accumulation

Plant cells are equipped with highly efficient mechanisms to perceive, transduce and respond to a wide variety of internal and external signals during their growth and development. Perception of signals via receptors results in generation or synthesis of nonproteinaceous molecules often termed messengers such as calcium which control diverse cellular processes through calcium sensors which is also known as calcium binding proteins (Bowler and Fluhr, 2000; Reddy, 2001; Snedden and Fromm, 2001; White and Broadley, 2003).The intracellular calcium sensor protein calmodulin (CaM) interacts with a large number of proteins to regulate their biological functions in response to calcium stimulus. This molecular recognition process is diverse in its mechanism, but can be grouped into several classes based on structural and sequence information (Yap et al., 2000). CaM is a small (148 residues) multifunctional acidic protein arranged in two globular domains connected with a long flexible helix. Each globular domain contains a pair of intimately linked EF hands. CaM undergoes conformational changes on binding of four Ca2+ ions to their four EF-hand domains. On binding Ca2+, hydrophobic surfaces are exposed and allow the Ca2+-CaM complex to interact with, and to regulate the activity of, an array of target proteins. The activities of these proteins affect physiological responses to the vast array of specific stimuli received by plant cells (Yang and Poovaiah, 2003). It is a key calcium sensor in all eukaryotes, regulates diverse cellular processes by interacting with other proteins (Reddy et al., 2000).