A primary intracellular target for calcium ions acting as second messengers are calcium binding proteins. In plants, calmodulin is the only recognized and biochemically characterized calcium binding protein. Animals, on the other hand, contain a number of additional calcium-binding proteins (calmodulin-like proteins), which mediate cell- or tissue- specific calcium-regulated processes. The working hypothesis for this research, based on cDNA cloning and direct biochemical assays, is that plants also contain calmodulin-like proteins which may mediate calcium- regulated processes distinct from those mediated by calmodulin. To test and further extend this hypothesis the following specific goals are proposed: (1) to complete the characterization of a cDNA clone, isolated from Arabidopsis thaliana, which encodes a polypeptide that shares approximately 60% amino acid sequence identity with other higher plant calmodulins, by comparing the biochemical properties of the protein encoed by this clone with authentic calmodulin purified from Arabidopsis seedlings; (2) to develop an antobody6 probe for the protein encoded by the Arabidopsis cDNA, and to use this probe to ascertain the tissue- specificity of expression of the calmodulin-like polypeptide during Arabidopsis development, and to examine the subcellular distribution of target proteins that potentially interact with the calmodulin-like polypeptide; and (3) to examine the functional relationship between calmodulin and the Arabidopsis calmodulin-like protein using NAD kinase activation as a model target enzyme system. The long range goals of this research are to identify in plants the members of the family of calcium binding proteins, and to determine what physiological roles these proteins play in plant growth and development. Since similar proteins are known to be important in the regulation of many intracellular functions in animals, the characterization of these putative regulatory molecules in plants should greatly enhance our understanding of the regulation of plant cell function by calcium.
