Cloning of the cDNA Encoding Plant Calcium-Dependent Protein Kinase

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Soybean calcium-dependent protein kinase (CDPK) is the first Ca2+-dependent protein kinase from plants to be purified to homogeneity. This enzyme represents a new class of protein kinases that are dependent on micromolar calcium for activity but do not require phospholipids or calmodulin for activity. Preliminary immunocytochemical localization of the enzyme shows that CDPK is associated with actin filaments in soybean and onion root tip cells. This association suggests that CDPK may play a role in the regulation of plant actin. The purification and characterization of CDPK allows the study of both the role of calcium and protein phosphorylation in plants. This research investigates these roles by (1) fully characterizing the calcium-binding properties of CDPK, (2) determining the immunological properties of CDPK, (3) determining how CDPK binds to actin, and (4) identifying actin-associated proteins that are substrates of CDPK.%%% Many metabolic activities in plants and animals are regulated by phosphorylation/dephosphorylation mechanisms. Protein kinases play a major role in this type of regulation. Recently, a new class of protein kinases which directly bind calcium have been discovered. The experiments defined here will provide for investigation of the potential role of these calcium-dependent protein kinases in the regulation of the plant cytoskeleton and to better define its role in the regulation of plant cell function and in plant growth and development.***//