CA2+ - Mediated Signal Transduction in Plants

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Harper 9408108 The long range goal of this research is to understand the role of Ca2+ Dependent Protein Kinases(CDPKs)in plant growth and development. CDPKs are a novel family of protein kinases which are defined by a unique structural arrangement: Within a single polypeptide, a kinase domain is fused to a C-terminal calmodulin-like regulatory domain. The regulatory domain contains four Ca2+-binding EF-hands, which makes CDPKs a primary target (decoder) of Ca2+ signals. Understanding the process by which CDPKs decode and transduce a Ca2+ signal is the primary focus of the proposed research. The first specific aim addresses the question of how Ca2+ activates a CDPK? The second specific aim complements the first by investigating the mechanisms of autoinhibition and Ca2+ activation in the holo-enzyme. The third specific aim is to develop a tool which will permit the in vivo activity of CDPKs to be monitored using fluorescence ratio imaging on live cells. Finally, the fourth specific aim is to identify endogenous substrates for a specific CDPK isoform. Since there appear to be many CDPK isoforms, this research assumes that each may have a different substrate specificity, and that each may have evolved to decode a different Ca2+ signal. The short-term objective of this combined research is to propose a potential function for one specific CDPK, isoform AK1 from Arabidopsis. %%% In plants, calcium signals are involved in many aspects of growth and development, including regulation of water use, activation of plant pathogen defenses, and the ability to respond to gravity. The long range goal of the proposed research is to understand how calcium ions are used to communicate information within a cell. This research is being conducted with a model plant system, Arabidopsis, and will contribute to our basic knowledge of cellular function. It is anticipated that this research will be useful in exploring new approaches to improved agricultural crops and practices. The focus of the proposed research is on the structure and function of a family of novel protein kinases, called CDPKs. Protein kinases regulate many cellular functions by modifying key enzymes through phosphorylation. CDPKs, unlike any other protein kinase, are directly activated by calcium, making them primary targets of calcium signals. Nevertheless, it is not known what cellular functions are controlled by these kinases. ***