Calcium-Dependent Protein Kinase and Stress Signal Transduction in Plants

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The long-term goal of this research is to elucidate the molecular mechanisms underlying stress and abscisic acid (ABA) signal transduction mediated by calcium-dependent protein kinases (CDPKs) in plants. The experimental plan is based on the recent discovery that CDPK1 and CDPK1a (96% similarity) act as specific positive regulators to activate multiple stress responsive promoters in maize leaf protoplasts. This is the first demonstration that intracellular calcium signals triggered by stresses or a plant stress hormone can be perceived by specific CDPKs and alter transcription in the nucleus of plant cells. Furthermore, two closely related protein phosphatase 2Cs (ABI1 and AtPP2C) have been shown to be negative regulators in the CDPK1 signal pathway. It is proposed that CDPK1 and CDPK1a are key regulators in stress signal transduction pathways that use calcium as a second messenger in plant cells. Experiments will test the hypotheses that CDPK1 plays an essential role in stress and ABA responses during plant growth and development, and that CDPK1 directly or indirectly phosphorylates and activates specific transcription factors that control stress and ABA responsive genes. There are five specific objectives: (1) to establish the function of CDPK1 in plants, (2) to identify and analyze regulatory components downstream of CDPK1, (3) to determine CDPK1 subcellular location and action, (4) to investigate the role of PP2C as a negative regulator, and (5) to isolate and characterize CDPK1-interacting proteins and substrates. Abiotic stresses, such as drought, cold, and salinity, reduce crop productivity by an order of magnitude greater than all biotic factors combined. Understanding the molecular basis of stress signal transduction may provide valuable and novel tools for agricultural improvement. CDPK1 is the focus of this research, since it is potentially one of the master switches that can turn on many downstream genes and confer multiple stress tolerance in plants.