Analyses and Identification of molecular mechanisms underlying Calcium-sensor function and priming in guard cells

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Studies in a number of laboratories have shown cytosolic Ca2+ dependent processes in the transduction of ABA-induced stomatal closing. However, recent studies indicated that cytosolic Ca2+ elevations can occur spontaneously and even during stomatal opening stimuli, such as low CO2. These observations suggest that additional molecular mechanisms are required to “prime” calcium sensors in order to allow calcium signalling. Two calcium sensors (CPK3 and CPK6) of the ABA signalling pathway have recently been identified in the host laboratory (1). I will investigate the working hypothesis, that during Ca2+-dependent signalling, Ca2+ sensor proteins, such as CPK3 and CPK6 and Calcineurin B-like proteins (CBL’s), could be “primed” by posttranslational modifications, such as phosphorylations, or by changing their intracellular localization, in order to allow them to respond to calcium transitions (1, 2). To identify modulators of calcium signalling I want to identify further components of ABA signalling. Proteins that are modified or induced during ABA signalling will be identified by mass spectrometry and substrates of CPK6 and CPK3 will be analyzed using biochemical methods and peptide arrays. This Ca2+ sensor priming hypothesis may also contribute basic knowledge and a new perspective to understanding how the numerous Ca2+ sensory proteins encoded in plant genomes can mediate specificity in the many Ca2+-dependent signaling processes in plants.