Ca²⁺-Mediated Signaling in Plants

I am interested in understanding how Ca²⁺-mediated signaling is regulated and integrated with other signaling pathways to elicit a variety of physiological responses in plants, including: guard cell function, polarized growth (seen in root hairs and pollen tubes), and responses to pathogens and insects. Changes in Ca²⁺ concentration are generated in the cytoplasm and nuclei of all eukaryotes as a second messenger in response to an array of hormonal and environmental stimuli. Our main focus is on understanding how the Ca²⁺ receptor protein calmodulin (CaM) communicates Ca²⁺ signals to help de-code Ca²⁺ signals. CaM functions by binding other proteins and modulating their activities. Current estimates are that there are more than two-dozen proteins that specifically interact with CaM; this means that CaM represents a crucial link in the pathways by which Ca²⁺ signals are de-coded.

We use a combination of biochemical, molecular and genetic strategies to dissect the processes involved in Ca²⁺-mediated signal transduction. We have identified lines of mutant plants in which different genes encoding CaM have been knocked out by insertional mutation. The goal of this project is to determine whether one particular CaM gene plays a dominant role in controlling several well-characterized Ca²⁺-mediated responses in plants. Ca²⁺ signaling mediated by CaM is carried out by physical interaction between CaM and other proteins. We measure this interaction using fluorescent fusion proteins that report CaM binding; we call these fluorescent indicator proteins (FIPs). By expressing FIPs in transgenic plants, we are asking whether there are spatial differences in the pattern of CaM activation in cells stimulated to generate Ca²⁺ signals.