9317359 Quarmby The goal of this proposal is to analyze the signaling pathways in Chlamydomonas, a unicellular, biflagellate alga. Chlamydomonas exhibits three behaviors that all involve increases in Ca++: these are phototaxis, mating and flagellar excision. The ultimate objective is to understand the mechanisms by which different stress stimuli are transduced to flagellar excision, while other stimuli, such as light, result in the change of swimming behavior and not in flagellar excision, even though all these pathways appear to involve Ca++ in signaling. The proposal has two objectives. The first is to isolate and characterize excision mutants of C. reinhardtii to test the hypothesis that low pH activates a signaling pathway that is different from the signaling pathways activated by the chemical inducers of flagellar excision. The hypothesis for such a dual pathway is supported by physiological and pharmacological data, but a genetic analysis will verify the existence of independent signaling pathways leading to a common response. Mutants will be generated by insertion of exogenous DNA and selected for signaling defects. Heterocaryon analysis will be used to study the relationship of selected mutants. The second objective is to use Ca++ flux and electrophysiology to test the hypothesis that activation of a Ca++ channel is a key event in low pH induced flagellar excision. Dr. Quarmby has strong circumstantial evidence that influx of Ca++ that is stimulated by decreasing pH is necessary for acid-induced flagellar excision. %%% The research objectives chosen by the PI provide a powerful experimental system to study how different signals elicit the same response, and how the different signals that use Ca++ elicit distinctly different physiological responses. Because it is presently thought that the fundamental mechanisms of such signaling pathways have been conserved throughout evolution, results of these studies will be instrumental in our understa nding of how intracellular communication takes place in living organisms. ***
