Towards an action spectrum for photoentrainment of the Chlamydomonas circadian clock

Christa Gaskill1 and Sigrid Jacobshagen

Department of Biology, Western Kentucky University, Bowling Green, KY, USA

Chlamydomonas reinhardtii is an important model organism used to study circadian clock components. The circadian clock is the molecular mechanism by which nearly every organism measures time. Timekeeping is largely based on clock gene feedback loops where protein products repress transcription of their own genes. This central oscillator mechanism is robust and free running but adjusts to external stimuli such as light and temperature through input pathways. The output pathway carries signals that regulate activities for the appropriate time of day. An example for an activity controlled by the circadian clock in C. reinhardtii is its phototactic behavior. A suggestion on the identity of the photoreceptors involved in the input pathways can be obtained from an action spectrum, which plots the strength of entraining ability against the visible spectrum of light. To this end, we are currently determining the optimal time for an entraining white light pulse in a wild-type strain of C. reinhardtii. Circadian rhythm data such as the shift in phase upon a light pulse are collected using an automated phototaxis machine and analyzed using a new algorithm. Once the optimal time to give a light pulse is determined, we will use narrow-band interference filters to test the effect of particular wavelengths at graded intensities.

e-mail address of presenting author: gaskicf@wku.edu