Chlamydomonas: The Eyespot

Vision evolved in motile, single-celled, green algae to enhance photosynthetic capability. A specialized structure within the cell, the eyespot, aids in the detection of light direction and is key to improving the efficiency of phototactic behavior. The Chlamydomonas reinhardtii eyespot is the most well-studied photoreceptive structure guiding cellular movement. Crucial features required for function as a light-sensing organelle and signal transducer affecting swimming behavior are (1) a light-signal transduction cascade, i.e., photon capture, membrane depolarization, and flagellar waveform change; (2) a structure that allows discernment of light direction, i.e., the elaborate layered membrane organization of the eyespot; and (3) precise placement of the organelle relative to the flagella, required for coupling the space/time of light reception to the space/time of the flagellar response accurately. Here we summarize what is known about eyespot function, assembly and placement, and highlight the development of new tools and approaches that will aid in illuminating Chlamydomonas eyespot structure and function.