Orient in the World with a Single Eye: The Green Algal Eyespot and Phototaxis

Abstract

Motile algae exhibit well-defined movement responses toward or away from a light source, known as positive and negative phototaxis, respectively. To optimize this essential behavior, algae often possess a complex directional optical device, the eyespot. Interest in eyespots has increased considerably during the last decade due to their elaborate ultrastructure and the presence of unique photoreceptors. The latter form an important basis for ongoing developments of optogenetic tools in the field of neurobiology and cell biology. Green algal eyespots, especially that of Chlamydomonas reinhardtii P. A. Dangeard, are the best studied with respect to their biophysical function, assembly, positioning, and signaling cascade(s) finally leading to the oriented movement. Here we give a short general introduction to the eyespot and the phototactic orientation of this algal group and summarize recent progress in the diverse eyespot-related areas. We also address emerging novel insights in the homeostatic feedback regulation of phototactic sensitivity by the cells’ physiological activities.