The green algal eyespot apparatus: a primordial visual system and more?
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- Kreimer, G. Curr Genet (2009) 55: 19. doi:10.1007/s00294-008-0224-8
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Most flagellate green algae exhibiting phototaxis posses a singular specialized light sensitive organelle, the eyespot apparatus (EA). Its design principles are similar in all green algae and produce, in conjunction with the movement pattern of the cell, a highly directional optical device. It enables an oriented movement response with respect to the direction and intensity of light. The functional EA involves local specializations of different compartments (plasma membrane, cytosol, and chloroplast) and utilizes specialized microbial-type rhodopsins, which act as directly light-gated ion channels. Due to their elaborate structures and the presence of retinal-based photoreceptors in some lineages, algal EAs are thought to play an important role in the evolution of photoreception and are thus not only of interest to plant biologists. In green algae considerable progress in the molecular dissection of components of this primordial visual system has been made by genetic and proteomic approaches in recent years. This review summarizes general aspects of the green algal EA as well as recent progress in the identification of proteins related to it. Further, novel data supporting a link between eyespot globules and plastoglobules will be presented and potential additional roles of the EA besides those in photoreception will be discussed.
KeywordsChlamydomonas reinhardtii Channelrhodopsins Eyespot function Light perception Phototaxis Plastoglobules
Supplemental video This video demonstrates eyespot reflectivity at a reduced frame rate (15 frames per second). Cells of C. reinhardtii close to and partially sticking to the surface of a petridish were analyzed with epireflection microscopy. Note the dependence of the reflection signal from the relative orientation of the eyespot towards the light source. A bright reflection signal only appears when the eyespot is oriented towards the light source. (MOV 6096 kb)