Meeting Abstract
In many organisms, from protists to humans, simple photoreceptors monitor ambient lighting. They function to assess the time of day for circadian rhythms and seasonal changes, as well as for the detection of harmful UV light and as depth gauges in the water column. Photoreceptors can be organized into eyespots, and in a wide variety of unicellular organisms, including Chlamydomonas, Euglena and several species of dinoflagellates, eyespots are light-sensitive organelles residing within the cell. Eyespots can be composed of photoreceptor proteins and red-orange carotenoid screening pigments. This association of photopigment with screening pigment allows for detecting light directionality, leading to light-guided behaviors such as positive and negative phototaxis. In Chlamydomonas, the eyespot is part of the chloroplast and its light-sensitive photopigment is the microbial channelrhodopsin (ChR1 and ChR2). Dinoflagellates are unicellular protists that are ecologically important constituents of the phytoplankton. They exhibit a great deal of diversity in morphology, nutritional modes and symbioses, and can be photosynthetic or heterotrophic, feeding on smaller phytoplankton. Certain dinoflagellates, such as Kryptoperidinium foliaceium, have eyespots that are used for light-mediated tasks such as phototaxis. Other dinoflagellates belonging to the family, Warnowiaceae, have a more elaborate eye. Their eye-organelle is a large structure consisting of a focusing lens, highly ordered retinal membranes and a shield of dark pigment. This complex eye-organelle is similar to multicellular camera eyes, such as our own. Unraveling the molecular makeup, structure and function of dinoflagellate eyes, as well as light-guided behaviors in phytoplankton can inform us about the selective forces that drove evolution in the important steps from light detection to vision.
