Eyespot-dependent determination of the phototactic sign in Chlamydomonas reinhardtii.
The biflagellate green alga Chlamydomonas reinhardtii exhibits both positive and negative phototaxis to inhabit areas with proper light conditions. It has been shown that treatment of cells with reactive oxygen species (ROS) reagents biases the phototactic sign to positive, whereas that with ROS scavengers biases it to negative. Taking advantage of this property, we isolated a mutant, lts1-211, which displays a reduction-oxidation (redox) dependent phototactic sign opposite to that of the wild type. This mutant has a single amino acid substitution in phytoene synthase, an enzyme that functions in the carotenoid-biosynthesis pathway. The eyespot contains large amounts of carotenoids and is crucial for phototaxis. Most lts1-211 cells have no detectable eyespot and reduced carotenoid levels. Interestingly, the reversed phototactic-sign phenotype of lts1-211 is shared by other eyespot-less mutants. In addition, we directly showed that the cell body acts as a convex lens. The lens effect of the cell body condenses the light coming from the rear onto the photoreceptor in the absence of carotenoid layers, which can account for the reversed-phototactic-sign phenotype of the mutants. These results suggest that light-shielding property of the eyespot is essential for determination of phototactic sign.
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan; Department of Biological Sciences, Graduate School of Science and Engineering, Chuo University, Tokyo 112-8551, Japan;
Noriko
N
Ueki
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan;
Takahiro
T
Ide
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan;
Shota
S
Mochiji
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan;
Yuki
Y
Kobayashi
Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki 444-8585, Japan; Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki 444-8585, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Chiyoda-Ku, Tokyo 102-0076, Japan;
Ryutaro
R
Tokutsu
Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki 444-8585, Japan;
Norikazu
N
Ohnishi
Functional Genomics Facility, National Institute for Basic Biology, Okazaki 444-8585, Japan;
Katsushi
K
Yamaguchi
Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki 444-8585, Japan; Functional Genomics Facility, National Institute for Basic Biology, Okazaki 444-8585, Japan;
Shuji
S
Shigenobu
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Chiyoda-Ku, Tokyo 102-0076, Japan;
Kan
K
Tanaka
Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki 444-8585, Japan; Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki 444-8585, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Chiyoda-Ku, Tokyo 102-0076, Japan;
Jun
J
Minagawa
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Chiyoda-Ku, Tokyo 102-0076, Japan;
Toru
T
Hisabori
Department of Frontier Bioscience, Hosei University, Tokyo 184-8584, Japan.
Masafumi
M
Hirono
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan; wakaba@res.titech.ac.jp.
Ken-Ichi
K
Wakabayashi
D000818:Animals; D002338:Carotenoids / Q000502:physiology* / Q000528:radiation effects; D002465:Cell Movement / Q000502:physiology* / Q000528:radiation effects; D016825:Chlamydomonas reinhardtii / Q000166:cytology / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology* / Q000528:radiation effects; D000071444:Phototaxis / Q000502:physiology*; D010858:Pigmentation / Q000502:physiology / Q000528:radiation effects; D011829:Radiation Dosage
D002338:Carotenoids
Chlamydomonas; carotenoids; eyespot; lens; phototaxis