Eyespot-dependent determination of the phototactic sign in Chlamydomonas reinhardtii

Noriko Ueki, Takahiro Ide, Shota Mochiji, Yuki Kobayashi, Ryutaro Tokutsu, Norikazu Ohnishi, Katsushi Yamaguchi, Shuji Shigenobu, Kan Tanaka, Jun Minagawa, Toru Hisabori, Masafumi Hirono, Ken Ichi Wakabayashi

Research output: Contribution to journalArticlepeer-review

53 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)5299-5304
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number19
Publication statusPublished - May 10 2016


  • Carotenoids
  • Chlamydomonas
  • Eyespot
  • Lens
  • Phototaxis

ASJC Scopus subject areas

  • General


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