Phototropin is the blue-light receptor that controls multiple steps in the sexual life cycle of the green alga Chlamydomonas reinhardtii.

Blue light as an environmental cue plays a pivotal role in controlling the progression of the sexual life cycle in the green alga Chlamydomonas reinhardtii. Phototropin was considered a prime candidate for the blue-light receptor involved. By using the RNA interference method, knockdown strains with reduced phototropin levels were isolated. Those with severely reduced levels of this photoreceptor were partially impaired in three steps of the life cycle: in gametogenesis, the maintenance of mating ability, and the germination of zygotes. These observations suggest that phototropin is the principal sensory molecule used by this alga for the control of its life cycle by light.