title: Eukaryotic algal phytochromes span the visible spectrum.
abstract: Plant phytochromes are photoswitchable red/far-red photoreceptors that allow competition with neighboring plants for photosynthetically active red light. In aquatic environments, red and far-red light are rapidly attenuated with depth; therefore, photosynthetic species must use shorter wavelengths of light. Nevertheless, phytochrome-related proteins are found in recently sequenced genomes of many eukaryotic algae from aquatic environments. We examined the photosensory properties of seven phytochromes from diverse algae: four prasinophyte (green algal) species, the heterokont (brown algal) Ectocarpus siliculosus, and two glaucophyte species. We demonstrate that algal phytochromes are not limited to red and far-red responses. Instead, different algal phytochromes can sense orange, green, and even blue light. Characterization of these previously undescribed photosensors using CD spectroscopy supports a structurally heterogeneous chromophore in the far-red-absorbing photostate. Our study thus demonstrates that extensive spectral tuning of phytochromes has evolved in phylogenetically distinct lineages of aquatic photosynthetic eukaryotes.
authors.affiliation: Department of Molecular and Cellular Biology, University of California, Davis, CA 95616.
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Rockwell
authors.forename: Deqiang
authors.initials: D
authors.lastname: Duanmu
authors.forename: Shelley S
authors.initials: SS
authors.lastname: Martin
authors.forename: Charles
authors.initials: C
authors.lastname: Bachy
authors.forename: Dana C
authors.initials: DC
authors.lastname: Price
authors.forename: Debashish
authors.initials: D
authors.lastname: Bhattacharya
authors.forename: Alexandra Z
authors.initials: AZ
authors.lastname: Worden
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
mesh_terms: D001483:Base Sequence; D057486:Carbon Cycle; D000460:Chlorophyta / Q000235:genetics* / Q000378:metabolism; D002942:Circular Dichroism; D058108:Glaucophyta / Q000235:genetics* / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D010834:Phytochrome / Q000235:genetics* / Q000502:physiology*; D011487:Protein Conformation; D017422:Sequence Analysis, DNA; D058009:Stramenopiles / Q000235:genetics* / Q000378:metabolism
chemical_list: D010834:Phytochrome
keywords: bilin; biliprotein; photochemistry; photoswitch; tetrapyrrole