title: A single chromoprotein with triple chromophores acts as both a phytochrome and a phototropin.
abstract: Plants sense their environmental light conditions by using three photoreceptors that absorb in the UV, blue/near UV, and red/far-red spectral ranges. These photoreceptors have specific chromophore components corresponding to their absorption spectra. Phytochrome, a red/far-red light receptor, has phytochromobilin as its chromophore, whereas the blue/near UV photoreceptors cryptochrome and phototropin have a pair of flavin derivatives. Plants use these various photoreceptors to assess the surrounding light environment. Phytochrome 3 (PHY3) is a red light receptor found in some ferns, which preferentially grow under weak light. PHY3 is composed of a phytochrome chromophore-binding domain in its N-terminal portion and an almost full-length phototropin in its C-terminal half. This unusual domain organization implies that two different light-sensing systems coexist in this single photoreceptor, although these light-sensing systems usually reside in independent photoreceptors. Here, we show that PHY3 acts as a dual-channel photoreceptor that possesses both the red light-sensing system of phytochrome and the blue light-sensing system of phototropin. Furthermore, red- and blue-light signals perceived by PHY3 are processed synergistically within this single chromoprotein. These unusual properties might confer an enhanced light sensitivity on PHY3, allowing ferns to grow under a low-light canopy.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Faculty of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan. tkanegae@comp.metro-u.ac.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kanegae
authors.forename: Emi
authors.initials: E
authors.lastname: Hayashida
authors.forename: Chihiro
authors.initials: C
authors.lastname: Kuramoto
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Wada
mesh_terms: D035681:Adiantum / Q000235:genetics*; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins; D056931:Cryptochromes; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D008027:Light; D010786:Photoreceptor Cells / Q000378:metabolism*; D018524:Phototropism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D056931:Cryptochromes; D005420:Flavoproteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins