title: A phytochrome/phototropin chimeric photoreceptor of fern functions as a blue/far-red light-dependent photoreceptor for phototropism in Arabidopsis.
abstract: In the fern Adiantum capillus-veneris, the phototropic response of the protonemal cells is induced by blue light and partially inhibited by subsequent irradiation with far-red light. This observation strongly suggests the existence of a phytochrome that mediates this blue/far-red reversible response; however, the phytochrome responsible for this response has not been identified. PHY3/NEO1, one of the three phytochrome genes identified in Adiantum, encodes a chimeric photoreceptor composed of both a phytochrome and a phototropin domain. It was demonstrated that phy3 mediates the red light-dependent phototropic response of Adiantum, and that phy3 potentially functions as a phototropin. These findings suggest that phy3 is the phytochrome that mediates the blue/far-red response in Adiantum protonemata. In the present study, we expressed Adiantum phy3 in a phot1 phot2 phototropin-deficient Arabidopsis line, and investigated the ability of phy3 to induce phototropic responses under various light conditions. Blue light irradiation clearly induced a phototropic response in the phy3-expressing transgenic seedlings, and this effect was fully inhibited by simultaneous irradiation with far-red light. In addition, experiments using amino acid-substituted phy3 indicated that FMN-cysteinyl adduct formation in the light, oxygen, voltage (LOV) domain was not necessary for the induction of blue light-dependent phototropism by phy3. We thus demonstrate that phy3 is the phytochrome that mediates the blue/far-red reversible phototropic response in Adiantum. Furthermore, our results imply that phy3 can function as a phototropin, but that it acts principally as a phytochrome that mediates both the red/far-red and blue/far-red light responses.
authors.affiliation: Department of Biological Sciences, Graduate School of Science and Technology, Tokyo Metropolitan University, Minami Osawa, Hachioji, Tokyo, 192-0397, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kanegae
authors.affiliation: Department of Biological Sciences, Graduate School of Science and Technology, Tokyo Metropolitan University, Minami Osawa, Hachioji, Tokyo, 192-0397, Japan.
authors.forename: Izumi
authors.initials: I
authors.lastname: Kimura
mesh_terms: D035681:Adiantum / Q000235:genetics / Q000502:physiology*; D017360:Arabidopsis / Q000378:metabolism*; D056949:Phototropins / Q000235:genetics*; D018524:Phototropism / Q000502:physiology*; D010834:Phytochrome / Q000235:genetics*
chemical_list: D056949:Phototropins; D010834:Phytochrome
keywords: Adiantum capillus-veneris; fern; neochrome; phototropin; phototropism; phytochrome