title: Arabidopsis phytochrome a is modularly structured to integrate the multiple features that are required for a highly sensitized phytochrome.
abstract: Phytochrome is a red (R)/far-red (FR) light-sensing photoreceptor that regulates various aspects of plant development. Among the members of the phytochrome family, phytochrome A (phyA) exclusively mediates atypical phytochrome responses, such as the FR high irradiance response (FR-HIR), which is elicited under prolonged FR. A proteasome-based degradation pathway rapidly eliminates active Pfr (the FR-absorbing form of phyA) under R. To elucidate the structural basis for the phyA-specific properties, we systematically constructed 16 chimeric phytochromes in which each of four parts of the phytochrome molecule, namely, the N-terminal extension plus the Per/Arnt/Sim domain (N-PAS), the cGMP phosphodiesterase/adenyl cyclase/FhlA domain (GAF), the phytochrome domain (PHY), and the entire C-terminal half, was occupied by either the phyA or phytochrome B sequence. These phytochromes were expressed in transgenic Arabidopsis thaliana to examine their physiological activities. Consequently, the phyA N-PAS sequence was shown to be necessary and sufficient to promote nuclear accumulation under FR, whereas the phyA sequence in PHY was additionally required to exhibit FR-HIR. Furthermore, the phyA sequence in PHY alone substantially increased the light sensitivity to R. In addition, the GAF phyA sequence was important for rapid Pfr degradation. In summary, distinct structural modules, each of which confers different properties to phyA, are assembled on the phyA molecule.
authors: Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan.
authors: Yoshito
authors: Y
authors: Oka
authors: Yuya
authors: Y
authors: Ono
authors: Gabriela
authors: G
authors: Toledo-Ortiz
authors: Keio
authors: K
authors: Kokaji
authors: Minami
authors: M
authors: Matsui
authors: Nobuyoshi
authors: N
authors: Mochizuki
authors: Akira
authors: A
authors: Nagatani
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003624:Darkness; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D008027:Light; D009154:Mutation; D051942:Phytochrome A / Q000235:genetics / Q000378:metabolism*; D051939:Phytochrome B / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins; D036226:Seedlings / Q000235:genetics / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; C497973:PHYA protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; D051942:Phytochrome A; D011993:Recombinant Fusion Proteins; D051939:Phytochrome B