title: A short amino-terminal part of Arabidopsis phytochrome A induces constitutive photomorphogenic response.
abstract: Phytochrome A (phyA) is the dominant photoreceptor of far-red light sensing in Arabidopsis thaliana. phyA accumulates at high levels in the cytoplasm of etiolated seedlings, and light-induced phyA signaling is mediated by a complex regulatory network. This includes light- and FHY1/FHL protein-dependent translocation of native phyA into the nucleus in vivo. It has also been shown that a short N-terminal fragment of phyA (PHYA406) is sufficient to phenocopy this highly regulated cellular process in vitro. To test the biological activity of this N-terminal fragment of phyA in planta, we produced transgenic phyA-201 plants expressing the PHYA406-YFP (YELLOW FLUORESCENT PROTEIN)-DD, PHYA406-YFP-DD-NLS (nuclear localization signal), and PHYA406-YFP-DD-NES (nuclear export signal) fusion proteins. Here, we report that PHYA406-YFP-DD is imported into the nucleus and this process is partially light-dependent whereas PHYA406-YFP-DD-NLS and PHYA406-YFP-DD-NES display the expected constitutive localization patterns. Our results show that these truncated phyA proteins are light-stable, they trigger a constitutive photomorphogenic-like response when localized in the nuclei, and neither of them induces proper phyA signaling. We demonstrate that in vitro and in vivo PHYA406 Pfr and Pr bind COP1, a general repressor of photomorphogenesis, and co-localize with it in nuclear bodies. Thus, we conclude that, in planta, the truncated PHYA406 proteins inactivate COP1 in the nuclei in a light-independent fashion.
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62., H-6726 Szeged, Hungary.
authors.forename: András
authors.initials: A
authors.lastname: Viczián
authors.forename: Éva
authors.initials: É
authors.lastname: Ádám
authors.forename: Iris
authors.initials: I
authors.lastname: Wolf
authors.forename: János
authors.initials: J
authors.lastname: Bindics
authors.forename: Stefan
authors.initials: S
authors.lastname: Kircher
authors.forename: Marc
authors.initials: M
authors.lastname: Heijde
authors.forename: Roman
authors.initials: R
authors.lastname: Ulm
authors.forename: Eberhard
authors.initials: E
authors.lastname: Schäfer
authors.forename: Ferenc
authors.initials: F
authors.lastname: Nagy
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects; D018546:Hypocotyl / Q000254:growth & development / Q000528:radiation effects; D042541:Intracellular Space / Q000378:metabolism / Q000528:radiation effects; D008027:Light; D009024:Morphogenesis / Q000528:radiation effects*; D019913:Nuclear Localization Signals / Q000378:metabolism; D010641:Phenotype; D051942:Phytochrome A / Q000737:chemistry* / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011485:Protein Binding / Q000528:radiation effects; D021381:Protein Transport / Q000528:radiation effects; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects; D013329:Structure-Activity Relationship; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D019913:Nuclear Localization Signals; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; D011993:Recombinant Fusion Proteins; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases