title: High-level expression and phosphorylation of phytochrome B modulates flowering time in Arabidopsis.
abstract: Optimal timing of flowering in higher plants is crucial for successful reproduction and is coordinated by external and internal factors, including light and the circadian clock. In Arabidopsis, light-dependent stabilization of the rhythmically expressed CONSTANS (CO) is required for the activation of FLOWERING LOCUS T (FT), resulting in the initiation of flowering. Phytochrome A and cryptochrome photoreceptors stabilize CO in the evening by attenuating the activity of the CONSTITUTIVE PHOTOMORPHOGENIC 1-SUPPRESSOR OF PHYA-105 1 (COP1-SPA1) ubiquitin ligase complex, which promotes turnover of CO. In contrast, phytochrome B (phyB) facilitates degradation of CO in the morning and delays flowering. Accordingly, flowering is accelerated in phyB mutants. Paradoxically, plants overexpressing phyB also show early flowering, which may arise from an early phase of rhythmic CO expression. Here we demonstrate that overexpression of phyB induces FT transcription at dusk and in the night without affecting the phase or level of CO transcription. This response depends on the light-activated Pfr form of phyB that inhibits the function of the COP1-SPA1 complex by direct interactions. Our data suggest that attenuation of COP1 activity results in the accumulation of CO protein and subsequent induction of FT. We show that phosphorylation of Ser-86 inhibits this function of phyB by accelerating dark reversion and thus depletion of Pfr forms in the night. Our results explain the early flowering phenotype of phyB overexpression and reveal additional features of the molecular machinery by which photoreceptors mediate photoperiodism.
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, H-6726, Hungary.
authors.forename: Anita
authors.initials: A
authors.lastname: Hajdu
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, H-6726, Hungary.
authors.forename: Éva
authors.initials: É
authors.lastname: Ádám
authors.affiliation: Faculty of Biology, University of Freiburg, Freiburg, 79104, Germany.
authors.forename: David J
authors.initials: DJ
authors.lastname: Sheerin
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, H-6726, Hungary.
authors.forename: Orsolya
authors.initials: O
authors.lastname: Dobos
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, H-6726, Hungary.
authors.forename: Péter
authors.initials: P
authors.lastname: Bernula
authors.affiliation: Faculty of Biology, University of Freiburg, Freiburg, 79104, Germany.|BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, 79104, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hiltbrunner
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, H-6726, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Kozma-Bognár
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, H-6726, Hungary.|School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3JR, UK.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Nagy
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D057906:Circadian Clocks / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D035264:Flowers / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D010766:Phosphorylation / Q000235:genetics; D051939:Phytochrome B / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C418905:FT protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; C118571:SPA1 protein, Arabidopsis; D014157:Transcription Factors; D051939:Phytochrome B; D012694:Serine; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases
keywords: Arabidopsis thaliana; CONSTANS; COP1; circadian clock; flowering; phytochrome