title: Phosphorylation of CONSTANS and its COP1-dependent degradation during photoperiodic flowering of Arabidopsis.
abstract: Seasonal flowering involves responses to changes in day length. In Arabidopsis thaliana, the CONSTANS (CO) transcription factor promotes flowering in the long days of spring and summer. Late flowering in short days is due to instability of CO, which is efficiently ubiquitinated in the dark by the CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) E3 ligase complex. Here we show that CO is also phosphorylated. Phosphorylated and unphosphorylated forms are detected throughout the diurnal cycle but their ratio varies, with the relative abundance of the phosphorylated form being higher in the light and lower in the dark. These changes in relative abundance require COP1, because in the cop1 mutant the phosphorylated form is always more abundant. Inactivation of the PHYTOCHROME A (PHYA), CRYPTOCHROME 1 (CRY1) and CRYPTOCHROME 2 (CRY2) photoreceptors in the phyA cry1 cry2 triple mutant most strongly reduces the amount of the phosphorylated form so that unphosphorylated CO is more abundant. This effect is caused by increased COP1 activity, as it is overcome by introduction of the cop1 mutation in the cop1 phyA cry1 cry2 quadruple mutant. Degradation of CO is also triggered in red light, and as in darkness this increases the relative abundance of unphosphorylated CO. Finally, a fusion protein containing truncated CO protein including only the carboxy-terminal region was phosphorylated in transgenic plants, locating at least one site of phosphorylation in this region. We propose that CO phosphorylation contributes to the photoperiodic flowering response by enhancing the rate of CO turnover via activity of the COP1 ubiquitin ligase.
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Liron
authors.initials: L
authors.lastname: Sarid-Krebs
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Kishore C S
authors.initials: KC
authors.lastname: Panigrahi
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Fabio
authors.initials: F
authors.lastname: Fornara
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Hayama
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Seonghoe
authors.initials: S
authors.lastname: Jang
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Vicky
authors.initials: V
authors.lastname: Tilmes
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: Federico
authors.initials: F
authors.lastname: Valverde
authors.affiliation: Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, Cologne, D-50829, Germany.
authors.forename: George
authors.initials: G
authors.lastname: Coupland
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D056931:Cryptochromes / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D003624:Darkness; D035264:Flowers / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017440:Photoperiod; D051942:Phytochrome A / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D059748:Proteolysis; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; C538962:CRY1 protein, Arabidopsis; C103618:CRY2 protein, Arabidopsis; D056931:Cryptochromes; D004268:DNA-Binding Proteins; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; D014157:Transcription Factors; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases
keywords: Arabidopsis thaliana; phosphorylation; photoperiodic flowering; phytochrome; ubiquitination