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      Arabidopsis COP1 shapes the temporal pattern of CO accumulation conferring a photoperiodic flowering response

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          Abstract

          The transcriptional regulator CONSTANS (CO) promotes flowering of Arabidopsis under long summer days (LDs) but not under short winter days (SDs). Post-translational regulation of CO is crucial for this response by stabilizing the protein at the end of a LD, whereas promoting its degradation throughout the night under LD and SD. We show that mutations in CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a component of a ubiquitin ligase, cause extreme early flowering under SDs, and that this is largely dependent on CO activity. Furthermore, transcription of the CO target gene FT is increased in cop1 mutants and decreased in plants overexpressing COP1 in phloem companion cells. COP1 and CO interact in vivo and in vitro through the C-terminal region of CO. COP1 promotes CO degradation mainly in the dark, so that in cop1 mutants CO protein but not CO mRNA abundance is dramatically increased during the night. However, in the morning CO degradation occurs independently of COP1 by a phytochrome B-dependent mechanism. Thus, COP1 contributes to day length perception by reducing the abundance of CO during the night and thereby delaying flowering under SDs.

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          Most cited references49

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          The CONSTANS gene of Arabidopsis promotes flowering and encodes a protein showing similarities to zinc finger transcription factors.

          The vegetative and reproductive (flowering) phases of Arabidopsis development are clearly separated. The onset of flowering is promoted by long photoperiods, but the constans (co) mutant flowers later than wild type under these conditions. The CO gene was isolated, and two zinc fingers that show a similar spacing of cysteines, but little direct homology, to members of the GATA1 family were identified in the amino acid sequence. co mutations were shown to affect amino acids that are conserved in both fingers. Some transgenic plants containing extra copies of CO flowered earlier than wild type, suggesting that CO activity is limiting on flowering time. Double mutants were constructed containing co and mutations affecting gibberellic acid responses, meristem identity, or phytochrome function, and their phenotypes suggested a model for the role of CO in promoting flowering.
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            Targeted destabilization of HY5 during light-regulated development of Arabidopsis.

            Arabidopsis seedlings display contrasting developmental patterns depending on the ambient light. Seedlings grown in the light develop photomorphogenically, characterized by short hypocotyls and expanded green cotyledons. In contrast, seedlings grown in darkness become etiolated, with elongated hypocotyls and dosed cotyledons on an apical hook. Light signals, perceived by multiple photoreceptors and transduced to downstream regulators, dictate the extent of photomorphogenic development in a quantitative manner. Two key downstream components, COP1 and HY5, act antagonistically in regulating seedling development. HY5 is a bZIP transcription factor that binds directly to the promoters of light-inducible genes, promoting their expression and photomorphogenic development. COP1 is a RING-finger protein with WD-40 repeats whose nuclear abundance is negatively regulated by light. COP1 interacts directly with HY5 in the nucleus to regulate its activity negatively. Here we show that the abundance of HY5 is directly correlated with the extent of photomorphogenic development, and that the COP1-HY5 interaction may specifically target HY5 for proteasome-mediated degradation in the nucleus.
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              FKF1 and GIGANTEA complex formation is required for day-length measurement in Arabidopsis.

              Precise timing of CONSTANS (CO) gene expression is necessary for day-length discrimination for photoperiodic flowering. The FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1), and GIGANTEA (GI) proteins regulate CO transcription in Arabidopsis. We demonstrate that FKF1 and GI proteins form a complex in a blue-light-dependent manner. The timing of this interaction regulates the timing of daytime CO expression. FKF1 function is dependent on GI, which interacts with a CO repressor, CYCLING DOF FACTOR 1 (CDF1), and controls CDF1 stability. GI, FKF1, and CDF1 proteins associate with CO chromatin. Thus, the FKF1-GI complex forms on the CO promoter in late afternoon to regulate CO expression, providing a mechanistic view of how the coincidence of light with circadian timing regulates photoperiodic flowering.
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                Author and article information

                Journal
                EMBO J
                The EMBO Journal
                Nature Publishing Group
                0261-4189
                1460-2075
                23 April 2008
                03 April 2008
                : 27
                : 8
                : 1277-1288
                Affiliations
                [1 ]Department of Plant Developmental Biology, Max Planck Institute for Plant Breeding Research, Cologne, Germany
                [2 ]Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT, USA
                [3 ]Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC, Universidad de Sevilla, Sevilla, Spain
                Author notes
                [a ]Department of Plant Developmental Biology, Max Planck Institute for Plant Breeding Research, Carl von Linne Weg 10, Cologne 50829, Germany. Tel.: +49 221 5062 205; Fax: +49 221 5062 207; E-mail: coupland@ 123456mpiz-koeln.mpg.de
                [*]

                Present address: Department of Plant Biology, Carnegie Institution of Washington, 260 Panama Street, Stanford, CA 94305, USA

                Article
                emboj200868
                10.1038/emboj.2008.68
                2291449
                18388858
                8eeeedf3-2066-41a8-bb0a-65e5232bbcef
                Copyright © 2008, European Molecular Biology Organization

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits distribution, and reproduction in any medium, provided the original author and source are credited. This license does not permit commercial exploitation or the creation of derivative works without specific permission.

                History
                : 19 November 2007
                : 10 March 2008
                Page count
                Pages: 12
                Categories
                Article

                Molecular biology
                flowering,photomorphogenesis,ubiquitin ligase,constans
                Molecular biology
                flowering, photomorphogenesis, ubiquitin ligase, constans

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