title: The degradation of HFR1, a putative bHLH class transcription factor involved in light signaling, is regulated by phosphorylation and requires COP1.
abstract: All developmental transitions throughout the life cycle of a plant are influenced by light. In Arabidopsis, multiple photoreceptors including the UV-A/blue-sensing cryptochromes (cry1-2) and the red/far-red responsive phytochromes (phyA-E) monitor the ambient light conditions. Light-regulated protein stability is a major control point of photomorphogenesis. The ubiquitin E3 ligase COP1 (constitutively photomorphogenic 1) regulates the stability of several light-signaling components. HFR1 (long hypocotyl in far-red light) is a putative transcription factor with a bHLH domain acting downstream of both phyA and the cryptochromes. HFR1 is closely related to PIF1, PIF3, and PIF4 (phytochrome interacting factor 1, 3 and 4), but in contrast to the latter three, there is no evidence for a direct interaction between HFR1 and the phytochromes. Here, we show that the protein abundance of HFR1 is tightly controlled by light. HFR1 is an unstable phosphoprotein, particularly in the dark. The proteasome and COP1 are required in vivo to degrade phosphorylated HFR1. In addition, HFR1 can interact with COP1, consistent with the idea of COP1 directly mediating HFR1 degradation. We identify a domain, conserved among several bHLH class proteins involved in light signaling , as a determinant of HFR1 stability. Our physiological experiments indicate that the control of HFR1 protein abundance is important for a normal de-etiolation response.
authors.affiliation: Department of Molecular Biology, University of Geneva, 30 quai Ernest Ansermet, 1211 Genève 4, Switzerland.
authors.forename: Paula D
authors.initials: PD
authors.lastname: Duek
authors.forename: Mireille V
authors.initials: MV
authors.lastname: Elmer
authors.forename: Vivian R
authors.initials: VR
authors.lastname: van Oosten
authors.forename: Christian
authors.initials: C
authors.lastname: Fankhauser
mesh_terms: D016960:Agrobacterium tumefaciens; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D056931:Cryptochromes; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005420:Flavoproteins / Q000502:physiology; D005822:Genetic Vectors; D047468:Immunoprecipitation; D008027:Light; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D010834:Phytochrome / Q000502:physiology; D030821:Plants, Genetically Modified; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D044767:Ubiquitin-Protein Ligases
chemical_list: D029681:Arabidopsis Proteins; D056931:Cryptochromes; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D005420:Flavoproteins; D009687:Nuclear Proteins; D010834:Phytochrome; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; C538962:CRY1 protein, Arabidopsis; C414438:At1g02340 protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis