title: HFR1, a phytochrome A-signalling component, acts in a separate pathway from HY5, downstream of COP1 in Arabidopsis thaliana.
abstract: HFR1, a basic helix-loop-helix protein, is known to be required for a subset of phytochrome A (phyA)-dependent photoresponses. To investigate the role of HFR1 in light signalling, we have examined the genetic interaction between HFR1 and HY5, a positive regulator of light signalling, and COP1, a repressor of photomorphogenesis. Double mutant analysis suggests that HFR1 mediates phyA-dependent inhibition of hypocotyl elongation independently of HY5. HFR1 was shown to be necessary for a subset of cop1-triggered photomorphogenic phenotypes in the dark, including inhibition of hypocotyl elongation, gravitropic hypocotyl growth, and expression of the light-inducible genes CAB and RBCS. Phenotypic analysis of the triple mutant cop1hy5hfr1 indicated that both HFR1 and HY5 are required for cop1-mediated photomorphogenic seedling development in darkness, consistent with their additive roles in phyA-dependent signalling. Taken together, these results suggest that HFR1 might act downstream of COP1, in a separate pathway from HY5, to mediate photomorphogenesis in Arabidopsis.
authors.affiliation: Kumho Life & Environmental Science Laboratory, 1 Oryong-Dong, Buk-Gu, Gwangju 500-712, Republic of Korea.
authors.forename: Young-Mi
authors.initials: YM
authors.lastname: Kim
authors.forename: Je-Chang
authors.initials: JC
authors.lastname: Woo
authors.forename: Pill-Soon
authors.initials: PS
authors.lastname: Song
authors.forename: Moon-Soo
authors.initials: MS
authors.lastname: Soh
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism* / Q000502:physiology; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003624:Darkness; D018522:Gravitropism / Q000502:physiology; D018546:Hypocotyl / Q000254:growth & development; D016350:Leucine Zippers / Q000502:physiology; D008027:Light; D009024:Morphogenesis / Q000502:physiology / Q000528:radiation effects; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism*; D010641:Phenotype; D010834:Phytochrome / Q000494:pharmacology*; D051942:Phytochrome A; D010940:Plant Proteins; D012097:Repressor Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D044767:Ubiquitin-Protein Ligases
chemical_list: D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010834:Phytochrome; D051942:Phytochrome A; D010940:Plant Proteins; D012097:Repressor Proteins; D044767:Ubiquitin-Protein Ligases; C414438:At1g02340 protein, Arabidopsis; C109254:HY5 protein, Arabidopsis; C497973:PHYA protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis