HFR1, a phytochrome A-signalling component, acts in a separate pathway from HY5, downstream of COP1 in Arabidopsis thaliana

Plant J. 2002 Jun;30(6):711-9. doi: 10.1046/j.1365-313x.2002.01326.x.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Arabidopsis / drug effects
  • Arabidopsis / genetics
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / metabolism*
  • Arabidopsis Proteins / physiology
  • Basic-Leucine Zipper Transcription Factors
  • Carrier Proteins / metabolism*
  • DNA-Binding Proteins / metabolism*
  • Darkness
  • Gravitropism / physiology
  • Hypocotyl / growth & development
  • Leucine Zippers / physiology
  • Light
  • Morphogenesis / physiology
  • Morphogenesis / radiation effects
  • Mutation
  • Nuclear Proteins / metabolism*
  • Phenotype
  • Phytochrome / pharmacology*
  • Phytochrome A
  • Plant Proteins*
  • Repressor Proteins / metabolism
  • Signal Transduction / physiology
  • Ubiquitin-Protein Ligases*


  • Arabidopsis Proteins
  • Basic-Leucine Zipper Transcription Factors
  • Carrier Proteins
  • DNA-Binding Proteins
  • HFR1 protein, Arabidopsis
  • HY5 protein, Arabidopsis
  • Nuclear Proteins
  • PHYA protein, Arabidopsis
  • Phytochrome A
  • Plant Proteins
  • Repressor Proteins
  • Phytochrome
  • AT2G32950 protein, Arabidopsis
  • Ubiquitin-Protein Ligases