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Gene Review

HFR1  -  transcription factor HFR1

Arabidopsis thaliana

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High impact information on HFR1

  • Taken together, our results show that HFR1 is ubiquitinated by COP1 E3 ligase and marked for post-translational degradation during photomorphogenesis [1].
  • We describe a new mutant, hfr1 (long hypocotyl in far-red), that exhibits a reduction in seedling responsiveness specifically to continuous far-red light (FRc), thereby suggesting a locus likely to be involved in phytochrome A (phyA) signal transduction [2].
  • Thus, HFR1 may function to modulate phyA signaling via heterodimerization with PIF3 [2].
  • HFR1 encodes an atypical bHLH protein that acts in phytochrome A signal transduction [2].
  • Under blue light, shb1 suppressed LONG HYPOCOTYL IN FAR-RED LIGHT1 (HFR1) expression and showed several deetiolation phenotypes similar to hfr1-201 [3].

Biological context of HFR1


Anatomical context of HFR1

  • In Arabidopsis, phytochrome A (phyA) is the major photoreceptor both for high irradiance responses to far-red light and broad spectrum very low fluence responses, but little is known of its signaling pathway(s). rsf1 was isolated as a recessive mutant with reduced sensitivity to far-red inhibition of hypocotyl elongation [8].

Physical interactions of HFR1


Enzymatic interactions of HFR1

  • Both HFR1 and HFR1(DeltaN) can be ubiquitinated by COP1, although with different efficiencies [1].

Regulatory relationships of HFR1


Other interactions of HFR1

  • 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 [11].
  • Double mutant analysis suggests that HFR1 mediates phyA-dependent inhibition of hypocotyl elongation independently of HY5 [11].
  • HFR1, a basic helix-loop-helix protein, is known to be required for a subset of phytochrome A (phyA)-dependent photoresponses [11].

Analytical, diagnostic and therapeutic context of HFR1

  • Cloning of the Arabidopsis RSF1 gene by using a mapping strategy based on high-density DNA arrays and denaturing high-performance liquid chromatography [6].
  • We isolated the gene responsible for the recessive mutation rsf1 (for reduced sensitivity to far-red light) in the Arabidopsis Columbia accession by using classical genetic analysis and two recently developed technologies: genotyping high-density oligonucleotide DNA array and denaturing high-performance liquid chromatography (DHPLC) [6].


  1. HFR1 is targeted by COP1 E3 ligase for post-translational proteolysis during phytochrome A signaling. Jang, I.C., Yang, J.Y., Seo, H.S., Chua, N.H. Genes Dev. (2005) [Pubmed]
  2. HFR1 encodes an atypical bHLH protein that acts in phytochrome A signal transduction. Fairchild, C.D., Schumaker, M.A., Quail, P.H. Genes Dev. (2000) [Pubmed]
  3. Arabidopsis SHORT HYPOCOTYL UNDER BLUE1 contains SPX and EXS domains and acts in cryptochrome signaling. Kang, X., Ni, M. Plant Cell (2006) [Pubmed]
  4. The central coiled-coil domain and carboxyl-terminal WD-repeat domain of Arabidopsis SPA1 are responsible for mediating repression of light signaling. Yang, J., Wang, H. Plant J. (2006) [Pubmed]
  5. The degradation of HFR1, a putative bHLH class transcription factor involved in light signaling, is regulated by phosphorylation and requires COP1. Duek, P.D., Elmer, M.V., van Oosten, V.R., Fankhauser, C. Curr. Biol. (2004) [Pubmed]
  6. Cloning of the Arabidopsis RSF1 gene by using a mapping strategy based on high-density DNA arrays and denaturing high-performance liquid chromatography. Spiegelman, J.I., Mindrinos, M.N., Fankhauser, C., Richards, D., Lutes, J., Chory, J., Oefner, P.J. Plant Cell (2000) [Pubmed]
  7. REP1, a basic helix-loop-helix protein, is required for a branch pathway of phytochrome A signaling in arabidopsis. Soh, M.S., Kim, Y.M., Han, S.J., Song, P.S. Plant Cell (2000) [Pubmed]
  8. RSF1, an Arabidopsis locus implicated in phytochrome A signaling. Fankhauser, C., Chory, J. Plant Physiol. (2000) [Pubmed]
  9. Repression of light signaling by Arabidopsis SPA1 involves post-translational regulation of HFR1 protein accumulation. Yang, J., Lin, R., Hoecker, U., Liu, B., Xu, L., Wang, H. Plant J. (2005) [Pubmed]
  10. Multisite phosphorylation of Arabidopsis HFR1 by casein kinase II and a plausible role in regulating its degradation rate. Park, H.J., Ding, L., Dai, M., Lin, R., Wang, H. J. Biol. Chem. (2008) [Pubmed]
  11. HFR1, a phytochrome A-signalling component, acts in a separate pathway from HY5, downstream of COP1 in Arabidopsis thaliana. Kim, Y.M., Woo, J.C., Song, P.S., Soh, M.S. Plant J. (2002) [Pubmed]
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