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Gene Review

TED4  -  heme oxygenase 1

Arabidopsis thaliana

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Disease relevance of HY1


High impact information on HY1

  • We have identified at least three Arabidopsis nuclear genes (GUN1, GUN2, and GUN3) necessary for coupling the expression of some nuclear genes to the functional state of the chloroplast [2].
  • Here, we describe a new Arabidopsis mutant, laf1 (long after far-red light 1) that has an elongated hypocotyl specifically under far-red light [3].
  • Conditional suppression of CIP4 expression resulted in an elongated hypocotyl and reduced chlorophyll content in the light, indicating that CIP4 is required for the promotion of photomorphogenesis [4].
  • These results indicate that the Arabidopsis HY1 gene encodes a plastid heme oxygenase necessary for phytochrome chromophore biosynthesis [1].
  • The accumulation of the HY1 protein in plastids was detected by using immunoblot analysis with an anti-HY1 antiserum [1].

Biological context of HY1


Anatomical context of HY1

  • The product of the HY1 gene shows significant similarity to animal heme oxygenases and contains a possible transit peptide for transport to plastids [1].
  • The HY1 gene of Arabidopsis encodes a plastid heme oxygenase (AtHO1) required for the synthesis of the chromophore of the phytochrome family of plant photoreceptors [5].
  • Heme oxygenase activity could also be reconstituted using photoreduced ferredoxin generated through light irradiation of isolated thylakoid membranes, suggesting that ferredoxin may be the electron donor in vivo [5].

Associations of HY1 with chemical compounds

  • Through a phenotypic analysis of T-DNA insertion mutants affecting HO3 and HO4 in combination with mutants affecting HY1 or HO2, we demonstrate that both of the encoded proteins also have roles in photomorphogenesis, especially in the absence of HY1 [6].
  • Like HY1, the HO3 and HO4 proteins have the capacity to synthesize BV from heme [6].
  • Heme oxygenase catalyzes the oxygenation of heme to biliverdin, an activity that is necessary for phytochrome chromophore biosynthesis [1].
  • We also show that gun2 and gun3 are alleles of the known photomorphogenic mutants, hy1 and hy2, which are required for phytochromobilin synthesis from heme [7].

Other interactions of HY1

  • These results can be interpreted as a metabolic (rather than genetic) interaction between HY1 and GUN4 or GUN5, and this in turn supports the involvement of tetrapyrroles as plastid signals [8].
  • The antisense-BnCRY1 Brassica transgenic seedlings accumulated negligible levels of CRY1 protein and displayed an elongated hypocotyl when grown under continuous white or blue light (but not under red or far-red light); the accumulation of anthocyanins was also reduced significantly [9].


  1. The Arabidopsis photomorphogenic mutant hy1 is deficient in phytochrome chromophore biosynthesis as a result of a mutation in a plastid heme oxygenase. Muramoto, T., Kohchi, T., Yokota, A., Hwang, I., Goodman, H.M. Plant Cell (1999) [Pubmed]
  2. Signal transduction mutants of Arabidopsis uncouple nuclear CAB and RBCS gene expression from chloroplast development. Susek, R.E., Ausubel, F.M., Chory, J. Cell (1993) [Pubmed]
  3. LAF1, a MYB transcription activator for phytochrome A signaling. Ballesteros, M.L., Bolle, C., Lois, L.M., Moore, J.M., Vielle-Calzada, J.P., Grossniklaus, U., Chua, N.H. Genes Dev. (2001) [Pubmed]
  4. Cip4, a new COP1 target, is a nucleus-localized positive regulator of Arabidopsis photomorphogenesis. Yamamoto, Y.Y., Deng, X., Matsui, M. Plant Cell (2001) [Pubmed]
  5. Expression and biochemical properties of a ferredoxin-dependent heme oxygenase required for phytochrome chromophore synthesis. Muramoto, T., Tsurui, N., Terry, M.J., Yokota, A., Kohchi, T. Plant Physiol. (2002) [Pubmed]
  6. Multiple heme oxygenase family members contribute to the biosynthesis of the phytochrome chromophore in Arabidopsis. Emborg, T.J., Walker, J.M., Noh, B., Vierstra, R.D. Plant Physiol. (2006) [Pubmed]
  7. Arabidopsis genomes uncoupled 5 (GUN5) mutant reveals the involvement of Mg-chelatase H subunit in plastid-to-nucleus signal transduction. Mochizuki, N., Brusslan, J.A., Larkin, R., Nagatani, A., Chory, J. Proc. Natl. Acad. Sci. U.S.A. (2001) [Pubmed]
  8. Interactions between hy1 and gun mutants of Arabidopsis, and their implications for plastid/nuclear signalling. Vinti, G., Hills, A., Campbell, S., Bowyer, J.R., Mochizuki, N., Chory, J., López-Juez, E. Plant J. (2000) [Pubmed]
  9. Cryptochrome 1 from Brassica napus is up-regulated by blue light and controls hypocotyl/stem growth and anthocyanin accumulation. Chatterjee, M., Sharma, P., Khurana, J.P. Plant Physiol. (2006) [Pubmed]
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