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Gene Review

HY2  -  phytochromobilin:ferredoxin oxidoreductase

Arabidopsis thaliana

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Disease relevance of HY2


High impact information on HY2

  • 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].
  • Database searches and hybridization studies suggest that HY2 is a unique gene in the Arabidopsis genome that is related to a family of proteins found in oxygenic photosynthetic bacteria [3].
  • The HY2 transit peptide is sufficient to localize the reporter green fluorescent protein to plastids [3].
  • Purified mature recombinant HY2 protein exhibits P Phi B synthase activity (i.e., ferredoxin-dependent reduction of biliverdin IX alpha to P Phi B), as confirmed by HPLC and by the ability of the bilin reaction products to combine with apophytochrome to yield photoactive holophytochrome [3].
  • By expressed sequence tag (EST)-based screening of sequence databases, we found a tomato gene that encodes a protein homologous to Arabidopsis HY2 for phytochromobilin synthase catalyzing the last step of phytochrome chromophore biosynthesis [4].

Associations of HY2 with chemical compounds

  • 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 [5].


  1. Functional genomic analysis of the HY2 family of ferredoxin-dependent bilin reductases from oxygenic photosynthetic organisms. Frankenberg, N., Mukougawa, K., Kohchi, T., Lagarias, J.C. Plant Cell (2001) [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. The Arabidopsis HY2 gene encodes phytochromobilin synthase, a ferredoxin-dependent biliverdin reductase. Kohchi, T., Mukougawa, K., Frankenberg, N., Masuda, M., Yokota, A., Lagarias, J.C. Plant Cell (2001) [Pubmed]
  4. The tomato photomorphogenetic mutant, aurea, is deficient in phytochromobilin synthase for phytochrome chromophore biosynthesis. Muramoto, T., Kami, C., Kataoka, H., Iwata, N., Linley, P.J., Mukougawa, K., Yokota, A., Kohchi, T. Plant Cell Physiol. (2005) [Pubmed]
  5. 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]
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