The phytochromes: a biochemical mechanism of signaling in sight?

Bioessays. 1997 Jul;19(7):571-9. doi: 10.1002/bies.950190708.


The biochemical mechanism by which the phytochrome family of plant sensory photoreceptors transmit perceived informational light signals downstream to transduction pathway components is undertermined. The recent sequencing of the entire genome of the cyanobacterium Synechocystis, however, has revealed a protein that has an NH2-terminal domain with striking sequence similarity to the photosensory NH2-terminal domain of the phytochromes, and a COOH-terminal domain strongly related to the transmitter histidine kinase module of bacterial two-component sensors. The Synechocystis protein is capable of autocatalytic chromophore ligation and exhibits photoreversible light-absorption changes analogous to the phytochromes, indicating its capacity to function as an informational photoreceptor. Together with earlier observations that the COOH-terminal domains of the plant phytochromes also have sequence similarity to the histidine kinases, these data suggest that the cyanobacteria utilize photoregulated histidine kinases as a sensory system and that the plant phytochromes may be evolutionary descendants of these photoreceptors.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Consensus Sequence
  • Cyanobacteria / genetics
  • Evolution, Molecular
  • Histidine Kinase
  • Light
  • Molecular Sequence Data
  • Photoreceptor Cells / chemistry*
  • Phytochrome / chemistry*
  • Phytochrome / genetics
  • Phytochrome / physiology
  • Protein Conformation
  • Protein Kinases / chemistry*
  • Protein Kinases / genetics
  • Protein Kinases / physiology
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / genetics
  • Protozoan Proteins / physiology
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Signal Transduction / physiology*
  • Signal Transduction / radiation effects
  • Species Specificity
  • Vision, Ocular / physiology


  • Protozoan Proteins
  • Phytochrome
  • Protein Kinases
  • Histidine Kinase