Pathways of intracellular communication: tetrapyrroles and plastid-to-nucleus signaling

Bioessays. 2003 Jul;25(7):631-6. doi: 10.1002/bies.10308.


Retrograde plastid-to-nucleus signaling plays a central role in coordinating nuclear and plastid gene expression. The gun (genomes uncoupled) mutants of Arabidopsis have been used to demonstrate that Mg-protoporphyrin (Mg-Proto) acts as a plastid signal to repress the transcription of nuclear photosynthesis genes (1). It is unclear how Mg-Proto triggers repression, but several components of this pathway have been recently identified. These include the products of GUN4 and GUN5. GUN5 is the ChlH subunit of Mg-chelatase, which produces Mg-Proto, and GUN4 is a regulator of ChlH activity (2). GUN4 might also play a role in photoprotection and in the trafficking of Mg-Proto.

Publication types

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

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / physiology
  • Carrier Proteins / physiology
  • Cell Communication / physiology*
  • Cell Nucleus / physiology*
  • Genome, Plant
  • Intracellular Signaling Peptides and Proteins*
  • Models, Biological
  • Photosynthesis / genetics
  • Plastids / physiology
  • Pyrroles / metabolism
  • Signal Transduction / physiology*
  • Tetrapyrroles
  • Transcription, Genetic


  • Arabidopsis Proteins
  • Carrier Proteins
  • GUN4 protein, Arabidopsis
  • Intracellular Signaling Peptides and Proteins
  • Pyrroles
  • Tetrapyrroles