RpaA regulates the accumulation of monomeric photosystem I and PsbA under high light conditions in Synechocystis sp. PCC 6803

PLoS One. 2012;7(9):e45139. doi: 10.1371/journal.pone.0045139. Epub 2012 Sep 14.


The response regulator RpaA was examined by targeted mutagenesis under high light conditions in Synechocystis sp. PCC 6803. A significant reduction in chlorophyll fluorescence from photosystem I at 77 K was observed in the RpaA mutant cells under high light conditions. Interestingly, the chlorophyll fluorescence emission from the photosystem I trimers at 77 K are similar to that of the wild type, while the chlorophyll fluorescence from the photosystem I monomers was at a much lower level in the mutant than in the wild type under high light conditions. The RpaA inactivation resulted in a dramatic reduction in the monomeric photosystem I and the D1 protein but not the CP47 content. However, there is no significant difference in the transcript levels of psaA or psbA or other genes examined, most of which are involved in photosynthesis, pigment biosynthesis, or stress responses. Under high light conditions, the growth of the mutant was affected, and both the chlorophyll content and the whole-chain oxygen evolution capability of the mutant were found to be significantly lower than those of the wild type, respectively. We propose that RpaA regulates the accumulation of the monomeric photosystem I and the D1 protein under high light conditions. This is the first report demonstrating that inactivation of a stress response regulator has specifically reduced the monomeric photosystem I. It suggests that PS I monomers and PS I trimers can be regulated independently for acclimation of cells to high light stress.

Publication types

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

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Cell Fractionation
  • Chlorophyll / metabolism
  • Light*
  • Mutation
  • Oxygen Consumption
  • Photosynthesis / genetics
  • Photosystem I Protein Complex / metabolism*
  • Photosystem II Protein Complex / metabolism*
  • Pigments, Biological / biosynthesis
  • Protein Multimerization
  • Stress, Physiological
  • Synechocystis / genetics
  • Synechocystis / growth & development
  • Synechocystis / metabolism*
  • Transcription, Genetic


  • Bacterial Proteins
  • Photosystem I Protein Complex
  • Photosystem II Protein Complex
  • Pigments, Biological
  • photosystem II, psbA subunit
  • Chlorophyll

Grant support

This work was supported by National Science Foundation grant MCB 1120153 (http://www.nsf.gov/) and by Program on Key Basic Research Project (2011CB200902). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.