The Chlamydomonas chloroplast HLP protein is required for nucleoid organization and genome maintenance

Mol Plant. 2009 Nov;2(6):1223-32. doi: 10.1093/mp/ssp083. Epub 2009 Oct 29.


The chloroplasts genome (plastome) occurs at high copy numbers per cell. Several chloroplast genome copies are densely packed into nucleoprotein particles called nucleoids. How genome packaging occurs and which proteins organize chloroplast nucleoids are largely unknown. Here, we have analyzed the Chlamydomonas reinhardtii homolog of the bacterial architectural DNA-binding protein HU, the histone-like protein HLP. We show that the Chlamydomonas HLP protein is targeted to chloroplasts and associates with nucleoids. Knockdown of HLP gene expression by RNA interference (RNAi) alters the structure of chloroplast nucleoids and appears to reduce the level of compaction of chloroplast DNA. Unexpectedly, also chloroplast genome copy numbers are significantly decreased in the RNAi strains, suggesting that, in addition to its architectural role in nucleoid formation, the HLP protein is also involved in chloroplast genome maintenance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Cell Nucleus / genetics*
  • Chlamydomonas reinhardtii / genetics*
  • Chloroplasts / genetics
  • Chloroplasts / physiology
  • Cloning, Molecular
  • Cyanobacteria / genetics
  • Genome, Plant*
  • Molecular Sequence Data
  • Plant Proteins / genetics
  • Plant Proteins / physiology
  • Restriction Mapping
  • Sequence Alignment
  • Sequence Homology, Amino Acid


  • Plant Proteins