Journal Article

Overexpression of Molecular Chaperone Genes in Nucleomorph Genomes

Yoshihisa Hirakawa, Shigekatsu Suzuki, John M. Archibald, Patrick J. Keeling and Ken-ichiro Ishida

in Molecular Biology and Evolution

Published on behalf of Society for Molecular Biology and Evolution

Volume 31, issue 6, pages 1437-1443
Published in print June 2014 | ISSN: 0737-4038
Published online March 2014 | e-ISSN: 1537-1719 | DOI:
Overexpression of Molecular Chaperone Genes in Nucleomorph Genomes

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  • Evolutionary Biology
  • Molecular and Cell Biology


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Chlorarachniophytes and cryptophytes possess complex plastids that were acquired by the ingestion of a green and red algal endosymbiont, respectively. The plastids are surrounded by four membranes, and a relict nucleus, called the nucleomorph, remains in the periplastidal compartment, which corresponds to the remnant cytoplasm of the endosymbiont. Nucleomorphs contain a greatly reduced genome that possesses only several hundred genes with high evolutionary rates. We examined the relative transcription levels of the genes of all proteins encoded by the nucleomorph genomes of two chlorarachniophytes and three cryptophytes using an RNA-seq transcriptomic approach. The genes of two heat shock proteins, Hsp70 and Hsp90, were highly expressed under normal conditions. It has been shown that molecular chaperone overexpression allows an accumulation of genetic mutations in bacteria. Our results suggest that overexpression of heat shock proteins in nucleomorph genomes may play a role in buffering the mutational destabilization of proteins, which might allow the high evolutionary rates of nucleomorph-encoded proteins.

Keywords: endosymbiosis; plastid; algae; evolutionary rates; transcriptome

Journal Article.  2693 words.  Illustrated.

Subjects: Evolutionary Biology ; Molecular and Cell Biology

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