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Mol Biol Evol. 2014 Jun;31(6):1437-43. doi: 10.1093/molbev/msu092. Epub 2014 Mar 6.

Overexpression of molecular chaperone genes in nucleomorph genomes.

Author information

1
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan hirakawa.yoshi.fp@u.tsukuba.ac.jp.
2
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
3
Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, CanadaCanadian Institute for Advanced Research, Program in Integrated Microbial Biodiversity.
4
Canadian Institute for Advanced Research, Program in Integrated Microbial BiodiversityDepartment of Botany, University of British Columbia, Vancouver, British Columbia, Canada.
5
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.

Abstract

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:

algae; endosymbiosis; evolutionary rates; plastid; transcriptome

PMID:
24603278
DOI:
10.1093/molbev/msu092
[Indexed for MEDLINE]
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