title: Overexpression of molecular chaperone genes in nucleomorph genomes.
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.
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan hirakawa.yoshi.fp@u.tsukuba.ac.jp.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Hirakawa
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Shigekatsu
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, CanadaCanadian Institute for Advanced Research, Program in Integrated Microbial Biodiversity.
authors.forename: John M
authors.initials: JM
authors.lastname: Archibald
authors.affiliation: Canadian Institute for Advanced Research, Program in Integrated Microbial BiodiversityDepartment of Botany, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Keeling
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Ishida
mesh_terms: D002467:Cell Nucleus / Q000235:genetics; D000460:Chlorophyta / Q000145:classification / Q000166:cytology / Q000235:genetics*; D002875:Chromosomes; D044785:Cryptophyta / Q000145:classification / Q000166:cytology / Q000235:genetics*; D019143:Evolution, Molecular; D054627:Genome, Plastid; D018832:Molecular Chaperones / Q000235:genetics*; D059645:Mutation Rate; D010802:Phylogeny; D018087:Plastids / Q000235:genetics*; D017423:Sequence Analysis, RNA; D013559:Symbiosis; D015854:Up-Regulation
chemical_list: D018832:Molecular Chaperones
keywords: algae; endosymbiosis; evolutionary rates; plastid; transcriptome