期刊
GENOME BIOLOGY AND EVOLUTION
卷 4, 期 11, 页码 1162-1175出版社
OXFORD UNIV PRESS
DOI: 10.1093/gbe/evs090
关键词
nucleomorph; cryptophyte; endosymbiosis; genome reduction; comparative genomics
资金
- Canadian Institutes of Health Research (CIHR)
- Nova Scotia Regional Partnership Program [ROP85016]
- Canadian Institute for Advanced Research (Program in Integrated Microbial Biodiversity)
- Tula Foundation
- Centre for Comparative Genomics and Evolutionary Bioinformatics at Dalhousie University
- Natural Sciences and Engineering Research Council of Canada
Cryptophytes are a diverse lineage of marine and freshwater, photosynthetic and secondarily nonphotosynthetic algae that acquired their plastids (chloroplasts) by secondary (i.e., eukaryote-eukaryote) endosymbiosis. Consequently, they are among the most genetically complex cells known and have four genomes: amitochondrial, plastid, master nuclear, and residual nuclear genome of secondary endosymbiotic origin, the so-called nucleomorph genome. Sequenced nucleomorph genomes are similar to 1,000-kilobase pairs (Kbp) or less in size and are comprised of three linear, compositionally biased chromosomes. Although most functionally annotated nucleomorph genes encode proteins involved in core eukaryotic processes, up to 40% of the genes in these genomes remain unidentifiable. To gain insight into the function and evolutionary fate of nucleomorph genomes, we used 454 and Illumina technologies to completely sequence the nucleomorph genome of the cryptophyte Chroomonas mesostigmatica CCMP1168. At 702.9 Kbp in size, the C. mesostigmatica nucleomorph genome is the largest and the most complex nucleomorph genome sequenced to date. Our comparative analyses reveal the existence of a highly conserved core set of genes required for maintenance of the cryptophyte nucleomorph and plastid, as well as examples of lineage-specific gene loss resulting in differential loss of typical eukaryotic functions, e.g., proteasome-mediated protein degradation, in the four cryptophyte lineages examined.
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