The mitochondrial genome and transcriptome of the basal dinoflagellate Hematodinium sp.: character evolution within the highly derived mitochondrial genomes of dinoflagellates.
Genome Biol Evol. 2011 Nov 23;
Authors: Jackson CJ, Gornik SG, Waller RF
The sister phyla dinoflagellates and apicomplexans inherited a drastically reduced mitochondrial genome (mtDNA) containing only three protein-coding (cob, cox1 and cox3) and two rRNA genes. In apicomplexans single copies of these genes are encoded on the smallest known mtDNA chromosome (6 kb). In dinoflagellates, however, the genome has undergone further substantial modifications, including massive genome amplification and recombination resulting in multiple copies of each gene and gene fragments linked in numerous combinations. Further, protein-encoding genes have lost standard stop codons, trans-splicing of mRNAs is required to generate complete cox3 transcripts, and extensive RNA editing recodes most genes. From taxa investigated to date, it is unclear when many of these unusual dinoflagellate mtDNA characters evolved. To address this question, we investigated the mitochondrial genome and transcriptome character states of the deep branching dinoflagellate Hematodinium sp.. Genomic data shows that like later-branching dinoflagellates Hematodinium sp. also contains an inflated, heavily recombined genome of multi-copy genes and gene fragments. While stop codons are also lacking for cox1 and cob, cox3 still encodes a conventional stop codon. Extensive editing of mRNAs also occurs in Hematodinium sp.. The mtDNA of basal dinoflagellate Hematodinium sp. indicates that much of the mtDNA modification in dinoflagellates occurred early in this lineage, including genome amplification and recombination, and decreased use of standard stop codons. Trans-splicing, on the other hand, occurred after Hematodinium sp. diverged. Only RNA editing presents a non-linear pattern of evolution in dinoflagellates as this process occurs in Hematodinium sp., but is absent in some later-branching taxa indicating that this process was either lost in some lineages, or developed more than once during the evolution of the highly unusual dinoflagellate mtDNA.
PMID: 22113794 [PubMed – as supplied by publisher]