Abstract
BackgroundHorizontal gene transfer (HGT), the non-genealogical transfer of genetic material between different organisms, is considered a potentially important mechanism of genome evolution in eukaryotes. Using phylogenomic analyses of expressed sequence tag (EST) data generated from a clonal cell line of a free living dinoflagellate alga Karenia brevis, we investigated the impact of HGT on genome evolution in unicellular chromalveolate protists.ResultsWe identified 16 proteins that have originated in chromalveolates through ancient HGTs before the divergence of the genera Karenia and Karlodinium and one protein that was derived through a more recent HGT. Detailed analysis of the phylogeny and distribution of identified proteins demonstrates that eight have resulted from independent HGTs in several eukaryotic lineages.ConclusionRecurring intra- and interdomain gene exchange provides an important source of genetic novelty not only in parasitic taxa as previously demonstrated but as we show here, also in free-living protists. Investigating the tempo and mode of evolution of horizontally transferred genes in protists will therefore advance our understanding of mechanisms of adaptation in eukaryotes.
Highlights
Horizontal gene transfer (HGT), the non-genealogical transfer of genetic material between different organisms, is considered a potentially important mechanism of genome evolution in eukaryotes
Our data screening approach was designed to retrieve relatively ancient cases of HGT that occurred before the divergence of two closely related genera of dinoflagellate algae, Karenia and Karlodinium
Using a sequence similarity search (BLAST; e-value ≤ 10-10) we identified 3,341 genes shared by K. brevis and at least 1/5 dinoflagellate species for which expressed sequence tag (EST) data are available [18]
Summary
Horizontal gene transfer (HGT), the non-genealogical transfer of genetic material between different organisms, is considered a potentially important mechanism of genome evolution in eukaryotes. 96 potential cases of prokaryote-to-eukaryote HGT were identified in the genome of an intestinal parasite of humans and animals Entamoeba histolytica [7], 84 in the fish parasite Spironucleus salmonicida [8], 152 in a sexually transmitted human pathogen Trichomonas vaginalis [9], 24 in Cryptosporidium parvum [10], and 148 in anaerobic rumen ciliates [11]. These numbers comprise up to 4% of genes in the extremely reduced genomes of these anaerobic protists. It is believed that the acquisition of bacterial genes by these eukaryotes accelerated their adaptation to anaerobic environments and the transition to a parasitic life (page number not for citation purposes)
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