Abstract
BackgroundThe evolutionary importance of horizontal gene transfer (HGT) from Wolbachia endosymbiotic bacteria to their eukaryotic hosts is a topic of considerable interest and debate. Recent transfers of genome fragments from Wolbachia into insect chromosomes have been reported, but it has been argued that these fragments may be on an evolutionary trajectory to degradation and loss.ResultsWe have discovered a case of HGT, involving two adjacent genes, between the genomes of Wolbachia and the currently Wolbachia-uninfected mosquito Aedes aegypti, an important human disease vector. The lower level of sequence identity between Wolbachia and insect, the transcription of all the genes involved, and the fact that we have identified homologs of the two genes in another Aedes species (Ae. mascarensis), suggest that these genes are being expressed after an extended evolutionary period since horizontal transfer, and therefore that the transfer has functional significance. The association of these genes with Wolbachia prophage regions also provides a mechanism for the transfer.ConclusionThe data support the argument that HGT between Wolbachia endosymbiotic bacteria and their hosts has produced evolutionary innovation.
Highlights
The evolutionary importance of horizontal gene transfer (HGT) from Wolbachia endosymbiotic bacteria to their eukaryotic hosts is a topic of considerable interest and debate
We have discovered a case of HGT involving adjacent genes in the genomes of Ae. aegypti and two Wolbachia strains
The Ae. aegypti gene AAEL004181 shares around 50% amino acid identity with two genes in the genome of Wolbachia strain wPip [15] from the mosquito Culex quinquefasciatus, WP1348 and WP1346), which were probably originally a single gene split by insertion of IS element WP1347, and with WD0513 in strain wMel from Drosophila melanogaster [16]
Summary
The evolutionary importance of horizontal gene transfer (HGT) from Wolbachia endosymbiotic bacteria to their eukaryotic hosts is a topic of considerable interest and debate. Wolbachia pipientis is an intracellular inherited bacterium found in arthropods, where it manipulates host reproduction using phenotypes such as cytoplasmic incompatibility (CI), male killing, parthenogenesis and feminization, and can spread rapidly through insect populations [1]. It is an obligate mutualist of a number of filarial nematode species [2]. Several cases where sections of the Wolbachia genome, sometimes large, have been transferred to the host chromosomes are known in both insects and nematodes [3,4,5] These are either recent events where Wolbachia and host sequences are highly similar or involve extensive pseudogenization [4]. It has been suggested that these fragments are on (page number not for citation purposes)
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