Abstract
Ribosome inactivating proteins (RIPs) are RNA N-glycosidases that depurinate a specific adenine residue in the conserved sarcin/ricin loop of 28S rRNA. These enzymes are widely distributed among plants and their presence has also been confirmed in several bacterial species. Recently, we reported for the first time in silico evidence of RIP encoding genes in metazoans, in two closely related species of insects: Aedes aegypti and Culex quinquefasciatus. Here, we have experimentally confirmed the presence of these genes in mosquitoes and attempted to unveil their evolutionary history. A detailed study was conducted, including evaluation of taxonomic distribution, phylogenetic inferences and microsynteny analyses, indicating that mosquito RIP genes derived from a single Horizontal Gene Transfer (HGT) event, probably from a cyanobacterial donor species. Moreover, evolutionary analyses show that, after the HGT event, these genes evolved under purifying selection, strongly suggesting they play functional roles in these organisms.
Highlights
In a previous work, we have described that the phylogeny of Ribosome inactivating proteins (RIPs) genes shows incongruence with that of the species
We found in silico evidence for the presence of genes coding for RIP-containing proteins in two closely related species of Metazoa: Aedes aegypti and Culex quinquefasciatus[11]
Ribosome inactivating proteins form a very interesting protein family displaying a patchy taxonomic distribution. As it was mentioned above, in a previous report we have found in silico evidence of the presence of RIP genes in two closely related species of mosquitoes[11]
Summary
We have described that the phylogeny of RIP genes shows incongruence with that of the species Most of these inconsistencies can be explained by gene duplication, loss and/or lineage sorting[11]. Two emblematic cases illustrating these issues are the initial conclusion that the human genome contained a high percent of bacterial derived genes[22], and the recent claim that tardigrade genomes contain significant amounts of foreign DNA23. In both cases, subsequent sounder analyses demonstrated that contamination or incomplete sampling better explained the available data[24, 25]. We provide solid evidence supporting the hypothesis that these genes derive from a single prokaryotic transferred gene
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