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 bacteria. Previously, we have described for the first time RIP genes in mosquitoes belonging to the Culicidae family. We showed that these genes are derived from a single event of horizontal gene transfer (HGT) from a prokaryotic donor. Mosquito RIP genes are evolving under purifying selection, strongly suggesting that these toxins have acquired a functional role. In this work, we show the existence of two RIP encoding genes in the genome of the whitefly Bemisia tabaci, a hemiptera species belonging to the Aleyrodidae family distantly related to mosquitoes. Contamination artifacts were ruled out analyzing three independent B. tabaci genome databases. In contrast to mosquito RIPs, whitefly genes harbor introns and according to transcriptomic evidence are transcribed and spliced. Phylogeny and the taxonomic distribution strongly support that whitefly RIP genes are derived from an independent HGT event from a plant source. These results, along with our previous description of RIPs in Diptera, suggest that the acquired genes are functional in these insects and confer some fitness advantage.
Highlights
Our results are consistent with two independent Horizontal gene transfer (HGT) events of RIP encoding genes to different insect lineages
In the course of routine database searches, we found two RIP encoding sequences in the hemiptera B. tabaci MEAM 1
BtRIP2 expression level is in the top quartile of B. tabaci genes, suggesting a relevant functional role for this protein (Supplementary Figure S3)
Summary
We demonstrate that RIP genes are present in genomes of a second lineage of insects: the hemiptera whiteflies (Aleyrodidae family). These genes are not closely related to mosquito homologues, instead they form a clade along with plant-derived RIPs. Altogether our results are consistent with two independent HGT events of RIP encoding genes to different insect lineages. Results and discussion Bemisia tabaci genome harbors two RIP encoding genes.
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