Evolution of an insect immune barrier through horizontal gene transfer mediated by a parasitic wasp

Horizontal gene transfer (HGT) is a fascinating topic, well within the purview of gene-environment interactions. HGT is a mechanism of “accidental acquisition of genetic material by means other than reproduction.” In some lineages, such as prokaryotes (organisms such as bacteria having single, not paired, chromosomes), HGT is considered THE major driving force in genome evolution. In theory, all genes may undergo HGT; however, current evidence with prokaryotes indicates that housekeeping genes (i.e. those modulating cellular functions), are significantly more likely to be transferred, from one species to another, than regulatory genes.


In eukaryotes (organisms having paired chromosomes), HGT occurrence in unicellular organisms has been frequently reported. In contrast, HGT had been considered rare in multicellular organisms until the advent of high-throughput sequencing technologies. Now we know that HGT occurrence is frequent both in vertebrates (having a spine) and invertebrates (having no spine) with bacteria and protists being the major gene donors; this is because bacteria and protists (single-celled organisms of the kingdom Protista, such as a protozoan or simple alga) have often established an extensive variety of symbiotic associations with higher organisms, which favors intimate contact and exchange of genetic material. Thus, HGT complements the major role played by transposable elements (‘jumping genes’) in shaping genome evolution.


Authors [see attached report] elucidate the functional role of gasmin* (a gene of a symbiotic virus of a parasitic wasp that has been transferred to an ancestor of the moth species Spodoptera littoralis and domesticated). This gene is highly expressed in circulating immune cells (hemocytes) of larval stages, where it is strikingly up-regulated (in response to injection of microorganisms into the body cavity). RNA interference-silencing of gasmin generated a phenotype characterized by precocious suppression of phagocytic activity (protecting the host by eating harmful foreign particles, bacteria, and dead or dying cells) by hemocytes; this suppression trait was rescued when these immune cells were incubated in plasma samples of control larvae, containing high levels of the encoded gasmin protein.


Using proteomics analysis, authors demonstrated that the protein gasmin is released by hemocytes into the hemolymph, where it opsonizes (i.e. makes it more susceptible to being eaten by the phagocytic hemocytes) the invading bacteria to promote their phagocytosis, both in cell culture and in the intact insect. These data show that important survival traits do not necessarily originate from evolution of pre-existing genes, but rather can be acquired by HGT events through unique pathways of symbiotic evolution. These findings also show that insects can paradoxically acquire selective advantages with the help of their natural enemies..!!    🙂




* “Gasmin” is not in any gene or protein database that I could uncover. I could only find “gasmin” in an article in which Dr. Gasmi named this unknown protein after himself…!!

Dev Comp Immunol. 2016 Mar;56:37-45

Gasmin (BV2-5), a polydnaviral-acquired gene in Spodoptera exigua. Trade-off in the defense against bacterial and viral infections.

Gasmi L1Jakubowska AK1Herrero S2.


PLoS Genet Mar 2o19; 15: e1007998

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