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

Genome sequencing data have recently demonstrated that eukaryote evolution
has been remarkably influenced by the acquisition of a large number of
genes by horizontal gene transfer (HGT) across different kingdoms.
However, in depth-studies on the physiological traits conferred by these
accidental DNA acquisitions are largely lacking. Here we elucidate the
functional role of Sl 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 (haemocytes) of larval stages, where its
transcription is rapidly boosted by injection of microorganisms into the
body cavity. RNAi silencing of Sl gasmin generated a phenotype
characterized by a precocious suppression of phagocytic activity by
haemocytes, which was rescued when these immune cells were incubated in
plasma samples of control larvae, containing high levels of the encoded
protein. Proteomic analysis demonstrated that the protein Sl gasmin is
released by haemocytes into the haemolymph, where it opsonizes the
invading bacteria to promote their phagocytosis, both in vitro and in
vivo. Our results show that important physiological traits do not
necessarily originate from evolution of pre-existing genes, but can be
acquired by HGT events, through unique pathways of symbiotic evolution.
These findings indicate that insects can paradoxically acquire selective
advantages with the help of their natural enemies.