Characterization of a putative laccase from the venom of Megarhyssa (Hymenoptera: Ichneumonidae)

The giant parasitoid wasp, Megarhyssa (Hymenoptera: Ichneumonidae), uses its gracile egg-laying appendage (ovipositor) to penetrate up to six inches of wood in a matter of minutes in order to lay an egg on its host. It is postulated that enzymes are secreted from the ovipositor to facilitate this process and in this study we investigate the venom of Megarhyssa for the presence of such enzymes. We used a combined transcriptomics and proteomics approach to identify 64 putative venom proteins. Eleven of these do not contain known conserved protein domains; the remainder are predicted to code for 24 different proteins among which is a putative laccase. In wood-rotting fungi and wood-feeding insects, laccases are implicated in the degradation of lignin present in the plant cell wall and we propose that Megarhyssa secretes this venom laccase during oviposition to aid the penetration of wood. The sequence of the putative laccase was confirmed by reverse-transcriptase PCR and subsequently subjected to phylogenetic analysis. Its placement in the resulting phylogeny indicates a close relationship to the predicted laccase of Orussus abietinus (Hymenoptera: Orussidae), another parasitoid wasp that uses a long ovipositor to penetrate wood, lending support to our hypothesis.