Abstract
BackgroundMeloidae (blister beetles) are known to synthetize cantharidin (CA), a toxic and defensive terpene mainly stored in male accessory glands (MAG) and emitted outward through reflex-bleeding. Recent progresses in understanding CA biosynthesis and production organ(s) in Meloidae have been made, but the way in which self-protection is achieved from the hazardous accumulation and release of CA in blister beetles has been experimentally neglected. To provide hints on this pending question, a comparative de novo assembly transcriptomic approach was performed by targeting two tissues where CA is largely accumulated and regularly circulates in Meloidae: the male reproductive tract (MRT) and the haemolymph. Differential gene expression profiles in these tissues were examined in two blister beetle species, Lydus trimaculatus (Fabricius, 1775) (tribe Lyttini) and Mylabris variabilis (Pallas, 1781) (tribe Mylabrini). Upregulated transcripts were compared between the two species to identify conserved genes possibly involved in CA detoxification and transport.ResultsBased on our results, we hypothesize that, to avoid auto-intoxication, ABC, MFS or other solute transporters might sequester purported glycosylated CA precursors into MAG, and lipocalins could bind CA and mitigate its reactivity when released into the haemolymph during the autohaemorrhaging response. We also found an over-representation in haemolymph of protein-domains related to coagulation and integument repairing mechanisms that likely reflects the need to limit fluid loss during reflex-bleeding.ConclusionsThe de novo assembled transcriptomes of L. trimaculatus and M. variabilis here provided represent valuable genetic resources to further explore the mechanisms employed to cope with toxicity of CA in blister beetle tissues. These, if revealed, might help conceiving safe and effective drug-delivery approaches to enhance the use of CA in medicine.
Highlights
Meloidae are known to synthetize cantharidin (CA), a toxic and defensive terpene mainly stored in male accessory glands (MAG) and emitted outward through reflex-bleeding
We found a higher percentage of duplicated Benchmarking set of universal single-copy orthologues (BUSCO) (D) in Lydus trimaculatus (LT) than in Mylabris variabilis (MV) (Table 1)
By selecting the longest transcript isoform for each Trinity unigene cluster and using the Annocript pipeline, we observed that 47.7% (LT) and 33.4% (MV) could be annotated with Basic local alignment search tool (BLAST) searches against UniRef [mostly from Tribolium castaneum Herbst, 1787; Coleoptera, Tenebrionidae], whereas 30.0% (LT) and 20.8% (MV) were annotated against Swiss-Prot [mostly from Drosophila melanogaster Fallén, 1823; Diptera, Drosophilidae]
Summary
Meloidae (blister beetles) are known to synthetize cantharidin (CA), a toxic and defensive terpene mainly stored in male accessory glands (MAG) and emitted outward through reflex-bleeding. Recent progresses in understanding CA biosynthesis and production organ(s) in Meloidae have been made, but the way in which selfprotection is achieved from the hazardous accumulation and release of CA in blister beetles has been experimentally neglected. To provide hints on this pending question, a comparative de novo assembly transcriptomic approach was performed by targeting two tissues where CA is largely accumulated and regularly circulates in Meloidae: the male reproductive tract (MRT) and the haemolymph. Autohaemorrhaging is common in several species from different families of Coleoptera (e.g. Erotylidae, Lampyridae, Coccinellidae), but represent a typical trait of blister beetles (Meloidae) [6]
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