Proteotranscriptomic Analysis and Toxicity Assay Suggest the Functional Distinction between Venom Gland Chambers in Twin-Spotted Assassin Bug, Platymeris biguttatus

SIMPLE SUMMARY: Assassin bugs are one of the diversified groups of venomous predatory insects. Their venom is secreted from three different lumens of the salivary gland and can lead to paralysis, lethality, and liquidation of the prey, respectively. Nevertheless, most reduviid venom components responsible for these effects are not clear. In this study, we use transcriptomics and proteomics to determine the effective salivary protein components in the separate lumen of salivary gland from twin-spotted assassin bug Platymeris biguttatus and to conduct toxicological analysis on the function of the salivary gland compartments. Our study sheds light on the functional cooperation between different salivary gland lumens of assassin bugs and will further the understanding of physiological adaptations of venom-based predation and defense in venomous hemipterans. ABSTRACT: Assassin bugs use their salivary venoms for various purposes, including defense, prey paralyzation, and extra-oral digestion, but the mechanisms underlying the functional complexity of the venom remain largely unclear. Since venom glands are composed of several chambers, it is suggested that individual chambers may be specialized to produce chemically distinct venoms to exert different functions. The current study assesses this hypothesis by performing toxicity assays and transcriptomic and proteomic analysis on components from three major venom gland chambers including the anterior main gland (AMG), the posterior main gland (PMG), and the accessory gland (AG) of the assassin bug Platymeris biguttatus. Proteotranscriptomic analysis reveals that AMG and PMG extracts are rich in hemolytic proteins and serine proteases, respectively, whereas transferrin and apolipophorin are dominant in the AG. Toxicity assays reveal that secretions from different gland chambers have distinct effects on the prey, with that from AG compromising prey mobility, that from PMG causing prey death and liquifying the corpse, and that from AMG showing no significant physiological effects. Our study reveals a functional cooperation among venom gland chambers of assassin bugs and provides new insights into physiological adaptations to venom-based predation and defense in venomous predatory bugs.