Molecular basis of the explosive defense response of the bombardier beetle Brachinus crepitans
Bombardier beetles have evolved a sophisticated chemical defense mechanism in which controlled explosions within the pygidial glands produce a hot benzoquinone-based defensive spray. The molecular basis of this mechanism is not well characterized. We therefore combined the transcriptomic and proteomic analysis of different gland compartments in the bombardier beetle Brachinus crepitans to identify abundant transcripts and gland-specific proteins with key defensive functions, such as catalases, peroxidases and enzymes involved in hydroquinone synthesis. By combining precise dissections with protein sequence analysis, we built a comprehensive description of the relevant proteins and their spatiotemporal organization. We found that glucose plays important roles as a precursor for hydrogen peroxide and to maintain a stable hydroquinone precursor supply, which, together with gland-specific peroxidase and catalases proteins initiates the explosive defense reaction.