Doratifera vulnerans isolate:GDNA001 Genome sequencing
Gene duplication followed by adaptation to new selection pressures has been proposed to be of central importance in the evolution of venom toxins. Coupling of high-quality genome data with quantitative bioactivity readouts can be used to understand how venom toxins have evolved, but studies of this type are rare. In this study, we report a near chromosomal-level assembly of the genome of the venomous caterpillar Doratifera vulnerans (Lepidoptera: Limacodidae). We identify 115 gene loci that produce the polypeptide toxins in D. vulnerans venom, including numerous multigene families that are tandemly arrayed as well as many single-copy genes. Cecropin-like venom toxins that have previously been shown to permeabilise mammalian peripheral neurons to cause pain were encoded by a single gene cluster on chromosome 7. This cluster encoded diverse cecropins and cecropin-like peptides that either retained the ancestral antimicrobial activity of cecropins or were specialised as pain-causing venom toxins. Dv13, which was present in venom as a trace component, showed sequence features conserved with canonical cecropin A, potently inhibited growth of Gram-negative bacteria and fungi, but only weakly permeabilised mammalian neurons with EC50 values more than 100 microM. By contrast, Dv11 and Dv12, which were abundant in venom, had derived sequence features and potently disrupted mammalian neuronal membranes with EC50 values as low as 190 nM, but had reduced activity against Gram-negative bacteria and fungi. These data provide evidence for gene duplication of innate immune peptides followed by adaptation of some daughter genes as specialised defensive toxins, and provide a natural experiment providing insights into the structure-activity relationships of cecropins.