Identification, classification and gene expression analysis of antimicrobial peptides (AMPs) in the stick insect Peruphasma schultei

The Phasmatodea, or stick and leaf insects, are an understudied clade of insects whose pathology is of interest to cultivators and conservationists. Part of an insect's innate immunity are antimicrobial peptides (AMPs), which have therapeutic potential in human and veterinary medicine. We exposed stick insects to a mixture of pathogens to induce an immune response, and used RNA-Seq to identify subsequently differentially and/or highly expressed genes in Peruphasma schultei. AMPs were identified in the attacin, coleoptericin, defensin, thaumatin, and tachystatin families. We also found C- and i-lysozymes and several pattern recognition proteins [gram-negative bacteria-binding proteins and peptidoglycan recognition proteins]; as well as a large group of short, cysteine-rich, secreted peptides, many of which were highly induced and predicted to potentially have AMP activity. We also found 45 different sequences of hemolymph lipopolysaccharide-binding proteins, which is an unusually large number for insects. This is the first work to look at AMPs and immunity in stick insects, with implications for Phasmatodea conservation and pathology.