Transcriptome Analysis Reveals Early Hemocyte Responses upon In Vivo Stimulation with LPS in the Stick Insect Bacillus rossius (Rossi, 1788)

Non-model insect species such as B. rossius suffer from a profound gap of knowledge regarding the temporal progression of physiological responses following the challenge with bacterial pathogens or cell wall components thereof. The reason for this mostly lies in the lack of genomic/transcriptomic resources, which would provide an unparalleled in-depth capacity in the analysis of molecular, biochemical, and metabolic mechanisms. We present a high-quality transcriptome obtained from high-coverage sequencing of hemocytes harvested from adult stick insect specimens both pre- and post-LPS stimulation. Such a resource served as the basis for a stringent differential gene expression and functional enrichment analyses, the results of which were characterized and discussed in depth. Selected transcripts encoding for C-type lectins and ML-domain containing proteins were further investigated from a phylogenetic perspective. Overall, these findings shed light on the physiological responses driven by a short-term LPS stimulation in the European stick insect. Despite a growing number of non-model insect species is being investigated in recent years, a greater understanding of their physiology is prevented by the lack of genomic resources. This is the case of the common European stick insect Bacillus rossius (Rossi, 1788): in this species, some knowledge is available on hemocyte-related defenses, but little is known about the physiological changes occurring in response to natural or experimental challenges. Here, the transcriptional signatures of adult B. rossius hemocytes were investigated after a short-term (2 h) LPS stimulation in vivo: a total of 2191 differentially expressed genes, mostly involved in proteolysis and carbohydrate and lipid metabolic processes, were identified in the de novo assembled transcriptome and in-depth discussed. Overall, the significant modulation of immune signals-such as C-type lectins, ML domain-containing proteins, serpins, as well as Toll signaling-related molecules-provide novel information on the early progression of LPS-induced responses in B. rossius.