RNA-seq Analysis Reveals the Response of Tribolium castaneum to the Eugenol Exposure

The red flour beetle, Tribolium castaneum, is a notorious worldwide pest of stored grains and farinaceous materials. Eugenol, one of the compositions of Artemisia vulgaris essential oils, has insecticidal activity to T. castaneum. Nevertheless, how insects systemically respond to eugenol on the RNA levels is still indistinct. In this study, we detected four enzymes (acetyl choline esterase, AChE; cytochrome p450 CYP; glutathione-S-transferase, GST; carboxylesterase, CarE), and the activity of AChE/GST associated with metabolic detoxification and nerve conduction were significantly inhibited. Then, a total of 362 differentially expressed genes (DEGs), including 206 up-regulated and 156 down-regulated genes between eugenol-exposure and control samples were identified by RNA-sequencing analysis. Based on gene ontology (GO) functional analyses, a fair amount of DEGs mapped into terms related to xenobiotics detoxification and mitochondrial function. Furthermore, a major of DEGs were gathered in the metabolism pathway concerned with metabolism of xenobiotics and respiration in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database, including CYPs, UDP-glucuronosyltransferases (UGTs), glutathione S-transferases (GSTs), odorant binding proteins (OBPs), chemosensory proteins (CSPs), ATP-binding cassette transporters (ABC transporters),multidrug resistance protein (MRPs), flavin adenine dinucleotide (FAD) and tricarboxylic acid cycle (TCA) related genes, as well as some DEGs mapped into the lysosome pathway. According to above results, we proposed two modes of T. castaneum in response to eugenol exposure, which was eugenol can change the xenobiotic biodegradation and metabolic systems or eugenol impeded the electron flow of mitochondrial respiratory chain, resulting in regulation of oxygen consumption and the amount of carbon dioxide released. Subsequently, the up-regulated expressed OBP/GST were detected by qRT-PCR and RNAi against these genes significantly increased mortality of T. castaneum exposed to eugenol, providing further evidence for the involvement of OBP/GST in eugenol metabolic detoxification in T. castaneum. Collectively, our results will be of service to the insecticidal mechanisms of eugenol and provide the basics for developing its relative essential oils as a novel pesticide.