Insect glutathione S-transferases (GSTs) play a crucial role in the detoxification of exogenous compounds, especially insecticides and plant allelochemicals. A sigma class GST gene, TcGSTS7 , mediates the response to eugenol in Tribolium castaneum . However, the mechanism underlying this effect remains largely unknown. In this study, TcGSTS7 , which exhibits a structural motif and domain organization characteristic of GSTs, was cloned from the T. castaneum genome. Spatiotemporal expression analysis revealed that TcGSTS7 was most highly expressed at the late larva stage and was mainly expressed in the fat body and epidermis of larvae and adults, suggesting that TcGSTS7 may play a potential role in the protection against toxic xenobiotics in T. castaneum . Furthermore, the expression of TcGSTS7 was significantly induced after exposure to eugenol, while RNA interference (RNAi) targeting TcGSTS7 enhanced the sensitivity of the beetle to eugenol, indicating that TcGSTS7 is involved in the tolerance of T. castaneum to this insecticide. Interestingly, the depletion of TcCncC , which encodes a transcription factor of the CncC pathway that has been associated with the regulation of detoxification-related genes in insects, led to a reduction in the TcGSTS7 transcript level following exposure to eugenol, which suggests that TcGSTS7 acts downstream of the CncC pathway. Combined, these results indicated that TcGSTS7 participates in the tolerance of T. castaneum to phytochemicals in a CncC pathway-dependent manner. These findings have implications for the development of novel drugs for use in pest control.
Zhang Yonglei,Gao Shanshan,Zhang Ping,Sun Haidi,Lu Ruixue,Yu Runnan,Li Yanxiao,Zhang Kunpeng,Li Bin
Eugenol, a plant-derived component possessing small side effects, has an insecticidal activity to Tribolium castaneum ; however, the underlying molecular mechanisms of eugenol acting on T. castaneum are currently unclear. Here, a nerve conduction carboxylesterase and a detoxifying glutathione S-transferase were significantly inhibited after eugenol exposure, resulting in the paralysis or death of beetles. Then, RNA-sequencing of eugenol-exposed and control samples identified 362 differentially expressed genes (DEGs), containing 206 up-regulated and 156 down-regulated genes. RNA-seq data were validated further by qRT-PCR. GO analysis revealed that DEGs were associated with 1308 GO terms of which the most enriched GO terms were catalytic activity, and integral component of membrane; KEGG pathway analysis showed that these DEGs were distributed in 151 different pathways, of which some pathways associated with metabolism of xenobiotics or drug were significantly enriched, which indicated that eugenol most likely disturbed the processes of metabolism, and detoxication. Moreover, several DEGs including Hexokinase type 2 , Isocitrate dehydrogenase , and Cytochrome b-related protein , might participate in the respiratory metabolism of eugenol-exposed beetles. Some DEGs encoding CYP , UGT , GST , OBP , CSP , and ABC transporter were involved in the xenobiotic or drug metabolism pathway, which suggested that these genes of T. castaneum participated in the response to eugenol exposure. Additionally, TcOBPC11/ TcGSTs7 , detected by qRT-PCR and RNA-interference against these genes, significantly increased the mortality of eugenol-treated T. castaneum , providing further evidence for the involvement of OBP/GST in eugenol metabolic detoxification in T. castaneum . These results aid eugenol insecticidal mechanisms and provide the basis of insect control.
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