Activation of CncC pathway is involved in the regulation of P450 genes responsible for clothianidin resistance in Bradysia odoriphaga.

Abstract

Insect cytochrome P450 monooxygenases (P450s) play a key role in the detoxification metabolism of insecticides and their overexpression is often associated with insecticide resistance. Our previous research showed that the overexpression of four P450 genes is responsible for clothianidin resistance in B. odoriphaga. In this study, we characterized another P450 gene CYP6FV21 associated with clothianidin resistance. However, the molecular basis for the overexpression of P450 genes in clothianidin resistant strain remains obscure in B. odoriphaga. In this study, the CYP6FV21 gene was significantly overexpressed in the clothianidin resistant (CL-R) strain. Clothianidin exposure significantly increased the expression level of CYP6FV21. Knockdown of CYP6FV21 significantly increased the susceptibility of B. odoriphaga larvae to clothianidin. The transcription factor Cap 'n' Collar isoform-C (CncC) was highly expressed in the midgut of larvae in B. odoriphaga. The expression level of CncC was higher in the CL-R strain compared with the susceptible (SS) strain. Clothianidin exposure caused reactive oxygen species (ROS) accumulation and significantly increased the expression level of CncC. Knockdown of CncC cause a significant decrease in the expression of CYP3828A1 and CYP6FV21 and P450 enzyme activity, and leads to a significant increase in mortality after exposure to LC30 clothianidin. After treatment with CncC agonist curcumin, the P450 activity and the expression levels of CYP3828A1 and CYP6FV21 significantly increased, and larval sensitivity to clothianidin decreased. The ROS scavenger NAC treatment significantly inhibited the expression levels of CncC, CYP3828A1 and CYP6FV21 in response to clothianidin exposure and increased larval sensitivity to clothianidin. Taken together, these results indicate that activation of the CncC pathway by the ROS burst plays a critical role in clothianidin resistance by regulating the expression of CYP3828A1 and CYP6FV21 genes in B. odoriphaga. This study provides more insight into the mechanisms underlying B. odoriphaga larval resistance to clothianidin.