A transcriptome-based screen of carboxylesterase-like genes that are involved in chlorpyrifos resistance in Laodelphax striatellus (Fallen)

Carboxylesterase (CarE)-mediated detoxification is one of the most important mediators of resistance to organophosphate insecticides (OPs). However, the molecular mechanisms by which CarEs mediate OP resistance are largely unknown. Our previous studies indicated that increased CarE activity was critical for chlorpyrifos (an OP) resistance in Laodelphax striatellus. In this study, 28 CarE and CarE-like genes (CarEs) were identified in the transcriptome of L. striatellus. Real-time quantitative PCR (qPCR) was performed to assess the relative expression of these 28 CarEs. Compared with the susceptible (YN) strain, Ls.CarE1 and Ls.CarE2 were significantly overexpressed in the chlorpyrifos-resistant (YN-CPF) strain by 32.06- and 8.52-fold, respectively. The expression levels of Ls.CarE1 and Ls.CarE2 were analyzed by qPCR to verify the correlation between overexpressed CarEs in the YN-CPF strain and chlorpyrifos resistance. Chlorpyrifos bioassays and CarE activity assays were subsequently performed on the chlorpyrifos relaxed selection (YN-RSF) strain. The results demonstrated that CarE activity was significantly higher in the YN-CPF and YN-RSF strains (4.15- and 1.92-fold, respectively) than in the YN strain, which was consistent with their respective degrees of chlorpyrifos resistance (214.0-fold for YN-CPF and 83.3-fold for YN-RSF). Ls.CarE1 was significantly overexpressed in both the YN-CPF and the YN-RSF strains (32.06-fold for YN-CPF and 8.6-fold for YN-RSF) compared with the YN strain, and a high degree of proportionality was observed between the expression level of Ls.CarE1 and the degree of resistance to chlorpyrifos across the three strains. However, the expression level of Ls.CarE2 in the YN-RSF and the YN strains was not significantly different. These data suggest that overexpressed Ls.CarE1 might be involved in chlorpyrifos resistance in the YN-CPF strain of L. striatellus. (c) 2012 Elsevier Inc. All rights reserved.