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Carboxylesterases (CarEs) play vital roles in metabolising different physiologically important endogenous compounds and in detoxifying various harmful exogenous compounds in insects. Multiple studies of CarEs have focused on pesticide metabolism in insects, while few studies have aimed to identify CarE functions in oxidative resistance, particularly in Apis cerana cerana . In this study, we isolated a carboxylesterase gene, esterase FE4, from Apis cerana cerana and designated it towards an exploration of its roles as an antioxidant and in detoxification. We investigated AcceFE4 expression patterns in response to various stressors. A quantitative real-time PCR analysis revealed that AcceFE4 was up-regulated by H 2 O 2 , imidacloprid, and paraquat, and was down-regulated by 4 °C, UV radiation, CdCl 2 , and HgCl 2 . Additionally, the protein expression of this gene was down-regulated at 4 °C and up-regulated by H 2 O 2 . Disc diffusion assays showed that the AcceFE4 recombinant protein-expressing bacteria had a smaller killing zone than the control group with the paraquat, HgCl 2 and cumyl hydroperoxide treatments. Moreover, when the gene was knocked down by RNA interference, we observed that multiple oxidant genes (i.e., AccSOD , AccGST , AccTrx , AccMsrA, and others) were down-regulated in the knockdown samples. Superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity levels were reduced in the knockdown samples relative to the control group. Finally, we measured the enzyme activity of carboxylesterase and found that the enzyme activity was also reduced in the silent samples. Together, these data suggest that AcceFE4 may be involved in the oxidative resistance response during adverse stress. [ABSTRACT FROM AUTHOR]

Abstract: Glutaredoxins (Grxs) and thioredoxins (Trxs) play important roles in maintaining intracellular thiol-redox homeostasis by scavenging reactive oxygen species. However, few Grxs and Trxs have been functionally characterized in Apis cerana cerana. In this study, we identified three genes, AccGrx1, AccGrx2, and AccTrx1, and investigated their connection to antioxidant defense. AccGrx1 and AccGrx2 were mainly detected in dark-eyed pupae, whereas AccTrx1 was highly concentrated in 15-day postemergence adults. The expression levels of AccGrx1 and AccTrx1 were the highest in fat body and epidermis, respectively. However, the expression level of AccGrx2 was the highest in muscle, followed by the epidermis. AccGrx1, AccGrx2, and AccTrx1 were induced by 4, 16, and 42°C; H2O2; and pesticide (acaricide, paraquat, cyhalothrin, and phoxime) treatments and repressed by UV light. AccGrx1 and AccGrx2 were upregulated by HgCl2 treatment, whereas AccTrx1 was downregulated. We investigated the knockdown of AccGrx1, AccGrx2, AccTpx-3, and AccTrx1 in A. cerana cerana and surprisingly found that knockdown of the these four genes enhanced the enzymatic activities of CAT and POD; the metabolite contents of hydrogen peroxide, carbonyls, and ascorbate; and the ratios of GSH/GSSG and NADP+/NADPH. In addition, we also analyzed the transcripts of other antioxidant genes and found that some were upregulated and others were downregulated, revealing that the upregulated genes may be involved in compensating for the knockdown of AccGrx1, AccGrx2, AccTpx-3, and AccTrx1. Taken together, these results suggest that AccGrx1, AccGrx2, AccTpx-3, and AccTrx1 may play critical roles in antioxidant defense. [Copyright &y& Elsevier]