Overexpression of two α-esterase genes mediates metabolic resistance to malathion in the oriental fruit fly, Bactrocera dorsalis (Hendel).

Esterase has been reported to be involved in malathion resistance in the oriental fruit fly, Bactrocera dorsalis (Hendel). However, the underlying molecular mechanism of the esterase-mediated resistance remains largely unknown in this species. Here, with the use of a strain selected for malathion resistance in the laboratory (MR), we found that two overexpressed α-esterase genes, namely BdCarE4 and BdCarE6, predominant in the adult midgut and fat body, function in conferring malathion resistance in B. dorsalis. Notably, these two genes were found to be mostly close to the esterase E3, which are usually implicated in detoxifying organophosphate insecticides. The transcript levels of BdCarE4 and BdCarE6 were investigated and compared between the MR and a susceptible (MS) strain of B. dorsalis. Both genes were significantly up-regulated in the MR strain, which was consistent with the enhanced esterase activity in the MR strain. However, no changes in either the coding sequence or gene copy number were observed between the two strains. Subsequently, heterologous expression combined with cytotoxicity assay in Sf9 cells demonstrated that BdCarE4 and BdCarE6 can probably detoxify malathion. Furthermore, RNA interference-mediated knockdown of each of these two genes significantly increased malathion susceptibility in the MR strain adults. In conclusion, these results expand our molecular understanding of the important role of α-esterases during the development of resistance to organophosphorous insecticides in B. dorsalis.

De novo characterization of the Dialeurodes citri transcriptome: mining genes involved in stress resistance and simple sequence repeats (SSRs) discovery.

The citrus whitefly, Dialeurodes citri (Ashmead), is one of the three economically important whitefly species that infest citrus plants around the world; however, limited genetic research has been focused on D. citri, partly because of lack of genomic resources. In this study, we performed de novo assembly of a transcriptome using Illumina paired-end sequencing technology (Illumina Inc., San Diego, CA, USA). In total, 36,766 unigenes with a mean length of 497 bp were identified. Of these unigenes, we identified 17,788 matched known proteins in the National Center for Biotechnology Information database, as determined by Blast search, with 5731, 4850 and 14,441 unigenes assigned to clusters of orthologous groups (COG), gene ontology (GO), and SwissProt, respectively. In total, 7507 unigenes were assigned to 308 known pathways. In-depth analysis of the data showed that 117 unigenes were identified as potentially involved in the detoxification of xenobiotics and 67 heat shock protein (Hsp) genes were associated with environmental stress. In addition, these enzymes were searched against the GO and COG database, and the results showed that the three major detoxification enzymes and Hsps were classified into 18 and 3, 6, and 8 annotations, respectively. In addition, 149 simple sequence repeats were detected. The results facilitate the investigation of molecular resistance mechanisms to insecticides and environmental stress, and contribute to molecular marker development. The findings greatly improve our genetic understanding of D. citri, and lay the foundation for future functional genomics studies on this species.