Abstract
BackgroundCarboxylesterase is a multifunctional superfamily and ubiquitous in all living organisms, including animals, plants, insects, and microbes. It plays important roles in xenobiotic detoxification, and pheromone degradation, neurogenesis and regulating development. Previous studies mainly used Dipteran Drosophila and mosquitoes as model organisms to investigate the roles of the insect COEs in insecticide resistance. However, genome-wide characterization of COEs in phytophagous insects and comparative analysis remain to be performed.ResultsBased on the newly assembled genome sequence, 76 putative COEs were identified in Bombyx mori. Relative to other Dipteran and Hymenopteran insects, alpha-esterases were significantly expanded in the silkworm. Genomics analysis suggested that BmCOEs showed chromosome preferable distribution and 55% of which were tandem arranged. Sixty-one BmCOEs were transcribed based on cDNA/ESTs and microarray data. Generally, most of the COEs showed tissue specific expressions and expression level between male and female did not display obvious differences. Three main patterns could be classified, i.e. midgut-, head and integument-, and silk gland-specific expressions. Midgut is the first barrier of xenobiotics peroral toxicity, in which COEs may be involved in eliminating secondary metabolites of mulberry leaves and contaminants of insecticides in diet. For head and integument-class, most of the members were homologous to odorant-degrading enzyme (ODE) and antennal esterase. RT-PCR verified that the ODE-like esterases were also highly expressed in larvae antenna and maxilla, and thus they may play important roles in degradation of plant volatiles or other xenobiotics.ConclusionB. mori has the largest number of insect COE genes characterized to date. Comparative genomic analysis suggested that the gene expansion mainly occurred in silkworm alpha-esterases. Expression evidence indicated that the expanded genes were specifically expressed in midgut, integument and head, implying that these genes may have important roles in detoxifying secondary metabolites of mulberry leaves, contaminants in diet, and odorants. Our results provide some new insights into functions and evolutionary characteristics of COEs in phytophagous insects.
Highlights
Carboxylesterase is a multifunctional superfamily and ubiquitous in all living organisms, including animals, plants, insects, and microbes
Annotation and phylogeny of B. mori COEs Drosophila melanogaster, Anopheles gambiae and Apis mellifera COEs were retrieved from GenBank and used for blast
Through genomic analysis and gene prediction, 76 putative COE genes were identified in the silkworm genome (Additional file 1)
Summary
Carboxylesterase is a multifunctional superfamily and ubiquitous in all living organisms, including animals, plants, insects, and microbes. It plays important roles in xenobiotic detoxification, and pheromone degradation, neurogenesis and regulating development. Based on sequence similarity and substrate specificity, insect COE genes can be subdivided into eight subfamilies: α-esterase (ae), β-esterase (be), juvenile hormone esterase (jhe), gliotactins (gli), acetylcholinesterases (ace, AChE), neurotactins (nrt), neuroligins (nlg), and glutactin (glt) class [3]. Carboxylesterases are a class of the metabolic enzymes involved in insecticide resistance, which are implicated in the resistance of insects to OPs, carbamates, and pyrethroids through gene amplification, upregulation and coding sequence mutations [6]. Carboxylesterases can serve as noncatalytic adhesive proteins involved in cell-to-cell interactions [5] and participate in other functions, such as pheromone degradation in moths [7] and hydrolysis of the neurotransmitter acetylcholine and juvenile hormone (JH) [8,9]
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