Abstract
Carboxylesterases (CXEs) belong to a family of metabolic enzymes. Some CXEs act as odorant-degrading enzymes (ODEs), which are reportedly highly expressed in insect olfactory organs and participate in the rapid deactivation of ester pheromone components and plant volatiles. The tea geometrid Ectropis obliqua Prout produces sex pheromones consisting of non-ester functional compounds but relies heavily on acetic ester plant volatiles to search for host plants and locate oviposition sites. However, studies characterizing putative candidate ODEs in this important tea plant pest are still relatively scarce. In the present study, we identified 35 candidate EoblCXE genes from E. obliqua chemosensory organs based on previously obtained transcriptomic data. The deduced amino acid sequences possessed the typical characteristics of the insect CXE family, including oxyanion hole residues, the Ser-Glu-His catalytic triad, and the Ser active included in the conserved pentapeptide characteristic of esterases, Gly-X-Ser-X-Gly. Phylogenetic analyses revealed that the EoblCXEs were diverse, belonging to several different insect esterase clades. Tissue- and sex-related expression patterns were studied via reverse-transcription and quantitative real-time polymerase chain reaction analyses (RT- and qRT-PCR). The results showed that 35 EoblCXE genes presented a diversified expression profile; among these, 12 EoblCXEs appeared to be antenna-biased, two EoblCXEs were non-chemosensory organ-biased, 12 EoblCXEs were ubiquitous, and nine EoblCXEs showed heterogeneous expression levels among different tissues. Intriguingly, two EoblCXE genes, EoblCXE7 and EoblCXE13, were not only strongly localized to antennal sensilla tuned to odorants, such as the sensilla trichodea (Str I and II) and sensilla basiconica (Sba), but were also expressed in the putative gustatory sensilla styloconica (Sst), indicating that these two CXEs might play multiple physiological roles in the E. obliqua chemosensory processing system. This study provides the first elucidation of CXEs in the chemosensory system of a geometrid moth species and will enable a more comprehensive understanding of the functions of insect CXEs across lepidopteran species.
Highlights
The sophisticated olfactory system, the peripheral chemical signal coding, is essential for insects to find mates, locate food, and avoid predators (Dweck et al, 2013; Tauxe et al, 2013; Strauch et al, 2014; Li and Liberles, 2015)
We identified and characterized 35 candidate genes encoding EoblCXEs from the chemosensory organs of the moth E. obliqua through transcriptomic analysis, including 28 full-length sequences
Phylogenetic analyses and tissue- and sex-related expression profiling showed that EoblCXEs exhibited diverse sequence structures, multiple subfamily clades and distinct expression patterns, suggesting potential differentiation of physiological functions among EoblCXEs
Summary
The sophisticated olfactory system, the peripheral chemical signal coding, is essential for insects to find mates, locate food, and avoid predators (Dweck et al, 2013; Tauxe et al, 2013; Strauch et al, 2014; Li and Liberles, 2015). Airborne odorants enter the hydrosoluble sensillum lymph through the sensilla pores, bind to OBPs, activate ORs and trigger signal transduction cascades and olfactory coding; odorants are rapidly removed from the vicinity of the ORs by ODEs to restore the sensitivity of the sensory neuron (Rützler and Zwiebel, 2005; Vogt, 2005; Pelosi et al, 2006; Leal, 2013). The highly sensitive odorant signal transduction pathway of insects represents an excellent model that researchers can use to develop new environmentally friendly pest-management strategies through targeting key molecules and screening biologically active compounds for behavioral control. Given that the rapid degradation of redundant odorants can rescue the sensitivity of odorant sensory neurons, putative genes encoding insect ODEs that are highly expressed in the chemosensory system should be identified, and their potential roles in odorant degradation deserve thorough exploration
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