Carboxyl/cholinesterases: a case study of the evolution of a successful multigene family

Study on the virulence of Metarhizium anisopliae against Spodoptera frugiperda (J. E. Smith, 1797)

This study examined the impact of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) conidia on the eggs, larvae, pupae, and adults of Spodoptera frugiperda. The results showed that eggs, larvae, pupae, and adults exhibited mortality rates that were dependent on the dose. An increased amount of conidia (1.5 × 109 conidia/mL) was found to be toxic to larvae, pupae, and adults after 9 days of treatment, resulting in a 100% mortality rate in eggs, 98% in larvae, 76% in pupae, and 85% in adults. A study using earthworms as bioindicators found that after 3 days of exposure, M. anisopliae conidia did not cause any harmful effects on the earthworms. In contrast, the chemical treatment (positive control) resulted in 100% mortality at a concentration of 40 ppm. Histopathological studies showed that earthworm gut tissues treated with fungal conidia did not show significant differences compared with those of the negative control. The gut tissues of earthworms treated with monocrotophos exhibited significant damage, and notable differences were observed in the chemical treatment. The treatments with 70 and 100 µg/mL solutions of Eudrilus eugeniae epidermal mucus showed no fungal growth. An analysis of the enzymes at a biochemical level revealed a decrease in the levels of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase in S. frugiperda larvae after exposure to fungal conidia. This study found that M. anisopliae is effective against S. frugiperda, highlighting the potential of this entomopathogenic fungus in controlling this agricultural insect pest.

Phylogenomics of the Ecdysteroid Kinase-like (EcKL) Gene Family in Insects Highlights Roles in Both Steroid Hormone Metabolism and Detoxification

The evolutionary dynamics of large gene families can offer important insights into the functions of their individual members. While the ecdysteroid kinase-like (EcKL) gene family has previously been linked to the metabolism of both steroid molting hormones and xenobiotic toxins, the functions of nearly all EcKL genes are unknown, and there is little information on their evolution across all insects. Here, we perform comprehensive phylogenetic analyses on a manually annotated set of EcKL genes from 140 insect genomes, revealing the gene family is comprised of at least 13 subfamilies that differ in retention and stability. Our results show the only two genes known to encode ecdysteroid kinases belong to different subfamilies and therefore ecdysteroid metabolism functions must be spread throughout the EcKL family. We provide comparative phylogenomic evidence that EcKLs are involved in detoxification across insects, with positive associations between family size and dietary chemical complexity, and we also find similar evidence for the cytochrome P450 and glutathione S-transferase gene families. Unexpectedly, we find that the size of the clade containing a known ecdysteroid kinase is positively associated with host plant taxonomic diversity in Lepidoptera, possibly suggesting multiple functional shifts between hormone and xenobiotic metabolism. Our evolutionary analyses provide hypotheses of function and a robust framework for future experimental studies of the EcKL gene family. They also open promising new avenues for exploring the genomic basis of dietary adaptation in insects, including the classically studied coevolution of butterflies with their host plants.

Characteristics of CXE family of Salvia miltiorrhiza and identification of interactions between SmGID1s and SmDELLAs

Carboxylesterase (CXE) is a class of hydrolases that contain an α/β folding domain, which plays critical roles in plant growth, development, and stress responses. Based on the genomic and transcriptomic data of Salvia miltiorrhiza, the SmCXE family was systematically analyzed using bioinformatics. The results revealed 34 SmCXE family members in S. miltiorrhiza, and the SmCXE family could be divided into five groups (Group I, Group II, Group III, Group IV, and Group V). Cis-regulatory elements indicated that the SmCXE promoter region contained tissue-specific and development-related, hormone-related, stress-related, and photoresponsive elements. Transcriptome analysis revealed that the expression levels of SmCXE2 were highest in roots and flowers (SmCXE8 was highest in stems and SmCXE19 was highest in leaves). Further, two GA receptors SmCXE1 (SmGID1A) and SmCXE2 (SmGID1B) were isolated from the SmCXE family, which are homologous to other plants. SmGID1A and SmGID1B have conserved HGGSF motifs and active amino acid sites (Ser-Asp-Val/IIe), which are required to maintain their GA-binding activities. SmGID1A and SmGID1B were significantly responsive to gibberellic acid (GA3) and methyl jasmonate (MeJA) treatment. A subcellular assay revealed that SmCXE1 and SmCXE2 resided within the nucleus. SmGID1B can interact with SmDELLAs regardless of whether GA3 exists, whereas SmGID1A can only interact with SmDELLAs in the presence of GA3. A Further assay showed that the GRAS domain mediated the interactions between SmGID1s and SmDELLAs. This study lays a foundation for further elucidating the role of SmCXE in the growth and development of S. miltiorrhiza.

A chromosome-scale genome assembly of the grape powdery mildew pathogen Erysiphe necator reveals its genomic architecture and previously unknown features of its biology

Erysiphe necator is an obligate fungal pathogen that causes grape powdery mildew, globally the most important disease on grapevines. Previous attempts to obtain a quality genome assembly for this pathogen were hindered by its high repetitive DNA content. Here, chromatin conformation capture (Hi-C) with long-read PacBio sequencing was combined to obtain a chromosome-scale assembly and a high-quality annotation for E. necator isolate EnFRAME01. The resulting 81.1 Mb genome assembly is 98% complete and consists of 34 scaffolds, 11 of which represent complete chromosomes. All chromosomes contain large centromeric-like regions and lack synteny to the 11 chromosomes of the cereal PM pathogen Blumeria graminis. Further analysis of their composition showed that repeats and transposable elements (TEs) occupy 62.7% of their content. TEs were almost evenly interspersed outside centromeric and telomeric regions and massively overlapped with regions of annotated genes, suggesting that they could have a significant functional impact. Abundant gene duplicates were observed as well, particularly in genes encoding candidate secreted effector proteins. Moreover, younger in age gene duplicates exhibited more relaxed selection pressure and were more likely to be located physically close in the genome than older duplicates. A total of 122 genes with copy number variations among six isolates of E. necator were also identified and were enriched in genes that were duplicated in EnFRAME01, indicating they may reflect an adaptive variation. Taken together, our study illuminates higher-order genomic architectural features of E. necator and provides a valuable resource for studying genomic structural variations in this pathogen. IMPORTANCE Grape powdery mildew caused by the ascomycete fungus Erysiphe necator is economically the most important and recurrent disease in vineyards across the world. The obligate biotrophic nature of E. necator hinders the use of typical genetic methods to elucidate its pathogenicity and adaptation to adverse conditions, and thus comparative genomics has been a major method to study its genome biology. However, the current reference genome of E. necator isolate C-strain is highly fragmented with many non-coding regions left unassembled. This incompleteness prohibits in-depth comparative genomic analyses and the study of genomic structural variations (SVs) that are known to affect several aspects of microbial life, including fitness, virulence, and host adaptation. By obtaining a chromosome-scale genome assembly and a high-quality gene annotation for E. necator, we reveal the organization of its chromosomal content, unearth previously unknown features of its biology, and provide a reference for studying genomic SVs in this pathogen.

Comparative evolutionary analyses of eight whitefly Bemisia tabaci sensu lato genomes: cryptic species, agricultural pests and plant-virus vectors

BACKGROUND

The group of > 40 cryptic whitefly species called Bemisia tabaci sensu lato are amongst the world's worst agricultural pests and plant-virus vectors. Outbreaks of B. tabaci s.l. and the associated plant-virus diseases continue to contribute to global food insecurity and social instability, particularly in sub-Saharan Africa and Asia. Published B. tabaci s.l. genomes have limited use for studying African cassava B. tabaci SSA1 species, due to the high genetic divergences between them. Genomic annotations presented here were performed using the 'Ensembl gene annotation system', to ensure that comparative analyses and conclusions reflect biological differences, as opposed to arising from different methodologies underpinning transcript model identification.

RESULTS

We present here six new B. tabaci s.l. genomes from Africa and Asia, and two re-annotated previously published genomes, to provide evolutionary insights into these globally distributed pests. Genome sizes ranged between 616-658 Mb and exhibited some of the highest coverage of transposable elements reported within Arthropoda. Many fewer total protein coding genes (PCG) were recovered compared to the previously published B. tabaci s.l. genomes and structural annotations generated via the uniform methodology strongly supported a repertoire of between 12.8-13.2 × 10³ PCG. An integrative systematics approach incorporating phylogenomic analysis of nuclear and mitochondrial markers supported a monophyletic Aleyrodidae and the basal positioning of B. tabaci Uganda-1 to the sub-Saharan group of species. Reciprocal cross-mating data and the co-cladogenesis pattern of the primary obligate endosymbiont 'Candidatus Portiera aleyrodidarum' from 11 Bemisia genomes further supported the phylogenetic reconstruction to show that African cassava B. tabaci populations consist of just three biological species. We include comparative analyses of gene families related to detoxification, sugar metabolism, vector competency and evaluate the presence and function of horizontally transferred genes, essential for understanding the evolution and unique biology of constituent B. tabaci. s.l species.

CONCLUSIONS

These genomic resources have provided new and critical insights into the genetics underlying B. tabaci s.l. biology. They also provide a rich foundation for post-genomic research, including the selection of candidate gene-targets for innovative whitefly and virus-control strategies.

Two Antenna-Enriched Carboxylesterases Mediate Olfactory Responses and Degradation of Ester Volatiles in the German Cockroach Blattella germanica

Insects have evolved an extremely sensitive olfactory system that is essential for a series of physiological and behavioral activities. Some carboxylesterases (CCEs) comprise a major subfamily of odorant-degrading enzymes (ODEs) playing a crucial role in odorant signal inactivation to maintain the odorant receptor sensitivity. In this study, 93 CCEs were annotated in the genome of the German cockroach Blattella germanica, a serious urban pest. Phylogenetic and digital tissue expression pattern analyses identified two antenna-enriched CCEs, BgerCCE021e3 and BgerCCE021d1, as candidate ODEs. RNA interference (RNAi)-mediated knockdown of BgerCCE021e3 and BgerCCE021d1 resulted in partial anosmia with experimental insects exhibiting reduced attraction to ester volatile resources and slower olfactory responses than controls. Furthermore, enzymatic conversion of geranyl acetate by crude male antennal extracts from BgerCCE021e3 and BgerCCE021d1 RNAi insects was also significantly reduced. Our results provide evidence for CCE function in German cockroach olfaction and provide a basis for further exploring behavioral inhibitors that target olfactory-related CCEs.

Dynamic Roles of Insect Carboxyl/Cholinesterases in Chemical Adaptation

Insects have evolved several intricate defense mechanisms to adapt to their chemical environment. Due to their versatile capabilities in hydrolytic biotransformation, insect carboxyl/cholinesterases (CCEs) play vital roles in the development of pesticide resistance, facilitating the adaptation of insects to their host plants, and manipulating insect behaviors through the olfaction system. CCEs confer insecticide resistance through the mechanisms of qualitative or quantitative changes of CCE-mediated enhanced metabolism or target-site insensitivity, and may contribute to the host plant adaptation. CCEs represent the first odorant-degrading enzymes (ODEs) discovered to degrade insect pheromones and plant odors and remain the most promising ODE candidates. Here, we summarize insect CCE classification, currently characterized insect CCE protein structure characteristics, and the dynamic roles of insect CCEs in chemical adaptation.

The Functional Characterization of Carboxylesterases Involved in the Degradation of Volatile Esters Produced in Strawberry Fruits

Volatile ester compounds are important contributors to the flavor of strawberry, which affect consumer preference. Here, the GC-MS results showed that volatile esters are the basic aroma components of strawberry, banana, apple, pear, and peach, and the volatile esters were significantly accumulated with the maturation of strawberry fruits. The main purpose of this study is to discuss the relationship between carboxylesterases (CXEs) and the accumulation of volatile ester components in strawberries. FaCXE2 and FaCXE3 were found to have the activity of hydrolyzing hexyl acetate, Z-3-hexenyl acetate, and E-2-hexenyl acetate to the corresponding alcohols. The enzyme kinetics results showed that FaCXE3 had the higher affinity for hexyl acetate, E-2-hexenyl acetate, and Z-3-hexenyl acetate compared with FaCXE2. The volatile esters were mainly accumulated at the maturity stages in strawberry fruits, less at the early stages, and the least during the following maturation stages. The expression of FaCXE2 gradually increased with fruit ripening and the expression level of FaCXE3 showed a decreasing trend, which suggested the complexity of the true function of CXEs. The transient expression of FaCXE2 and FaCXE3 genes in strawberry fruits resulted in a significantly decreased content of volatile esters, such as Z-3-hexenyl acetate, methyl hexanoate, methyl butyrate, and other volatile esters. Taken together, FaCXE2 and FaCXE3 are indeed involved in the regulation of the synthesis and degradation of strawberry volatile esters.

Esterases as emerging biocatalysts: Mechanistic insights, genomic and metagenomic, immobilization, and biotechnological applications

Esterase enzymes are a family of hydrolases that catalyze the breakdown and formation of ester bonds. Esterases have gained a prominent position in today's world's industrial enzymes market. Due to their unique biocatalytic attributes, esterases contribute to environmentally sustainable design approaches, including biomass degradation, food and feed industry, dairy, clothing, agrochemical (herbicides, insecticides), bioremediation, biosensor development, anticancer, antitumor, gene therapy, and diagnostic purposes. Esterases can be isolated by a diverse range of mammalian tissues, animals, and microorganisms. The isolation of extremophilic esterases increases the interest of researchers in the extraction and utilization of these enzymes at the industrial level. Genomic, metagenomic, and immobilization techniques have opened innovative ways to extract esterases and utilize them for a longer time to take advantage of their beneficial activities. The current study discusses the types of esterases, metagenomic studies for exploring new esterases, and their biomedical applications in different industrial sectors.

Strawberry fruit FanCXE1 carboxylesterase is involved in the catabolism of volatile esters during the ripening process

Volatile compounds produced during ripening of strawberry are key determinants of fruit quality and consumer preference. Strawberry volatiles are largely esters which are synthesized by alcohol acyltransferases (AATs) and degraded by carboxylesterases (CXEs). Although CXE activity can have a marked influence on volatile contents in ripe strawberry fruits, CXE function and regulation in them are poorly known. Here, we report the biochemical and functional characterization of the fruit receptacle-specific and ripening-related carboxylesterase FanCXE1. The expression of the corresponding gene was found to be antagonistically regulated by auxins and abscisic acid, key hormones that regulate fruit growth and ripening in strawberry. In vitro, FanCXE1 was able to hydrolyze artificial ester substrates similar to those produced by ripe strawberry fruits. Transient suppression of the FanCXE1 gene by RNAi resulted in an increase of important volatile esters such as methyl hexanoate, methyl butanoate and ethyl hexanoate as well as a decrease of the alcohols hexenol and linanool. The results of this work enhance our understanding of the molecular basis for volatile syntheses and facilitate production of better flavored strawberry fruits by introduction of the relevant alleles into common cultivars.

A masculinizing supergene underlies an exaggerated male reproductive morph in a spider

In many species, individuals can develop into strikingly different morphs, which are determined by a simple Mendelian locus. How selection shapes loci that control complex phenotypic differences remains poorly understood. In the spider Oedothorax gibbosus, males develop either into a 'hunched' morph with conspicuous head structures or as a fast-developing 'flat' morph with a female-like appearance. We show that the hunched-determining allele contains a unique genomic fragment of approximately 3 megabases that is absent in the flat-determining allele. This fragment comprises dozens of genes that duplicated from genes found at the same as well as different chromosomes. All functional duplicates, including a duplicate of the key sexual differentiation regulatory gene doublesex, show male-specific expression, which illustrates their integrated role as a masculinizing supergene. Our findings demonstrate how extensive indel polymorphisms and duplications of regulatory genes may contribute to the evolution of co-adapted gene clusters, sex-limited reproductive morphs and the enigmatic evolution of exaggerated sexual traits in general.

Genomic analysis of the carboxylesterase family in the salmon louse (Lepeophtheirus salmonis)

The pyrethroid deltamethrin and the macrocyclic lactone emamectin benzoate (EMB) are used to treat infestations of farmed salmon by parasitic salmon lice, Lepeophtheirus salmonis. While the efficacy of both compounds against Atlantic populations of the parasite has decreased as a result of the evolution of resistance, the molecular mechanisms of drug resistance in L. salmonis are currently not fully understood. The functionally diverse carboxylesterases (CaE) family includes members involved in pesticide resistance phenotypes of terrestrial arthropods. The present study had the objective to characterize the CaE family in L. salmonis and assess its role in drug resistance. L. salmonis CaE homologues were identified by homology searches in the parasite's transcriptome and genome. The transcript expression of CaEs predicted to be catalytically competent was studied using quantitative reverse-transcription PCR in drug susceptible and multi-resistant L. salmonis. The above strategy led to the identification of 21 CaEs genes/pseudogenes. Phylogenetic analyses assigned 13 CaEs to clades involved in neurodevelopmental signaling and cell adhesion, while three sequences were predicted to encode secreted enzymes. Ten CaEs were identified as being potentially catalytically competent. Transcript expression of acetylcholinesterase (ace1b) was significantly increased in multi-resistant lice compared to drug-susceptible L. salmonis, with transcript abundance further increased in preadult-II females following EMB exposure. In summary, results from the present study demonstrate that L. salmonis possesses fewer CaE gene family members than most arthropods characterized so far. Drug resistance in L. salmonis was associated with overexpression of ace1b.

Carboxylesterase genes in nitenpyram-resistant brown planthoppers, Nilaparvata lugens

Carboxylesterases (CarEs) represent one of the major detoxification enzyme families involved in insecticide resistance. However, the function of specific CarE genes in insecticide resistance is still unclear in the insect Nilaparvata lugens (Stål), a notorious rice crop pest in Asia. In this study, a total of 29 putative CarE genes in N. lugens were identified, and they were divided into seven clades; further, the β-esterase clade was significantly expanded. Tissue-specific expression analysis found that 17 CarE genes were abundantly distributed in the midgut and fat body, while 12 CarE genes were highly expressed in the head. The expression of most CarE genes was significantly induced in response to the challenge of nitenpyram, triflumezopyrim, chlorpyrifos, isoprocarb and etofenprox. Among these, the expression levels of NlCarE2, NlCarE4, NlCarE9, NlCarE17 and NlCarE24 were increased by each insecticide. Real-time quantitative polymerase chain reaction and RNA interference assays revealed the NlCarE1 gene to be a candidate gene mainly involved in nitenpyram resistance, while simultaneously silencing NlCarE1 and NlCarE19 produced a stronger effect than silencing either one individually, suggesting a cooperative relationship in resistance formation. These findings lay the foundation for further clarification of insecticide resistance mediated by CarE in N. lugens.

The Draft Genome of Yellow Stem Borer, an Agriculturally Important Pest, Provides Molecular Insights into Its Biology, Development and Specificity Towards Rice for Infestation

Simple Summary

Yellow stem borer (YSB), is the most destructive and widely occurring pest that attacks rice throughout the growing season. Rice (Oryza sativa L.) is a major staple cereal worldwide, providing essential caloric requirements for more than half of the world’s population. Annual losses to rice borers are approximately 5–10%, but losses in individual fields may reach up to 50–60%. The use of traditional pest management strategies in controlling YSB is somewhat challenging due to its unique internal feeding habit. Genome sequence information of economically important crop pests is important for designing or developing pest-resistant rice varieties. In an approach to achieve this, we present our first-ever study on the draft genome sequence of YSB. The information provided from our current study might be useful in developing genome-based approaches for the management of pest species.

Abstract

Yellow stem borer (YSB), Scirpophaga incertulas (Walker) (Lepidoptera: Crambidae), a major monophagous insect pest of rice, causes significant yield losses. The rice–YSB interaction is very dynamic, making it difficult for management. The development of resistant lines has been unsuccessful as there are no effective resistant sources in the germplasm. Genome information is necessary for a better understanding of interaction with rice in terms of its recognition, response, and infestation mechanism. The draft genome of YSB is predicted to have 46,057 genes with an estimated size of 308 Mb, being correlated with the flow cytometry analysis. The existence of complex metabolic mechanisms and genes related to specific behavior was identified, being conditioned by a higher level of regulation. We deciphered the possible visual, olfactory, and gustatory mechanisms responsible for its evolution as a monophagous pest. Comparative genomic analysis revealed that YSB is unique in the way it has evolved. The obvious presence of high-immunity-related genes, well-developed RNAi machinery, and diverse effectors provides a means for developing genomic tools for its management. The identified 21,696 SSR markers can be utilized for diversity analysis of populations across the rice-growing regions. We present the first draft genome of YSB. The information emanated paves a way for biologists to design novel pest management strategies as well as for the industry to design new classes of safer and specific insecticide molecules.

Two carboxylesterase genes in Plutella xylostella associated with sex pheromones and plant volatiles degradation

BACKGROUND

Carboxyl/cholinesterases (CCEs) are thought to play a pivotal role in the degradation of sex pheromones and plant-derived odorants in insects, but their exact biochemistry and physiological functions remain unclear.

RESULTS

In this study, two paralogous antennae-enriched CCEs from Plutella xylostella (PxylCCE16a and 16c) were identified and functionally characterized. High-purity protein preparations of active recombinant PxylCCE16a and 16c have been obtained from Sf9 insect cells by Ni²⁺ affinity purification. Our results revealed that the purified recombinant PxylCCE016c is able to degrade two sex pheromone components Z9-14:Ac and Z11-16:Ac at 27.64 ± 0.79% and 24.40 ± 3.07%, respectively, while PxylCCE016a presented relatively lower activity. Additionally, a similar difference in activity was measured in plant-derived odorants. Furthermore, both CCEs displayed obvious preferences for the two sex pheromone components, especially on Z11-16:Ac (K_m values are in the range 7.82-45.06 μmol L^-1 ) which much lower than plant odorants (K_m values are in the range 1290-4030 μmol L^-1 ). Furthermore, the activity of the two newly identified CCEs is pH-dependent. The activity at pH 6.5 is obviously higher than that at pH 5.0. Interestingly, only PxylCCE016c can be inhibited by a common esterase inhibitor triphenyl phosphate (TPP) with LC₅₀ of 1570 ± 520 μmol L^-1 .

CONCLUSION

PxylCCE16c plays a more essential role in odorant degradation than PxylCCE16a. Moreover, the current study provides novel potential pesticide targets for the notorious moth Plutella xylostella. © 2021 Society of Chemical Industry.

An Overview of Antennal Esterases in Lepidoptera

Lepidoptera are used as a model for the study of insect olfactory proteins. Among them, odorant degrading enzymes (ODEs), that degrade odorant molecules to maintain the sensitivity of antennae, have received less attention. In particular, antennal esterases (AEs; responsible for ester degradation) are crucial for intraspecific communication in Lepidoptera. Currently, transcriptomic and genomic studies have provided AEs in several species. However, efforts in gene annotation, classification, and functional assignment are still lacking. Therefore, we propose to combine evidence at evolutionary, structural, and functional level to update ODEs as well as key information into an easier classification, particularly of AEs. Finally, the kinetic parameters for putative inhibition of ODEs are discussed in terms of its role in future integrated pest management (IPM) strategies.

Brown marmorated stink bug, Halyomorpha halys (Stål), genome: putative underpinnings of polyphagy, insecticide resistance potential and biology of a top worldwide pest

BACKGROUND

Halyomorpha halys (Stål), the brown marmorated stink bug, is a highly invasive insect species due in part to its exceptionally high levels of polyphagy. This species is also a nuisance due to overwintering in human-made structures. It has caused significant agricultural losses in recent years along the Atlantic seaboard of North America and in continental Europe. Genomic resources will assist with determining the molecular basis for this species' feeding and habitat traits, defining potential targets for pest management strategies.

RESULTS

Analysis of the 1.15-Gb draft genome assembly has identified a wide variety of genetic elements underpinning the biological characteristics of this formidable pest species, encompassing the roles of sensory functions, digestion, immunity, detoxification and development, all of which likely support H. halys' capacity for invasiveness. Many of the genes identified herein have potential for biomolecular pesticide applications.

CONCLUSIONS

Availability of the H. halys genome sequence will be useful for the development of environmentally friendly biomolecular pesticides to be applied in concert with more traditional, synthetic chemical-based controls.

Proteo-Transcriptomic Characterization of the Venom from the Endoparasitoid Wasp Pimpla turionellae with Aspects on Its Biology and Evolution

Within mega-diverse Hymenoptera, non-aculeate parasitic wasps represent 75% of all hymenopteran species. Their ovipositor dual-functionally injects venom and employs eggs into (endoparasitoids) or onto (ectoparasitoids) diverse host species. Few endoparasitoid wasps such as Pimpla turionellae paralyze the host and suppress its immune responses, such as encapsulation and melanization, to guarantee their offspring's survival. Here, the venom and its possible biology and function of P. turionellae are characterized in comparison to the few existing proteo-transcriptomic analyses on parasitoid wasp venoms. Multiple transcriptome assembly and custom-tailored search and annotation strategies were applied to identify parasitoid venom proteins. To avoid false-positive hits, only transcripts were finally discussed that survived strict filter settings, including the presence in the proteome and higher expression in the venom gland. P. turionella features a venom that is mostly composed of known, typical parasitoid enzymes, cysteine-rich peptides, and other proteins and peptides. Several venom proteins were identified and named, such as pimplin2, 3, and 4. However, the specification of many novel candidates remains difficult, and annotations ambiguous. Interestingly, we do not find pimplin, a paralytic factor in Pimpla hypochondriaca, but instead a new cysteine inhibitor knot (ICK) family (pimplin2), which is highly similar to known, neurotoxic asilid1 sequences from robber flies.

Molecular evolution of juvenile hormone esterase-like proteins in a socially exchanged fluid

Socially exchanged fluids are a direct means by which an organism can influence conspecifics. It was recently shown that when workers of the carpenter ant Camponotus floridanus feed larval offspring via trophallaxis, they transfer Juvenile Hormone III (JH), a key developmental regulator, as well as paralogs of JH esterase (JHE), an enzyme that catalyzes the hydrolysis of JH. Here we combine proteomic, phylogenetic and selection analyses to investigate the evolution of this esterase subfamily. We show that Camponotus JHE-like proteins have undergone multiple duplications, experienced positive selection, and changed tissue localization to become abundantly and selectively present in trophallactic fluid. The Camponotus trophallactic esterases have maintained their catalytic triads and contain a number of positively-selected amino acid changes distributed throughout the protein, which possibly reflect an adaptation to the highly acidic trophallactic fluid of formicine ants. To determine whether these esterases might regulate larval development, we fed workers with a JHE-specific pharmacological inhibitor to introduce it into the trophallactic network. This inhibitor increased the likelihood of pupation of the larvae reared by these workers, similar to the influence of food supplementation with JH. Together, these findings suggest that JHE-like proteins have evolved a new role in the inter-individual regulation of larval development in the Camponotus genus.

The Development of Bacterial Carboxylesterase Biological Recognition Elements for Cocaine Detection

Enzyme recognition element-based biosensors are very attractive for biosensor application due to a variety of measurable reaction products arising from a catalytic process. In this study, biosensor recognition elements have been developed via engineer bacterial enzymes (carboxylesterases (CEs)) which will used for narcotic detection because of their role in narcotics metabolism. The modification (insertion of cys-tag) allows the enzyme to bind into a transducer surface of a biosensor which will translate the reaction product into the detection system. The results demonstrate the successful isolation, cloning, expression, and purification of recombinant (pnbA1 and pnbA2), and engineered (pnbA1-cys and pnbA2-cys) bacterial carboxylesterases. Enzyme capability to hydrolyse cocaine into benzoylecgonine and methanol was quantified using HPLC. Both enzymes showed broad maximal activity between pH (8.0, 8.5, and 9.0), PnbA1 temperature stability ranging between (25 and 45 °C); however, PnbA2 stability range was (25-40 °C). Insertion of cys-tag at the N-terminal of the enzyme did not limit entrance to the active site which is located at the base of a cavity with dimensions 20 by 13 by 18 Å, and did not prevent substrate hydrolysis. Bacterial carboxylesterases pnbA1 and pnbA2 mimic hCE1 and not hCE2 in its reaction pathways hydrolysing cocaine into benzoylecgonine and methanol rather than ecgonine methyl ester and benzoic acid. These results are the first experimental evidence confirming the capability of bacterial carboxylesterase to hydrolyse cocaine into its main metabolites, therefore opening up the possibility to use these enzymes in numerous biotechnological applications in addition to a cocaine biosensor.

Identification of carboxylesterase genes associated with pyrethroid resistance in the malaria vector Anopheles sinensis (Diptera: Culicidae)

BACKGROUND

Carboxylesterases (CCEs) are one of three large detoxification enzyme families. Some CCEs are active on synthetic insecticides with ester structures. Anopheles sinensis is an important malaria vector in eastern Asia. This study identified and characterized the CCE genes in the A. sinensis genome and determined CCE genes associated with pyrethroid resistance using RNA sequencing (RNA-seq) and quantitative reverse transcription - polymerase chain reaction (qRT-PCR), in A. sinensis from Anhui, Chongqing, and Yunnan in China.

RESULTS

Fifty-seven putative CCEs were identified and placed into three classes, 12 subfamilies and 14 clades through phylogenetic and homology analyses. Exon sizes ranged from 31 to 4317 bp, with 49 CCEs having two to five exons and eight having six to 11 exons. A total of 183 introns were recognized with sizes ranging from 31 to 4317 bp. The 57 CCEs were located on 14 scaffolds, with 70% located on four scaffolds. The alpha-esterase subfamily was significantly expanded compared with that of Anopheles gambiae. In a pyrethroid-resistant strain, RNA-seq detected five upregulated CCE genes and qRT-PCR detected 12 upregulated CCE genes. The α-esterase 10 (AsAe10) and acetylcholinesterase 1 (AsAce1) genes were the main CCE genes associated with pyrethroid resistance.

CONCLUSION

This information will be useful for further study of the CCE gene family and pyrethroid resistance mechanisms mediated by CCEs. © 2017 Society of Chemical Industry.

Identification and Expression Patterns of Putative Diversified Carboxylesterases in the Tea Geometrid Ectropis obliqua Prout

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.

Functional characterization of BdB1, a well-conserved carboxylesterase among tephritid fruit flies associated with malathion resistance in Bactrocera dorsalis (Hendel)

There are many evidences that insect carboxylesterase possess important physiological roles in xenobiotic metabolism and are implicated in the detoxification of organophosphate (OP) insecticides. Despite the ongoing resistance development in the oriental fruit fly, Bactrocera dorsalis (Hendel), the molecular basis of carboxylesterase and its ability to confer OP resistance remain largely obscure. This study was initiated to provide a better understanding of carboxylesterase-mediated resistance mechanism in a tephritid pest fly. Here, we narrow this research gap by demonstrating a well-conserved esterase B1 gene, BdB1, mediates malathion resistance development via gene upregulation with the use of a laboratory selected malathion-resistant strain (MR) of B. dorsalis. No sequence mutation of BdB1 was detected between MR and the susceptible strain (MS) of B. dorsalis. BdB1 is predominantly expressed in the midgut, a key insect tissue for detoxification. As compared with transcripts in MS, BdB1 was significantly more abundant in multiple tissues in the MR. RNA interference (RNAi)-mediated knockdown of BdB1 significantly increased malathion susceptibility. Furthermore, heterologous expression along with cytotoxicity assay revealed BdB1 could probably have the function of malathion detoxification.

Carboxylesterase Precursor (EST-1) Mediated the Fungicide Jinggangmycin-Suppressed Reproduction of Sogatella furcifera (Hemiptera: Delphacidae)

The jinggangmycin (JGM) is a widely used fungicide for controlling the rice sheath blight, Rhizoctonia solani, in China. Previous experiments under lab conditions showed that JGM foliar spray suppressed Sogatella furcifera (Horvath) reproduction. However, the molecular mechanisms of JGM-driven changes in S. furcifera reproduction are unclear. Therefore, we selected carboxylesterase precursor (EST-1) as a target gene for silencing by RNAi based on gene expression profiles. The present results demonstrated that JGM and control + dsSfEST-1 treatments significantly reduced the number of eggs laid (down by 58% and 54%, respectively), oviposition period (down by 57% and 38%, respectively), and longevity (down by 32% and 38%, respectively) in adult females compared with untreated controls, while no pronounced differences in the preoviposition period were observed. Meanwhile, the dietary control + dsSfEST-1 treatment also severely impeded protein synthesis, specifically soluble ovarian protein content (down by 20% and 24%, respectively) and soluble sugar content (down by 42% and 35%, respectively), which led to stunted growth and reduced body weight in adult females. We thereby speculate that downregulated SfEST-1 expression may be one molecular mechanism underlying JGM-driven reproduction in S. furcifera.

The Glutathione-S-Transferase, Cytochrome P450 and Carboxyl/Cholinesterase Gene Superfamilies in Predatory Mite Metaseiulus occidentalis

Pesticide-resistant populations of the predatory mite Metaseiulus (= Typhlodromus or Galendromus) occidentalis (Arthropoda: Chelicerata: Acari: Phytoseiidae) have been used in the biological control of pest mites such as phytophagous Tetranychus urticae. However, the pesticide resistance mechanisms in M. occidentalis remain largely unknown. In other arthropods, members of the glutathione-S-transferase (GST), cytochrome P450 (CYP) and carboxyl/cholinesterase (CCE) gene superfamilies are involved in the diverse biological pathways such as the metabolism of xenobiotics (e.g. pesticides) in addition to hormonal and chemosensory processes. In the current study, we report the identification and initial characterization of 123 genes in the GST, CYP and CCE superfamilies in the recently sequenced M. occidentalis genome. The gene count represents a reduction of 35% compared to T. urticae. The distribution of genes in the GST and CCE superfamilies in M. occidentalis differs significantly from those of insects and resembles that of T. urticae. Specifically, we report the presence of the Mu class GSTs, and the J’ and J” clade CCEs that, within the Arthropoda, appear unique to Acari. Interestingly, the majority of CCEs in the J’ and J” clades contain a catalytic triad, suggesting that they are catalytically active. They likely represent two Acari-specific CCE clades that may participate in detoxification of xenobiotics. The current study of genes in these superfamilies provides preliminary insights into the potential molecular components that may be involved in pesticide metabolism as well as hormonal/chemosensory processes in the agriculturally important M. occidentalis.

Oral delivery mediated RNA interference of a carboxylesterase gene results in reduced resistance to organophosphorus insecticides in the cotton Aphid, Aphis gossypii Glover

Background

RNA interference (RNAi) is an effective tool to examine the function of individual genes. Carboxylesterases (CarE, EC 3.1.1.1) are known to play significant roles in the metabolism of xenobiotic compounds in many insect species. Previous studies in our laboratory found that CarE expression was up-regulated in Aphis gossypii (Glover) (Hemiptera: Aphididae) adults of both omethoate and malathion resistant strains, indicating the potential involvement of CarE in organophosphorus (OP) insecticide resistance. Functional analysis (RNAi) is therefore warranted to investigate the role of CarE in A. gossypii to OPs resistance.

Result

CarE expression in omethoate resistant individuals of Aphis gossypii was dramatically suppressed following ingestion of dsRNA-CarE. The highest knockdown efficiency (33%) was observed at 72 h after feeding when dsRNA-CarE concentration was 100 ng/µL. The CarE activities from the CarE knockdown aphids were consistent with the correspondingly significant reduction in CarE expression. The CarE activity in the individuals of control aphids was concentrated in the range of 650–900 mOD/per/min, while in the individuals of dsRNA-CarE-fed aphids, the CarE activity was concentrated in the range of 500–800 mOD/per/min. In vitro inhibition experiments also demonstrated that total CarE activity in the CarE knockdown aphids decreased significantly as compared to control aphids. Bioassay results of aphids fed dsRNA-CarE indicated that suppression of CarE expression increased susceptibility to omethoate in individuals of the resistant aphid strains.

Conclusion

The results of this study not only suggest that ingestion of dsRNA through artificial diet could be exploited for functional genomic studies in cotton aphids, but also indicate that CarE can be considered as a major target of organophosphorus insecticide (OPs) resistance in A. gossypii. Further, our results suggest that the CarE would be a propitious target for OPs resistant aphid control, and insect-resistant transgenic plants may be obtained through plant RNAi-mediated silencing of insect CarE expression.

Purification and characterization of a specific late-larval esterase from two species of the Drosophila repleta group: contributions to understand its evolution

Background

After duplication, one copy of an original gene can become redundant and decay toward a pseudogene status or functionally diverge. Here, we performed the purification and biochemical characterization of EST-4 (a late larval β-esterase) from two Drosophila repleta group species, Drosophila mulleri and Drosophila arizonae, in order to establish comparative parameters between these enzymes in these species and to contribute to better understand their evolution.

Results

In D. mulleri, EST-4 had an optimal activity in temperatures ranging from 40° to 45°C and at pH 7.5, maintaining stability in alkaline pH (8.0 to 10.0). It was classified as serine esterase as its activity was inhibited by PMSF. No ion negatively modulated EST-4 activity, and iron had the most positive modulating effect. In D. arizonae, it showed similar optimum temperature (40°C), pH (8.0), and was also classified as a serine esterase, but the enzymatic stability was maintained in an acidic pH (5.5 to 6.5). Fe+2 had the opposite effect found in D. mulleri, that is, negative modulation. Al+3 almost totally inhibited the EST-4 activity, and Na+ and Cu+2 had a positive modulation effect. Kinetic studies, using ρ-nitrophenyl acetate as substrate, showed that EST-4 from D. mulleri had higher affinity, while in D. arizonae, it showed higher V max and catalytic efficiency in optimal reaction conditions.

Conclusions

EST-4 from D. mulleri and D. arizonae are very closely related and still maintain several similar features; however, they show some degree of differentiation. Considering that EST-4 from D. mulleri has more conspicuous gel mobility difference among all EST-4 studied so far and a lower catalytic efficiency was observed here, we proposed that after duplication, this new copy of the original gene became redundant and started to decay toward a pseudogene status in this species, which probably is not occurring in D. arizonae.

RNA interference revealed the roles of two carboxylesterase genes in insecticide detoxification in Locusta migratoria

Carboxylesterases (CarEs) play key roles in metabolism of specific hormones and detoxification of dietary and environmental xenobiotics in insects. We sequenced and characterized CarE cDNAs putatively derived from two different genes named LmCesA1 and LmCesA2 from the migratory locust, Locusta migratoria, one of the most important agricultural pests in the world. The full-length cDNAs of LmCesA1 (1892 bp) and LmCesA2 (1643 bp) encode 543 and 501 amino acid residues, respectively. The two deduced CarEs share a characteristic α/β-hydrolase structure, including a catalytic triad composed of Ser-Glu (Asp)-His and a consensus sequence GQSAG, which suggests that both CarEs are biologically active. Phylogenetic analysis grouped both LmCesA1 and LmCesA2 into clade A which has been suggested to be involved in dietary detoxification. Both transcripts were highly expressed in all the nymphal and adult stages, but only slightly expressed in eggs. Analyses of tissue-dependent expression and in situ hybridization revealed that both transcripts were primarily expressed in gastric caeca. RNA interference (RNAi) of LmCesA1 and LmCesA2 followed by a topical application of carbaryl or deltamethrin did not lead to a significantly increased mortality with either insecticide. However, RNAi of LmCesA1 and LmCesA2 increased insect mortalities by 20.9% and 14.5%, respectively, when chlorpyrifos was applied. These results suggest that these genes might not play a significant role in detoxification of carbaryl and deltamethrin but are most likely to be involved in detoxification of chlorpyrifos in L. migratoria.

Candidate chemosensory genes in the Stemborer Sesamia nonagrioides

The stemborer Sesamia nonagrioides is an important pest of maize in the Mediterranean Basin. Like other moths, this noctuid uses its chemosensory system to efficiently interact with its environment. However, very little is known on the molecular mechanisms that underlie chemosensation in this species. Here, we used next-generation sequencing (454 and Illumina) on different tissues from adult and larvae, including chemosensory organs and female ovipositors, to describe the chemosensory transcriptome of S. nonagrioides and identify key molecular components of the pheromone production and detection systems. We identified a total of 68 candidate chemosensory genes in this species, including 31 candidate binding-proteins and 23 chemosensory receptors. In particular, we retrieved the three co-receptors Orco, IR25a and IR8a necessary for chemosensory receptor functioning. Focusing on the pheromonal communication system, we identified a new pheromone-binding protein in this species, four candidate pheromone receptors and 12 carboxylesterases as candidate acetate degrading enzymes. In addition, we identified enzymes putatively involved in S. nonagrioides pheromone biosynthesis, including a ∆11-desaturase and different acetyltransferases and reductases. RNAseq analyses and RT-PCR were combined to profile gene expression in different tissues. This study constitutes the first large scale description of chemosensory genes in S. nonagrioides.

Functional fat body proteomics and gene targeting reveal in vivo functions of Drosophila melanogaster α-Esterase-7

Carboxylesterases constitute a large enzyme family in insects, which is involved in diverse functions such as xenobiotic detoxification, lipid metabolism and reproduction. Phylogenetically, many insect carboxylesterases are represented by multienzyme clades, which are encoded by evolutionarily ancient gene clusters such as the α-Esterase cluster. Much in contrast to the vital importance attributed to carboxylesterases in general, the in vivo function of individual α-Esterase genes is largely unknown. This study employs a functional proteomics approach to identify esterolytic enzymes of the vinegar fly Drosophila melanogaster fat body. One of the fat body carboxylesterases, α-Esterase-7, was selected for mutational analysis by gene targeting to generate a deletion mutant fly. Phenotypic characterization of α-Esterase-7 null mutants and transgenic flies, which overexpress a chimeric α-Esterase-7:EGFP gene, reveals important functions of α-Esterase-7 in insecticide tolerance, lipid metabolism and lifespan control. The presented first deletion mutant of any α-Esterase in the model insect D. melanogaster generated by gene targeting not only provides experimental evidence for the endogenous functions of this gene family. It also offers an entry point for in vivo structure-function analyses of α-Esterase-7, which is of central importance for naturally occurring insecticide resistance in wild populations of various dipteran insect species.

Carboxylesterases from the seeds of an underutilized legume, Mucuna pruriens; isolation, purification and characterization

Two carboxylesterases (ME-III and ME-IV) have been purified to apparent homogeneity from the seeds of Mucuna pruriens employing ammonium sulfate fractionation, cation exchange chromatography on CM-cellulose, gel-permeation chromatography on Sephadex G-100 and preparative PAGE. The homogeneity of the purified preparations was confirmed by polyacrylamide gel electrophoresis (PAGE), gel-electrofocussing and SDS-PAGE. The molecular weights determined by gel-permeation chromatography on Sephadex G-200 were 20.89 kDa (ME-III) and 31.62 kDa (ME-IV). The molecular weights determined by SDS-PAGE both in the presence and absence of 2-mercaptoethanol were 21 kDa (ME-III) and 30.2 kDa (ME-IV) respectively, suggesting a monomeric structure for both the enzymes. The enzymes were found to have Stokes radius of 2.4 nm (ME-III) and 2.7 nm (ME-IV). The isoelectric pH values of the enzymes, ME-III and ME-IV, were 6.8 and 7.4, respectively. ME-III and ME-IV were classified as carboxylesterases employing PAGE in conjunction with substrate and inhibitor specificity. The K(m) of ME-III and ME-IV with 1-naphthyl acetate as substrate was 0.1 and 0.166 mM while with 1-naphthyl propionate as substrate the K(m) was 0.052 and 0.0454 mM, respectively. As the carbon chain length of the acyl group increased, the affinity of the substrate to the enzyme increased indicating hydrophobic nature of the acyl group binding site. The enzymes exhibited an optimum temperature of 45°C (ME-III) and 37°C (ME-IV), an optimum pH of 7.0 (ME-III) and 7.5 (ME-IV) and both the enzymes (ME-III and ME-IV) were stable up to 120 min at 35°C. Both the enzymes were inhibited by organophosphates (dichlorvos and phosphamidon), but resistant towards carbamates (carbaryl and eserine sulfate) and sulphydryl inhibitors (p-chloromercuricbenzoate, PCMB).

Biochemical characterisation of MdCXE1, a carboxylesterase from apple that is expressed during fruit ripening

Esters are an important component of apple (Malus×domestica) flavour. Their biosynthesis increases in response to the ripening hormone ethylene, but their metabolism by carboxylesterases (CXEs) is poorly understood. We have identified 16 members of the CXE multigene family from the commercial apple cultivar, 'Royal Gala', that contain all the conserved features associated with CXE members of the α/β hydrolase fold superfamily. The expression of two genes, MdCXE1 and MdCXE16 was characterised in an apple fruit development series and in a transgenic line of 'Royal Gala' (AO3) that is unable to synthesise ethylene in fruit. In wild-type MdCXE1 is expressed at low levels during early stages of fruit development, rising to a peak of expression in apple fruit at harvest maturity. It is not significantly up-regulated by ethylene in the skin of AO3 fruit. MdCXE16 is expressed constitutively in wild-type throughout fruit development, and is up-regulated by ethylene in skin of AO3 fruit. Semi-purified recombinant MdCXE1 was able to hydrolyse a range of 4-methyl umbelliferyl ester substrates that included those containing acyl moieties that are found in esters produced by apple fruit. Kinetic characterisation of MdCXE1 revealed that the enzyme could be inhibited by organophosphates and that its ability to hydrolyse esters showed increasing affinity (K(m)) but decreasing turnover (k(cat)) as substrate acyl carbon length increases from C2 to C16. Our results suggest that MdCXE1 may have an impact on apple flavour through its ability to hydrolyse relevant flavour esters in ripe apple fruit.

Two single mutations commonly cause qualitative change of nonspecific carboxylesterases in insects

Carboxylesterases provide key mechanisms of resistance to insecticides, particularly organophosphates (OPs), in insects. One resistance mechanism is a qualitative change in the properties of a carboxylesterase. Two mutant forms, G151D and W271L, have been observed, mostly in dipteran species, to affect substrate specificity of enzymes. But whether these two single mutations can commonly change character of insect carboxylesterases is unknown. In our study carboxylesterase genes from seven insects distributed among four orders were cloned, mutated at position 151 or 271 and expressed in Escherichia coli. The kinetics of the purified recombinant proteins was examined towards an artificial carboxylester and two OP insecticides. The G/A151D and W271L mutation significantly reduced carboxylesterase activity in 87.5% and 100% cases, respectively, and at the same time conferred OP hydrolase activities in 62.5% and 87.5% cases, respectively. Thus, the change at position 271 is more effective to influence substrate specificity than that at position 151. These results may suggest that these two mutations have the potential to cause insecticide resistance broadly in insects.

Characterization of an antennal carboxylesterase from the pest moth Spodoptera littoralis degrading a host plant odorant

BACKGROUND

Carboxyl/cholinesterases (CCEs) are highly diversified in insects. These enzymes have a broad range of proposed functions, in neuro/developmental processes, dietary detoxification, insecticide resistance or hormone/pheromone degradation. As few functional data are available on purified or recombinant CCEs, the physiological role of most of these enzymes is unknown. Concerning their role in olfaction, only two CCEs able to metabolize sex pheromones have been functionally characterized in insects. These enzymes are only expressed in the male antennae, and secreted into the lumen of the pheromone-sensitive sensilla. CCEs able to hydrolyze other odorants than sex pheromones, such as plant volatiles, have not been identified.

METHODOLOGY

In Spodoptera littoralis, a major crop pest, a diversity of antennal CCEs has been previously identified. We have employed here a combination of molecular biology, biochemistry and electrophysiology approaches to functionally characterize an intracellular CCE, SlCXE10, whose predominant expression in the olfactory sensilla suggested a role in olfaction. A recombinant protein was produced using the baculovirus system and we tested its catabolic properties towards a plant volatile and the sex pheromone components.

CONCLUSION

We showed that SlCXE10 could efficiently hydrolyze a green leaf volatile and to a lesser extent the sex pheromone components. The transcript level in male antennae was also strongly induced by exposure to this plant odorant. In antennae, SlCXE10 expression was associated with sensilla responding to the sex pheromones and to plant odours. These results suggest that a CCE-based intracellular metabolism of odorants could occur in insect antennae, in addition to the extracellular metabolism occurring within the sensillar lumen. This is the first functional characterization of an Odorant-Degrading Enzyme active towards a host plant volatile.

Genomic analysis of the carboxylesterases: identification and classification of novel forms

Large species differences in the expression of carboxylesterases (CE) have been described, but the interrelationships of CEs across species are not well characterized. In the current analyses, sequences with genomic structures similar to human CEs were found in piscine, avian, and mammalian genomes. Analyses of these genes suggest that four CE groups existed prior to mammalian divergence, with another form occurring after eutherian-marsupial divergence, yielding five distinct mammalian CE groups. The CE1 and CE2 groupings appear to have undergone extensive gene duplication in species with herbivorous and omnivorous diets underscoring the potential importance of these two groups in xenobiotic metabolism. However, CE3, CE4, and CE5 have remained at one gene per species in almost all observed cases. In avian and piscine genomes, only two CE groupings each were observed in the currently available sequence data. Finally, this study presents considerations for a broader phylogenetic-based nomenclature that could encompass other serine hydrolases in addition to the CEs.

Comparative analysis of detoxification enzymes in Acyrthosiphon pisum and Myzus persicae

Herbivorous insects use detoxification enzymes, including cytochrome P450 monooxygenases, glutathione S-transferases, and carboxy/cholinesterases, to metabolize otherwise deleterious plant secondary metabolites. Whereas Acyrthosiphon pisum (pea aphid) feeds almost exclusively from the Fabaceae, Myzus persicae (green peach aphid) feeds from hundreds of species in more than forty plant families. Therefore, M. persicae as a species would be exposed to a greater diversity of plant secondary metabolites than A. pisum, and has been predicted to require a larger complement of detoxification enzymes. A comparison of M. persicae cDNA and A. pisum genomic sequences is partially consistent with this hypothesis. There is evidence of at least 40% more cytochrome P450 genes in M. persicae than in A. pisum. In contrast, no major differences were found between the two species in the numbers of glutathione S-transferases, and carboxy/cholinesterases. However, given the incomplete M. persicae cDNA data set, the number of identified detoxification genes in this species is likely to be an underestimate.

A diversity of putative carboxylesterases are expressed in the antennae of the noctuid moth Spodoptera littoralis

Recent studies have suggested that pheromone-degrading enzymes belonging to the carboxylesterase family could play a role in the dynamics of the olfactory response to acetate sex pheromones in insects. Bioinformatic analyses of a male antennal expressed sequence tag library allowed the identification of 19 putative esterase genes expressed in the antennae of the moth Spodoptera littoralis. Phylogenetic analysis revealed that these genes belong to different insect esterase clades, defined by their putative cellular localization and substrate preferences. Interestingly, two of the 19 genes appeared to be antennal specific, suggesting a specific role in olfactory processing. This high esterase diversity suggested that the antennae are the location for intense esterase-based metabolism, against potentially a large range of exogenous and endogenous molecules.

Birth and death of genes and functions in the beta-esterase cluster of Drosophila

Here we analyze the molecular evolution of the β-esterase gene cluster in the Drosophila genus using the recently released genome sequences of 12 Drosophila species. Molecular evolution in this small cluster is noteworthy because it contains contrasting examples of the types and stages of loss of gene function. Specifically, missing orthologs, pseudogenes, and null alleles are all inferred. Phylogenetic analyses also suggest a minimum of 9 gene gain–loss events; however, the exact number and age of these events is confounded by interparalog recombination. A previous enigma, in which allozyme loci were mapped to β-esterase genes that lacked catalytically essential amino acids, was resolved through the identification of neighbouring genes that contain the canonical catalytic residues and thus presumably encode the mapped allozymes. The originally identified genes are evolving with selective constraint, suggesting that they have a “noncatalytic” function. Curiously, 3 of the 4 paralogous β-esterase genes in the D. ananassae genome sequence have single inactivating (frame-shift or nonsense) mutations. To determine whether these putatively inactivating mutations were fixed, we sequenced other D. ananassae alleles of these four loci. We did not find any of the 3 inactivating mutations of the sequenced strain in 12 other strains; however, other inactivating mutations were observed in the same 3 genes. This is reminiscent of the high frequency of null alleles observed in one of the β-esterase genes (Est7/EstP) of D. melanogaster.

Applications of carboxylesterase activity in environmental monitoring and toxicity identification evaluations (TIEs)

This review has examined a number of issues surrounding the use of carboxylesterase activity in environmental monitoring. It is clear that carboxylesterases are important enzymes that deserve increased study. This class of enzymes appears to have promise for employment in environmental monitoring with a number of organisms and testing scenarios, and it is appropriate for inclusion in standard monitoring assays. Given the ease of most activity assays, it is logical to report carboxylesterase activity levels as well as other esterases (e.g., acetylcholinesterase). Although it is still unclear as to whether acetylcholinesterase or carboxylesterase is the most "appropriate" biomarker, there are sufficient data to suggest that at the very least further studies should be performed with carboxylesterases. Most likely, data will show that it is optimal to measure activity for both enzymes whenever possible. Acetylcholinesterase has the distinct advantage of a clear biological function, whereas the endogenous role of carboxylesterases is still unclear. However, a combination of activity measurements for the two enzyme systems will provide a much more detailed picture of organism health and insecticide exposure. The main outstanding issues are the choice of substrate for activity assays and which tissues/organisms are most appropriate for monitoring studies. Substrate choice is very important, because carboxylesterase activity consists of multiple isozymes that most likely fluctuate on an organism- and tissue-specific basis. It is therefore difficult to compare work in one organism with a specific substrate with work performed in a different organism with a different substrate. An attempt should therefore be made to standardize the method. The most logical choice is PNPA (p-nitrophenyl acetate), as this substrate is commercially available, requires inexpensive optics for assay measurements, and has been used extensively in the literature. However, none of these beneficial properties indicates that the substrate is an appropriate surrogate for a specific compound, e.g., pyrethroid-hydrolyzing activity. It will most likely be necessary to have more specific surrogate substrates for use in assays that require information on the ability to detoxify/hydrolyze specific environmental contaminants. The use of carboxylesterase activity in TIE protocols appears to have excellent promise, but there are further technical issues that should be addressed to increase the utility of the method. The main concerns include the large amount of nonspecific protein added to the testing system, which can lead to undesirable side effects including nonspecific reductions in observed toxicity, decrease in dissolved oxygen content, and organism growth. It is probable that these issues can be resolved with further assay development. The ideal solution would be to have a commercial recombinant carboxylesterase that possessed elevated pyrethroid-hydrolysis activity and which was readily available, homogeneous, and inexpensive. The availability of such an enzyme would address nearly all the current method shortcomings. Such a preparation would be extremely useful for the aquatic toxicology community. Further work should focus on screening available esterases for stability, cost, and activity on pyrethroids, with specific focus on esterases capable of distinguishing type I from type II pyrethroids. It would also be beneficial to identify esterases that are not sensitive to OP insecticides. Many esterases and lipases are available as sets to test chemical reactions for green chemistry, enabling large-scale screening. Other potential approaches to increase the utility of the enzyme include derivatization with polyethylene glycol (PEG) or cyanuric acid chloride to increase stability and reduce microbial degradation. It is also possible that the enzyme could be formulated in a sol gel preparation to increase stability. It is likely that the use of carboxylesterase addition will increase for applications in sediment TIEs. Carboxylesterases are an interesting and useful enzyme family that deserves further study for applications in environmental monitoring as well as to increase our understanding of the fundamental biological role(s) of these enzymes. There are, of course, other enzymes that show high esterase activity on pyrethroids but are not technically carboxylesterases in the alpha/beta-hydrolase fold protein family. These enzymes should also be examined for use in TIE protocols and "esterase" arrays as well as for general applications in environmental monitoring. One can envision the creation of a standardized screen of enzymes with esterase activity to (1) identify environmental contaminants, (2) estimate the potential toxic effects of new compounds on a range of organisms, and (3) monitor organism exposure to agrochemicals (and potentially other contaminants). This approach would provide a multibiomarker integrative assessment of esterase-inhibiting potential of a compound or mixture. In conclusion, much is still unknown about this enzyme family, indicating that this area is still wide open to researchers interested in the applications of carboxylesterase activity as well as basic biological questions into the nature of enzyme activity and the endogenous role of the enzyme.

Biochemical and genetic polymorphisms for carboxylesterase and acetylesterase in grape clones of Vitis vinifera L. (Vitaceae) cultivars

Native polyacrylamide gel electrophoresis (PAGE) was employed to show the highest number of esterase loci and to detect alpha- and beta-esterase polymorphisms in leaf buds of Vitis vinifera cultivars. A total of 16 esterase isozymes were detected in leaf buds from 235 plants including Italia, Rubi, Benitaka, and Brasil cultivars. Biochemical characterization of the grape esterases using ester substrates revealed alpha-, beta-, and alpha/beta-esterases with inhibitor tests distinguishing both carboxylesterases (EST-2, EST-3, EST-5, EST-6, EST-7, EST-8, EST-9, EST-10, and EST-16 isozymes) and acetylesterases (EST-4, EST-11, EST-12, EST-13, EST-14, EST-15 isozymes). No allele variation for alpha-, beta-, and alpha/beta-esterases was detected; however, EST-3 alpha-carboxylesterase was absent in 61.7% of vines, and EST-4 alpha/beta-acetylesterase was absent in one vine of Rubi cv. Null EST-3 carboxylesterase phenotype (61.7%) cannot be explained in this article, but the high genetic polymorphism in four V. vinifera clones is a positive aspect for genetic selection and development of new clones with different characteristics.

Role of a Carboxylesterase in Herbicide Bioactivation in Arabidopsis thaliana

Arabidopsis thaliana contains multiple carboxyesterases (AtCXEs) with activities toward xenobiotics, including herbicide esters that are activated to their phytotoxic acids upon hydrolysis. On the basis of their susceptibility to inhibition by organophosphates, these AtCXEs are all serine hydrolases. Using a trifunctional probe bearing a fluorophosphonate together with biotin and rhodamine to facilitate detection and recovery, four dominant serine hydrolases were identified in the proteome of Arabidopsis. Using a combination of protein purification, capture with the trifunctional probe and proteomics, one of these hydrolases, AtCXE12, was shown to be the major carboxyesterase responsible for hydrolyzing the pro-herbicide methyl-2,4-dichlorophenoxyacetate (2,4-D-methyl) to the phytotoxic acid 2,4-dichlorophenoxyacetic acid. Recombinant expression of the other identified hydrolases showed that AtCXE12 was unique in hydrolyzing 2,4-D-methyl. To determine the importance of AtCXE12 in herbicide metabolism and efficacy, the respective tDNA knock-out (atcxe12) plants were characterized and shown to lack expression of AtCXE12 and have greatly reduced levels of 2,4-D-methyl-hydrolyzing activity. Young atcxe12 seedlings were less sensitive than wild type plants to 2,4-D-methyl, confirming a role for the enzyme in herbicide bioactivation in Arabidopsis.

Do mosquitoes acquire organophosphate resistance by functional changes in carboxylesterases?

Carboxylesterase-based metabolic resistance to organophosphates (OPs) in insects has been shown to originate either from mutations in esterase-encoding sequences or from amplification of esterase genes. This study aimed to test the hypothesis that mosquitoes can acquire OP resistance by functional changes in carboxylesterases. Mutations were introduced into the esterase B1 of mosquito Culex pipiens by site-directed mutagenesis at positions 110 and 224. Three single mutants (G110D, W224L, and W224S) and two double mutants (G110D/W224L and G110D/W224S) were expressed and purified. All five mutants lost native carboxylesterase activity. Mutation W224L converted esterase B1 to an OP hydrolase and increased its malathion carboxylesterase activity. No obvious OP hydrolysis was observed by G110D or W224S. Our data strongly support our hypothesis and suggest that mutation W224L might occur in natural populations of mosquitoes. Sequence comparison shows that the site 224 is especially highly conserved among various insect carboxylesterases. This leads to another hypothesis: that the position 224 plays a key role in insect carboxylesterases' switching from their native physiological functions to other functional niches under selection pressure exerted by insecticides.

Molecular population genetics of the alpha-esterase5 gene locus in original and colonized populations of Drosophila buzzatii and its sibling Drosophila koepferae

Several studies have suggested that esterase-2 (EST-2) may be the target of natural selection in the cactophilic fly Drosophila buzzatii. In this work, we analyzed nucleotide variation in a fragment of alpha-esterase5 (alphaE5), the gene encoding EST-2, in original (Argentinian) and colonized (Australian) populations of D. buzzatii and in its sibling D. koepferae. Estimates of nucleotide heterozygosity in D. buzzatii were similar in Australia and Argentina, although we detected a loss of singletons in colonized populations, suggesting a moderate founder effect. Interspecific comparisons revealed that D. buzzatii was more polymorphic for nonsynonymous variation, whereas D. koepferae was more variable for synonymous and noncoding sites. The two major chromosomal arrangements (2st and 2j) in D. buzzatii displayed similar levels of nucleotide variation, whereas 2jz3 was monomorphic. The sequenced region allowed the discrimination of a greater number of EST-2 protein variants in the Australian sample than in the Argentinean sample. In D. koepferae, nucleotide variation in alphaE5 does not depart from neutral expectations, although tests of population structure were significant for silent variation. In contrast, D. buzzatii has probably undergone a recent population expansion in its South American range. In addition, the McDonald and Kreitman test revealed an excess of nonsynonymous polymorphism in both original and colonized populations of this species.

Baculovirus expression of BmAChE3, a cDNA encoding an acetylcholinesterase of Boophilus microplus (Acari: Ixodidae)

The complete cDNA sequence encoding a Boophilus microplus (Canestrini) (Acari: Ixodidae) acetylcholinesterase (AChE3) was expressed in the baculovirus system. The recombinant AChE3 protein (rBmAChE3) was secreted as a soluble form into the cell culture medium and was identified as a functional AChE by substrate specificity and by inhibition with the AChE-specific inhibitors eserine sulfate and BW284c51. Inhibition kinetics of rBmAChE3, in the presence of the organophosphate paraoxon, revealed sensitivity comparable with that of adult, organophosphate-susceptible neural AChE. To our knowledge, this is the first report of the cloning and successful expression of a functional ixodid AChE.