Modulation of Juvenile Hormone Esterase Gene Expression Against Development of Plutella xylostella (Lepidoptera: Plutellidae)

Mechanisms underlying the effects of low concentrations of chlorantraniliprole on development and reproduction of the fall armyworm, Spodoptera frugiperda

It is well known that sublethal dose of insecticides induces life history trait changes of both target and non-target insect species, however, the underlying mechanisms remain not well understood. In this study, the effects of low concentrations of the anthranilic diamide insecticide chlorantraniliprole on the development and reproduction of the fall armyworm (FAW), Spodoptera frugiperda, were evaluated, and the underlying mechanisms were explored. The results showed that exposure of FAW to LC₁₀ and LC₃₀ chlorantraniliprole prolonged the larvae duration, decreased the mean weight of the larvae and pupae, and lowered the pupation rate as well as emergence rate. The fecundity of female adults was also negatively affected by treatment with low concentrations of chlorantraniliprole. Consistently, we found that exposure of FAW to LC₃₀ chlorantraniliprole downregulated the mRNA expression of juvenile hormone (JH) esterase (SfJHE), leading to the increase of JH titer in larvae. We also found that treatment with low concentrations of chlorantraniliprole suppressed the expression of ribosomal protein S6 kinase1 (SfS6K1) in female adults, resulting in the downregulation of the gene encoding vitellogenin (SfVg). These results provided insights into the mechanisms underlying the effects of low concentrations of insecticides on insect pests, and had applied implications for the control of FAW.

Novel miR-108 and miR-234 target juvenile hormone esterase to regulate the response of Plutella xylostella to Cry1Ac protoxin

Insect hormones, such as juvenile hormone (JH), precisely regulate insect life-history traits. The regulation of JH is tightly associated with the tolerance or resistance to Bacillus thuringiensis (Bt). JH esterase (JHE) is a primary JH-specific metabolic enzyme which plays a key role in regulating JH titer. Here, we characterized a JHE gene from Plutella xylostella (PxJHE), and found it was differentially expressed in the Bt Cry1Ac resistant and susceptible strains. Suppression of PxJHE expression with RNAi increased the tolerance of P. xylostella to Cry1Ac protoxin. To investigate the regulatory mechanism of PxJHE, two target site prediction algorithms were applied to predict the putative miRNAs targeting PxJHE, and the resulting putative miRNAs were subsequently verified for their function targeting PxJHE using luciferase reporter assay and RNA immunoprecipitation. MiR-108 or miR-234 agomir delivery dramatically reduced PxJHE expression in vivo, whilst only miR-108 overexpression consequently increased the tolerance of P. xylostella larvae to Cry1Ac protoxin. By contrast, reduction of miR-108 or miR-234 dramatically increased PxJHE expression, accompanied by the decreased tolerance to Cry1Ac protoxin. Furthermore, injection of miR-108 or miR-234 led to developmental defects in P. xylostella, whilst injection of antagomir did not cause any obvious abnormal phenotypes. Our results indicated that miR-108 or miR-234 can be applied as potential molecular targets to combat P. xylostella and perhaps other lepidopteran pests, providing novel insights into miRNA-based integrated pest management.

The inhibition of ecdysone signal pathway was the key of pyriproxyfen poisoning for silkworm, Bombyx mori

Pyriproxyfen is a juvenile hormone-like pesticide. Once intake occurs, it leads to a series of poisoning characters consequences in silkworm, Bombyx mori (ID: 7091, Lepidoptera), such as non- cocooning, non-pupation, production of low-active eggs, and extended stages. However, the poisoning mechanism is still unclear. Here, silkworms were fed mulberry leaves soaked with different pyriproxyfen concentrations, and the heads were dissected for transcriptome analysis, while the hemolymph was used for determinations of ecdysone and juvenile hormone titers. As a result, after conjoint analysis of 3 feeding groups and a control group, 555 differentially expressed genes (DEGs) were obtained, which were mainly involved in hormone metabolism, glycometabolism and protein metabolism. Meanwhile, 119 genes were significantly correlated with the pyriproxyfen concentrations, and they were mainly involved in drug metabolism and glycometabolism. The ecdysone titers in several feeding groups were significantly lower than those of the control group, while juvenile hormone was not detected in all groups, including the control and feeding groups. Correspondingly, due to activation of the juvenile hormone signaling pathway by pyriproxyfen, key genes in the ecdysone synthesis pathway were downregulated, and a large number of downstream genes were up- or downregulated. In addition, nearly all genes in the detoxification pathway were upregulated. These results suggested that, affected by the juvenile hormone signaling pathway, ecdysone titers decreased and further affected a series of downstream processes, and this was the key reason for pyriproxyfen poisoning in silkworm, B. mori, which could lay a foundation for the study of pyriproxyfen resistance in silkworm.

Enhanced Degradation of Juvenile Hormone Promotes Reproductive Diapause in the Predatory Ladybeetle Coccinella Septempunctata

Improved knowledge on the regulation of reproductive diapause in Coccinella septempunctata, an important predator of aphids, is crucial for improving shelf-life and mass production of the ladybeetles. In many insects, the absence of juvenile hormone (JH) is a central regulator of reproductive diapause. JH is principally degraded by JH esterase (JHE) and JH epoxide hydrolase (JHEH). Previous studies have shown that genes encoding these enzymes were upregulated in early diapause of C. septempunctata, but whether increased JH degradation contributes to the reduction of JH levels and facilitates reproductive diapause remains unknown. Here, we investigate the role of JH and JH degradation genes during reproductive diapause in C. septempunctata females. Applying methoprene, a JH analogue, to the diapause preparation females clearly elevated JH signaling and reversed diapause program, suggesting that a lower level of JH is critical for the induction of reproductive diapause in the ladybeetle. Full-length cDNA sequences of JHE and JHEH were cloned and characterized, and their deduced proteins contain all the conserved active domains and typical motifs as identified in other insects. The expressions of JHE and JHEH were both significantly increased in diapause preparation and remained at a high level for a period throughout diapause, and then decreased after the termination of diapause. Knocking down these JH degradation genes clearly increased the expression levels of JH-inducible genes Krüppel-homolog 1 (Kr-h1) and vitellogenin (Vg), indicating an elevated JH level. Simultaneously, silencing JH degradation genes distinctly reduced diapause-related features and promotes reproduction, indicated by accelerated ovary growth, yolk deposition, and suppressed lipid accumulation. These results indicate that the enhanced JH degradation plays a critical role in regulating reproductive diapause of C. septempunctata.

The JH-Met2-Kr-h1 pathway is involved in pyriproxyfen-induced defects of metamorphosis and silk protein synthesis in silkworms, Bombyx mori

Environmental residues of pryriproxyfen, a juvenile hormone analogue (JHA) type pesticide, may have on unintended consequences on non-target insects. However, the mechanism of pyriproxyfen action and silk protein synthesis in silkworms has not been reported. In the present study, we treated the silkworms with trace pyriproxyfen (1 × 10^-4 mg/L) and found that the silkworm larvae showed no obvious poisoning symptoms, while the development of silk glands and cocoon-forming function were both seriously damaged due to the accumulation of pyriproxyfen in posterior silk gland (PSG). The titer of the juvenile hormone (JH) was increased, whereas the content of 20-hydroxyecdysone (20E) was reduced in pyriproxyfen-exposed hemolymph. Met2 is a component of the JH receptor complex and JH can promote its phosphorylation. We found Met2 and SRC were up-regulated in the larval stage after pyriproxyfen exposure, the JH-Met2/SRC complex led to the up-regulation of downstream genes Kr-h1, and Dimm, and then specifically inhibited the transcription of Fib-H. Meanwhile, the transcription of ecdysone inducible transcription factor Br-C Z4 was also inhibited by pyriproxyfen and resulted in the defects of metamorphosis. In conclusion, the trace pyriproxyfen could affect the metamorphosis and silk protein synthesis through the Met2-mediated pathway. Our study provided new evidence that Met2 might be a potential target gene of JHA in Lepidoptera.

Molecular characterization and enzyme inhibition studies of NADP+- farnesol dehydrogenase from diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Juvenile hormone III (JH III) plays an important role in insect reproduction, development, and behavior. The second branch of JH III production includes oxidation of farnesol to farnesal by farnesol dehydrogenase. This study reported the identification and characterization of Plutella xylostella farnesol dehydrogenase (PxFoLDH). Our results showed that PxFoLDH belongs to the short-chain dehydrogenase/reductase superfamily, consisting of a single domain with a structurally conserved Rossman fold, an NAD(P) (H)-binding region and a structurally diverse C-terminal region. The purified enzyme displayed maximum activity at 55$\ $°C with pH 9.5 and was stable in the temperature below 70$\ ^\circ $C. PxFoLDH was determined to be a monomer with a relative molecular weight of 27 kDa and highly specific for trans, trans-farnesol, and NADP+. Among analog inhibitors tested, farnesyl acetate was the most effective inhibitor with the lowest Ki value of 0.02 µm. Our findings showed this purified enzyme may represent as NADP+-farnesol dehydrogenase.

Regulation of Juvenile Hormone on Summer Diapause of Geleruca daurica and Its Pathway Analysis

Simple Summary

Diapause is an arrestment state in development, and plays an important role in life history in insects. It has been thought that a lack in juvenile hormone (JH) results in reproductive diapause occurring at the adult stage. However, we do not fully know about the underlying molecular mechanism. In this study, we proved that the topical application of a JH analog methoprene caused the changes at the transcriptional levels of a great number of genes, inhibited lipid accumulation, and finally delayed the adults entering diapause. Therefore, JH signaling plays an important role in regulating reproductive diapause of G. daurica, a new pest with great outbreaks in Inner Mongolia.

Abstract

Juvenile hormone (JH) signaling plays an important role in regulation of reproductive diapause in insects. However, we have little understanding of the effect of JH on gene expression at the transcriptome level in diapause. Galeruca daurica is a new pest in the Inner Mongolia grasslands with obligatory summer diapause in the adult stage. Topical application of a JH analog methoprene at the pre-diapause stage delayed the adults entering diapause and inhibited lipid accumulation whereas it did not during diapause. Using Illumina sequencing technology and bioinformatics tools, 54 and 138 differentially expressed genes (DEGs) were detected at 1 and 2 d after treatment, respectively. The KEGG analysis showed that the DEGs were mainly enriched in the metabolism pathways. qRT-PCR analysis indicated that methoprene promoted the expression of genes encoding vitellogenin, fork head transcription factor and Krüppel homolog 1, whereas suppressed the expression of genes encoding juvenile hormone-binding protein, juvenile hormone esterase, juvenile hormone acid methyltransferase, juvenile hormone epoxide hydrolase and fatty acid synthase 2. These results indicate that JH signaling plays an important role in regulating reproductive diapause of G. daurica.

Transcriptomics-Based Approach Identifies Spinosad-Associated Targets in the Colorado Potato Beetle, Leptinotarsa decemlineata

Simple Summary

The Colorado potato beetle Leptinotarsa decemlineata is a potato pest that can cause substantial damages to potato crops worldwide. Multiple approaches have been leveraged to control this pest including the use of a variety of insecticides. Resistance to different insecticides aimed at controlling this insect has been reported and much work has been conducted in recent years to elucidate the underlying molecular changes associated with insecticide resistance in L. decemlineata. However, information is sparse regarding the molecular impact associated with spinosad treatment in this insect pest. The current study thus explores transcriptional changes associated with spinosad response in L. decemlineata exposed to this compound using high-throughput sequencing. Results presented show multiple transcripts of interest that exhibit differential expression in spinosad-treated L. decemlineata and provide a preliminary footprint of transcripts affected by this insecticide in this potato pest. Select targets identified in this signature should be further explored in follow-up studies to better characterize their contribution, if any, in the process of spinosad resistance.

Abstract

The Colorado potato beetle Leptinotarsa decemlineata is an insect pest that threatens potato crops globally. The primary method to control its damage on potato plants is the use of insecticides, including imidacloprid, chlorantraniliprole and spinosad. However, insecticide resistance has been frequently observed in Colorado potato beetles. The molecular targets and the basis of resistance to imidacloprid and chlorantraniliprole have both been previously quantified. This work was undertaken with the overarching goal of better characterizing the molecular changes associated with spinosad exposure in this insect pest. Next-generation sequencing was conducted to identify transcripts that were differentially expressed between Colorado potato beetles exposed to spinosad versus control insects. Results showed several transcripts that exhibit different expression levels between the two conditions, including ones coding for venom carboxylesterase-6, chitinase 10, juvenile hormone esterase and multidrug resistance-associated protein 4. In addition, several microRNAs, such as miR-12-3p and miR-750-3p, were also modulated in the investigated conditions. Overall, this work reveals a molecular footprint underlying spinosad response in Colorado potato beetles and provides novel leads that could be targeted as part of RNAi-based approaches to control this insect pest.

Transcriptome Analysis and Knockdown of the Juvenile Hormone Esterase Gene Reveal Abnormal Feeding Behavior in the Sugarcane Giant Borer

The sugarcane giant borer (SGB), Telchin licus licus, is a pest that has strong economic relevance for sugarcane producers. Due to the endophytic behavior of the larva, current methods of management are inefficient. A promising biotechnological management option has been proposed based on RNA interference (RNAi), a process that uses molecules of double-stranded RNA (dsRNA) to specifically knock down essential genes and reduce insect survival. The selection of suitable target genes is often supported by omic sciences. Studies have shown that genes related to feeding adaptation processes are good candidates to be targeted by RNAi for pest management. Among those genes, esterases are highlighted because of their impact on insect development. In this study, the objective was to evaluate the transcriptome responses of the SGB’s gut in order to provide curated data of genes that could be used for pest management by RNAi in future studies. Further, we validated the function of an esterase-coding gene and its potential as a target for RNAi-based control. We sequenced the gut transcriptome of SGB larvae by Illumina HiSeq and evaluated its gene expression profiles in response to different diets (sugarcane stalk and artificial diet). We obtained differentially expressed genes (DEGs) involved in detoxification, digestion, and transport, which suggest a generalist mechanism of adaptation in SGB larvae. Among the DEGs, was identified and characterized a candidate juvenile hormone esterase gene (Tljhe). We knocked down the Tljhe gene by oral delivery of dsRNA molecules and evaluated gene expression in the gut. The survival and nutritional parameters of the larvae were measured along the developmental cycle of treated insects. We found that the gene Tljhe acts as a regulator of feeding behavior. The knockdown of Tljhe triggered a forced starvation state in late larval instars that significantly reduced the fitness of the larvae. However, the mechanism of action of this gene remains unclear, and the correlation between the expression of Tljhe and the levels of juvenile hormone (JH) metabolites in the hemolymph of the SGB must be assessed in future research.

Genomic Characterization and Expression of Juvenile Hormone Esterase-Like Carboxylesterase Genes in Pacific White Shrimp, Litopenaeus vannamei

The sesquiterpenoid methyl farnesoate (MF), a juvenile hormone (JH) analog, plays important roles in many physiological processes of crustaceans, such as morphogenesis, molting and reproduction. Juvenile hormone esterase-like (JHE-like) carboxylesterase (CXE) is a key enzyme in MF degradation, playing a significant role in regulating MF titer. However, its function is barely known in shrimp. In this study, a total of 21 JHE-like CXEs (LvCXEs) were characterized in Pacific white shrimp Litopenaeus vannamei, based on the full genome and multi-transcriptomic data. LvCXE has a conserved triplet catalytic site (Ser-Glu-His) and a characteristic GxSxG motif. Most LvCXEs were highly expressed in the hepatopancreas, which was the main site for MF degradation. LvCXEs containing a GESAG motif showed a specific expansion in the L. vannamei genome. Those GESAG-containing LvCXEs presented differential expressions at different larvae stages and different molting stages of L. vannamei, which suggested their potential functions in development and molting. Additionally, when the transcription level of CXEs was inhibited, it could lead to failed molt and death of L. vannamei. When we further detected the expression levels of the key ecdysone responsive transcription factors including LvE75, LvBr-C, LvHr3 and LvFtz-f1 after the CXE inhibitor was injected into L. vannamei, they all showed apparent down-regulation. These results suggested that the expansion of LvCXEs in the L. vannamei genome should contribute to the regulation of metamorphosis at larvae stages and frequent molting during the growth of L. vannamei.

Effect of Treatment With 3-Octylthio-1,1,1-Trifluoropropan-2-One in the Diamondback Moth (Lepidoptera: Plutellidae) to the Toxicity of Diafenthiuron, Indoxacarb, and Bacillus thuringiensis

The diamondback moth, Plutella xylostella (L.), is a worldwide insect pest of cruciferous crops. Although insecticides have long been used for its control, diamondback moth rapidly evolves resistance to almost any insecticide. In insects, juvenile hormone (JH) is critically involved in almost all biological processes. The correct activity of JH depends on the precise regulation of its titer, and juvenile hormone esterase (JHE) is the key regulator. Thus, JH and JHE have become important targets for new insecticide development. Trifluoromethyl ketones are specific JHE inhibitors, among which 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP) has the highest activity. The interaction effects between pretreatment with or combination of OTFP and the insecticides diafenthiuron, indoxacarb, and Bacillus thuringiensis (Bt) were investigated in diamondback moth larvae to determine OTFP's potential as an insecticide synergist. In third-instar larvae, both pretreatment and combination treatment with OTFP decreased or antagonized the toxicities of diafenthiuron, indoxacarb, and Bt at all set concentrations. In fourth-instar larvae, combination treatment with OTFP decreased or antagonized the toxicities of diafenthiuron and indoxacarb at all set concentrations. However, it increased or synergized the toxicity of Bt at lower concentrations despite the limited effect at higher concentrations. Our results indicated that the effect of OTFP on the toxicities of insecticides varied with the type and concentration, larval stage, and treatment method. These findings contribute to the better use of OTFP in diamondback moth control.

Molecular cloning, expression profiling, and functional analysis of a broad-complex isoform 2/3 (Br-Z2/Z3) transcription factor in the diamondback moth, Plutella xylostella (L.)

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a widespread and destructive pest of cruciferous crops. New strategies for controlling it are needed because it is rapidly developing resistance to conventional pesticides. In insects, transcription factors (TFs) including broad-complex (Br-C) are thought to be useful for insecticide development because they are able to regulate the transcription of functional genes involved in responses to external stimuli including insecticides. In the present study, we cloned and sequenced the open reading frames (ORFs) of three BTB-ZF encoding genes from the diamondback moth deposited in the National Center for Biotechnology Information (NCBI) database under accessions MG753773, MG288674, and MG753772. The lengths of these ORFs were 1,680, 1,428, and 1,647 bp, respectively. The phylogenetic analysis based on the predicted amino acid sequences of ZF domains showed that MG753773 and MG288674 belonged to Z2/Z3 and Z7 of Br-C while MG753772 belonged to Ttk types. In the agreement, the highest expression level of MG753773 occurred during the prepupal stage, MG288674 and MG753772 were expressed during all stages and peaked in the adult and egg stages, respectively. RNA interference silencing of MG753773 in the late third instar larvae significantly decreased survival and pupation of the insects. With precocene II, transcription of MG753773 increased (4×) in the fourth instar larva 24 hr later; 48 hr later the rate of prepupation and pupation was significantly higher. These findings will contribute to the development of new regulators of the growth and development for diamondback moth control.

Juvenile hormone regulates the differential expression of putative juvenile hormone esterases via methoprene-tolerant in non-diapause-destined and diapause-destined adult female beetle

Juvenile hormone (JH) plays an essential role in regulating molting, metamorphosis, reproduction, and diapause (dormancy), in many insects and crustaceans. JH esterases (JHEs) can control JH titer by regulating JH degradation. Although the biochemistry and structure of JHEs have been well studied, regulation of their expression remains unclear. We identified three putative JHEs (JHE1, JHE2, JHE3) in the cabbage beetle Colaphellus bowringi, and investigated the regulation of their expression by JH signaling in non-diapause-destined (NDD, reproductive) and diapause-destined (DD) female adults. Sequence and phylogenetic tree analyses indicate that the three putative JHEs shared conserved motifs with the JHEs of other insects and one crustacean, and were similar to Coleopteran, Dipteran, Orthopteran, Hymenopteran, and Decapodan JHEs. They were, however, less closely related to Hemipteran and Lepidopteran JHEs. JHEs were more highly expressed in NDD female adults than in DD female adults. JH analog induction in DD female adults significantly upregulated the expression of JHE1 and JHE2, but had no effect on the expression of JHE3. Knockdown of the JH candidate receptor methoprene-tolerant (Met) in NDD female adults downregulated the expression of all three JHEs. These results suggest that JHE expression is positively correlated with JH signaling, and that Met may be involved in the JH-mediated differential expression of JHE in DD and NDD adult female C. bowringi.

Multiple resistance to pirimiphos-methyl and bifenthrin in Tribolium castaneum involves the activity of lipases, esterases, and laccase2

Several recent studies have elucidated the molecular mechanisms that confer insecticide resistance on insect pests. However, little is known about multiple resistance in red flour beetle (Tribolium castaneum) at molecular level. The multiple resistance is characterized as resistance to different classes of insecticides that have different target sites, and is mediated by several enzymatic systems. In this study, we investigated the biochemical and molecular mechanisms involved in multiple resistance of T. castaneum to bifenthrin (pyrethroid [Pyr]) and pirimiphos-methyl (organophosphate [Org]). We used artificial selection, biochemical and in silico approaches including structural computational biology. After five generations of artificial selection in the presence of bifenthrin (F5Pyr) or pirimiphos-methyl (F5Org), we found high levels of multiple resistance. The hierarchical enzymatic cluster revealed a pool of esterases (E), lipases (LIPs) and laccase2 (LAC2) potentially contributing to the resistance in different ways throughout development, after one or more generations in the presence of insecticides. The enzyme-insecticide interaction network indicated that E2, E3, LIP3, and LAC2 are enzymes potentially required for multiple resistance phenotype. Kinetic analysis of esterases from F5Pyr and F5Org showed that pirimiphos-methyl and specially bifenthrin promote enzyme inhibition, indicating that esterases mediate resistance by sequestering bifenthrin and pirimiphos-methyl. Our computational data were in accordance with kinetic results, indicating that bifenthrin has higher affinity at the active site of esterase than pirimiphos-methyl. We also report the capability of these insecticides to modify the development in T. castaneum. Our study provide insights into the biochemical mechanisms employed by T. castaneum to acquire multiple resistance.