Control of juvenile hormone biosynthesis in Bombyx mori: cloning of the enzymes in the mevalonate pathway and assessment of their developmental expression in the corpora allata

Structural Characterization and Functional Analysis of Mevalonate Kinase from Tribolium castaneum (Red Flour Beetle)

Mevalonate kinase (MevK) is an important enzyme in the mevalonate pathway that catalyzes the phosphorylation of mevalonate into phosphomevalonate and is involved in juvenile hormone biosynthesis. Herein, we present a structure model of MevK from the red flour beetle Tribolium castaneum (TcMevK), which adopts a compact α/β conformation that can be divided into two parts: an N-terminal domain and a C-terminal domain. A narrow, deep cavity accommodating the substrate and cofactor was observed at the junction between the two domains of TcMevK. Computational simulation combined with site-directed mutagenesis and biochemical analyses allowed us to define the binding mode of TcMevK to cofactors and substrates. Moreover, TcMevK showed optimal enzyme activity at pH 8.0 and an optimal temperature of 40 °C for mevalonate as the substrate. The expression profiles and RNA interference of TcMevK indicated its critical role in controlling juvenile hormone biosynthesis, as well as its participation in the production of other terpenoids in T. castaneum. These findings improve our understanding of the structural and biochemical features of insect Mevk and provide a structural basis for the design of MevK inhibitors.

Structural Insights into the Substrate Binding of Farnesyl Diphosphate Synthase FPPS1 from Silkworm, Bombyx mori

Farnesyl diphosphate synthase (FPPS) is an important enzyme involved in the juvenile hormone (JH) biosynthesis pathway. Herein, we report the crystal structure of a type-I Lepidopteran FPPS from Bombyx mori (BmFPPS1) at 2.80 Å resolution. BmFPPS1 adopts an α-helix structure with a deep cavity at the center of the overall structure. Computational simulations combined with biochemical analysis allowed us to define the binding mode of BmFPPS1 to its substrates. Structural comparison revealed that BmFPPS1 adopts a structural pattern similar to that of type-II FPPS but exhibits a distinct substrate-binding site. These findings provide a structural basis for understanding substrate preferences and designing FPPS inhibitors. Furthermore, the expression profiles and RNA interference of BmFPPSs indicated that they play critical roles in the JH biosynthesis and larval-pupal metamorphosis. These findings enhance our understanding of the structural features of type-I Lepidopteran FPPS while providing direct evidence for the physiological role of BmFPPSs in silkworm development.

The genome and sex-dependent responses to temperature in the common yellow butterfly, Eurema hecabe

BACKGROUND

Lepidoptera (butterflies and moths) is one of the most geographically widespread insect orders in the world, and its species play important and diverse ecological and applied roles. Climate change is one of the biggest challenges to biodiversity this century, and lepidopterans are vulnerable to climate change. Temperature-dependent gene expression differences are of relevance under the ongoing climate crisis. However, little is known about how climate affects gene expression in lepidopterans and the ecological consequences of this, particularly with respect to genes with biased expression in one of the sexes. The common yellow butterfly, Eurema hecabe (Family Pieridae), is one of the most geographically widespread lepidopterans that can be found in Asia, Africa, and Australia. Nevertheless, what temperature-dependent effects there may be and whether the effects differ between the sexes remain largely unexplored.

RESULTS

Here, we generated high-quality genomic resources for E. hecabe along with transcriptomes from eight developmental stages. Male and female butterflies were subjected to varying temperatures to assess sex-specific gene expression responses through mRNA and microRNA transcriptomics. We find that there are more temperature-dependent sex-biased genes in females than males, including genes that are involved in a range of biologically important functions, highlighting potential ecological impacts of increased temperatures. Further, by considering available butterfly data on sex-biased gene expression in a comparative genomic framework, we find that the pattern of sex-biased gene expression identified in E. hecabe is highly species-specific, rather than conserved across butterfly species, suggesting that sex-biased gene expression responses to climate change are complex in butterflies.

CONCLUSIONS

Our study lays the foundation for further understanding of differential responses to environmental stress in a widespread lepidopteran model and demonstrates the potential complexity of sex-specific responses of lepidopterans to climate change.

RNAi-mediated CrebA silencing inhibits reproduction and immunity in Locusta migratoria manilensis

Locusta migratoria manilensis is a major agricultural pest that causes severe direct and indirect damage to several crops. Thus, to provide a theoretical foundation for pest control, the role of CrebA in the reproduction and immune regulation of L. migratoria was investigated. CrebA is a bZIP transcription factor that critically regulates intracellular protein secretion. In this study, CrebA was widely expressed in the brain, fat body, integument, midgut, and reproductive tissues of different maturity stages of adult locusts, especially in the female fat body. RNA interfering (RNAi)-mediated silencing of CrebA inhibited locusts ovarian development, and key reproduction gene expressions, Vgs, VgRs, Chico, and JHAMT were downregulated. After the locusts were injected with Micrococcus luteus or Escherichia coli, M. luteus activated lysozyme expression, while the E. coli activated both phenol oxidase cascade and lysozyme expression. Furthermore, both bacteria stimulated the upregulation of the antimicrobial peptide genes DEF3 and DEF4. However, CrebA silencing is fatal to locusts infection with E. coli, with a mortality rate of up to 96.3%, and resulted in a significant decrease in the expression of DEF3 and DEF4 and changes in the activities of phenol oxidase and lysozyme of locusts infected by bacteria. Collectively, CrebA may be involved in diverse biological processes, including reproduction and immunity. CrebA inhibited locusts reproduction by regulating JH signaling pathway and inhibits the expression of immune genes TLR6, IMD, and AMPs. These results demonstrate CrebA seems to play a crucial role in reproduction and innate immunity.

Structural characterization and functional analysis of juvenile hormone acid methyltransferase JHAMT3 from the silkworm, Bombyx mori

Juvenile hormone acid methyltransferase (JHAMT) is a rate-limiting enzyme of juvenile hormone (JH) biosynthesis in insects. It transfers the methyl group of S-adenosyl methionine to either the carboxyl group of JH acids or farnesoic acid to produce JH. Six JHAMT paralogues have been identified in the silkworm (Bombyx mori); among them, JHAMT1 and JHAMT2 display a methyltransferase activity. Here, the three-dimensional crystal structure of inactive JHAMT3 and the binary complex of JHAMT3 with its cofactor S-adenosyl-l-homocysteine were determined through X-ray crystallization. Comparative structural analysis revealed that JHAMT3 adopted a similar structural pattern to that of functional JHAMT2, which comprised one core Rossmann fold domain and one substrate-binding domain. Similar to JHAMT2, JHAMT3 underwent a conformational change at the Rossmann fold domain because of cofactor binding, which promoted ligand accommodation. However, it exhibited a relatively rigid substrate-binding pocket compared with that of JHAMT2. JHAMT3 was also highly expressed in the silk gland of fourth- and fifth-instar B. mori larvae. The results of expression profiling combined with activity analysis suggested that JHAMT3 might function as a binding protein of JH acids for the regulation of JH acid titers. These findings provide a structural basis for enhancing the understanding of the physiological function of JHAMT3 and a rational framework for the development of potent and specific inhibitors of JHAMT family members.

Structural insights into the substrate binding of phosphomevalonate kinase from the silkworm, Bombyx mori

Phosphomevalonate kinase (PMK) is an important enzyme involved in the juvenile hormone (JH) biosynthesis pathway that catalyzes the phosphorylation of mevalonate 5-phosphate into mevalonate 5-diphosphate in the mevalonate pathway. Herein, we report the crystal structure of insect PMK from Bombyx mori (BmPMK) at a resolution of 1.60 Å. The overall structure of BmPMK adopts a compact α/β conformation with two parts: the core and lid regions. The interface between the core and lid regions forms a continuous and negatively charged groove to accommodate the substrates. Using computational simulation combined with site-directed mutagenesis and biochemical analysis, we define the binding mode of BmPMK with the cofactor and the substrate, which provides a structural basis for understanding the catalytic mechanism and the design of inhibitors of PMK. Moreover, BmPMK showed the optimal enzyme activity at pH 8.0, and the optimal temperature was 30 °C, using mevalonate 5-phosphate as the substrate. The expression profiles and kinetic analyses of BmPMK indicated that it plays critical role in the control of JH biosynthesis in silkworms. Collectively, these findings provide a better understanding of the structural and biochemical features of insect PMK.

Regulation of juvenile hormone and ecdysteroid analogues on the development of the predatory spider, Pardosa pseudoannulata, and its regulatory mechanisms

Insecticides harm the beneficial organisms, such as predatory spiders, through direct killing or regulation of the development and reproduction. In this study, the bioassay showed that the treatment of juvenile hormone (JH) analogue fenoxycarb delayed the moulting of Pardosa pseudoannulata, a dominant predatory spider in paddy fields. In order to figure out the regulatory mechanism of fenoxycarb on the spider development, we systematically analyzed JH biosynthesis in P. pseudoannulata. All genes involved in JH biosynthesis pathway were retrieved from the genome of P. pseudoannulata, except for CYP15A1. The absence of CYP15A1 was in agreement with the identification of methyl farnesoate (MF) rather than JH III in the spider. The delayed moulting and decreased expression of JH biosynthesis-related genes in the MF-applied spiderlings supported that MF was an active JH. Fenoxycarb treatment significantly upregulated the transcriptional level of JH biosynthesis-related genes and consequently delayed the spiderling moulting. In the spider development, ecdysteroid played the opposite role, in contrast to MF, to accelerate the development, as our previous study. Here we found that the treatment of ecdysteroid analogue tebufenozide accelerated P. pseudoannulata spiderling moulting, which resulted from the expressional suppression of ecdysteroid biosynthesis-related genes. In total, the JH and ecdysteroid analogues affected the development of P. pseudoannulata by the expressional regulation of biosynthesis-related genes, which would be helpful for the evaluation of hormone analogue insecticides in environmental safety, and useful for the protection and application of P. pseudoannulate and related spider species.

Identification and Evolution Analysis of the Complete Methyl Farnesoate Biosynthesis and Related Pathway Genes in the Mud Crab, Scylla paramamosain

The sesquiterpenoid hormone methyl farnesoate (MF) plays a vital role during crustacean development, which is mainly evidenced by its varied titers during different developmental stages. However, the biosynthesis pathways of MF remain obscure to some extent. In this study, we identified the complete MF biosynthesis and related pathway genes in Scylla paramamosain, including three involved in acetyl-CoA metabolism, eight in the mevalonate pathway, five in the sesquiterpenoids synthesis pathway, and five in the methionine cycle pathway. Bioinformatics, genomic structure, and phylogenetic analysis indicated that the JH biosynthesis genes might have experienced evolution after species differentiation. The mRNA tissue distribution analysis revealed that almost all genes involving in or relating to MF syntheses were highly expressed in the mandibular organ (MO), among which juvenile hormone acid methyltransferase was exclusively expressed in the MO, suggesting that most of these genes might mainly function in MF biosynthesis and that the methionine cycle pathway genes might play a crucial regulatory role during MF synthesis. In addition, the phylogenetic and tissue distribution analysis of the cytochrome P450 CYP15-like gene suggested that the epoxidized JHs might exist in crustaceans, but are mainly synthesized in hepatopancreas rather than the MO. Finally, we also found that betaine-homocysteine S-methyltransferase genes were lost in insects while methionine synthase was probably lost in most insects except Folsomia candida, indicating a regulatory discrepancy in the methionine cycle between crustaceans and insects. This study might increase our understanding of synthetic metabolism tailored for sesquiterpenoid hormones in S. paramamosain and other closely related species.

MicroRNA let-7 is required for hormonal regulation of metamorphosis in the silkworm, Bombyx mori

The heterochronic microRNA let-7, which was first identified in Caenorhabditis elegans, controls the timing of developmental programs, and let-7 triggers the onset of the juvenile-adult transition in bilaterians. The expression of let-7 is strongly induced during the last larval stage of C. elegans and is highly expressed in the late last instar larvae/nymphs of the fly Drosophila melanogaster and the cockroach Blattella germanica. In the silkworm Bombyx mori, the expression of let-7 remarkably increases in the corpus cardiacum-corpus allatum complex (CC-CA) at the beginning of the last larval instar and is maintained at high levels during this instar. To determine the biological function of let-7 in B. mori, we generated a let-7 knockout line and a transgenic UAS-let-7 line. The let-7 knockout larvae were developmentally arrested in the prepupal stage and became pupal-adult intermediates after apolysis. When let-7 was ubiquitously overexpressed under the transcriptional control of an Actin3-GAL4 driver, developmental timing and growth of larvae were severely impaired in the penultimate (L4) instar, and these larvae underwent precocious metamorphosis from L4. Furthermore, our results showed that reception and signaling of ecdysteroids and juvenile hormones (JHs) normally occurred in the absence of let-7, whereas the biosynthesis of ecdysone and JHs were affected by disruption and overexpression of let-7. Together, the present study demonstrates that let-7 is required for the coordination of the biosynthesis of ecdysone and JH to ensure the developmental transition during the metamorphosis of B. mori.

Cloning, expression analysis and RNAi of farnesoic acid O-methylransferase gene from Neocaridina denticulata sinensis

Methyl farnesoate (MF) is an essential endocrine hormone in crustaceans, which can promote the occurrence of crustaceans molting, control morphogenesis, affect gonad development, and regulate the stress stimulation to the external environment. The farnesoic acid O-methyltransferase (FAMeT) is a key rate-limiting enzyme in MF synthesis, catalyzing the conversion of farnesoic acid (FA) into MF. Neocaridina denticulata sinensis [Decapoda] is a suitable animal model for studying crustaceans because it can reproduce many times under artificial control and has a short reproductive cycle. According to its transcriptomic and genomic information, the full-length cDNA sequence of FAMeT from N. denticulata sinensis (NdFAMeT) was cloned and the characterization of its deduced amino acid sequence was also analyzed. The relative expression of NdFAMeT in different tissues was determined. The NdFAMeT protein was recombinantly expressed in E. coli and its enzyme activity was determined. After gene knockdown by RNAi technology, the protein activity of shrimp was decreased and the individual phenotype was also observed.

POU-M2 promotes juvenile hormone biosynthesis by directly activating the transcription of juvenile hormone synthetic enzyme genes in Bombyx mori

Juvenile hormone (JH) plays a key role in preventing larval precocious metamorphosis, maintaining larval state, controlling adult sexual development and promoting insect egg maturation. Genetic studies have shown that POU factor ventral veins lacking regulates JH synthesis to control the timing of insect metamorphosis. However, how POU factor regulates JH synthesis is largely unknown. Here, we found POU-M2 was highly expressed in corpora allata (CA) and specifically localized in the nucleus of CA. The overexpression of POU-M2 promoted the expression of JH synthase genes and kr-h1 and enhanced the activity of JH synthase genes promoter. Further, POU-M2 promoted the transcription of JH acid O-methyltransferase (JHAMT) by directly binding to the key cis-regulatory elements -207, -249 and -453 within the proximal regions of JHAMT promoter. Both the POU domain and homeodomain were vital for the activation of POU-M2 on JHAMT transcription. Our study reveals the mechanism by which POU-M2 regulates JHAMT transcription.

Toxicity of Ribavirin to Spodoptera litura by Inhibiting the Juvenile Hormone

Ribavirin is an antiviral drug showing high and delayed toxicity to the destructive agricultural pest Spodoptera litura. Larvae fed with artificial diets containing ribavirin could not molt successfully and showed abnormal phenotypes, including cuticle melanization and heavy wrinkle of the newly formed procuticle. RNA-Seq analysis suggested that ribavirin has great negative influence on cuticle. Quantitative real-time-polymerase chain reaction results indicated that ribavirin treatment decreased the expression of key genes in juvenile hormone (JH) biosynthesis (CYP15C1 and JH acid methyltransferase) and most cuticle protein genes, whereas the genes in melanin biosynthesis and bursicon genes were upregulated by ribavirin treatment. These results coincided with the decreased titer of JH I, JH II, and JH III determined by enzyme-linked immunosorbent assay, the much thinner procuticle layer exhibited by histopathological examination, and the cuticle melanization after ribavirin treatment. These results provided a valuable theoretical basis for the creation of green insecticides targeting JH and the development of new insecticide derivatives from 1,2,4-triazole.

Functional Characterization of Allatostatin C (PISCF/AST) and Juvenile Hormone Acid O-Methyltransferase in Dendroctonus armandi

Allatostatin C (PISCF/AST) is a neuropeptide gene that affects juvenile hormone (JH) synthesis in the corpora allata. Juvenile hormone acid O-methyltransferase (JHAMT) is a key gene in the JH biosynthetic pathway. In this study, two genes encoding DaAST and DaJHAMT were cloned. Both DaAST and DaJHAMT were expressed in the larvae, pupae and adults of Chinese white pine beetle (Dendroctonus armandi), and highly expressed in the head and the gut. The expression of the two genes was induced by JH analog (JHA) methoprene and the functions of the two genes were then investigated by RNAi. Considering the role of hormones in metamorphosis, JHA significantly induced DaAST and DaJHAMT in the larval stage. DaAST knockdown in larvae, pupae and adults significantly increased the DaJHAMT mRNA levels. Moreover, knockdown of DaAST instead of DaJHAMT increased pupae mortality and the abnormal rate of emergence morphology and reduced emergence rates. However, knockdown of DaJHAMT instead of DaAST significantly reduced frontalin biosynthesis in adult males. The results showed that DaAST acts as an allatostatin and inhibits JH biosynthesis, and that JHAMT is a key regulatory enzyme for JH synthesis in the D. armandi.

Juvenile Hormone Synthesis Pathway Gene SfIPPI Regulates Sogatella furcifera Reproduction

Simple Summary

The juvenile hormone is essential for insect growth, development, and reproduction. Isopentenyl pyrophosphate isomerase is a key isomerase involved in the synthesis of the juvenile hormone. This study evaluates the effect of the targeted silencing of the SfIPPI gene on the reproduction of Sogatella furcifera (white-backed planthopper). We found that SfIPPI silencing significantly inhibits the ovarian development and egg production in female adults of S. furcifera and significantly inhibits the transcription of downstream genes in the juvenile hormone synthesis pathway. Our data provide insight into the function of juvenile hormone biosynthetic pathway genes in insect reproduction, which could be a potential target to control and prevent agricultural pests.

Abstract

The juvenile hormone (JH) is crucial for insect reproduction, and isopentenyl pyrophosphate isomerase (IPPI) is a key enzyme in the JH synthesis pathway. However, few studies have investigated how IPPI regulates insect reproduction. This study identifies and characterizes the IPPI gene (SfIPPI) from the important agricultural pest Sogatella furcifera. A phylogenetic analysis reveals a high homology of SfIPPI with the IPPI amino acid sequences of Laodelphax striatellus and Nilaparvata lugens (Stål). Furthermore, SfIPPI is expressed at various developmental stages and in various tissues of S. furcifera, and is significantly higher on the 5th day of adult emergence and in integument tissue, while lower levels are found on the 3rd day of adult emergence and in fat body and gut tissue. After silencing SfIPPI using RNA interference, the ovarian development is significantly inhibited and the fecundity is significantly reduced when compared with the control group. Additionally, SfIPPI silencing significantly decreases the expression levels of downstream JH signal transduction pathway genes (SfJHAMT, SfFAMeT, and SfKr-h1) and SfVg. Our findings are helpful in elucidating the molecular mechanism underlying the regulation of insect reproduction through genes in the JH synthesis pathway, and they provide a theoretical basis for the development of pest control treatments targeting SfIPPI.

Transcriptomic analysis of Bombyx mori corpora allata with comparison to prothoracic glands in the final instar larvae

The corpus allatum (CA) is an endocrine organ of insects that synthesizes juvenile hormone (JH). Yet little is known regarding the global gene expression profile for the CA, although JH signaling pathway has been well-studied in insects. Here, we report the availability of the transcriptome resource of the isolated CA from the final (fifth) instar larvae of the silkworm, Bombyx mori when the JH titer is low. We also compare it with prothoracic gland (PG) that produces the precursor of 20-hydroxyecdysone (20E), to find some common features in the JH and 20E related genes between the two organs. A total of 17,262 genes were generated using a combination of genome-guided assembly and annotation, in which 10,878 unigenes were enriched in 58 Gene Ontology terms, representing almost all expressed genes in the CA of the 5th instar larvae of B. mori. Transcriptome analysis confirmed that gene for Torso, the receptor of prothoracicotropic hormone (PTTH), is present in the PG but not in the CA. Transcriptome comparison and quantitative real time-PCR indicated that 11 genes related to JH biosynthesis and regulation and six genes for 20E are expressed in both the CA and PG, suggesting that the two organs may cross talk with each other through these genes. The temporal expression profiles of the two genes for the multifunctional neurohormonal factor sericotropin precursor and the uncharacterized protein LOC114249572, the most abundant in the CA and PG transcriptomes respectively, suggested that they might play important roles in the JH and 20E biosynthesis. The present work provides new insights into the CA and PG.

De novo RNA-Seq and Annotation of Sesquiterpenoid and Ecdysteroid Biosynthesis Genes and MicroRNAs in a Spider Mite Eotetranychus kankitus

Eotetranychus kankitus is an important mite pest in citrus, but molecular data on the developmental processes of E. kankitus are lacking. The different development stages mix of E. kankitus was used to sequence for transcriptome and small RNAs to identify genes and predict miRNAs associated with sesquiterpenoid and ecdysteroid biosynthesis and signaling pathways. More than 36 million clean reads were assembled and 67,927 unigenes were generated. Of the unigenes, 19,300 were successfully annotated through annotation databases NR, SwissProt, COG, GO, KEGG, PFAM, and KOG. The transcripts were involved in sesquiterpenoid biosynthesis (11 genes) and ecdysteroid biosynthesis and signaling pathway (13 genes). Another, small RNA library was obtained and 31 conserved miRNAs were identified. Five most abundant miRNAs were Ek-miR-5735, Ek-miR-1, Ek-miR-263a, Ek-miR-184, and Ek-miR-8. The target genes related to sesquiterpenoid and ecdysteroid showed that 10 of the conserved miRNAs could potentially target the sesquiterpenoid and ecdysteroid pathway according to four-prediction software, sRNAT, miRanda, RNAhybrid, and Risearch2. Thus, the results of this study will provide bioinformatics information for further molecular studies of E. kankitus which may facilitate improved pest control strategies.

RNA-seq analysis of gene expression changes in cuticles during the larval-pupal metamorphosis of Plutella xylostella

The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) is a holometabolous insect that its cuticles must undergo the significant changes during the larval-pupal metamorphosis development. To elucidate these changes at molecular levels, RNA-seq analysis of cuticles from LLS (later fourth instar larval stage), PPS (prepupal stage) and PS (pupal stage) were performed in P. xylostella. In this paper, a total of 17,710 transcripts were obtained in the larval-pupal transition of P. xylostella, and out of which 2293 (881 up-regulated and 1412 down-regulated) and 2989 transcripts (2062 up-regulated and 927 down-regulated) were identified to be differentially expressed between LLS and PPS, as well as PPS and PS, respectively. The further GO and KEGG analysis of differentially expressed genes (DEGs) revealed that the 'structural constituent of cuticle', 'chitin metabolic process', 'chitin binding', 'tyrosine metabolism' and 'insect hormone biosynthesis' pathways were significantly enriched, indicating these pathways might be involved in the process of larval pupation in P. xylostella. Then, we found some genes that encoded cuticular proteins, chitinolytic enzymes, chitin synthesis enzymes, and cuticle tanning proteins changed their expression levels remarkably, indicating these genes might play important roles in the restruction (degradation and biosynthesis) of insect cuticles during the larval metamorphosis. Additionally, the significant changes in the mRNA levels of 20-hydroxyecdysone (20E) and juvenile hormone (JH) related genes suggested their crucial roles in regulating cuticle remodeling during the larval metamorphosis of P. xylostella. In conclusion, the present study provide us the comprehensive gene expression profiles to explore the molecular mechanisms of cuticle metamorphosis in P. xylostella, which laid a molecular basis to study roles of specific pathways and genes in insect development.

Identification and function of ETH receptor networks in the silkworm Bombyx mori

Insect ecdysis triggering hormones (ETHs) released from endocrine Inka cells act on specific neurons in the central nervous system (CNS) to activate the ecdysis sequence. These primary target neurons express distinct splicing variants of ETH receptor (ETHR-A or ETHR-B). Here, we characterized both ETHR subtypes in the moth Bombyx mori in vitro and mapped spatial and temporal distribution of their expression within the CNS and peripheral organs. In the CNS, we detected non-overlapping expression patterns of each receptor isoform which showed dramatic changes during metamorphosis. Most ETHR-A and a few ETHR-B neurons produce multiple neuropeptides which are downstream signals for the initiation or termination of various phases during the ecdysis sequence. We also described novel roles of different neuropeptides during these processes. Careful examination of peripheral organs revealed ETHRs expression in specific cells of the frontal ganglion (FG), corpora allata (CA), H-organ and Malpighian tubules prior to each ecdysis. These data indicate that PETH and ETH are multifunctional hormones that act via ETHR-A and ETHR-B to control various functions during the entire development—the ecdysis sequence and associated behaviors by the CNS and FG, JH synthesis by the CA, and possible activity of the H-organ and Malpighian tubules.

Rational design of Lepidoptera-specific insecticidal inhibitors targeting farnesyl diphosphate synthase, a key enzyme of the juvenile hormone biosynthetic pathway

Reducing the use of broad-spectrum insecticides is one of the many challenges currently faced by insect pest management practitioners. For this reason, efforts are being made to develop environmentally benign pest-control products through bio-rational approaches that aim at disrupting physiological processes unique to specific groups of pests. Perturbation of hormonal regulation of insect development and reproduction is one such strategy. It has long been hypothesized that some enzymes in the juvenile hormone biosynthetic pathway of moths, butterflies and caterpillars (order Lepidoptera) display unique structural features that could be targeted for the development of Lepidoptera-specific insecticides, a promising avenue given the numerous agricultural and forest pests belonging to this order. Farnesyl diphosphate synthase, FPPS, is one such enzyme, with recent work suggesting that it has structural characteristics that may enable its selective inhibition. This review synthesizes current knowledge on FPPS and summarizes recent advances in its use as a target for insecticide development.

Phosphonate and Bisphosphonate Inhibitors of Farnesyl Pyrophosphate Synthases: A Structure-Guided Perspective

Phosphonates and bisphosphonates have proven their pharmacological utility as inhibitors of enzymes that metabolize phosphate and pyrophosphate substrates. The blockbuster class of drugs nitrogen-containing bisphosphonates represent one of the best-known examples. Widely used to treat bone-resorption disorders, these drugs work by inhibiting the enzyme farnesyl pyrophosphate synthase. Playing a key role in the isoprenoid biosynthetic pathway, this enzyme is also a potential anticancer target. Here, we provide a comprehensive overview of the research efforts to identify new inhibitors of farnesyl pyrophosphate synthase for various therapeutic applications. While the majority of these efforts have been directed against the human enzyme, some have been targeted on its homologs from other organisms, such as protozoan parasites and insects. Our particular focus is on the structures of the target enzymes and how the structural information has guided the drug discovery efforts.

Genome-wide identification and analysis of the thiolase family in insects

Thiolases are important enzymes involved in lipid metabolism in both prokaryotes and eukaryotes, and are essential for a range of metabolic pathways, while, little is known for this important family in insects. To shed light on the evolutionary models and functional diversities of the thiolase family, 137 thiolase genes were identified in 20 representative insect genomes. They were mainly classified into five classes, namely cytosolic thiolase (CT-thiolase), T1-thiolase, T2-thiolase, trifunctional enzyme thiolase (TFE-thiolase), and sterol carrier protein 2 thiolase (SCP2-thiolase). The intron number and exon/intron structures of the thiolase genes reserve large diversification. Subcellular localization prediction indicated that all the thiolase proteins were mitochondrial, cytosolic, or peroxisomal enzymes. Four highly conserved sequence fingerprints were found in the insect thiolase proteins, including CxS-, NEAF-, GHP-, and CxGGGxG-motifs. Homology modeling indicated that insect thiolases share similar 3D structures with mammals, fishes, and microorganisms. In Bombyx mori, microarray data and reverse transcription-polymerase chain reaction (RT-PCR) analysis suggested that some thiolases might be involved in steroid metabolism, juvenile hormone (JH), and sex pheromone biosynthesis pathways. In general, sequence and structural characteristics were relatively conserved among insects, bacteria and vertebrates, while different classes of thiolases might have differentiation in specific functions and physiological processes. These results will provide an important foundation for future functional validation of insect thiolases.

Structural characterization and functional analysis of juvenile hormone diol kinase from the silkworm, Bombyx mori

Juvenile hormone diol kinase (JHDK) is an important enzyme involved in the juvenile hormone metabolism pathway, which catalyzes the phosphorylation of juvenile hormone diol to form the polar metabolite JH diol phosphate. Here, we reported the first crystal structure of insect JHDK from Bombyx mori, BmJHDK-L2, determined at a resolution of 1.22 Å. The structure of BmJHDK-L2 mainly comprises of eight α-helical segments linked with loops, forming four helix-loop-helix motifs. In these four helix-loop-helix motifs with only one calcium ion bound in the first motif. Circular dichroism spectra indicated that BmJHDK-L2 has strong thermal stability, which is independent of the divalent cation. The structure of BmJHDK-L2 further allowed us to define an ATP-binding site using computational simulation and binding assays, providing a structural basis for development of inhibitor of JHDK. Moreover, the expression profile of BmJHDK-L2 indicated a predominant role in juvenile hormone metabolism in the Malpighian tubules of silkworm. Collectively, these findings expand our knowledge regarding the structural and biochemical features of insect JHDK proteins.

Precocious Downregulation of Krüppel-Homolog 1 in the Migratory Locust, Locusta migratoria, Gives Rise to An Adultoid Phenotype with Accelerated Ovarian Development but Disturbed Mating and Oviposition

Krüppel-homolog 1 (Kr-h1) is a zinc finger transcription factor maintaining the status quo in immature insect stages and promoting reproduction in adult insects through the transduction of the Juvenile Hormone (JH) signal. Knockdown studies have shown that precocious silencing of Kr-h1 in the immature stages results in the premature development of adult features. However, the molecular characteristics and reproductive potential of these premature adult insect stages are still poorly understood. Here we report on an adult-like or 'adultoid' phenotype of the migratory locust, Locusta migratoria, obtained after a premature metamorphosis induced by the silencing of LmKr-h1 in the penultimate instar. The freshly molted adultoid shows precocious development of adult features, corresponding with increased transcript levels of the adult specifier gene LmE93. Furthermore, accelerated ovarian maturation and vitellogenesis were observed in female adultoids, coinciding with elevated expression of LmCYP15A1 in corpora allata (CA) and LmKr-h1 and vitellogenin genes (LmVg) in fat body, whereas LmE93 and Methoprene-tolerant (LmMet) transcript levels decreased in fat body. In adultoid ovaries, expression of the Halloween genes, Spook (LmSpo) and Phantom (LmPhm), was elevated as well. In addition, the processes of mating and oviposition were severely disturbed in these females. L. migratoria is a well-known, swarm-forming pest insect that can destroy crops and harvests in some of the world's poorest countries. As such, a better understanding of factors that are capable of significantly reducing the reproductive potential of this pest may be of crucial importance for the development of novel locust control strategies.

Transcriptomic analysis at the first instar larval stage of nonmolting Bombyx mori mutant (a42)

The life cycle of the holometabolous insect Bombyx mori (Linnaeus) consists of the embryo, larva, pupa, and adult stages with six larval molts. Ecdysone and juvenile hormones play important roles in the growth and development of the silkworms. The a42 silkworm mutant is recessive and homozygous lethal by exhibiting a dark-colored and small body size and fails to molt to second instar. We compared the gene expression of a42 mutants with normal individuals at the first larval molting stage to elucidate the physiological influence of the a42 mutation on the growth and development of silkworms. The transcriptomic sequencing results revealed that 1,411 genes are differentially expressed in a42 mutants, compared with wild-type control silkworms, in which 791 genes are upregulated and 620 genes are downregulated. Gene Ontology/Kyoto Encyclopedia of Genes and Genomes analyses identified differentially expressed genes (DEGs) assigned to biological pathways, such as pentose and glucoronate interconversions, glycerolipid metabolism, folate biosynthesis, amino sugar, and nucleotide sugar metabolism. Two hydroxylases of phenylalanine hydroxylase (BmPAH) and tyrosine hydroxylase (BmTh) are upregulated in a42 mutants. The influence of a42 mutation on these DEGs reveals that melanin metabolism plays an important role during the molting process in silkworms.

The juvenile hormone described in Rhodnius prolixus by Wigglesworth is juvenile hormone III skipped bisepoxide

Juvenile hormones (JHs) are sesquiterpenoids synthesized by the corpora allata (CA). They play critical roles during insect development and reproduction. The first JH was described in 1934 as a “metamorphosis inhibitory hormone” in Rhodnius prolixus by Sir Vincent B. Wigglesworth. Remarkably, in spite of the importance of R. prolixus as vectors of Chagas disease and model organisms in insect physiology, the original JH that Wigglesworth described for the kissing-bug R. prolixus remained unidentified. We employed liquid chromatography mass spectrometry to search for the JH homologs present in the hemolymph of fourth instar nymphs of R. prolixus. Wigglesworth’s original JH is the JH III skipped bisepoxide (JHSB3), a homolog identified in other heteropteran species. Changes in the titer of JHSB3 were studied during the 10-day long molting cycle of 4^th instar nymph, between a blood meal and the ecdysis to 5^th instar. In addition we measured the changes of mRNA levels in the CA for the 13 enzymes of the JH biosynthetic pathway during the molting cycle of 4^th instar. Almost 90 years after the first descriptions of the role of JH in insects, this study finally reveals that the specific JH homolog responsible for Wigglesworth’s original observations is JHSB3.

Mevalonate Pathway Promiscuity Enables Noncanonical Terpene Production

Lepidoptera (butterflies and moths) make the six-carbon compounds homoisopentenyl pyrophosphate (HIPP) and homodimethylallyl pyrophosphate (HDMAPP) that are incorporated into 16, 17, and 18 carbon farnesyl pyrophosphate (FPP) analogues. In this work we heterologously expressed the lepidopteran modified mevalonate pathway, a propionyl-CoA ligase, and terpene cyclases in E. coli to produce several novel terpenes containing 16 carbons. Changing the terpene cyclase generated different novel terpene product profiles. To further validate the new compounds we confirmed ¹³C propionate was incorporated, and that the masses and fragmentation patterns were consistent with novel 16 carbon terpenes by GC-QTOF. On the basis of the available farnesyl pyrophosphate analogues lepidoptera produce, this approach should greatly expand the reachable biochemical space with applications in areas where terpenes have traditionally found uses.

Reconstruction of insect hormone pathways in an aquatic firefly, Sclerotia aquatilis (Coleoptera: Lampyridae), using RNA-seq

Insect hormones: ecdysteroids and juvenile hormones have crucial functions during the regulation of different developmental pathways in insects. Insect metamorphosis is one of the primary pathways regulated by these hormones. The insect hormone biosynthetic pathway is conserved among arthropods, including insects, with some variations in the form of hormones used among each group of insects. In this study, the candidate genes involved in the insect hormone pathways and their functional roles were assessed in an aquatic firefly, Sclerotia aquatilis using a high-throughput RNA sequencing technique. Illumina next-generation sequencing (NGS) was used to generate transcriptome data for the different developmental stages (i.e., larva, pupa, and adult) of S. aquatilis. A total of 82,022 unigenes were generated across all different developmental stages. Functional annotation was performed for each gene, based on multiple biological databases, generating 46,230 unigenes. These unigenes were subsequently mapped using KEGG pathways. Accordingly, 221 protein-encoding genes involved in the insect hormone pathways were identified, including, JHAMT, CYP15A1, JHE, and Halloween family genes. Twenty potential gene candidates associated with the biosynthetic and degradation pathways for insect hormones were subjected to real-time PCR, reverse transcriptase PCR (RT-PCR) and sequencing analyses. The real-time PCR results showed similar expression patterns as those observed for transcriptome expression profiles for most of the examined genes. RT-PCR and Sanger sequencing confirmed the expressed coding sequences of these gene candidates. This study is the first to examine firefly insect hormone pathways, facilitating a better understanding of firefly growth and development.

Spatiotemporal expression profiling of the farnesyl diphosphate synthase genes in aphids and analysis of their associations with the biosynthesis of alarm pheromone

The alarm behavior plays a key role in the ecology of aphids, but the site and molecular mechanism for the biosynthesis of aphid alarm pheromone are largely unknown. Farnesyl diphosphate synthase (FPPS) catalyzes the synthesis of FPP, providing the precursor for the alarm pheromone (E)-β-farnesene (EβF), and we speculate that FPPS is closely associated with the biosynthetic pathway of EβF. We firstly analyzed the spatiotemporal expression of FPPS genes by using quantitative reverse transcription-polymerase chain reaction, showing that they were expressed uninterruptedly from the embryonic stage to adult stage, with an obvious increasing trend from embryo to 4th-instar in the green peach aphid Myzus persicae, but FPPS1 had an overall significantly higher expression level than FPPS2; both FPPS1 and FPPS2 exhibited the highest expression in the cornicle area. This expression pattern was verified in Acyrthosiphon pisum, suggesting that FPPS1 may play a more important role in aphids and the cornicle area is most likely the site for EβF biosynthesis. We thus conducted a quantitative measurement of EβF in M. persicae by gas chromatography-mass spectrometry. The data obtained were used to perform an association analysis with the expression data, revealing that the content of EβF per aphid was significantly correlated with the mean weight per aphid (r = 0.8534, P = 0.0307) and the expression level of FPPS1 (r = 0.9134, P = 0.0109), but not with that of FPPS2 (r = 0.4113, P = 0.4179); the concentration of EβF per milligram of aphid was not correlated with the mean weight per aphid or the expression level of FPPS genes. These data suggest that FPPS1 may play a key role in the biosynthesis of aphid alarm pheromone.

Both farnesyl diphosphate synthase genes are involved in the production of alarm pheromone in the green peach aphid Myzus persicae

Farnesyl diphosphate synthase (FPPS) catalyzes the formation of FPP, providing the precursor for the biosynthesis of (E)-β-farnesene (EβF) in plants, but it is unknown if FPPS supplies the precursor for the biosynthesis of EβF, the major component of aphid alarm pheromone, though our previous studies support the hypothesis that EβF is synthesized by the aphid itself. Here, we used two cohorts of the green peach aphid Myzus persicae separately, reared on pepper plant and artificial diet to test the correlations among droplet emission, EβF quantity, and FPPS gene expression. It was found that the proportion of aphids emitting cornicle droplets and the quantity of EβF per milligram of aphid were both significantly different between the two cohorts, which were positively correlated with the expression of the two FPPS genes ( MpFPPS1/ 2) in M. persicae. These results were further confirmed by RNAi-mediated knockdown of MpFPPS1/ 2. Specifically, knockdown of MpFPPS1/ 2 imposed no significant cost on the survival of aphid but remarkably increased the number of offspring per aphid; most importantly, knockdown of MpFPPS1/ 2 significantly reduced the proportion of aphids emitting droplets and the quantity of EβF calculated as per the weight of aphid. Our results suggest that both FPPS genes are involved in the production of EβF in M. persicae and cornicle droplet emission is closely associated with the EβF release in the aphid.

Juvenile hormone and sesquiterpenoids in arthropods: Biosynthesis, signaling, and role of MicroRNA

Arthropod molting and reproduction are precisely controlled by the levels of sesquiterpenoids, a class of C15 hormones derived from three isoprene units. The two major functional arthropod sesquiterpenoids are juvenile hormone (JH) and methyl farnesoate (MF). In hemimetabolous insects (such as the aphids, bugs, and cockroaches) and holometabolous insects (such as beetles, bees, butterflies, and flies), dramatic decrease in the titers of JH and/or MF promote metamorphosis from larvae to adults either directly or through an intermediate pupal stage, respectively. JH is absent in crustaceans (lobster, shrimp, crab) and other arthropods (chelicerates such as ticks, mites, spiders, scorpions and myriapods such as millipede and centipedes). In some crustaceans, molting and reproduction is dependent on changing levels of MF. The regulation of sesquiterpenoid production is thus crucial in the life cycle of arthropods. Dynamic and complex mechanisms have evolved to regulate sesquiterpenoid production. Noncoding RNAs such as the microRNAs are primary regulators. This article provides an overview of microRNAs that are known to regulate sesquiterpenoid production in arthropods.

Expression of juvenile hormone acid O-methyltransferase and juvenile hormone synthesis in Blattella germanica

Juvenile hormone (JH), a sesquiterpenoid synthetized by the insect corpora allata (CA), plays critical roles in metamorphosis and reproduction. Penultimate or last step of JH synthesis is catalyzed by juvenile hormone acid O-methyltransferase (JHAMT). Here we report the cloning and expression analysis of the JHAMT orthologue in the cockroach, Blattella germanica (L.) (BgJHAMT). BgJHAMT is mainly expressed in CA, with only expression traces in ovary. Three different isoforms, differing in the 3'-UTR sequence, were identified. Isoform A shows between 35 and 65 times higher expression than B and C in CA from penultimate nymphal instar and adult females. RNAi-triggered knock down of BgJHAMT produces a dramatic reduction of JH synthesis, concomitant with a decrease of fat body vitellogenin expression and basal follicle length. BgJHAMT mRNA levels in CA of females along the gonadotrophic cycle parallel, with a slight advancement, JH synthesis profile. BgJHAMT mRNA levels were reduced in starved females and in females in which we reduced nutritional signaling by knocking down insulin receptor and target of rapamycin (TOR). Results show that conditions that modify JH synthesis in adult B. germanica females show parallel changes of BgJHAMT mRNA levels and that the JH-specific branch of the JH synthesis pathway is regulated in the same way as the mevalonate branch. Furthermore, we demonstrate that nutrition and its signaling through the insulin receptor and TOR pathways are essential for activating BgJHAMT expression, which suggests that this enzyme can be a checkpoint for the regulation of JH production in relation to nutritional status.

Omics approaches to study juvenile hormone synthesis

The juvenile hormones (JHs) are a family of insect acyclic sesquiterpenoids produced by the corpora allata (CA), a pair of endocrine glands connected to the brain. They are involved in the regulation of development, reproduction, behavior, caste determination, diapause, stress response, and numerous polyphenisms. In the post-genomics era, comprehensive analyses using functional 'omics' technologies such as transcriptomics, proteomics and metabolomics have increased our understanding of the activity of the minute CA. This review attempts to summarize some of the 'omics' studies that have contributed to further understand JH synthesis in insects, with an emphasis on our own research on the mosquito Aedes aegypti.

RNA-seq analysis of gene expression changes during pupariation in Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Background

The oriental fruit fly, Bactrocera dorsalis (Hendel) has been considered to be one of the most important agricultural pest around the world. As a holometabolous insect, larvae must go through a metamorphosis process with dramatic morphological and structural changes to complete their development. To better understand the molecular mechanisms of these changes, RNA-seq of B. dorsalis from wandering stage (WS), late wandering stage (LWS) and white puparium stage (WPS) were performed.

Results

In total, 11,721 transcripts were obtained, out of which 1914 genes (578 up-regulated and 1336 down-regulated) and 2047 genes (655 up-regulated and 1392 down-regulated) were found to be differentially expressed between WS and LWS, as well as between WS and WPS, respectively. Of these DEGs, 1862 and 1996 genes were successfully annotated in various databases. The analysis of RNA-seq data together with qRT-PCR validation indicated that during this transition, the genes in the oxidative phosphorylation pathway, and genes encoding P450s, serine protease inhibitor, and cuticular proteins were down-regulated, while the serine protease genes were up-regulated. Moreover, we found some 20-hydroxyecdysone (20E) biosynthesis and signaling pathway genes had a higher expression in the WS, while the genes responsible for juvenile hormone (JH) synthesis, degradation, signaling and transporter pathways were down-regulated, suggesting these genes might be involved in the process of larval pupariation in B. dorsalis. For the chitinolytic enzymes, the genes encoding chitinases (chitinase 2, chitinase 5, chitinase 8, and chitinase 10) and chitin deacetylase might play the crucial role in the degradation of insect chitin with their expressions significantly increased during the transition. Here, we also found that chitin synthase 1A might be involved in the chitin synthesis of cuticles during the metamorphosis in B. dorsalis.

Conclusions

Significant changes at transcriptional level were identified during the larval pupariation of B. dorsalis. Importantly, we also obtained a vast quantity of RNA-seq data and identified metamorphosis associated genes, which would all help us to better understand the molecular mechanism of metamorphosis process in B. dorsalis.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5077-z) contains supplementary material, which is available to authorized users.

Sexual dimorphism of sleep regulated by juvenile hormone signaling in Drosophila

Sexually dimorphic phenotypes are a universal phenomenon in animals. In the model animal fruit fly Drosophila, males and females exhibit long- and short-sleep phenotypes, respectively. However, the mechanism is still a mystery. In this study, we showed that juvenile hormone (JH) is involved in regulation of sexually dimorphic sleep in Drosophila, in which gain of JH function enlarges differences of the dimorphic sleep phenotype with higher sleep in males and lower sleep in females, while loss of JH function blurs these differences and results in feminization of male sleep and masculinization of female sleep. Further studies indicate that germ cell-expressed (GCE), one of the JH receptors, mediates the response in the JH pathway because the sexually dimorphic sleep phenotypes cannot be rescued by JH hormone in a gce deletion mutant. The JH-GCE regulated sleep dimorphism is generated through the sex differentiation-related genes -fruitless (fru) and doublesex (dsx) in males and sex-lethal (sxl), transformer (tra) and doublesex (dsx) in females. These are the “switch” genes that separately control the sleep pattern in males and females. Moreover, analysis of sleep deprivation and circadian behaviors showed that the sexually dimorphic sleep induced by JH signals is a change of sleep drive and independent of the circadian clock. Furthermore, we found that JH seems to also play an unanticipated role in antagonism of an aging-induced sleep decrease in male flies. Taken together, these results indicate that the JH signal pathway is critical for maintenance of sexually dimorphic sleep by regulating sex-relevant genes.

Sleep is a very important biological behavior in all animals and takes up around one third of the lifespan in many animals. In both insects and mammals (including humans), sleep differences between male and female (sexually dimorphic sleep) have been described over the past decades. However, its internal regulation mechanism is still unclear. The fruit fly Drosophila melanogaster, sharing most sleep characteristics with humans, has been used for sleep studies as a powerful model for genetic analysis. In this study, we reported that Juvenile hormone (JH) induces completely different sleep effects between males and females with higher sleep in males and lower sleep in females, while loss of JH function blurs these differences and results in feminization of male sleep and masculinization of female sleep. Further studies indicate that the sexual dimorphism of sleep is generated through the sex differentiation-related genes regulated by JH and its receptor GCE (germ cell-expressed) signaling. Furthermore, we found that JH seems to also play an unanticipated role in aging-induced sleep changes.

Structural characterization of a lepidopteran type-II farnesyl diphosphate synthase from the spruce budworm, Choristoneura fumiferana: Implications for inhibitor design

Farnesyl diphosphate synthase (FPPS) is an enzyme from the class of short chain (E)-prenyltransferases that catalyzes the condensation of two molecules of isopentenyl diphosphate (IPP, C₅) with dimethylallyl diphosphate (DMAPP, C₅) to generate the C₁₅ product FPP. In insects, FPPS plays a key role in the biosynthesis of the morphogenetic and gonadotropic "juvenile hormone" (JH). Lepidopteran genomes encode two very distinct FPPS paralogs, one of which ("type-II") is expressed almost exclusively in the JH-producing glands, the corpora allata. This paralog has been hypothesized to display structural features that enable the binding of the bulkier precursors required for the biosynthesis of lepidopteran ethyl-branched JHs. Here, we report on the first crystal structures of an insect FPPS solved to date. Apo, ligand-bound, and inhibitor-bound structures of type-II FPPS (FPPS2) from the spruce budworm, Choristoneura fumiferana (Order: Lepidoptera), were obtained. Comparison of apo and inhibitor-bound enzymes revealed differences in both inhibitor binding and structural plasticity of CfFPPS2 compared to other FPPSs. Our data showed that IPP is not essential to the closure of the C-terminal tail. Ortho-substituted pyridinium bisphosphonates, previously shown to inhibit CfFPPS2, bound to the allylic site, as predicted; however, their alkyl groups were oriented towards the homoallylic binding site, with the bulkier propyl-substituted inhibitor penetrating deeply into the IPP binding pocket. The current study sheds light on the structural basis of substrate specificity of type-II FPPS of the spruce budworm. Through a comparison with other inhibitor-bound FPPSs, we propose several approaches to improve inhibitor selectivity and potency.

Identification and characterization of genes involving the early step of Juvenile Hormone pathway in Helicoverpa armigera

Juvenile hormones (JHs) are crucial regulators for multiple physiological processes in insects. In the current study, 10 genes in mevalonate pathway involved in JH biosynthesis were identified from Helicoverpa armigera. Tissue-specific expression analysis showed that six genes were highly expressed in the head which contained the JH biosynthetic gland (corpora allata). Temporal expression pattern showed that 10 of 12 genes were highly transcribed in the late 2^nd-instar when the in vivo JH titer reached the peak, indicating a tight correlation between JH titer and the transcription of JH synthetic pathway genes. Moreover, ingestion of methoprene, a JH analogue, significantly suppressed the transcription of nine JH biosynthetic genes and caused a feedback upregulation of the JH degradation enzyme. Particularly, the Acetoacetyl CoA thiolase (HaAce) and Farnesyl diphosphate synthase gene 4 (HaFpps4) showed high transcript abundance, and their temporal expressions keep pace with JH fluctuations. Further study by RNAi showed that knockdown of HaFpps4 caused the decrease of JH titer, led to a negative effect on the transcript levels of other genes in JH pathway, and resulted in molting disturbance in larvae. Altogether, these results contribute to our understanding of JH biosynthesis in H. armigera and provide target genes for pest control based on JH-dependent regulation.

Sublethal effects of chlorantraniliprole on juvenile hormone levels and mRNA expression of JHAMT and FPPS genes in the rice stem borer, Chilo suppressalis

BACKGROUND

Juvenile hormone (JH) regulates the development and reproduction of insects. The sublethal effects of chlorantraniliprole on JH levels and mRNA expression of JH acid methyltransferase gene (CsJHAMT) and farnesyl diphosphate synthase genes (CsFPPS1 and CsFPPS2) in Chilo suppressalis (Walker) were investigated.

RESULTS

Exposure of sublethal concentrations of chlorantraniliprole (LC₁₀ and LC₃₀ ) to the third instar larvae of C. suppressalis significantly increased the JH levels in all developmental stages investigated including larvae 72 h after treatment, the first, third and fifth day of female pupae, as well as newly emerged, 12-h-old and 24-h-old female adults. A general trend of increased mRNA expression levels of CsJHAMT, CsFPPS1and CsFPPS2 was also observed in LC₁₀ and LC₃₀ treatment groups. Notably, the mRNA expression level of CsJHAMT significantly increased by 7.46-fold in the larvae 72 h after LC₃₀ treatment. A significant increase of the mRNA expression levels of CsFPPS2 was also observed in the fifth day female pupae of LC₁₀ and LC₃₀ treatment groups (2.60-fold and 2.62-fold, respectively) as well as in 12-h-old female adults of the LC₃₀ treatment group (3.45-fold).

CONCLUSION

Sublethal concentrations of chlorantraniliprole might upregulate the expression of JH biosynthesis genes and in turn result in an increase of JH level in C. suppressalis. © 2017 Society of Chemical Industry.

Differentially expressed genes in the head of the 2nd instar pre-molting larvae of the nm2 mutant of the silkworm, Bombyx mori

Molting is an important physiological process in the larval stage of Bombyx mori and is controlled by various hormones and peptides. The silkworm mutant that exhibits the phenotype of non-molting in the 2^nd instar (nm2) is incapable of molting in the 2^nd instar and dies after seven or more days. The ecdysone titer in the nm2 mutant is lower than that in the wildtype, and the mutant can be rescued by feeding with 20E and cholesterol. The results of positional cloning indicated that structural alteration of BmCPG10 is responsible for the phenotype of the nm2 mutant. To explore the possible relationship between BmCPG10 and the ecdysone titer as well as the genes affected by BmCPG10, digital gene expression (DGE) profile analysis was conducted in the nm2 mutant, with the wildtype strain C603 serving as the control. The results revealed 1727 differentially expressed genes, among which 651 genes were upregulated and 1076 were downregulated in nm2. BLASTGO analysis showed that these differentially expressed genes were involved in various biological processes, cellular components and molecular functions. KEGG analysis indicated an enrichment of these differentially expressed genes in 240 pathways, including metabolic pathways, pancreatic secretion, protein digestion and absorption, fat digestion and absorption and glycerolipid metabolism. To verify the accuracy of the DGE results, quantitative reverse transcription PCR (qRT-PCR) was performed, focusing on key genes in several related pathways, and the results were highly consistent with the DGE results. Our findings indicated significant differences in cuticular protein genes, ecdysone biosynthesis genes and ecdysone-related nuclear receptors genes, but no significant difference in juvenile hormone and chitin biosynthesis genes was detected. Our research findings lay the foundation for further research on the formation mechanism of the nm2 mutant.

A Transcriptome Survey Spanning Life Stages and Sexes of the Harlequin Bug, Murgantia histrionica

The harlequin bug, Murgantia histrionica (Hahn), is an agricultural pest in the continental United States, particularly in southern states. Reliable gene sequence data are especially useful to the development of species-specific, environmentally friendly molecular biopesticides and effective biolures for this insect. Here, mRNAs were sampled from whole insects at the 2nd and 4th nymphal instars, as well as sexed adults, and sequenced using Illumina RNA-Seq technology. A global assembly of these data identified 72,540 putative unique transcripts bearing high levels of similarity to transcripts identified in other taxa, with over 99% of conserved single-copy orthologs among insects being detected. Gene ontology and protein family analyses were conducted to explore the functional potential of the harlequin bug's gene repertoire, and phylogenetic analyses were conducted on gene families germane to xenobiotic detoxification, including glutathione S-transferases, carboxylesterases and cytochrome P450s. Genic content in harlequin bug was compared with that of the closely related invasive pest, the brown marmorated stink bug, Halyomorpha halys (Stål). Quantitative analyses of harlequin bug gene expression levels, experimentally validated using quantitative real-time PCR, identified genes differentially expressed between life stages and/or sexes.

Modeling the flux of metabolites in the juvenile hormone biosynthesis pathway using generalized additive models and ordinary differential equations

Juvenile hormone (JH) regulates development and reproductive maturation in insects. The corpora allata (CA) from female adult mosquitoes synthesize fluctuating levels of JH, which have been linked to the ovarian development and are influenced by nutritional signals. The rate of JH biosynthesis is controlled by the rate of flux of isoprenoids in the pathway, which is the outcome of a complex interplay of changes in precursor pools and enzyme levels. A comprehensive study of the changes in enzymatic activities and precursor pool sizes have been previously reported for the mosquito Aedes aegypti JH biosynthesis pathway. In the present studies, we used two different quantitative approaches to describe and predict how changes in the individual metabolic reactions in the pathway affect JH synthesis. First, we constructed generalized additive models (GAMs) that described the association between changes in specific metabolite concentrations with changes in enzymatic activities and substrate concentrations. Changes in substrate concentrations explained 50% or more of the model deviances in 7 of the 13 metabolic steps analyzed. Addition of information on enzymatic activities almost always improved the fitness of GAMs built solely based on substrate concentrations. GAMs were validated using experimental data that were not included when the model was built. In addition, a system of ordinary differential equations (ODE) was developed to describe the instantaneous changes in metabolites as a function of the levels of enzymatic catalytic activities. The results demonstrated the ability of the models to predict changes in the flux of metabolites in the JH pathway, and can be used in the future to design and validate experimental manipulations of JH synthesis.

Depletion of juvenile hormone esterase extends larval growth in Bombyx mori

Two major hormones, juvenile hormone (JH) and 20-hydroxyecdysone (20E), regulate insect growth and development according to their precisely coordinated titres, which are controlled by both biosynthesis and degradation pathways. Juvenile hormone esterase (JHE) is the primary JH-specific degradation enzyme that plays a key role in regulating JH titers, along with JH epoxide hydrolase (JHEH) and JH diol kinase (JHDK). In the current study, a loss-of-function analysis of JHE in the silkworm, Bombyx mori, was performed by targeted gene disruption using the transgenic CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/RNA-guided Cas9 nucleases) system. Depletion of B. mori JHE (BmJHE) resulted in the extension of larval stages, especially the penultimate and ultimate larval stages, without deleterious effects to silkworm physiology. The expression of JHEH and JHDK was upregulated in mutant animals, indicating the existence of complementary routes in the JH metabolism pathway in which inactivation of one enzyme will activate other enzymes. RNA-Seq analysis of mutant animals revealed that genes involved in protein processing in the endoplasmic reticulum and in amino acid metabolism were affected by BmJHE depletion. Depletion of JHE and subsequent delayed JH metabolism activated genes in the TOR pathway, which are ultimately responsible for extending larval growth. The transgenic Cas9 system used in the current study provides a promising approach for analysing the actions of JH, especially in nondrosophilid insects. Furthermore, prolonging larval stages produced larger larvae and cocoons, which is greatly beneficial to silk production.

Juvenile hormone biosynthesis in adult Blattella germanica requires nuclear receptors Seven-up and FTZ-F1

In insects, the transition from juvenile development to the adult stage is controlled by juvenile hormone (JH) synthesized from the corpora allata (CA) glands. Whereas a JH-free period during the last juvenile instar triggers metamorphosis and the end of the growth period, the reappearance of this hormone after the imaginal molt marks the onset of reproductive adulthood. Despite the importance of such transition, the regulatory mechanism that controls it remains mostly unknown. Here, using the hemimetabolous insect Blattella germanica, we show that nuclear hormone receptors Seven-up-B (BgSvp-B) and Fushi tarazu-factor 1 (BgFTZ-F1) have essential roles in the tissue- and stage-specific activation of adult CA JH-biosynthetic activity. Both factors are highly expressed in adult CA cells. Moreover, RNAi-knockdown of either BgSvp-B or BgFTZ-F1 results in adult animals with a complete block in two critical JH-dependent reproductive processes, vitellogenesis and oogenesis. We show that this reproductive blockage is the result of a dramatic impairment of JH biosynthesis, due to the CA-specific reduction in the expression of two key JH biosynthetic enzymes, 3-hydroxy-3-methylglutaryl coenzyme A synthase-1 (BgHMG-S1) and HMG-reductase (BgHMG-R). Our findings provide insights into the regulatory mechanisms underlying the specific changes in the CA gland necessary for the proper transition to adulthood.

Functional characterization of ASTC (allatostatin C) and ASTCC (allatostatin double C) in Clostera anastomosis (Lepidoptera: Notodontidae)

ASTC (allatostatin C) and ASTCC (allatostatin double C) are two neuropeptide genes that encode allatostatin C-like peptides. Whether these peptides inhibit or have other effects on juvenile hormone (JH) synthesis in the corpora allata remains in question. The juvenile hormone acid O-methyltransferase (JHAMT), a key gene in the JH biosynthesis pathway, was selected to study the effects of ASTC and ASTCC on juvenile hormones. In this study, we first characterized the expression patterns and correlations between ASTC and ASTCC in Clostera anastomosis under natural conditions, and then the functions of these two genes were investigated by RNAi. The results showed the expression of JHAMT was strongly positive correlated with ASTC and ASTCC in the heads of larvae after ASTC and ASTCC were knocked down simultaneously, while negative correlations were found in the heads of female adults. These results suggest that both ASTC and ASTCC may stimulate JH biosynthesis in larvae while inhibit in female adults of C. anastomosis. And after either ASTC or ASTCC was knocked down alone, the correlation between the two genes were positive, indicating ASTC and ASTCC may function dependently in female heads. In addition, simultaneous suppression of ASTC and ASTCC increased the mortalities of larvae and pupae.

Ascarosides coordinate the dispersal of a plant-parasitic nematode with the metamorphosis of its vector beetle

Insect vectors are required for the transmission of many species of parasitic nematodes, but the mechanisms by which the vectors and nematodes coordinate their life cycles are poorly understood. Here, we report that ascarosides, an evolutionarily conserved family of nematode pheromones, are produced not only by a plant-parasitic nematode, but also by its vector beetle. The pinewood nematode and its vector beetle cause pine wilt disease, which threatens forest ecosystems world-wide. Ascarosides secreted by the dispersal third-stage nematode L_III larvae promote beetle pupation by inducing ecdysone production in the beetle and up-regulating ecdysone-dependent gene expression. Once the beetle develops into the adult stage, it secretes ascarosides that attract the dispersal fourth-stage nematode L_IV larvae, potentially facilitating their movement into the beetle trachea for transport to the next pine tree. These results demonstrate that ascarosides play a key role in the survival and spread of pine wilt disease.

Many species of nematodes use pheromones called ascarosides to coordinate their behaviour and development. Here, Zhao et al. demonstrate that the beetle vector of the pinewood nematode (Bursaphelenchus xylophilus) also uses and responds to ascarosides in its interactions with the nematodes.

Knockdown of juvenile hormone acid methyl transferase severely affects the performance of Leptinotarsa decemlineata (Say) larvae and adults

BACKGROUND

Juvenile hormone (JH) plays a critical role in the regulation of metamorphosis in Leptinotarsa decemlineata, a notorious defoliator of potato. JH acid methyltransferase (JHAMT) is involved in one of the final steps of JH biosynthesis.

RESULTS

A putative JHAMT cDNA (LdJHAMT) was cloned. Two double-stranded RNAs (dsRNAs) (dsJHAMT1 and dsJHAMT2) against LdJHAMT were constructed and bacterially expressed. Experiments were conducted to investigate the effectiveness of RNAi in both second- and fourth-instar larvae. Dietary introduction of dsJHAMT1 and dsJHAMT2 successfully knocked down the target gene, lowered JH titre in the haemolymph and reduced the transcript of Krüppel homologue 1 gene. Ingestion of dsJHAMT caused larval death and weight loss, shortened larval developmental period and impaired pupation. Moreover, the dsJHAMT-fed pupae exhibited lower adult emergence rates. The resulting adults weighed an average of 50 mg less than the control group, and the females did not deposit eggs. Application of pyriproxyfen to the dsJHAMT-fed insects rescued all the negative effects.

CONCLUSIONS

LdJHAMT expresses functional JHAMT enzyme. The RNAi targeting LdJHAMT could be used for control of L. decemlineata. © 2015 Society of Chemical Industry.

Novel family of terpene synthases evolved from trans-isoprenyl diphosphate synthases in a flea beetle

Sesquiterpenes play important roles in insect communication, for example as pheromones. However, no sesquiterpene synthases, the enzymes involved in construction of the basic carbon skeleton, have been identified in insects to date. We investigated the biosynthesis of the sesquiterpene (6R,7S)-himachala-9,11-diene in the crucifer flea beetle Phyllotreta striolata, a compound previously identified as a male-produced aggregation pheromone in several Phyllotreta species. A (6R,7S)-himachala-9,11-diene-producing sesquiterpene synthase activity was detected in crude beetle protein extracts, but only when (Z,E)-farnesyl diphosphate [(Z,E)-FPP] was offered as a substrate. No sequences resembling sesquiterpene synthases from plants, fungi, or bacteria were found in the P. striolata transcriptome, but we identified nine divergent putative trans-isoprenyl diphosphate synthase (trans-IDS) transcripts. Four of these putative trans-IDSs exhibited terpene synthase (TPS) activity when heterologously expressed. Recombinant PsTPS1 converted (Z,E)-FPP to (6R,7S)-himachala-9,11-diene and other sesquiterpenes observed in beetle extracts. RNAi-mediated knockdown of PsTPS1 mRNA in P. striolata males led to reduced emission of aggregation pheromone, confirming a significant role of PsTPS1 in pheromone biosynthesis. Two expressed enzymes showed genuine IDS activity, with PsIDS1 synthesizing (E,E)-FPP, whereas PsIDS3 produced neryl diphosphate, (Z,Z)-FPP, and (Z,E)-FPP. In a phylogenetic analysis, the PsTPS enzymes and PsIDS3 were clearly separated from a clade of known coleopteran trans-IDS enzymes including PsIDS1 and PsIDS2. However, the exon-intron structures of IDS and TPS genes in P. striolata are conserved, suggesting that this TPS gene family evolved from trans-IDS ancestors.

Mevalonate-Farnesal Biosynthesis in Ticks: Comparative Synganglion Transcriptomics and a New Perspective

Juvenile hormone (JH) controls the growth, development, metamorphosis, and reproduction of insects. For many years, the general assumption has been that JH regulates tick and other acarine development and reproduction the same as in insects. Although researchers have not been able to find the common insect JHs in hard and soft tick species and JH applications appear to have no effect on tick development, it is difficult to prove the negative or to determine whether precursors to JH are made in ticks. The tick synganglion contains regions which are homologous to the corpora allata, the biosynthetic source for JH in insects. Next-gen sequencing of the tick synganglion transcriptome was conducted separately in adults of the American dog tick, Dermacentor variabilis, the deer tick, Ixodes scapularis, and the relapsing fever tick, Ornithodoros turicata as a new approach to determine whether ticks can make JH or a JH precursor. All of the enzymes that make up the mevalonate pathway from acetyl-CoA to farnesyl diphosphate (acetoacetyl-CoA thiolase, HMG-S, HMG-R, mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate decarboxylase, and farnesyl diphosphate synthase) were found in at least one of the ticks studied but most were found in all three species. Sequence analysis of the last enzyme in the mevalonate pathway, farnesyl diphosphate synthase, demonstrated conservation of the seven prenyltransferase regions and the aspartate rich motifs within those regions typical of this enzyme. In the JH branch from farnesyl diphosphate to JH III, we found a putative farnesol oxidase used for the conversion of farnesol to farnesal in the synganglion transcriptome of I. scapularis and D. variabilis. Methyltransferases (MTs) that add a methyl group to farnesoic acid to make methyl farnesoate were present in all of the ticks studied with similarities as high as 36% at the amino acid level to insect JH acid methyltransferase (JHAMT). However, when the tick MTs were compared to the known insect JHAMTs from several insect species at the amino acid level, the former lacked the farnesoic acid binding motif typical in insects. The P450s shown in insects to add the C10,11 epoxide to methyl farnesoate, are in the CYP15 family; this family was absent in our tick transcriptomes and in the I. scapularis genome, the only tick genome available. These data suggest that ticks do not synthesize JH III but have the mevalonate pathway and may produce a JH III precursor.