Identification and characterization of highly active promoters from the fall armyworm, Spodoptera frugiperda

The Elongation Factor 1 Alpha Promoter Drives the Functional Expression of Kir2A in Plutella xylostella Cells

Cell lines and their corresponding expression plasmids are extensively utilized in the study of insect physiology and pathology. In this research, four single-cell cultured lines (Px4-1 to Px4-4) of Plutella xylostella were established from eggs. The promoter for the P. xylostella elongation factor 1α (PxEF1α), known for its high driving activity in cells, was cloned and used to construct expression plasmids. Dual-luciferase activity assays and EGFP expression analyses demonstrated that the PxEF1α promoter exhibited the strongest driving activity in Px4-2 cells, comparable to that of the immediate-early 1 promoter associated with the homologous region 5 enhancer (AcIE1hr5) from the Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). In contrast, the driving activity of PxEF1α in cells derived from Spodoptera frugiperda, Trichoplusia ni, and Helicoverpa armigera was lower. Furthermore, the PxEF1α promoter was successfully employed to drive inward rectifier potassium 2A (Kir2A) expression in Px4-2 cells. The electrophysiological properties of the insect Kir2A channel were successfully characterized for the first time. It was observed that the PxKir2A channel possesses typical inward rectifier potassium channel properties and can be inhibited by nanomolar concentrations of VU625 and VU590. This study offers a novel approach for the expression and investigation of foreign gene function in insect cells and provides a valuable tool for the in-depth study of key biomolecules in P. xylostella.

β2-tubulin and its promoter in the brown planthopper: A versatile tool for genetic control strategies

At present, the application of CRISPR/Cas9 technology for genetic manipulation in insects is predominantly concentrated on Diptera model species, including Drosophila and mosquitoes. In contrast, non-model insects such as the brown planthoppers (BPH, Nilaparvata lugens), a major insect pest of rice, have received less attention in genetic manipulation due to insufficient tools. Here, the analysis of spatiotemporal expression patterns revealed that β2-tubulin in BPH (NlB2t) was predominantly concentrated in male adults and male testis, exhibiting high expression levels. Knockdown of NlB2t expression by using RNAi resulted in the obstruction of male testis development. Mating between the RNAi-treated males and wild-type females led to a notable reduction in the number of eggs laid and the hatching rate of those eggs by 58.2% and 50.6%, respectively. The longevity of RNAi males significantly increased, and females that had previously mated with RNAi males exhibited a diminished inclination for re-mating with wild-type males. The dual-luciferase reporter assay demonstrated robust promoter activity in the upstream 943 bp of NlB2t, capable of driving Cas9 protein expression in vivo and effectively inducing target gene knockout. These findings elucidated that NlB2t may be a key gene in BPH male testis development and reproduction, as a promising target for sterilization. Its upstream promoter serves as a germline promoter, significantly facilitating the development of genetic control tools based on CRISPR/Cas9 technology in BPH.

Characterization of ATP-binding cassette transporters associated with emamectin benzoate tolerance: from the model insect Drosophila melanogaster to the agricultural pest Spodoptera frugiperda

BACKGROUND

Multiple families of detoxification genes, including the increasingly recognized family of ATP-binding cassette (ABC) transporters, work together to influence the toxicity of synthetic insecticides and thus their resistance. Effective management of insecticide resistance requires identification of all toxicity-affecting members from each family of toxicity-related genes.

RESULTS

Here, we used emamectin benzoate (EB), ABC transporters and Spodoptera frugiperda as a working case to test whether the strategy of 'from the model insect Drosophila melanogaster to agricultural pests' can identify all or most ABC transporter members related to EB tolerance in S. frugiperda. After confirming the involvement of ABC transporters in the toxicity of EB against fruit fly with the ABC inhibitor verapamil, four ABC transporter genes (DmCG3327, DmCG11147, DmCG4822, and DmCG7627) were found to be involved in EB tolerance using RNA interference-based family-wide functional screening. A combination of phylogenic analysis and a reciprocal TBLASTN search identified five S. frugiperda ABC transporter members as homologs (SfABCC4, SfABCG1, and SfABCG23) or one-way best hits (SfABCG4 and SfABCG20) of the four fly ABC genes. Real-time quantitative polymerase chain reaction (qPCR) analysis found that all five S. frugiperda ABC transporter genes were inducible by EB, and expressed in all the developmental stages and larval tissues, but with significant quantitative differences among stages and tissues. A cytotoxicity assay of ABC-overexpressing Sf9 cell lines showed that all the five S. frugiperda ABC transporter genes made Sf9 cells tolerant to EB.

CONCLUSIONS

This study not only identifies nine ABC transporter genes related to EB tolerance from D. melanogaster (four genes) and S. frugiperda (five genes), but also demonstrates the utility and effectiveness of the 'model to pests' strategy to identify most toxicity-affecting members from a given family of toxicity-related genes. © 2024 Society of Chemical Industry.

Plant defense metabolites influence the interaction between an insect herbivore and an entomovirus

The tri-trophic interaction of plants, insect herbivores, and entomoviruses is an important topic in ecology and pest control. The susceptibility of insect herbivores to entomoviruses (e.g., nucleopolyhedroviruses) is influenced by host plants; however, the role of plant secondary metabolites in determining such susceptibility is poorly understood. Metabolomic analyses of Brassica oleracea, Glycine max, and Ipomoea aquatica plants, which differ in how they affect the susceptibility of Spodoptera exigua to nucleopolyhedroviruses among 14 plants, suggested that the plant secondary metabolites genistein, kaempferol, quercitrin, and coumarin play a role in influencing nucleopolyhedroviruses susceptibility. Subsequently, transcriptomic analysis of caterpillars, treated with nucleopolyhedroviruses alone or with one of these four phenolics, identified four genes (CYP340K4, CXE18, GSTe, and GSTe1) that were significantly downregulated by the phenolics. Functional characterization of these genes suggested that their downregulation significantly increased larval sensitivity to nucleopolyhedroviruses and altered aspects of the immune response. Our findings provide new insight into the role of plant defense metabolites in influencing the interactions between insect herbivores and entomopathogens and identify plant secondary metabolites as potential synergists of viral agents for the control of agricultural pests.

Chronologically inappropriate morphogenesis (Chinmo) is required for maintenance of larval stages of fall armyworm

Broad complex (Br-C) and eip93F (E93) transcription factors promote insect metamorphosis from larva to pupa and from pupa to adult, respectively. Recently, chronologically inappropriate morphogenesis (Chinmo) has been proposed as a larval specifier in Drosophila melanogaster. However, whether Chinmo is required for larval maintenance in lepidopteran insects, the underlying mechanisms involved in maintaining the larval stage, and its interactions with the JH signaling pathway are not well understood. Here, we used a binary transgenic CRISPR/Cas9 system to knockout Chinmo and Kr-h1 (primary response gene in the JH signaling pathway) in the fall armyworm (FAW). Kr-h1 knockout induced premature metamorphosis only after L5 (penultimate), whereas Chinmo and Kr-h1 double knockout induced premature metamorphosis in L3. Sequencing and differential gene expression (DEG) analysis of RNA isolated from mutants and single-cell multiome ATAC analysis of Chinmo, Kr-h1, and Chinmo and Kr-h1 double knockout Sf9 cells revealed that Chinmo participates in chromatin modifications that prevent the promoter accessibility and expression of metamorphosis promoting genes. These results suggest that Chinmo is a larval specifier that plays a major role in preventing metamorphosis in early larval stages by controlling chromatin accessibility near the promoters of genes such as Br-C and E93 required for pupal and adult development.

Identification and characterization of ATP-binding cassette transporters involved in chlorantraniliprole tolerance of model insect Drosophila melanogaster and agricultural pest Spodoptera frugiperda

ATP-binding cassette (ABC) transporter family is one of the largest transporter families, which plays an important role in insecticide tolerance. In this study, we found that the ABC transporter inhibitor verapamil could significantly enhance the toxicity of chlorantraniliprole (CHL) to the model insect Drosophila melanogaster. Forty-six ABC transporter genes of D. melanogaster were knocked down through the daughterless-GAL4 (Da-GAL4) strain. The subsequent bioassay result showed that D. melanogaster with DmCG5772, DmCG1494, and DmCG5853 genes silencing significantly increased mortality after CHL treatment. Based on the genome of the fall armyworm (FAW), three genes with the best hits were identified, and SfABCA1 (XM_035576510.2) and SfABCG10 (XM_035577893.2) were successfully cloned. Spatiotemporal expression pattern analysis showed that SfABCA1 and SfABCG10 were both highly expressed in adult and pupal stages. Hemolymph was also a tissue with high expression of these two genes. LC10 dose of CHL could induce the expression levels of SfABCA1 and SfABCG10, with SfABCG10 upregulated 8-fold after 48 h of CHL treatment. Furthermore, overexpression of SfABCA1 and SfABCG10 increased the viability of Sf9 cell under CHL treatment. Our findings indicate that SfABCA1 and SfABCG10 might associate with the tolerance of CHL in S. frugiperda. These results are not only helpful in understanding the role of ABC transporters in CHL tolerance of other agricultural pests, but also lay a theoretical foundation for delaying the development of CHL resistance in pest management.

Establishing a dominant early larval sex-selection strain in the Asian malaria vector Anopheles stephensi

BACKGROUND

Genetic biocontrol interventions targeting mosquito-borne diseases require the release of male mosquitoes exclusively, as only females consume blood and transmit pathogens. Releasing only males eliminates the risk of increasing mosquito bites and spreading pathogens while enabling effective population control. The aim of this study is to develop robust sex-sorting methods for early larval stages in mosquitoes, enabling scalable male-only releases for genetic biocontrol interventions.

METHODS

To address the challenge of sex-sorting in the Asian malaria vector Anopheles stephensi, we engineer Sexing Element Produced by Alternative RNA-splicing of a Transgenic Observable Reporter (SEPARATOR). This dominant fluorescent-based method, previously proven effective in Aedes aegypti, exploits sex-specific alternative splicing of a reporter to ensure exclusive male-specific expression early in development. The sex-specific alternative RNA splicing of the doublesex gene was selected as a target for engineering SEPARATOR due to its evolutionary conservation in insects. To expand SEPARATOR's applicability for genetic sexing, we assessed the cross-species sex-specific RNA splicing activity of the An. gambiae doublesex (AngDsx) splicing module in An. stephensi. Male-specific enhanced green fluorescent protein (EGFP) expression was verified throughout the mosquito life cycle using a fluorescent stereomicroscope.

RESULTS

Our results confirm that SEPARATOR regulates male-specific EGFP expression in An. stephensi and enables reliable positive male selection from the first instar larval stages. Molecular analysis demonstrates that male-specific EGFP expression is dependent on doublesex sex-specific splicing events. Additionally, the splicing module from An. gambiae operates effectively in An. stephensi, demonstrating evolutionary conservation in sex-specific splicing events between these species.

CONCLUSIONS

SEPARATOR's independence from sex-chromosome linkage provides resistance to breakage that could be mediated by meiotic recombination and chromosomal rearrangements, making it highly suitable for mass male releases. By enabling precise male selection from the first instar larval stages, SEPARATOR represents a significant advancement that will aid in the genetic biocontrol for Anopheles mosquitoes.

CRISPR/Cas9-Based Genome Editing of Fall Armyworm (Spodoptera frugiperda): Progress and Prospects

The fall armyworm (Spodoptera frugiperda) poses a substantial threat to many important crops worldwide, emphasizing the need to develop and implement advanced technologies for effective pest control. CRISPR/Cas9, derived from the bacterial adaptive immune system, is a prominent tool used for genome editing in living organisms. Due to its high specificity and adaptability, the CRISPR/Cas9 system has been used in various functional gene studies through gene knockout and applied in research to engineer phenotypes that may cause economical losses. The practical application of CRISPR/Cas9 in diverse insect orders has also provided opportunities for developing strategies for genetic pest control, such as gene drive and the precision-guided sterile insect technique (pgSIT). In this review, a comprehensive overview of the recent progress in the application of the CRISPR/Cas9 system for functional gene studies in S. frugiperda is presented. We outline the fundamental principles of applying CRISPR/Cas9 in S. frugiperda through embryonic microinjection and highlight the application of CRISPR/Cas9 in the study of genes associated with diverse biological aspects, including body color, insecticide resistance, olfactory behavior, sex determination, development, and RNAi. The ability of CRISPR/Cas9 technology to induce sterility, disrupt developmental stages, and influence mating behaviors illustrates its comprehensive roles in pest management strategies. Furthermore, this review addresses the limitations of the CRISPR/Cas9 system in studying gene function in S. frugiperda and explores its future potential as a promising tool for controlling this insect pest.

Establishing a Male-Positive Genetic Sexing Strain in the Asian Malaria Vector Anopheles stephensi

Genetic biocontrol interventions targeting mosquito-borne diseases require the release of male mosquitoes exclusively, as only females consume blood and transmit human pathogens. This reduces the risk of spreading pathogens while enabling effective population control. Robust sex sorting methods to enable early larval sorting in mosquitoes need to be developed to allow for scalable sex sorting for genetic biocontrol interventions. This study applies the SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) system, previously developed for Aedes aegypti, to the Asian malaria vector Anopheles stephensi. We hypothesized that the intron from the doublesex gene in Anopheles gambiae would function in An. stephensi due to evolutionary conservation. Our results confirm that the splicing module from An. gambiae operates effectively in An. stephensi, demonstrating evolutionary conservation in sex-specific splicing events between these species. This system enables reliable positive male selection from first instar larval to pupal stages. RT-PCR analysis demonstrates that male-specific EGFP expression is dependent on doublesex sex-specific splicing events. The SEPARATOR system's independence from sex-chromosome linkage confers resistance to meiotic recombination and chromosomal rearrangements. This approach may facilitate the mass release of males, and the cross-species portability of SEPARATOR establishes it as a valuable tool for genetic biocontrol interventions across various pest species.

Efficient sex separation by exploiting differential alternative splicing of a dominant marker in Aedes aegypti

Only female mosquitoes consume blood giving them the opportunity to transmit deadly human pathogens. Therefore, it is critical to remove females before conducting releases for genetic biocontrol interventions. Here we describe a robust sex-sorting approach termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) that exploits sex-specific alternative splicing of an innocuous reporter to ensure exclusive dominant male-specific expression. Using SEPARATOR, we demonstrate reliable sex selection from early larval and pupal stages in Aedes aegypti, and use a Complex Object Parametric Analyzer and Sorter (COPAS) to demonstrate scalable high-throughput sex-selection of first instar larvae. Additionally, we use this approach to sequence the transcriptomes of early larval males and females and find several genes that are sex-specifically expressed. SEPARATOR can simplify mass production of males for release programs and is designed to be cross-species portable and should be instrumental for genetic biocontrol interventions.

Efficient Sex Separation by Exploiting Differential Alternative Splicing of a Dominant Marker in Aedes aegypti

Only female mosquitoes consume blood and transmit deadly human pathogens. Therefore, it is critical to remove females before conducting releases for genetic biocontrol interventions. Here we describe a robust sex-sorting approach termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) that exploits sex-specific alternative splicing of an innocuous reporter to ensure exclusive dominant male-specific expression. Using SEPARATOR, we demonstrate reliable sex selection from larval and pupal stages in Aedes aegypti, and use a Complex Object Parametric Analyzer and Sorter (COPAS®) to demonstrate scalable high-throughput sex-selection of first instar larvae. Additionally, we use this approach to sequence the transcriptomes of early larval males and females and find several genes that are sex-specifically expressed in males. SEPARATOR can simplify mass production of males for release programs and is designed to be cross-species portable and should be instrumental for genetic biocontrol interventions.

Gene expression in Verson's glands of the fall armyworm suggests their role in molting and immunity

Verson's glands are segmental pairs of dermal glands attached to the epidermis in lepidopteran larvae. They produce macromolecules during intermolt period and empty them during each molt. Morphological, histochemical, developmental, and protein analysis studies have been conducted to determine the functions of Verson's glands. However, the exact role of Verson's glands remains unclear. In our previous study, a strain of transgenic fall armyworm, Spdoptera frugiperda expressing green fluorescence protein (GFP) and Systemic RNA interference defective protein 1 (SID1) from Caenorhabditis elegans was established to improve RNA interference (RNAi) efficiency. Unexpectedly, we found that GFP fluorescence was significantly brighter in Verson's glands than in other tissues. Also, RNAi efficiency improved more in Verson's glands than in other tissues. We took advantage of improved RNAi efficiency to explore the function of Verson's glands. RNA-seq analysis revealed that genes highly expressed in Verson's glands code for cuticular proteins, molting fluid proteins, hemolymph proteins, and antimicrobial peptides. Injection of dsRNA targeting essential genes, inhibitor of apoptosis (IAP), Actin, and vacuolar-type ATPase (VATPase) interfered with Verson's glands growth. These results revealed that Verson's glands may contribute to hemolymph, cuticle, molting fluid, and immune response during molting. This study also provide useful tools for future research in identifying the physiological role of Verson's glands in lepidopteran insects.

dsRNase1 contribution to dsRNA degradation activity in the Sf9 cells conditioned medium

RNA interference (RNAi) is inefficient in lepidopteran insects, including Spodoptera frugiperda. RNase activity in the lumen and hemocoel is known to contribute to low RNAi efficiency in these insects. Conditioned medium from Sf9 cells developed from ovaries of S. frugiperda shows high dsRNA degradation activity. But the enzymes responsible for this activity have not been identified. The nuclease genes that are highly expressed in Sf9 cells, REase, RNaseT2, and dsRNase1, were identified. Knockdown of dsRNase1 in Sf9 cells resulted in a reduction of dsRNA degradation activity in the Sf9 cells conditioned medium. Knockdown of dsRNase1 also increased RNAi efficiency in Sf9 cells. The results from these studies identified a major player in dsRNA degradation activity in the Sf9 cells conditioned medium. We also describe an efficient system that can be used to identify other genes responsible for dsRNA degradation and RNAi efficiency in Sf9 cells.

Identification of species-specific juvenile hormone response elements in the fall armyworm, Spodoptera frugiperda

Juvenile hormones (JH) regulate insect development and reproduction. The JH analogs (JHA) are used as insecticides. However, JHAs are rarely used in managing pests such as the fall armyworm, Spodoptera frugiperda that cause damage during larval stages. The insecticides that antagonize JH action and induce stoppage of feeding and precocious metamorphosis might work better to control these pests. Treating insects with JHA insecticides induces the expression of an early JH response gene, Krüppel homolog 1 (Kr-h1) by working through JH response elements (JHRE) present in its promoter. In this study, we identified JHREs present in the promoter of Kr-h1 gene of a global pest, S. frugiperda, and used them to develop a JHRE-reporter cell platform to screen for JH analogs. JHA, methoprene induced the expression of SfKr-h1 both in vitro and in vivo. JHRE present in the promoters of two SfKr-h1 isoforms, SfKr-h1α and SfKr-h1β were identified. In Sf9 cells, the knockout of isoform-specific JHRE affected JH response in an isoform-specific manner. We also found that S. frugiperda JHRE (SfJHRE) did not function in the mosquito Aedes aegypti Aag2 cells and Tribolium castaneum TcA cells. Similarly, Ae. aegypti AaJHRE and T. castaneum TcJHRE were only functional in cells derived from these insects. The nucleotide sequence at the 3'end to the conserved core JHRE E-box sequence seems to be responsible for the species specificity observed. Two stable cell lines expressing the luciferase and enhanced green fluorescent protein genes under the control of SfJHRE were established. These cell lines responded well to JHA; these two JHRE-reporter cell lines could be used in screening assays to identify insecticides to manage S. frugiperda and other major pests.

Optimization and Application of CRISPR/Cas9 Genome Editing in a Cosmopolitan Pest, Diamondback Moth

The CRISPR/Cas9 system is an efficient tool for reverse genetics validation, and the application of this system in the cell lines provides a new perspective on target gene analysis for the development of biotechnology tools. However, in the cell lines of diamondback moth, Plutella xylostella, the integrity of the CRISPR/Cas9 system and the utilization of this cell lines still need to be improved to ensure the application of the system. Here, we stabilize the transfection efficiency of the P. xylostella cell lines at different passages at about 60% by trying different transfection reagents and adjusting the transfection method. For Cas9 expression in the CRIPSPR/Cas9 system, we identified a strong endogenous promoter: the 217–2 promoter. The dual-luciferase and EGFP reporter assay demonstrated that it has a driving efficiency close to that of the IE1 promoter. We constructed pB-Cas9-Neo plasmid and pU6-sgRNA plasmid for CRISPR/Cas9 system and subsequent cell screening. The feasibility of the CRISPR/Cas9 system in P. xylostella cell lines was verified by knocking out endogenous and exogenous genes. Finally, we generated a transgenic Cas9 cell line of P. xylostella that would benefit future exploitation, such as knock-in and multi-threaded editing. Our works provides the validity of the CRISPR/Cas9 system in the P. xylostella cell lines and lays the foundation for further genetic and molecular studies on insects, particularly favoring gene function analysis.

SoxC is Required for Ecdysteroid Induction of Neuropeptide Genes During Insect Eclosion

In insects, the shedding of the old exoskeleton is accomplished through ecdysis which is typically followed by the expansion and tanning of the new cuticle. Four neuropeptides, eclosion hormone (EH), ecdysis triggering hormone (ETH), crustacean cardioactive peptide (CCAP) and bursicon (Bur) are known to control ecdysis. However, the regulation of these neuropeptide genes is still poorly understood. Here, we report that in the red flour beetle (RFB) Tribolium castaneum and the fall armyworm (FAW) Spodoptera frugiperda, knockdown or knockout of the SoxC gene caused eclosion defects. The expansion and tanning of wings were not complete. In both RFB and FAW, the knockdown or knockout of SoxC resulted in a decrease in the expression of EH gene. Electrophoretic mobility shift assays revealed that the SfSoxC protein directly binds to a motif present in the promoter of SfEH. The luciferase reporter assays in Sf9 cells confirmed these results. These data suggest that transcription factor SoxC plays a key role in ecdysteroid induction of genes coding for neuropeptides such as EH involved in the regulation of insect eclosion.

Identification of Helicoverpa armigera promoters for biotechnological applications

Helicoverpa armigera and Helicoverpa zea are highly polyphagous major agricultural pests with a global distribution. Their control is based on insecticides, however, new, effective, and environmentally friendly control tools are required to be developed and validated. In an effort to facilitate the development of advanced biotechnological tools in these species that will take advantage of new powerful molecular biology techniques like CRISPR/Cas9, we used available transcriptomic data and literature resources, in order to identify RNA polymerase II and III promoters active in RP-HzGUT-AW1(MG), a midgut derived cell line from Helicoverpa zea. Following functional analysis in insect cell lines, four RNA polymerase II promoters from the genes HaLabial, HaTsp-2A, HaPtx-I and HaCaudal were found to exhibit high transcriptional activity in vitro. The HaTsp-2A promoter did not exhibit any activity in the non-midgut derived cell lines Sf-9 and Hi-5 despite high sequence conservation among Lepidoptera, suggesting that it may function in a gut specific manner. Furthermore, considering the utility of RNA polymerase III U6 promoters in methodologies such as RNAi and CRISPR/Cas9, we identified and evaluated four different U6 promoters of H. armigera. In vitro experiments based on luciferase and GFP reporter assays, as well as in vivo experiments targeting an essential gene of Helicoverpa, indicate that these U6 promoters are functional and can be used to experimentally silence or knockout target genes through the expression of shRNAs and sgRNAs respectively. Taking our findings together, we provide a set of promoters useful for the genetic manipulation of Helicoverpa species, that can be used in various applications in the context of agricultural biotechnology.

Cis-regulatory elements of the cholinergic gene locus in the silkworm Bombyx mori

Genes of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter are encoded in the same gene locus, called the cholinergic gene locus. They are essential in cholinergic neurons to maintain their functional phenotype. The genomic structure of the cholinergic gene locus is conserved among invertebrates to mammals. However, the cholinergic gene expression in a specific subset of neurons is unknown in insects except for Drosophila melanogaster. In this study, we analysed the upstream sequence of cholinergic gene locus in the silkworm Bombyx mori to identify specific cis-regulatory regions. We found multiple enhancer regions that are localized within 1 kb upstream of the cholinergic gene locus. The combination of promoter assays using small deletions and bioinformatic analysis among insect species illuminates two conserved sequences in the cis-regulatory region: TGACGTA and CCAAT, which are known as the cAMP response element and CAAT box, respectively. We found that dibutyryl-cAMP, an analogue of cAMP, influences the expression of ChAT in B. mori. Tissue-specific expression analysis of transcriptional factors identified potential candidates that control the cholinergic gene locus expression. Our investigation provides new insight into the regulation mechanism of cholinergic neuron-specific gene machinery in this lepidopteran insect.

Caenorhabditis elegans systemic RNA interference defective protein 1 enhances RNAi efficiency in a lepidopteran insect, the fall armyworm, in a tissue-specific manner

RNA interference (RNAi) is an important tool for gene function studies in insects, especially in non-model insects. This technology is also being developed for pest control. However, variable RNAi efficiency among insects is limiting its use in insects. Systemic RNAi in Caenorhabditis elegans requires systemic RNA interference defective protein 1 (CeSid1). The expression of CeSid1 in insect cell lines was shown to improve RNAi. However, the mechanisms through which this double-stranded RNA (dsRNA) transporter improves RNAi efficiency in insects is not known. We stably expressed CeSid1 in two Spodoptera frugiperda cell lines, Sf9 and Sf17 cells derived from ovary and midgut, respectively. Expression of CeSid1 enhanced RNAi efficiency in ovarian Sf9 cells, but not in midgut Sf17 cells. Reduced accumulation of dsRNA in late endosomes and successful processing dsRNA to siRNA contribute to enhanced RNAi efficiency in Sf9 cells. Transgenic S. frugiperda expressing CeSid1 were produced and tested for RNAi efficiency. RNAi efficiency enhancement due to CeSid1 expression showed tissue specificity. Compared to RNAi efficiency in wild-type S. frugiperda, CeSid1 expressing transgenic S. frugiperda showed a significant improvement of RNAi in tissues such as Verson's glands. In contrast, no improvement in RNAi was observed in tissues such as midgut. The in vitro cell-type specific and in vivo tissue-specific enhancement of RNAi efficiency by CeSid1 in S. frugiperda provides valuable information for improving RNAi in insects such as those belonging to order Lepidoptera where RNAi is variable and inefficient.