Effects of chitin synthase double-stranded RNA on molting and oogenesis in the Chagas disease vector Rhodnius prolixus

RNAi silencing CHS1 gene shortens the mortality time of Plutella xylostella feeding Bt-transgenic Brassica napus

BACKGROUND

Insect-resistance genetically modified (GM) plants derived from Bacillus thuringiensis (Bt) have been cultivated to control pests, but continuous cultivation of Bt-transgenic plants at large-scale regions leads to the resistance evolution of target insects to transgenic plants. RNA interference (RNAi) technology is considered an effective strategy in delaying the resistance evolution of target insects.

RESULTS

We here developed a single transgenic oilseed rape (Brassica napus) line with hairpin RNA of the chitin-synthase 1 gene (CHS1) of Plutella xylostella (hpPxCHS1) and a pyramid transgenic B. napus line harboring hpPxCHS1 and Bt gene (Cry1Ac). Escherichia coli HT115 delivered hpPxCHS1 showed negative effects on the growth of P. xylostella. The single transgenic and pyramid transgenic B. napus significantly reduced the larval weight and length of P. xylostella and increased its lethality rate, with down-regulation expression of the PxCHS1 gene in insects.

CONCLUSION

Compared to Bt-transgenic B. napus, pyramid-transgenic B. napus shorted the mortality time of P. xylostella, indicating that RNAi technology synergistic with Bt protein improves the effectiveness of controlling target insects. Our results proved that RNAi can delay the resistance evolution of target insects to Bt-transgenic plants. © 2024 Society of Chemical Industry.

RNA Interference-Mediated Suppression of Ecdysone Signaling Inhibits Choriogenesis in Two Coleoptera Species

During choriogenesis in insects, chorion (eggshell) is formed by surrounding follicular epithelial cells in ovarioles. However, the regulatory endocrine factor(s) activating choriogenesis and the effect of chemical components on eggshell deserve further exploration. In two representative coleopterans, a coccinellid Henosepilachna vigintioctopunctata and a chrysomelid Leptinotarsa decemlineata, genes encoding the 20-hydroxyecdysone (20E) receptor heterodimer, ecdysone receptor (EcR) and ultraspiracle (USP), and two chitin biosynthesis enzymes UDP-N-acetylglucosamine pyrophosphorylase (UAP) and chitin synthase (ChS1), were highly expressed in ovaries of the young females. RNA interference (RNAi)-aided knockdown of either HvEcR or Hvusp in H. vigintioctopunctata inhibited oviposition, suppressed the expression of HvChS1, and lessened the positive signal of Calcofluor staining on the chorions, which suggests the reduction of a chitin-like substance (CLS) deposited on eggshells. Similarly, RNAi of LdEcR or Ldusp in L. decemlineata constrained oviposition, decreased the expression of LdUAP1 and LdChS1, and reduced CLS contents in the resultant ovaries. Knockdown of LdUAP1 or LdChS1 caused similar defective phenotypes, i.e., reduced oviposition and CLS contents in the L. decemlineata ovaries. These results, for the first time, indicate that 20E signaling activates choriogenesis in two coleopteran species. Moreover, our findings suggest the deposition of a CLS on the chorions.

Effect of four chitinase genes on the female fecundity in Sogatella furcifera (Horváth)

BACKGROUND

The white-backed planthopper (WPH), Sogatella furcifera (Horváth), is a destructive rice pest with strong reproductive capacity. To gain insights into the roles of chitinases in the reproductive process of this insect species, this study represents the first-ever endeavor to conduct an in-depth exploration into the reproductive functions of four chitinase genes.

RESULTS

In this study, it was observed that four chitinase genes were expressed in female adults, with a relatively high expression level in the ovaries. SfCht2 and SfIDGF1 were highly expressed during later ovarian development. while SfENGase increased and then decreased with ovarian development. SfCht2, SfCht6-2 and SfENGase were highly expressed in fat body on the first and second days after eclosion, whereas SfIDGF1 highest on day 7. Compared with control group, Silencing four chitinase genes inhibited ovarian development and significantly shortened the oviposition period of S. furcifera, reducing egg-laying capacity but not affecting egg hatching. The detection demonstrated that the expression levels of SfVg, SfVgR and 70-90% juvenile hormone (JH) signaling pathway-related reproductive genes was significantly down-regulated. Moreover, SfCht6-2 and SfENGase significantly affected the expression levels of Target of Rapamycin (TOR) signaling pathway genes. SfENGase had the ability to impact nutrient signaling pathways and fatty acid metabolism, repressing vitellogenin synthesis and ultimately influencing ovarian development of S. furcifera.

CONCLUSIONS

Overall, this study provides insight into the function of chitinases in insect fecundity and is of great significance for enriching the cognition of insect chitinase function. They will become the suitable target genes for controlling the most destructive rice planthoppers. © 2023 Society of Chemical Industry.

Advances in understanding insect chitin biosynthesis

Chitin, a natural polymer of N-acetylglucosamine chains, is a principal component of the apical extracellular matrix in arthropods. Chitin microfibrils serve as structural components of natural biocomposites present in the extracellular matrix of a variety of invertebrates including sponges, molluscs, nematodes, fungi and arthropods. In this review, we summarize the frontier advances of insect chitin synthesis. More specifically, we focus on the chitin synthase (CHS), which catalyzes the key biosynthesis step. CHS is also known as an attractive insecticidal target in that this enzyme is absent in mammals, birds or plants. As no insect chitin synthase structure have been reported so far, we review recent studies on glycosyltransferase domain structures derived from fungi and oomycetes, which are conserved in CHS from all species containing chitin. Auxiliary proteins, which coordinate with CHS in chitin biosynthesis and assembly, are also discussed.

Nanomedicine as a potential novel therapeutic approach against the dengue virus

Dengue is an arbovirus infection which is transmitted by Aedes mosquitoes. Its prompt detection and effective treatment is a global health challenge. Various nanoparticle-based vaccines have been formulated to present immunogen (antigens) to instigate an immune response or prevent virus spread, but no specific treatment has been devised. This review explores the role of nanomedicine-based therapeutic agents against dengue virus, taking into consideration the applicable dengue virus assays that are sensitive, specific, have a short turnaround time and are inexpensive. Various kinds of metallic, polymeric and lipid nanoparticles with safe and effective profiles present an alternative strategy that could provide a better remedy for eradicating the dengue virus.

Characterization of Chitin Synthase B Gene (HvChsb) and the Effects on Feeding Behavior in Heortia vitessoides Moore

The chitin synthase B gene is a key enzyme in the chitin synthesis of insect peritrophic matrix (PM), which affects insects' feeding behavior. The chitin synthase B gene was cloned from the transcription library of Heortia vitessoides Moore. RT-qPCR showed that HvChsb was highly expressed in the larval stage of H. vitessoides, especially on the first day of the pre-pupal stage, as well as in the midgut of larvae and the abdomen of adults. After starvation treatment, HvChsb was found to be significantly inhibited over time. After 48 h of starvation, the feeding experiment showed that HvChsb increased with the prolongation of the re-feeding time. The experimental data showed that feeding affected the expression of HvChsb. HvChsb was effectively silenced via RNA interference; thus, its function was lost, significantly decreasing the survival rate of H. vitessoides. The survival rate from larval-to-pupal stages was only 43.33%, and this rate was accompanied by abnormal phenotypes. It can be seen that HvChsb plays a key role in the average growth and development of H. vitessoides.

Structure and expression of Rhodnius prolixus GH18 chitinases and chitinase-like proteins: Characterization of the physiological role of RpCht7, a gene from subgroup VIII, in vector fitness and reproduction

Chitinases are enzymes responsible for the hydrolysis of glycosidic linkages within chitin chains. In insects, chitinases are typically members of the multigenic glycoside hydrolase family 18 (GH18). They participate in the relocation of chitin during development and molt, and in digestion in detritivores and predatory insects, and they control the peritrophic membrane thickness. Chitin metabolism is a promising target for developing vector control strategies, and knowledge of the roles of chitinases may reveal new targets and illuminate unique aspects of their physiology and interaction with microorganisms. Rhodnius prolixus is an important vector of Chagas disease, which is caused by the parasite Trypanosoma cruzi. In this study, we performed annotation and structural characterization of nine chitinase and chitinase-like protein genes in the R. prolixus genome. The roles of their corresponding transcripts were studied in more depth; their physiological roles were studied through RNAi silencing. Phylogenetic analysis of coding sequences showed that these genes belong to different subfamilies of GH18 chitinases already described in other insects. The expression patterns of these genes in different tissues and developmental stages were initially characterized using RT-PCR. RNAi screening showed silencing of the gene family members with very different efficiencies. Based on the knockdown results and the general lack of information about subgroup VIII of GH18, the RpCht7 gene was chosen for phenotype analysis. RpCht7 knockdown doubled the mortality in starving fifth-instar nymphs compared to dsGFP-injected controls. However, it did not alter blood intake, diuresis, digestion, molting rate, molting defects, sexual ratio, percentage of hatching, or average hatching time. Nevertheless, female oviposition was reduced by 53% in RpCht7-silenced insects, and differences in oviposition occurred within 14–20 days after a saturating blood meal. These results suggest that RpCht7 may be involved in the reproductive physiology and vector fitness of R. prolixus.

CARACTERIZACIÓN Y DISMINUCIÓN EN LA EXPRESIÓN DE UNA QUITINA SINTASA MEDIADA POR ARNi EN Hypothenemus hampei (CURCULIONIDAE)

La broca del café, Hypothenemus hampei, es un insecto plaga que causa daños significativos al grano de café y grandes pérdidas económicas a los productores en todo el mundo. Al igual que otros insectos, la broca de café requiere de quitina sintasas (CHS) para la biosíntesis de la quitina, componente principal del exoesqueleto del insecto, y de vital importancia para su crecimiento y desarrollo. En este estudio, el gen CHS1 de la broca del café (HhCHS1) fue identificado, caracterizado y posteriormente silenciado mediante el uso de ARNi, mecanismo que permite degradar el ARNm e interrumpir la expresión de proteínas de interés en un organismo. Los perfiles de expresión del gen HhCHS1, medidos por RT-qPCR, mostraron niveles de expresión diferencial en las diferentes etapas del desarrollo del insecto. Los niveles más altos de expresión se encontraron en larvas de segundo estadio (L2) y machos adultos. El ARNcd administrado por vía oral, a concentraciones de 2 µg/100 µL, generó un silenciamiento efectivo del gen HhCHS1 (84 %) después de 7 días de tratamiento. Estos resultados sugieren que el gen HhCHS1 desempeña un papel importante en el desarrollo del insecto, y que, por ende, podría usarse como objetivo para desarrollar nuevas estrategias de manejo de este insecto plaga, mediante el uso de ARNi.  Palabras Clave: ARNcd, café, insecto plaga, quitina-sintasa, RT-qPCR.

RNAi for chitin synthase 1 rather than 2 causes growth delay and molting defect in Henosepilachna vigintioctopunctata

Chitin synthase (CHS) plays a critical role in chitin synthesis and excretion. In most insects, CHSs have been segregated into 1 and 2 classes. CHS1 is responsible for chitin production in the ectodermally-derived epidermal cells. CHS2 is dedicated to chitin biosynthesis in the midgut peritrophic matrix (PM). Henosepilachna vigintioctopunctata is a serious pest of Solanaceae and Cucurbitaceae plants. In this study, we identified HvCHS1 and HvCHS2. We found that HvCHS1 was abundantly transcribed in the larval tracheae and epidermis, whereas HvCHS2 was mainly expressed in the guts. Escherichia coli HT115 expressed double stranded RNAs targeting HvCHS1 and HvCHS2 (dsCHS1 and dsCHS2) were used to immerse potato foliage and the treated leaves were provided to the newly-molted fourth- and third-instar larvae. Ingestion of dsCHS1 by the fourth-instar larvae significantly diminished the target mRNA level and had slight influence on the expression of HvCHS2. In contrast, consumption of dsCHS2 significantly lowered the target mRNA level but triggered the transcription of HvCHS1. Knockdown of HvCHS1, rather than HvCHS2, arrested larval development and impaired larva-pupa-adult transition. A large proportion of HvCHS1 hypomorphs became stunting prepupae, deformed pupae or misshapen adults. Moreover, knockdown of HvCHS1 damaged gut integrity, decreased cuticle thickness, and delayed the formation of newly-generated cuticle layer during ecdysis. Furthermore, depletion of HvCHS1 inhibited the development of trachea system and thinned tracheal taenidia. Ingestion of dsCHS1 at the third-instar stage caused similar but severe negative effects. Our results demonstrated that HvCHS1 is responsible for chitin biosynthesis during ecdysis. Moreover, HvCHS1 is a potential amenable target gene and young larvae are more susceptible to dsRNA.

The fitness advantages of bistrifluron resistance related to chitin synthase A in Spodoptera litura (Fab.) (Noctuidae: Lepidoptera)

BACKGROUND

Spodoptera litura is one of the major agricultural pests in China, and it has developed serious resistance to many traditional chemical insecticides. In the present study, the bistrifluron-resistant (Bis-SEL) strain accompanied by a higher oviposition, 113.8-fold RR compared to the bistrifluron-susceptible (Bis-UNSEL) strain, was obtained by bidirectional screening. A comparison of their gonad coefficiency and genes related to oviposition or resistance was used to elucidate the resurgence mechanism.

RESULTS

The ovarian index, oviposition, and potential egg production in the Bis-SEL strain of female adults were significantly higher than those in the Bis-UNSEL strain, and the length of ovariole in the Bis-SEL strain was also significantly elongated. The protein contents of vitellogenin (Vg) and vitellogenin receptor (VgR) in the Bis-UNSEL strain were lower than those in the Bis-SEL strain, consistent with their gene expressions levels, and there was a significantly positive linear correlation between Vg and VgR protein contents, further confirming that resistant strains have high reproductive fitness. Moreover, the chitin synthase A in the Bis-SEL strain was clearly up-regulated, and a mutation (H866Y) near the QRRRW in the catalytic domain caused a rise in the hydrogen bond between UDP-GlcNAc and chitin synthase, and its chitin content was higher than that in the Bis-UNSEL strain. Nevertheless, the sensitivity of the Bis-SEL strain to bistrifluron was significantly recovered when it was knocked down though RNA interference.

CONCLUSION

The fitness advantages of bistrifluron resistance may be related to the up-regulation and mution of chitin synthase A. © 2021 Society of Chemical Industry.

Physiological characterization of chitin synthase A responsible for the biosynthesis of cuticle chitin in Culex pipiens pallens (Diptera: Culicidae)

Background

The pathogens transmitted by mosquitoes to humans and animals cause several emerging and resurgent infectious diseases. Increasing insecticide resistance requires rational action to control the target vector population. Chitin is indispensable for insect growth and development and absent from vertebrates and higher plants. Chitin synthase A (CHSA) is a crucial enzyme in chitin synthesis; therefore, identifying and characterizing how CHSA determines chitin content may contribute to the development of novel vector control strategies.

Results

The injection of small interfering RNA targeting CHSA (siCHSA) to knockdown CHSA transcripts in larval, pupal and adult stages of Culex pipiens pallens resulted in the appearance of different lethal phenotypes. When larval and pupal stages were injected with siCHSA, CHSA knockdown prevented larval molting, pupation and adult eclosion, and affected the production of chitin and chitin degradation, which resulted in an ecdysis defect phenotype of mosquitoes. When siCHSA was injected into mosquitoes in the adult stage, CHSA knockdown also affected the laminar organization of the mesoderm and the formation of pseudo-orthogonal patterns of the large fibers of the endoderm.

Conclusion

We provide a systematic and comprehensive description of the effects of CHSA on morphogenesis and metamorphosis. The results show that CHSA not only affects chitin synthesis during molting, but also might be involved in chitin degradation. Our results further show that CHSA is important for the structural integrity of the adult mosquito cuticle.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04741-2.

Chitin Synthases Are Critical for Reproduction, Molting, and Digestion in the Salmon Louse (Lepeophtheirus salmonis)

Chitin synthase (CHS) is a large transmembrane enzyme that polymerizes Uridine diphosphate N-acetylglucosamine into chitin. The genomes of insects often encode two chitin synthases, CHS1 and CHS2. Their functional roles have been investigated in several insects: CHS1 is mainly responsible for synthesizing chitin in the cuticle and CHS2 in the midgut. Lepeophtheirus salmonis is an ectoparasitic copepod on salmonid fish, which causes significant economic losses in aquaculture. In the present study, the tissue-specific localization, expression, and functional role of L. salmonis chitin synthases, LsCHS1 and LsCHS2, were investigated. The expressions of LsCHS1 and LsCHS2 were found in oocytes, ovaries, intestine, and integument. Wheat germ agglutinin (WGA) chitin staining signals were detected in ovaries, oocytes, intestine, cuticle, and intestine in adult female L. salmonis. The functional roles of the LsCHSs were investigated using RNA interference (RNAi) to silence the expression of LsCHS1 and LsCHS2. Knockdown of LsCHS1 in pre-adult I lice resulted in lethal phenotypes with cuticle deformation and deformation of ovaries and oocytes in adult lice. RNAi knockdown of LsCHS2 in adult female L. salmonis affected digestion, damaged the gut microvilli, reduced muscular tissues around the gut, and affected offspring. The results demonstrate that both LsCHS1 and LsCHS2 are important for the survival and reproduction in L. salmonis.

Identification, Characterization, and Functional Analysis of Chitin Synthase Genes in Glyphodes pyloalis Walker (Lepidoptera: Pyralidae)

Glyphodes pyloalis Walker (G. pyloalis) causes significant damage to mulberry every year, and we currently lack effective and environmentally friendly ways to control the pest. Chitin synthase (CHS) is a critical regulatory enzyme related to chitin biosynthesis, which plays a vital role in the growth and development of insects. The function of CHS in G. pyloalis, however, has not been studied. In this study, two chitin synthase genes (GpCHSA and GpCHSB) were screened from our previously created transcriptome database. The complete coding sequences of the two genes are 5,955 bp and 5,896 bp, respectively. Expression of GpCHSA and GpCHSB could be detected throughout all developmental stages. Relatively high expression levels of GpCHSA occurred in the head and integument and GpCHSB was most highly expressed in the midgut. Moreover, silencing of GpCHSA and GpCHSB using dsRNA reduced expression of downstream chitin metabolism pathway genes and resulted in abnormal development and wings stretching, but did not affect normal pupating of larvae. Furthermore, the inhibitor of chitin synthesis diflubenzuron (DFB) was used to further validate the RNAi result. DFB treatment significantly improved expression of GpCHSA, except GpCHSB, and their downstream genes, and also effected G. Pyloali molting at 48 h (62% mortality rate) and 72 h (90% mortality rate), respectively. These results show that GpCHSA and GpCHSB play critical roles in the development and wing stretching in G. pyloalis adults, indicating that the genes are attractive potential pest control targets.

Transcriptional profiling and physiological roles of Aedes aegypti spermathecal-related genes

BACKGROUND

Successful mating of female mosquitoes typically occurs once, with the male sperm being stored in the female spermatheca for every subsequent oviposition event. The female spermatheca is responsible for the maintenance, nourishment, and protection of the male sperm against damage during storage. Aedes aegypti is a major vector of arboviruses, including Yellow Fever, Dengue, Chikungunya, and Zika. Vector control is difficult due to this mosquito high reproductive capacity.

RESULTS

Following comparative RNA-seq analyses of spermathecae obtained from virgin and inseminated females, eight transcripts were selected based on their putative roles in sperm maintenance and survival, including energy metabolism, chitin components, transcriptional regulation, hormonal signaling, enzymatic activity, antimicrobial activity, and ionic homeostasis. In situ RNA hybridization confirmed tissue-specific expression of the eight transcripts. Following RNA interference (RNAi), observed outcomes varied between targeted transcripts, affecting mosquito survival, egg morphology, fecundity, and sperm motility within the spermathecae.

CONCLUSIONS

This study identified spermatheca-specific transcripts associated with sperm storage in Ae. aegypti. Using RNAi we characterized the role of eight spermathecal transcripts on various aspects of female fecundity and offspring survival. RNAi-induced knockdown of transcript AeSigP-66,427, coding for a Na+/Ca2+ protein exchanger, specifically interfered with egg production and reduced sperm motility. Our results bring new insights into the molecular basis of sperm storage and identify potential targets for Ae. aegypti control.

RNAi-Mediated Knockdown of Chitin Synthase 1 (CHS1) Gene Causes Mortality and Decreased Longevity and Fecundity in Aphis gossypii

Chitin is a vital part of the insect exoskeleton and peritrophic membrane, synthesized by chitin synthase (CHS) enzymes. Chitin synthase 1 (CHS1) is a crucial enzyme in the final step of chitin biosynthetic pathway and consequently plays essential role towards insect growth and molting. RNA interference (RNAi) is an agent that could be used as an extremely target-specific and ecologically innocuous tactic to control different insect pests associated with economically important crops. The sole purpose of the current study is to use CHS1 as the key target gene against the cotton-melon aphid, Aphis gossypii, via oral feeding on artificial diets mixed with dsRNA-CHS1. Results revealed that the expression level of CHS1 gene significantly decreased after the oral delivery of dsRNA-CHS1. The knockdown of CHS1 gene caused up to 43%, 47%, and 59% mortality in third-instar nymph after feeding of dsCHS1 for 24, 48, and 72 h, respectively, as compared to the control. Consistent with this, significantly lower longevity (approximately 38%) and fecundity (approximately 48%) were also found in adult stage of cotton-melon aphids that were fed with dsCHS1 for 72 h at nymphal stage. The qRT-PCR analysis of gene expression demonstrated that the increased mortality rates and lowered longevity and fecundity of A. gossypii were attributed to the downregulation of CHS1 gene via oral-delivery-mediated RNAi. The results of current study confirm that CHS1 could be an appropriate candidate target gene for the RNAi-based control of cotton-melon aphids.

Progress and prospects of arthropod chitin pathways and structures as targets for pest management

Chitin is a structural component of the arthropod cuticular exoskeleton and the peritrophic matrix of the gut, which play crucial roles in growth and development. In the past few decades, our understanding of the composition, biosynthesis, assembly, degradation, and regulation of chitinous structures has increased. Many chemicals have been developed that target chitin biosynthesis (benzoyphenyl ureas, etoxazole), chitin degradation (allosamidin, psammaplin), and chitin regulation (benzoyl hydrazines), thus resulting in molting deformities and lethality. In addition, proteins that disrupt chitin structures, such as lectins, proteases, and chitinases have been utilized to halt feeding and induce mortality. Chitin-degrading enzymes, such as chitinases are also useful for improving the efficacy of bio-insecticides. Transgenic plants, baculoviruses, fungi, and bacteria have been engineered to express chitinases from a variety of organisms for control of arthropod pests. In addition, RNA interference targeting genes involved in chitin pathways and structures are now being investigated for the development of environmentally friendly pest management strategies. This review describes the chemicals and proteins used to target chitin structures and enzymes for arthropod pest management, as well as pest management strategies based upon these compounds, such as plant-incorporated-protectants and recombinant entomopathogens. Recent advances in RNA interference-based pest management, and how this technology can be used to target chitin pathways and structures are also discussed.

Glucose Utilization in the Regulation of Chitin Synthesis in Brown Planthopper

Glucose-6-phosphatase (G6Pase) and hexokinase (HK) are two key enzymes in the glycolysis and gluconeogenesis pathways, which catalyze the synthesis and degradation of glucose in insects, respectively. G6Pase and HK play an important role in insect growth by regulating the metabolism of glucose, leading to the efficient metabolism of other macromolecules. However, it is unclear whether these genes could be investigated for pest control through their actions on chitin metabolism. We studied the potential functions of G6Pase and HK genes in the regulation of chitin metabolism pathways by RNAi technology. Interference with G6Pase expression did not affect trehalose and chitin metabolism pathways in brown planthopper, Nilaparvata lugens (Stål). However, knockdown of the HK gene resulted in a significant decrease of expression of genes associated with the trehalose metabolic pathway but had no significant effect on trehalase activity, trehalose content, or glucogen content. Additionally, HK knockdown resulting in downregulation of the genes involved in chitin metabolism in the brown planthopper. These insects also showed wing deformities and difficulty in molting to varying degrees. We suggest that the silencing of HK expression directly inhibited the decomposition of glucose, leading to impaired chitin synthesis.

Impact of low lethal concentrations of buprofezin on biological traits and expression profile of chitin synthase 1 gene (CHS1) in melon aphid, Aphis gossypii

Buprofezin, a chitin synthesis inhibitor that can be used for the control of hemipteran pests, especially melon aphid, Aphis gossypii. The impact of low lethal concentrations of buprofezin on the biological parameters and expression profile of CHS1 gene were estimated for two successive generations of A. gossypii. The present result shows that the LC₁₅ and LC₃₀ of buprofezin significantly decreased the fecundity and longevity of both generations. Exposure of F₀ individuals to both concentrations delay the developmental period in F₁. Furthermore, the survival rate, intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R₀) were reduced significantly in progeny generation at both concentrations. However, the reduction in gross reproductive rate (GRR) was observed only at LC₃₀. Although, the mean generation time (T) prolonged substantially at LC₃₀. Additionally, expression of the CHS1 gene was significantly increased in F₀ adults. Significant increase in the relative abundance of CHS1 mRNA transcript was also observed at the juvenile and adult stages of F₁ generation following exposure to LC₁₅ and LC₃₀. Therefore, our results show that buprofezin could affect the biological traits by diminishing the chitin contents owing to the inhibition of chitin synthase activity in the succeeding generation of melon aphid.

Silencing of the Chitin Synthase Gene Is Lethal to the Asian Citrus Psyllid, Diaphorina citri

Chitin synthase is a critical enzyme that catalyzes N-acetylglucosamine to form chitin, which plays an important role in the growth and development of insects. In this study, we identified a chitin synthase gene (CHS) with a complete open reading frame (ORF) of 3180 bp from the genome database of Diaphorina citri, encoding a protein of 1059 amino acid residues with the appropriate signature motifs (EDR and QRRRW). Reverse transcription-quantitative PCR (RT-qPCR) analysis suggested that D. citri CHS (DcCHS) was expressed throughout all developmental stages and all tissues. DcCHS had the highest expression level in the integument and fifth-instar nymph stage. Furthermore, the effects of diflubenzuron (DFB) on D. citri mortality and DcCHS expression level were investigated using fifth-instar nymph through leaf dip bioassay, and the results revealed that the nymph exposed to DFB had the highest mortality compared with control group (Triton-100). Silencing of DcCHS by RNA interference resulted in malformed phenotypes and increased mortality with decreased molting rate. In addition, transmission electron microscopy (TEM) and fluorescence in situ hybridization (FISH) also revealed corresponding ultrastructural defects. Our results suggest that DcCHS might play an important role in the development of D. citri and can be used as a potential target for psyllid control.

Effects of RNAi-based silencing of chitin synthase gene on moulting and fecundity in pea aphids (Acyrthosiphon pisum)

The pea aphid, Acyrthosiphon pisum, is an important agricultural pest and an ideal model organism for various studies. Chitin synthase (CHS) catalyses chitin synthesis, a critical structural component of insect exoskeletons. Here, we identified a CHS gene from A. pisum, ApisCHS. The ApisCHS expression profiles showed that ApisCHS was expressed in various developmental stages and in all tested tissues of A. pisum, including the epidermis, embryo, gut and haemolymph. Notably, ApisCHS exhibited peak expression in the middle of each nymphal period and was extremely highly expressed in the epidermis and embryo. RNA interference (RNAi) showed that ~600 ng of dsRNA is an effective dose for gene silencing by injection for dsRNA delivery; moreover, 1200 ng·μL⁻¹ dsRNA induced CHS gene silencing by a plant-mediated feeding approach. A 44.7% mortality rate and a 51.3% moulting rate were observed 72 h after injection of dsApisCHS into fourth-instar nymphs, compared with the levels in the control (injected with dsGFP). Moreover, a longer period was required for nymph development and a 44.2% deformity rate among newborn nymphs was obtained upon ingestion of dsApisCHS. These results suggest that ApisCHS plays a critical role in nymphal growth and embryonic development in pea aphids, and is a potential target for RNAi-based aphid pest control.

Chitin in Arthropods: Biosynthesis, Modification, and Metabolism

Chitin is a structural constituent of extracellular matrices including the cuticle of the exoskeleton and the peritrophic matrix (PM) of the midgut in arthropods. Chitin chains are synthesized through multiple biochemical reactions, organized in several hierarchical levels and associated with various proteins that give their unique physicochemical characteristics of the cuticle and PM. Because, arthropod growth and morphogenesis are dependent on the capability of remodeling chitin-containing structures, chitin biosynthesis and degradation are highly regulated, allowing ecdysis and regeneration of the cuticle and PM. Over the past 20 years, much progress has been made in understanding the physiological functions of chitinous matrices. In this chapter, we mainly discussed the biochemical processes of chitin biosynthesis, modification and degradation, and various enzymes involved in these processes. We also discussed cuticular proteins and PM proteins, which largely determine the physicochemical properties of the cuticle and PM. Although rapid advances in genomics, proteomics, RNA interference, and other technologies have considerably facilitated our research in chitin biosynthesis, modification, and metabolism in recent years, many aspects of these processes are still partially understood. Further research is needed in understanding how the structural organization of chitin synthase in plasma membrane accommodate chitin biosynthesis, transport of chitin chain across the plasma membrane, and release of the chitin chain from the enzyme. Other research is also needed in elucidating the roles of chitin deacetylases in chitin organization and the mechanism controlling the formation of different types of chitin in arthropods.

Reverse chemical ecology-based approach leading to the accidental discovery of repellents for Rhodnius prolixus, a vector of Chagas diseases refractory to DEET

Rhodnius prolixus is one of the most important vectors of Chagas disease in Central and South America for which repellents and attractants are sorely needed. Repellents like DEET, picaridin, and IR3535 are widely used as the first line of defense against mosquitoes and other vectors, but they are ineffective against R. prolixus. Our initial goal was to identify in R. prolixus genome odorant receptors sensitive to putative sex pheromones. We compared gene expression of 21 ORs in the R. prolixus genome, identified 4 ORs enriched in male (compared with female) antennae. Attempts to de-orphanize these ORs using the Xenopus oocyte recording system showed that none of them responded to putative sex pheromone constituents. One of the them, RproOR80, was sensitive to 4 compounds in our panel of 109 odorants, namely, 2-heptanone, γ-octalactone, acetophenone, and 4-methylcychohexanol. Interestingly, these compounds, particularly 4-methylcyclohexanol, showed strong repellency activity as indicated not only by a significant decrease in residence time close to a host, but also by a remarkable reduction in blood intake. 4-Methylcyclohexanol-elicited repellency activity was abolished in RNAi-treated insects. In summary, our search for pheromone receptors led to the discovery of repellents for R. prolixus.

Identification and Functional Analysis of Chitin Synthase A in Oriental Armyworm, Mythimna separata

Chitin synthases are very important enzymes for chitin synthesis in various species, which makes them a specific target of insecticides. In the present study, the function of the chitin synthase A (CHSA) gene isolated from Mythimna separate is investigated. The majority of dsMysCHSA treated larvae (89.50%) exhibit lethal phenotypes, including three phenotypes with severe cuticle deformations. The dsMysCHSA treatment in adult females affects oogenesis, and significantly reduce the ovary size and the oviposition number compared with controls. To determine how MysCHSA affects female fecundity, combined analyses of RNA-sequencing (RNA-Seq) transcriptome and TMT proteome (tandem mass tags) data in M. separata after treatment with MysCHSA-RNAi is performed. The differentially expressed proteins and genes affect fecundity-related proteins, energy metabolism, fatty acid metabolism, amino sugars, and nucleotide sugar metabolism pathways. Taken together, these results suggest that MysCHSA acts on M. separata ecdysis and fecundity, and has the potential as a target gene for pest control.

Characterization and RNAi-mediated knockdown of Chitin Synthase A in the potato tuber moth, Phthorimaea operculella

Chitin is a major component of insect exoskeleton, tracheal system and gut where it is synthesized by chitin synthase (CHS) enzymes. In this paper, we report the isolation and RNAi of chitin synthase A (PhoCHSA) from the potato tuber moth Phthorimaea operculella. The full-length cDNA of PhoCHSA is 5,627 bp with 4,689 bp open reading frame coding for 1,563 amino acids. Structural analysis of conceptual amino acid translation showed three distinct regions found in all known insect CHS proteins; N-terminus region having 9 transmembrane helices, middle catalytic region containing several conserved domains identified in insect CHS enzymes, and C-terminus region containing seven transmembrane spans. Phylogenetic analysis showed that PhoCHSA protein clustered with CHSA enzymes identified from insects from different insect orders. RNAi targeting three different regions of the gene showed different efficacy against potato tuber moth larvae and dsRNA targeting the 5′ region has the highest efficacy. Results were verified by qRT-PCR which showed that dsRNA targeting the 5′ region caused the highest reduction in PhoCHSA mRNA level. Our results show the importance of selecting the RNAi target region and that chitin synthase A can be a suitable RNAi target for the potato tuber moth control.

MicroRNA and dsRNA targeting chitin synthase A reveal a great potential for pest management of the hemipteran insect Nilaparvata lugens

BACKGROUND

Two RNA silencing pathways in insects are known to exist that are mediated by short interfering RNAs (siRNAs) and microRNAs (miRNAs), which have been hypothesised to be promising methods for insect pest control. However, a comparison between miRNA and siRNA in pest control is still unavailable, particularly in targeting chitin synthase gene A (CHSA).

RESULTS

The dsRNA for Nilaparvata lugens CHSA (dsNlCHSA) and the microR-2703 (miR-2703) mimic targeting NlCHSA delivered via feeding affected the development of nymphs, reduced their chitin content and led to lethal phenotypes. The protein level of NlCHSA was downregulated after female adults were injected with dsNlCHSA or the miR-2703 mimic, but there were no significant differences in vitellogenin (NlVg) expression or in total oviposition relative to the control group. However, 90.68 and 46.13% of the eggs laid by the females injected with dsNlCHSA and miR-2703 mimic were unable to hatch, respectively. In addition, a second-generation miRNA and RNAi effect on N. lugens was observed.

CONCLUSION

Ingested miR-2703 seems to be a good option for killing N. lugens nymphs, while NlCHSA may be a promising target for RNAi-based pest management. These findings provide important evidence for applications of small non-coding RNAs (snRNAs) in insect pest management. © 2016 Society of Chemical Industry.

Neuropeptides in the regulation of Rhodnius prolixus physiology

In the kissing bug Rhodnius prolixus, events such as diuresis, antidiuresis, development and reproduction are triggered by blood feeding. Hence, these events can be accurately timed, facilitating physiological experiments. This, combined with its relatively big size, makes R. prolixus an excellent model in insect neuroendocrinological studies. The importance of R. prolixus as a Chagas' disease vector as much as an insect model has motivated the sequencing of its genome in recent years, facilitating genetic and molecular studies. Most crucial physiological processes are regulated by the neuroendocrine system, composed of neuropeptides and their receptors. The identification and characterization of neuropeptides and their receptors could be the first step to find targets for new insecticides. The sequences of 41 neuropeptide precursor genes and the receptors for most of them were identified in the R. prolixus genome. Functional information about many of these molecules was obtained, whereas many neuroendocrine systems are still unstudied in this model species. This review addresses the knowledge available to date regarding the structure, distribution, expression and physiological effects of neuropeptides in R. prolixus, and points to future directions in this research field.

Rhodnius prolixus: from physiology by Wigglesworth to recent studies of immune system modulation by Trypanosoma cruzi and Trypanosoma rangeli

This review is dedicated to the memory of Professor Sir Vincent B. Wigglesworth (VW) in recognition of his many pioneering contributions to insect physiology which, even today, form the basis of modern-day research in this field. Insects not only make vital contributions to our everyday lives by their roles in pollination, balancing eco-systems and provision of honey and silk products, but they are also outstanding models for studying the pathogenicity of microorganisms and the functioning of innate immunity in humans. In this overview, the immune system of the triatomine bug, Rhodnius prolixus, is considered which is most appropriate to this dedication as this insect species was the favourite subject of VW's research. Herein are described recent developments in knowledge of the functioning of the R. prolixus immune system. Thus, the roles of the cellular defences, such as phagocytosis and nodule formation, as well as the role of eicosanoids, ecdysone, antimicrobial peptides, reactive oxygen and nitrogen radicals, and the gut microbiota in the immune response of R. prolixus are described. The details of many of these were unknown to VW although his work gives indications of his awareness of the importance to R. prolixus of cellular immunity, antibacterial activity, prophenoloxidase and the gut microbiota. This description of R. prolixus immunity forms a backdrop to studies on the interaction of the parasitic flagellates, Trypanosoma cruzi and Trypanosoma rangeli, with the host defences of this important insect vector. These parasites remarkably utilize different strategies to avoid/modulate the triatomine immune response in order to survive in the extremely hostile host environments present in the vector gut and haemocoel. Much recent information has also been gleaned on the remarkable diversity of the immune system in the R. prolixus gut and its interaction with trypanosome parasites. This new data is reviewed and gaps in our knowledge of R. prolixus immunity are identified as subjects for future endeavours. Finally, the publication of the T. cruzi, T. rangeli and R. prolixus genomes, together with the use of modern molecular techniques, should lead to the enhanced identification of the determinants of infection derived from both the vector and the parasites which, in turn, could form targets for new molecular-based control strategies.

RNA interference of chitin synthase genes inhibits chitin biosynthesis and affects larval performance in Leptinotarsa decemlineata (Say)

Dietary introduction of bacterially expressed double-stranded RNA (dsRNA) has great potential for management of Leptinotarsa decemlineata. Identification of the most attractive candidate genes for RNA interference (RNAi) is the first step. In the present paper, three complete chitin synthase cDNA sequences (LdChSAa, LdChSAb and LdChSB) were cloned. LdChSAa and LdChSAb, two splicing variants of LdChSA gene, were highly expressed in ectodermally-derived epidermal cells forming epidermis, trachea, foregut and hindgut, whereas LdChSB was mainly transcribed in midgut cells. Feeding bacterially expressed dsChSA (derived from a common fragment of LdChSAa and LdChSAb), dsChSAa, dsChSAb and dsChSB in the second- and fourth-instar larvae specifically knocked down their target mRNAs. RNAi of LdChSAa+LdChSAb and LdChSAa lowered chitin contents in whole body and integument samples, and thinned tracheal taenidia. The resulting larvae failed to ecdyse, pupate, or emerge as adults. Comparably, knockdown of LdChSAb mainly affected pupal-adult molting. The LdChSAb RNAi pupae did not completely shed the old larval exuviae, which caused failure of adult emergence. In contrast, silencing of LdChSB significantly reduced foliage consumption, decreased chitin content in midgut sample, damaged midgut peritrophic matrix, and retarded larval growth. As a result, the development of the LdChSB RNAi hypomorphs was arrested. Our data reveal that these LdChSs are among the effective candidate genes for an RNAi-based control strategy against L. decemlineata.

miR-71 and miR-263 Jointly Regulate Target Genes Chitin synthase and Chitinase to Control Locust Molting

Chitin synthase and chitinase play crucial roles in chitin biosynthesis and degradation during insect molting. Silencing of Dicer-1 results in reduced levels of mature miRNAs and severely blocks molting in the migratory locust. However, the regulatory mechanism of miRNAs in the molting process of locusts has remained elusive. In this study, we found that in chitin metabolism, two crucial enzymes, chitin synthase (CHS) and chitinase (CHT) were regulated by miR-71 and miR-263 during nymph molting. The coding sequence of CHS1 and the 3'-untranslated region of CHT10 contain functional binding sites for miR-71 and miR-263, respectively. miR-71/miR-263 displayed cellular co-localization with their target genes in epidermal cells and directly interacted with CHS1 and CHT10 in the locust integument, respectively. Injections of miR-71 and miR-263 agomirs suppressed the expression of CHS1 and CHT10, which consequently altered chitin production of new and old cuticles and resulted in a molting-defective phenotype in locusts. Unexpectedly, reduced expression of miR-71 and miR-263 increased CHS1 and CHT10 mRNA expression and led to molting defects similar to those induced by miRNA delivery. This study reveals a novel function and balancing modulation pattern of two miRNAs in chitin biosynthesis and degradation, and it provides insight into the underlying molecular mechanisms of the molting process in locusts.

IDENTIFICATION AND HORMONE INDUCTION OF PUTATIVE CHITIN SYNTHASE GENES AND SPLICE VARIANTS IN Leptinotarsa decemlineata (SAY)

Chitin synthase (ChS) plays a critical role in chitin synthesis and excretion. In this study, two ChS genes (LdChSA and LdChSB) were identified in Leptinotarsa decemlineata. LdChSA contains two splicing variants, LdChSAa and LdChSAb. Within the first, second, and third larval instars, the mRNA levels of LdChSAa, LdChSAb, and LdChSB coincide with the peaks of circulating 20-hydroxyecdysone (20E) and juvenile hormone (JH). In vitro culture of midguts and an in vivo bioassay revealed that 20E and an ecdysteroid agonist halofenozide stimulated the expression of the three LdChSs. Conversely, a reduction of 20E by RNA interference (RNAi) of an ecdysteroidogenesis gene LdSHD repressed the expression of these LdChSs, and ingestion of halofenozide by LdSHD RNAi larvae rescued the repression. Moreover, disruption of 20E signaling by RNAi of LdEcR, LdE75, LdHR3, and LdFTZ-F1 reduced the expression levels of these genes. Similarly, in vitro culture and an in vivo bioassay showed that exogenous JH and a JH analog methoprene activated the expression of the three LdChSs, whereas a decrease in JH by RNAi of a JH biosynthesis gene LdJHAMT downregulated these LdChSs. It seems that JH upregulates LdChSs at the early stage of each instar, whereas a 20E pulse triggers the transcription of LdChSs during molting in L. decemlineata.

Identification, characterization and functional analysis of a chitin synthase gene in the brown citrus aphid, Toxoptera citricida (Hemiptera, Aphididae)

Chitin synthase (CHS) is a crucial enzyme involved in the final step of the insect chitin biosynthetic pathway. In this study, we cloned the full-length cDNA sequence of a chitin synthase gene (TCiCHS) from the brown citrus aphid, Toxoptera citricida, an important citrus pest and the main vector of citrus tristeza virus worldwide. TCiCHS was expressed during the entire lifecycle and in all insect tissues examined. Expression was highest in first-second-instar nymphs, nymph-adult transitions and in the abdomen (6.7-fold higher than head). Embryos had a higher expression level than the integument. Fourth-instar nymphs were exposed to 5 and 500 mg/l concentrations of the chitin synthesis inhibitor diflubenzuron (DFB) for 48 h and had the highest mortality at the 500 mg/l concentration. The mRNA expression levels of TCiCHS were significantly enhanced upon the exposure of nymphs to both low and high DFB concentrations. Silencing of TCiCHS occurred through plant-mediated double-stranded RNA (dsRNA) feeding. Most dsRNA-fed nymphs were unable to moult to the next stage, and the expression of TCiCHS decreased 48% compared with controls. These results demonstrate that TCiCHS plays an important role in nymph to adult development, is possibly help identify molecular targets for To. citricida control.

MOLECULAR IDENTIFICATION OF CYSTEINE AND TRYPSIN PROTEASE, EFFECT OF DIFFERENT HOSTS ON PROTEASE EXPRESSION, AND RNAI MEDIATED SILENCING OF CYSTEINE PROTEASE GENE IN THE SUNN PEST

Sunn pest, Eurygaster integriceps, is a serious pest of cereals in the wide area of the globe from Near and Middle East to East and South Europe and North Africa. This study described for the first time, identification of E. integriceps trypsin serine protease and cathepsin-L cysteine, transcripts involved in digestion, which might serve as targets for pest control management. A total of 478 and 500 base pair long putative trypsin and cysteine gene sequences were characterized and named Tryp and Cys, respectively. In addition, the tissue-specific relative gene expression levels of these genes as well as gluten hydrolase (Gl) were determined under different host kernels feeding conditions. Result showed that mRNA expression of Cys, Tryp, and Gl was significantly affected after feeding on various host plant species. Transcript levels of these genes were most abundant in the wheat-fed E. integriceps larvae compared to other hosts. The Cys transcript was detected exclusively in the gut, whereas the Gl and Tryp transcripts were detectable in both salivary glands and gut. Also possibility of Sunn pest gene silencing was studied by topical application of cysteine double-stranded RNA (dsRNA). The results indicated that topically applied dsRNA on fifth nymphal stage can penetrate the cuticle of the insect and induce RNA interference. The Cys gene mRNA transcript in the gut was reduced to 83.8% 2 days posttreatment. Also, it was found that dsRNA of Cys gene affected fifth nymphal stage development suggesting the involvement of this protease in the insect growth, development, and molting.

Silencing the odorant receptor co-receptor RproOrco affects the physiology and behavior of the Chagas disease vector Rhodnius prolixus

Olfaction is one of the main sensory modalities that allow insects to interpret their environment. Several proteins, including odorant-binding proteins (OBPs) and odorant receptors (ORs), are involved in this process. Odorant receptors are ion channels formed by a binding unit OR and an odorant receptor co-receptor (Orco). The main goal of this study was to characterize the Orco gene of Rhodnius prolixus (RproOrco) and to infer its biological functions using gene silencing. The full-length RproOrco gene sequence was downloaded from VectorBase. This gene has 7 introns and is located in the genome SuperContig GL563069: 1,017,713-1,023,165. RproOrco encodes a protein of 473 amino acids, with predicted 7 transmembrane domains, and is highly expressed in the antennae during all R. prolixus developmental stages. The RNAi technique effectively silenced RproOrco, reducing the gene's expression by approximately 73%. Interestingly, the effect of gene silencing persisted for more than 100 days, indicating a prolonged effect of dsRNA that was maintained even after molting. The phenotypic effects of silencing involved the following: (1) loss of the ability to find a vertebrate host in a timely manner, (2) decreased ingested blood volume, (3) delayed and decreased molt rate, (4) increased mortality rate, and (5) decreased egg laying. Our data strongly suggest that dsOrco disrupts R. prolixus host-finding behavior, which is further reflected in the blood ingestion, molting, mortality, and egg laying data. This study clearly demonstrates that Orco is an excellent target for controlling triatomine populations. Thus, the data presented here open new possibilities for the control of vector-borne diseases.

Chitin is a component of the Rhodnius prolixus midgut

Chitin is an essential component of the peritrophic matrix (PM), which is a structure that lines the insect's gut and protects against mechanical damage and pathogens. Rhodnius prolixus (Hemiptera: Reduviidae) does not have a PM, but it has an analogous structure, the perimicrovillar membrane (PMM); chitin has not been described in this structure. Here, we show that chitin is present in the R. prolixus midgut using several techniques. The FTIR spectrum of the KOH-resistant putative chitin-material extracted from the midgut bolus showed peaks characteristic of the chitin molecule at 3500, 1675 and 1085 cm(1). Both the midgut bolus material and the standard chitin NMR spectra showed a peak at 1.88 ppm, which is certainly due to methyl protons in the acetamide a group. The percentages of radioactive N-acetylglucosamine (CPM) incorporated were 2 and 4% for the entire intestine and bolus, respectively. The KOH-resistant putative chitin-material was also extracted and purified from the N-acetylglucosamine radioactive bolus, and the radioactivity was estimated through liquid scintillation. The intestinal CHS cDNA translated sequence was the same as previously described for the R. prolixus cuticle and ovaries. Phenotypic alterations were observed in the midgut of females with a silenced CHS gene after a blood meal, such as retarded blood meal digestion; the presence of fresh blood that remained red nine days after the blood meal; and reduced trachea and hemozoin content compared with the control. Wheat germ agglutinin (a specific probe that detects chitin) labeling proximal to the intestine (crop and midgut) was much lower in females with a silenced CHS gene, especially in the midgut region, where almost no fluorescence signal was detected compared with the control groups. Midguts from females with a CHS gene silenced by dsRNA-CHS and control midguts pre-treated with chitinase showed that the chitin-derived fluorescence signal decreased in the region around the epithelium, the region facing the midgut and projections towards the intestinal lumen when evaluated microscopically. The relative reduction in CHS transcripts by approximately 80% using an RNAi assay supports the phenotypical alterations in the midgut observed using fluorescence microscopy assays. These data show that chitin is present in the R. prolixus midgut epithelium and in its surface projections facing the lumen. The CHS gene expression and the presence of chitin in the R. prolixus midgut may suggest a target for controlling Chagas disease vectors and addressing this public health problem.

Biosynthesis, Turnover, and Functions of Chitin in Insects

Chitin is a major component of the exoskeleton and the peritrophic matrix of insects. It forms complex structures in association with different assortments of cuticle and peritrophic matrix proteins to yield biocomposites with a wide range of physicochemical and mechanical properties. The growth and development of insects are intimately coupled with the biosynthesis, turnover, and modification of chitin. The genes encoding numerous enzymes of chitin metabolism and proteins that associate with and organize chitin have been uncovered by bioinformatics analyses. Many of these proteins are encoded by sets of large gene families. There is specialization among members within each family, which function in particular tissues or developmental stages. Chitin-containing matrices are dynamically modified at every developmental stage and are under developmental and/or physiological control. A thorough understanding of the diverse processes associated with the assembly and turnover of these chitinous matrices offers many strategies to achieve selective pest control.