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

Insights Into a Chitin Synthase of Kuruma Shrimp Penaeus japonicus and Its Role in Peritrophic Membrane and Cuticle Formation

Synthesis of chitin is a subject of great interest in the fields of physiology and immunology of crustaceans. Chitinous tissues include not only the carapace, but also an acellular membrane in the intestine called the peritrophic membrane (PM). Here, we describe the first report of chitin synthase (CHS) of a penaeid shrimp, kuruma shrimp Penaeus japonicus. Histological observations showed that fecal matter in the midgut of kuruma shrimp was wrapped with a PM, which physically separated it from the midgut epithelium. Subsequently, the chitin synthase transcript was amplified from the midgut of the shrimp. The chitin synthase gene of kuruma shrimp (MjCHS) encodes 1,523 amino acid residues. Structural prediction analysis showed that the N-terminal region of MjCHS protein included nine transmembrane helices, the middle region included the catalytic region with several conserved motifs which are found in CHSs from other arthropods, and the C-terminal region included seven transmembrane helices. Although insects have distinct exoskeletal and intestinal chitin synthases, the phylogenetic analysis suggested that crustaceans have a single CHS. MjCHS mRNA was constantly detected in the digestive tract, including the midgut and hepatopancreas of both juvenile and adult kuruma shrimp, suggesting a stable synthesis of chitin in those organs. In contrast, MjCHS mRNA was also detected in the hindgut and uropod of juvenile shrimp. After molting, the mRNA levels of MjCHS in the stomach and uropod were higher than other molting cycles. These results suggest that MjCHS contributes to chitin synthesis in both the digestive tract and the epidermis, providing fundamental insights into chitin synthesis of crustaceans.

RNAi-mediated CHS-2 silencing affects the synthesis of chitin and the formation of the peritrophic membrane in the midgut of Aedes albopictus larvae

BACKGROUND

Mosquitoes are an important vector of viral transmission, and due to the complexity of the pathogens they transmit, vector control may be the most effective strategy to control mosquito-borne diseases. Chitin is required for insect growth and development and is absent in higher animals and plants, so regulating the chitin synthesis pathway can serve as a potentially effective means to control vector insects. Most of the current research on the chitin synthase (CHS) gene is focused on chitin synthase-1 (CHS-1), while relatively little is known about chitin synthase-2 (CHS-2).

RESULTS

The CHS-2 gene of Ae. albopictus is highly conserved and closely related to that of Aedes aegypti. The expression of CHS-2 in the third-instar larvae and pupal stage of Ae. albopictus was relatively high, and CHS-2 expression in adult mosquitoes reached the highest value 24 h after blood-feeding. In the fourth-instar larvae of Ae. albopictus, CHS-2 expression was significantly higher in the midgut than in the epidermis. Silencing CHS-2 in Ae. albopictus larvae had no effect on larval survival and emergence. The expression of four genes related to chitin synthesis enzymes was significantly upregulated, the expression level of three genes was unchanged, and only the expression level of GFAT was significantly downregulated. The expression of chitin metabolism-related genes was also upregulated after silencing. The level of chitin in the midgut of Ae. albopictus larvae was significantly decreased, while the chitinase activity was unchanged. The epithelium of the midgut showed vacuolization, cell invagination and partial cell rupture, and the structure of the peritrophic membrane was destroyed or even absent.

METHODS

The expression of CHS-2 in different developmental stages and tissues of Aedes albopictus was detected by real-time fluorescence quantitative PCR (qPCR). After silencing CHS-2 of the fourth-instar larvae of Ae. albopictus by RNA interference (RNAi), the expression levels of genes related to chitin metabolism, chitin content and chitinase activity in the larvae were detected. The structure of peritrophic membrane in the midgut of the fourth-instar larvae after silencing was observed by paraffin section and hematoxylin-eosin (HE) staining.

CONCLUSION

CHS-2 can affect midgut chitin synthesis and breakdown by regulating chitin metabolic pathway-related genes and is involved in the formation of the midgut peritrophic membrane in Ae. albopictus, playing an important role in growth and development. It may be a potential target for enhancing other control methods.

Expression and functional analysis of an odorant binding protein PopeOBP16 from Phthorimaea operculella (Zeller)

Odorant binding proteins (OBPs) are essential proteins in the peripheral olfactory system, responsible for odorant recognition and transport to olfactory receptors. Phthorimaea operculella (potato tuber moth) is an important oligophagous pest on Solanaceae crops in many countries and regions. PopeOBP16 is one of the OBPs in potato tuber moth. This study examined the expression profiles of PopeOBP16. The results of qPCR indicated that PopeOBP16 was highly expressed in the antennae of adults, especially in males, suggesting that it may be involved in odor recognition in adults. The electroantennogram (EAG) was used to screen candidate compounds with the antennae of P. operculella. The relative affinities of PopeOBP16 to 27 host volatiles and two sex pheromone components with the highest relative EAG responses were examined with competitive fluorescence-based binding assays. PopeOBP16 had the strongest binding affinity with the plant volatiles: nerol, 2-phenylethanol, linalool, 1,8-cineole, benzaldehyde, β-pinene, d-limonene, terpinolene, α-terpinene, and the sex pheromone component trans-4, cis-7, cis-10-tridecatrien-1-ol acetate. The results provide a foundation for further research into the functioning of the olfactory system and the potential development of green chemistry for control of the potato tuber moth.

Knockdown of GFAT disrupts chitin synthesis in Hyphantria cunea larvae

Glutamine-fructose-6-phosphate transaminase (GFAT) has been reported to regulate the hexosamine biosynthetic pathway as the first rate-limiting enzyme. As a key enzyme that catalyzes the substrate of glycosylation modification, which has a wide-ranging effect on cellular functions. However, there are few studies on the relationship between GFAT and chitin metabolism in insects. In the present study, the GFAT gene from Hyphantria cunea was identified based on transcriptome and bioinformatic analysis. The role of HcGFAT in regulating development and chitin synthesis was analyzed by RNA interference (RNAi) in H. cunea larvae. The full-length HcGFAT gene (2028 bp) encodes a 676 amino acid (aa) polypeptide had typical structural features of the SIS and Gn_AT_II superfamily. Phylogenetic analyses showed that GFAT of H. cunea shares the highest homology and identity with GFAT of Ostrinia furnacalis. Expression profiles indicated that HcGFAT was expressed throughout larval, pupal and three tissues (midgut, fat body, epidermis), and highly expressed in the last instar of larvae and strongly expressed in epidermis among three tissues. Bioassay results showed that knockdown of HcGFAT repressed larval growth and development, resulting in a significant loss of larval body weight. Meanwhile, HcGFAT knockdown also significantly caused larval developmental deformity. Knockdown of HcGFAT regulated the expression of four other critical genes in the chitin synthesis pathway (HcGNA, HcPAGM, HcUAP, HcCHSA), and ultimately resulted in decreased chitin content in the epidermis. In summary, these findings indicated that GFAT plays a critical role in larval growth and development, as well as chitin synthesis in H. cunea.

Reference Genes for Expression Analyses by qRT-PCR in Phthorimaea operculella (Lepidoptera: Gelechiidae)

Due to a lack of effective internal references, studies on functional genes in Phthorimaea operculella, a serious Lepidopteran pest attacking potatoes worldwide, have been greatly limited. To select suitable endogenous controls, ten housekeeping genes of actin (ACT), α-tubulin (α-TUB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), elongation factor 1α (EF1α), 18S and 28S ribosomal RNA (18S, 28S), ribosomal protein genes RPL4, RPL13 and RPL27 and superoxide dismutase (SOD) were tested. Their expression levels were determined under three different experimental conditions (developmental stages, tissues/organs and temperatures) using qRT-PCR technology. The stability was evaluated with five methods (Ct value, geNorm, NormFinder, BestKeeper and RefFinder). The results clarified that RPL13, EF1α and RPL27 are ranked as the best reference gene combination for measuring gene expression levels among different developing stages and under various temperatures; EF1α and RPL13 are recommended to normalize the gene expression levels among diverse tissues. EF1α and RPL13 are the best reference genes in all the experimental conditions. To validate the utility of the selected reference pair, EF1α and RPL13, we estimated the tissue-biased expression level of chitin synthase A gene (PoChSA). As expected, PoChSA was abundantly expressed in ectodermally derived epidermal cells, and lowly transcribed in the midgut. These findings will lay the foundation for future research on the molecular physiology and biochemistry of P. operculella.

Chitin metabolism as a potential target for RNAi-based control of the forestry pest Hyblaea puera Cramer (Lepidoptera: Hyblaeidae)

BACKGROUND

Hyblaea puera, commonly known as the teak defoliator, is a serious pest in teak plantations. Despite the availability of control measures, this pest causes losses in yield and quality of timber through voracious feeding. RNA interference (RNAi) is a promising strategy for the control of this pest. Chitin metabolism, which is vital for the growth and development of arthropods, is a potential target for developing RNAi-based insecticides.

RESULTS

To assess the effects of chitin metabolism inhibition, H. puera larvae were treated with a chitin synthesis inhibitor, diflubenzuron (DFB). DFB treatment caused pupal deformities and disrupted eclosion. Partial gene sequences for three key genes of H. puera chitin metabolism were cloned and sequenced: chitin synthase 1 (HpCHS1), chitinase-h (HpChi-h) and ecdysone receptor (HpEcR). Feeding dsRNA cognate for these three target genes to the first instar of H. puera resulted in mortality and reduction in the corresponding transcript levels as assessed through qRT-PCR. This is the first report of RNAi in this forestry pest. The highest mortality was 45.9%, in response to dsHpEcR treatment; HpChi-h transcripts were the most down-regulated in response to dsHpEcR feeding. DsHpEcR RNAi resulted in growth inhibition and molting arrest. The mortalities were 29.7% and 32.4% for dsHpCHS1 and dsHpChi-h feeding, respectively.

CONCLUSION

Chitin metabolism could be a potential target for RNAi-based control of H. puera, and HpCHS1, HpChi-h and HpEcR could be suitable target genes. However, the RNAi efficacy needs to be improved through formulations that improve stability and uptake, and employing better delivery strategies. © 2021 Society of Chemical Industry.

RNAi-Mediated Screening of Selected Target Genes Against Culex quinquefasciatus (Diptera: Culicidae)

Culex quinquefasciatus, a member of the Culex pipiens complex, is widespread in Saudi Arabia and other parts of the world. It is a vector for lymphatic filariasis, Rift Valley fever, and West Nile virus. Studies have shown the deleterious effect of RNA interference (RNAi)-mediated knockdown of various lethal genes in model and agricultural pest insects. RNAi was proposed as a tool for mosquito control with a focus on Aedes aegypti and Anopheles gambiae. In this study, we examined the effect of RNAi of selected target genes on both larval mortality and adult emergence of Cx. quinquefasciatus through two delivery methods: soaking and nanoparticles. Ten candidate genes were selected for RNAi based on their known lethal effect in other insects. Disruption of three genes, chitin synthase-1, inhibitor of apoptosis 1, and vacuolar adenosine triphosphatase, resulted in the highest mortality among the selected genes using the two treatment methods. Silencing the other seven genes resulted in a medium to low mortality in both assays. These three genes are also active against a wide range of insects and could be used for RNAi-based mosquito control in the future.

AOP Report: Inhibition of Chitin Synthase 1 Leading to Increased Mortality in Arthropods

Arthropods (including insects, crustaceans, and arachnids) rely on the synthesis of chitin to complete their life cycles (Merzendorfer 2011). The highly conserved chitin synthetic process and the absence of this process in vertebrates make it an exploitable target for pest management and veterinary medicines (Merzendorfer 2013; Junquera et al. 2019). Susceptible, nontarget organisms, such as insects and aquatic invertebrates, exposed to chitin synthesis inhibitors may suffer population declines, which may have a negative impact on ecosystems and associated services. Hence, it is important to properly identify, prioritize, and regulate relevant chemicals posing potential hazards to nontarget arthropods. The need for a more cost-efficient and mechanistic approach in risk assessment has been clearly evident and triggered the development of the adverse outcome pathway (AOP) framework (Ankley et al. 2010). An AOP links a molecular initiating event (MIE) through key events (KEs) to an adverse outcome. The mechanistic understanding of the underlying toxicological processes leading to a regulation-relevant adverse outcome is necessary for the utilization of new approach methodologies (NAMs) and efficient coverage of wider chemical and taxonomic domains. In the last decade, the AOP framework has gained traction and expanded within the (eco)toxicological research community. However, there exists a lack of mature invertebrate AOPs describing molting defect-associated mortality triggered by direct inhibition of relevant enzymes in the chitin biosynthetic pathway (chitin synthesis inhibitors) or interference with associated endocrine systems by environmental chemicals (endocrine disruptors). Arthropods undergo molting to grow and reproduce (Heming 2018). This process is comprised of the synthesis of a new exoskeleton, followed by the exuviation of the old exoskeleton (Reynolds 1987). The arthropod exoskeleton (cuticle) can be divided into 2 layers, the thin and nonchitinous epicuticle, which is the outermost layer of the cuticle, and the underlying chitinous procuticle. A single layer of epithelial cells is responsible for the synthesis and secretion of both cuticular layers (Neville 1975). The cuticle protects arthropods from predators and desiccation, acts as a physical barrier against pathogens, and allows for locomotion by providing support for muscular function (Vincent and Wegst 2004). Because the procuticle mainly consists of chitin microfibrils embedded in a matrix of cuticular proteins supplemented by lipids and minerals in insects (Muthukrishnan et al. 2012) and crustaceans (Cribb et al. 2009; Nagasawa 2012), chitin is a determinant factor for the appropriate composition of the cuticle and successful molting (Cohen 2001). A detailed overview of the endocrine mechanisms regulating chitin synthesis is given in Supplemental Data, Figure S1. The shedding of the old exoskeleton in insects is mediated by a sequence of distinct muscular contractions, the ecdysis motor program (EMP; Ayali 2009; Song et al. 2017a). Like the expression of chitin synthase isoform 1 (CHS-1), the expression of peptide hormones regulating the EMP is also controlled by ecdysteroids (Antoniewski et al. 1993; Gagou et al. 2002; Ayali 2009). Cuticular chitin is polymerized from uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) by the transmembrane enzyme CHS-1, which is localized in the epithelial plasma membrane in insects (Locke and Huie 1979; Binnington 1985; Merzendorfer and Zimoch 2003; Merzendorfer 2006). Because crustaceans are also dependent on the synthesis of chitin, the underlying mechanisms are believed to be similar, although less is known about different CHS isoforms and their localization (Rocha et al. 2012; Qian et al. 2014; Uddowla et al. 2014; Harðardóttir et al. 2019). Disruption of either chitin synthesis or the upstream endocrine pathways can lead to lethal molting disruption (Arakawa et al. 2008; Merzendorfer et al. 2012; Song et al. 2017a, 2017b). In the case of chitin synthesis inhibition, molting disruption can be referred to as "premature molting." If ecdysis cannot be completed because of decreased chitin synthesis, the organism may not successfully molt. Even if ecdysis can be completed on inhibition of chitin synthesis, the organism may not survive because of the poor integrity of the new cuticle. These effects are observed in arthropods following molting, which fail to survive subsequent molts (Arakawa et al. 2008; Chen et al. 2008) or animals being stuck in their exuviae (Wang et al. 2019) and ultimately dying as a result of insufficient food or oxygen intake (Camp et al. 2014; Song et al. 2017a). The term "premature molting" is used to differentiate from the term "incomplete ecdysis," which describes inhibition of ecdysis on a behavioral level, namely through reduction of the EMP (Song et al. 2017a). The present AOP describes molting-associated mortality through direct inhibition of the enzyme CHS-1. It expands the small but increasing number of invertebrate AOPs that have relevance to arthropods, the largest phylum within the animal kingdom (Bar-On et al. 2018). The development of this AOP will be useful in further research and regulatory initiatives related to assessment of CHS inhibitors and identification of critical knowledge gaps and may suggest new strategies for ecotoxicity testing efforts. Environ Toxicol Chem 2021;40:2112-2120. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Improvement of host-induced gene silencing efficiency via polycistronic-tRNA-amiR expression for multiple target genes and characterization of RNAi mechanism in Mythimna separata

Host-induced gene silencing (HIGS) emerged as a new strategy for pest control. However, RNAi efficiency is reported to be low in Lepidoptera, which are composed of many important crop pests. To address this, we generated transgenic plants to develop HIGS effects in a maize pest, Mythimna separata (Lepidoptera, Noctuidae), by targeting chitinase encoding genes. More importantly, we developed an artificial microRNA (amiR) based PTA (polycistronic-tRNA-amiR) system for silencing multiple target genes. Compared with hpRNA (hairpin RNA), transgenic expression of a PTA cassette including an amiR for the gut-specific dsRNA nuclease gene MsREase, resulted in improved knockdown efficiency and caused more pronounced developmental abnormalities in recipient insects. When target gene siRNAs were analysed after HIGS and direct dsRNA/siRNA feeding, common features such as sense polarity and siRNA hotspot regions were observed, however, they differed in siRNA transitivity and major 20-24nt siRNA species. Core RNAi genes were identified in M. separata, and biochemical activities of MsAGO2, MsSID1 and MsDcr2 were confirmed by EMSA (electrophoretic mobility shift assay) and dsRNA cleavage assays, respectively. Taken together, we provide compelling evidence for the existence of the RNAi mechanism in M. separata by analysis of both siRNA signatures and RNAi machinery components, and the PTA system could potentially be useful for future RNAi control of lepidopteran pests.

Annotation of chitin biosynthesis genes in Diaphorina citri, the Asian citrus psyllid

The polysaccharide chitin is critical for the formation of many insect structures, including the exoskeleton, and is required for normal development. Here we report the annotation of three genes from the chitin synthesis pathway in the Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae), the vector of Huanglongbing (citrus greening disease). Most insects have two chitin synthase (CHS) genes but, like other hemipterans, D. citri has only one. In contrast, D. citri is unusual among insects in having two UDP-N-acetylglucosamine pyrophosphorylase (UAP) genes. One of the D. citri UAP genes is broadly expressed, while the other is expressed predominantly in males. Our work helps pave the way for potential utilization of these genes as pest control targets to reduce the spread of Huanglongbing.

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.

RNAi-mediated silencing of vitellogenin gene curtails oogenesis in the almond moth Cadra cautella

Vitellogenins, major yolk protein precursors, play an essential role in the reproduction and spread of all oviparous species, including insects. To investigate reproductive strategies of the warehouse moth Cadra cautella at the molecular level, a partial transcript of the C. cautella vitellogenin (CcVg) gene was extended through the rapid amplification of cDNA ends PCR and sequenced. The complete CcVg mRNA transcript was 5,334 bp long, which encoded a protein of 1,778 amino acids, including the first 14 amino acids of the signal peptide. The deduced CcVg protein contained a putative cleavage site (RTRR) at the amino-terminal side, similar to several other insect species. DGQR and GI/LCG motifs were present at the CcVg gene C-terminus, followed by nine cysteine residues. CcVg harbored 131 putative phosphorylation sites, numbering 84, 19, and 28 sites for serine, threonine, and tyrosine, respectively. The transcript showed a great resemblance with other lepidopteran Vgs. CcVg protein analysis revealed three conserved regions: 1) vitellogenin-N domain, 2) DUF 1943 (domain of unknown function), and 3) a von Willebrand factor type D domain. Additionally, sex, stage-specific, and developmental expression profiles of the CcVg gene were determined through RT-PCR. The Vg was first expressed in 22-day-old female larvae, and its expression increased with growth. The phylogenetic analysis based on different insect Vgs revealed that the CcVg exhibited close ancestry with lepidopterans. The CcVg-based RNAi experiments were performed, and the effects were critically evaluated. The qRT-PCR results showed that CcVg-based dsRNA suppressed the Vg gene expression up to 90% at 48 h post-injection. Moreover, CcVg-based RNAi effects resulted in low fecundity and egg hatchability in the CcVg-based dsRNA-treated females. The females laid eggs, but because of insufficient yolk protein availability the eggs could not succeed to hatch. The significant difference in the fecundity and hatchability unveils the importance of CcVg gene silencing and confirmed that the Vg gene plays a key role in C. cautella reproduction and it has the potential to be used as a target for RNAi-mediated control of this warehouse pest.

Drosophila, Chitin and Insect Pest Management

Insects are a great menace in agriculture and vectors of human diseases. Hence, controlling insect populations is an important issue worldwide. A common strategy to control insects is the application of insecticides. However, insecticides entail three major problems. First, insecticides are chemicals that stress ecosystems and may even be harmful to humans. Second, insecticides are often unspecific and also eradicate beneficial insect species like the honeybee. Third, insects are able to develop resistance to insecticides. Therefore, the efficient generation of new potent insecticides and their intelligent delivery are the major tasks in agriculture. In addition, acceptance or refusal in society is a major issue that has to be considered in the application of a pest management strategy. In this paper, we unify two issues: 1) we illustrate that our molecular knowledge of the chitin synthesis and organization pathways may offer new opportunities to design novel insecticides that are environmentally harmless at the same time being specific to a pest species; and 2) we advocate that the fruit fly Drosophila melanogaster may serve as an excellent model of insect to study the effects of insecticides at the genetic, molecular and histology level in order to better understand their mode of action and to optimize their impact. Especially, chitin synthesis and organization proteins and enzymes are excellently dissected in the fruit fly, providing a rich source for new insecticide targets. Thus, D. melanogaster offers a cheap, efficient and fast assay system to address agricultural questions, as has been demonstrated to be the case in bio-medical research areas.

Cloning, functional characterization and screening of potential inhibitors for Chilo partellus chitin synthase A using in silico, in vitro and in vivo approaches

Chitin synthase (CHS) is one of the crucial enzymes that play an essential role in chitin synthesis during the molting process, and it is considered to be the specific target to control insect pests. Currently, there are no potent inhibitors available in the market, which specifically target this enzyme. Pyrimidine nucleoside peptide, nikkomycin Z, binds to nucleotide-binding sites of fungal and insect CHS. But, their mode of action is still fragmentary due to the lack of a 3Dstructure of CHS. Chilo partellus is a severe pest insect of major food crops such as maize and sorghum, in an attempt to target integument expressed cuticular CpCHS. The CpChsA cDNA was cloned, and subsequently, their developmental and tissue-specific expression was studied. The 3D structure of the CHS catalytic domain was modeled, after which natural compounds were screened using a virtual screening workflow and resulted in the identification of five hit molecules. Molecular dynamics simulations were performed to investigate the dynamics and interactions of hits with CpCHS. The obtained results revealed that the compounds kasugamycin, rutin and robinin could act as potent inhibitors of CpCHS. All three molecules were observed to significantly reduce the chitin production as validated using in vitro and in vivo studies. Thus, this study aims to provide a set of novel inhibitor molecules against CpCHS for controlling the pest population. Communicated by Ramaswamy H. Sarma.

Light/heat effects on RNA editing in chloroplast NADH-plastoquinone oxidoreductase subunit 2 (ndhB) gene of Calotropis (Calotropis procera)

Background

RNA editing is common in terrestrial plants, especially in mitochondria and chloroplast. In the photosynthesis process, NAD dehydrogenase plays a very important role. Subunit 2 of NADH-dehydrogenase is one of the major subunits in NAD dehydrogenase complex. Using desert plant Calotropis (Calotropis procera), this study focuses on the RNA editing activity of ndhB based on light time.

Results

NdhB (NADH-dehydrogenase subunit 2) gene accession no. MK144329 was isolated from Calotropis procera genomic data (PRJNA292713). Additionally, using RNA-seq data, the cDNA of the ndhB gene of C. procera was isolated at three daylight periods, i.e., dawn (accession no. MK165161), at midday (accession no. MK165160), and pre-dusk (accession no. MK165159). Seven RNA editing sites have been found in several different positions (nucleotide no. C467, C586, C611, C737, C746, C830, and C1481) within the ndhB coding region. The rate of these alterations was deferentially edited across the three daylight periods. RNA editing rate of ndhB gene was highest at dawn, (87.5, 79.6, 78.5, 76, 68.6, 39.3, and 96.9%, respectively), less in midday (74.8, 54.1, 62.6, 47.4, 45.5, 47.4, and 93.4%, respectively), and less at pre-dusk (67, 52.6, 56.9, 40.1, 40.7, 33.2, and 90%, respectively), also all these sites were validated by qRT-PCR.

Conclusion

The differential editing of chloroplast ndhB gene across light periods may be led to a somehow relations between the RNA editing and control of photosynthesis.

Molecular characterization, expression pattern and RNAi-mediated silencing of vitellogenin receptor gene in almond moth, Cadra cautella

The almond moth is an important pest of date fruits worldwide. The females produce several eggs; however, role of vitellogenin receptor (VgR) in oocyte development by mediating endocytosis of major yolk protein precursor Vg remains yet unexplored. To investigate the role of vitellogenin receptor (VgR) in reproduction, Cadra cautella vitellogenin receptor (CcVgR) transcript was obtained using rapid amplification of cDNA ends-polymerase chain reaction. Expression analysis of CcVgR was performed using reverse transcriptase and quantitative polymerase chain reaction (qPCR) in different developmental stages. RNA interference was performed by injecting CcVgR-based double-stranded (ds)RNA at different exposure times. The results revealed that CcVgR is 5421 bp long, encoded 1807 amino acid, belongs to low-density lipoprotein receptor superfamily and contains all conserved domains. Expression analysis confirmed that CcVgR is sex-specific and starts to express in female larvae on day 19. Additionally, RNA interference (RNAi) of CcVgR-based dsRNA inhibited CcVgR expression up to 83% after 72 h, reduced fecundity and hatchability, and confirmed involvement of CcVgR in C. cautella reproduction. This report provides a basis for gene silencing in this species, and proposes RNAi technology potential for pest management.

Molecular and physiological characterization of the chitin synthase B gene isolated from Culex pipiens pallens (Diptera: Culicidae)

BACKGROUND

The growth and development of insects is strictly dependent on the precise regulation of chitin synthase (CHS), which is absent in vertebrates and plants. Therefore, CHS represents an attractive target for insecticides. At present, the research on the CHS gene in mosquitoes, especially its biological functions, remains limited.

RESULTS

The full-length cDNA of the chitin synthase B gene in Culex pipiens pallens (CpCHSB) was prepared and consists of 5158 nucleotides with an open reading frame (ORF) of 4722 nucleotides encoding a protein of 1573 amino acid residues. Among different tissues, CpCHSB gene is mainly expressed in the midgut tissue with the highest expression in adult mosquitoes. Knockdown of CpCHSB in the larval stage significantly lowered the chitin content (16.5%) decreased body size (reduced by 25.6% in the larval stage and by 25.6% in the adult stage), and diminished reproduction (20%). Injecting siCHSB into adult mosquito mainly decreased reproduction (27%).

CONCLUSIONS

CpCHSB plays essential roles in growth and development, by severely reducing larval chitin content, midgut permeability, and reducing the number of female mosquito offspring. These results indicate that CHSB may serve as a potential novel target for exploring biosafe insecticides.

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.

Using de novo transcriptome assembly and analysis to study RNAi in Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

Phenacoccus solenopsis is one of the major polyphagous crop pests in India. Inadequate genomic or transcriptomic resources have limited the molecular studies in this insect despite its huge economic importance. The existing molecular sequence resources of this insect were supplemented through RNA sequencing, de novo transcriptome assembly and analysis, which generated 12, 925 CDS from 23,643 contigs with an average size of 1077.5 bp per CDS and 85.1% positive BLAST hits with NCBI Non redundant (nr) database. Twenty three genes involved in RNAi machinery identified through BLASTx search against NCBI nr database suggested the existence of robust RNAi in mealybug. RNAi in P. solenopsis was demonstrated through knockdown of IAP (Inhibitor of Apoptosis), AQP (Aquaporin), CAL (Calcitonin), VATPase (V-type proton ATPase subunit F 1), bursicon, chitin synthase, SNF7 and α-amylase by injecting sequence specific dsRNA of respective genes in adult female. Additionally, feeding RNAi has been demonstrated in 2nd instar nymph through dsRNA uptake in plant. The knockdown of core RNAi machinery genes such as Dicer, Argonaute and Staufen significantly hampered RNAi efficiency in this insect. However, downregulation of dsRNases improved RNAi efficiency. Sequential studies for understanding RNAi in P. solenopsis using transcriptome sequences have also been reported. The present study provides a base for future research on developing RNAi as strategy for management of this pest.

RNA interference-mediated knockdown of 3, 4-dihydroxyphenylacetaldehyde synthase affects larval development and adult survival in the mosquito Aedes aegypti

BACKGROUND

The cuticle is an indispensable structure that protects the mosquito against adverse environmental conditions and prevents pathogen entry. While most cuticles are hard and rigid, some parts of cuticle are soft and flexible to allow movement and blood-feeding. It has been reported that 3, 4-dihydroxyphenylacetaldehyde (DOPAL) synthase is associated with flexible cuticle formation in Aedes aegypti. However, the molecular function of DOPAL synthase in the ontogenesis of mosquito remains largely unknown. In this study, we characterized gene expression profiles of DOPAL synthase and investigated its functions in larvae and female adults of Aedes agypti by RNAi.

RESULTS

Our results suggest that the expression of DOPAL synthase is different during development and the transcriptional level reached its peak at the female white pupal stage, and DOPAL synthase was more highly expressed in the cuticle and midgut than other tissues in the adult. The development process from larva to pupa was slowed down strikingly by feeding the first-instar larvae with chitosan/DOPAL synthase dsRNA nanoparticles. A qRT-PCR analysis confirmed that the dsRNA-mediated transcription of the DOPAL synthase was reduced > 50% in fourth-instar larvae. Meanwhile, larval molt was abnormal during development. Transmission electron microscopy results indicated that the formation of endocuticle and exocuticle was blocked. In addition, we detected that the dsDOPAL synthase RNA caused significant mortality when injected into the female adult mosquitoes.

CONCLUSIONS

Our findings demonstrate that DOPAL synthase plays a critical role in mosquito larval development and adult survival and suggest that DOPAL synthase could be a good candidate gene in RNAi intervention strategies in mosquito control.

Chitinous Structures as Potential Targets for Insect Pest Control

Chitinous structures are physiologically fundamental in insects. They form the insect exoskeleton, play important roles in physiological systems and provide physical, chemical and biological protections in insects. As critically important structures in insects, chitinous structures are attractive target sites for the development of new insect-pest-control strategies. Chitinous structures in insects are complex and their formation and maintenance are dynamically regulated with the growth and development of insects. In the past few decades, studies on insect chitinous structures have shed lights on the physiological functions, compositions, structural formation, and regulation of the chitinous structures. Current understanding of the chitinous structures has indicated opportunities for exploring new target sites for insect control. Mechanisms to disrupt chitinous structures in insects have been studied and strategies for the potential development of new means of insect control by targeting chitinous structures have been proposed and are practically to be explored.