Structural glycoprotein LmAbd-9 is required for the formation of the endocuticle during locust molting

The cuticular protein gene ApCP7 and ApCP62 are essential for reproduction in Acyrthosiphon pisum, affecting ecdysis and survival

Cuticular proteins, in conjunction with chitin, compose the insect exoskeleton, and play a key role in the growth, development, and molting of insects. However, the specific functions of most cuticular protein genes in the growth, development, and reproductive processes of the pea aphid (Acyrthosiphon pisum) remain unclear. In this study, we have identified six cuticular protein genes in the pea aphid, namely ApCP7, ApCP10, ApCP19, ApCP19.8-like, ApCP35 and ApCP62. We found that the expression levels of six genes were highly expressed during the adult stage, and except for ApCP10, which is highly expressed in the pea aphid cuticle, other genes were highly expressed in the ovaries. Subsequently, we observed that the survival rate and fecundity of pea aphid were significantly lower than those of the control group after silencing ApCP7 and ApCP62 through RNA interference. Furthermore, when ApCP7 transcript levels were reduced, aphid encountered difficulties in molting, were smaller in body size, and exhibited a darker body color. These results indicate that ApCP7 and ApCP62 are involved in the development and reproduction of pea aphid, and could be used as RNAi targets for controlling pea aphid.

Characterization of an RR-2 cuticle protein DcCP8 and its potential application based on SPc nanoparticle-wrapped dsRNA in Diaphorina citri

BACKGROUND

The insect cuticle consists of chitin fibers and a protein matrix, which plays an important role in protecting the body from invasion of various pathogens and prevents water loss. Periodic synthesis and degradation of the cuticle is required for the growth and development of insects. Key genes involved in cuticle formation have long been considered a potential target for pest control.

RESULTS

In this study, a member of the RR-2 subfamily of cuticular protein 8 (DcCP8) was identified from the Diaphorina citri genome database. Immunofluorescence analysis suggested that DcCP8 was mainly located in the Diaphorina citri exocuticle and can be induced to up-regulate 12 h following 20-hydroxyecdysone (20E) treatment. Silencing of DcCP8 by RNA interference (RNAi) significantly disrupted the metamorphosis to the adult stage, and improved the permeability of the cuticle. Transmission electron microscopy (TEM) analysis revealed that the synthesis of the exocuticle was impressed after silencing of DcCP8. Furthermore, the recombinant DcCP8 protein exhibited chitin-binding properties in vitro, down-regulation of DcCP8 significantly inhibited expression levels of chitin metabolism-related genes. Additionally, a sprayable RNAi method targeting DcCP8 based on star polycation (SPc) nanoparticles-wrapped double-stranded RNA (dsRNA) significantly increased Diaphorina citri mortality. Transcriptome sequencing further confirmed that genes associated with the endocytic pathway and immune response were up-regulated in Diaphorina citri after SPc treatment.

CONCLUSIONS

The current study indicated that DcCP8 is critical for the formation of Diaphorina citri exocuticles, and lays a foundation for Diaphorina citri control based on large-scale dsRNA nanoparticles. © 2024 Society of Chemical Industry.

Sgabd-2 plays specific role in immune response against biopesticide Metarhizium anisopliae in Aphis citricola

Metarhizium anisopliae is an effective biopesticide for controlling Aphis citricola, which has developed resistance to many chemical pesticides. However, the powerful immune system of A. citricola has limited the insecticidal efficacy of M. anisopliae. The co-evolution between insects and entomogenous fungi has led to emergence of new antifungal immune genes, which remain incompletely understood. In this study, an important immune gene Sgabd-2 was identified from A. citricola through transcriptome analysis. Sgabd-2 gene showed high expression in the 4th instar nymph and adult stages, and was mainly distributed in the abdominal region of A. citricola. The recombinant protein (rSgabd-2) exhibited no antifungal activity but demonstrated clear agglutination activity towards the conidia of M. anisopliae. RNA interference of Sgabd-2 by dsRNA feeding resulted in decreased phenoloxidase (PO) activity and weakened defense for A. citricola against M. anisopliae. Simultaneous silence of GNBP-1 and Sgabd-2 effectively reduced the immunity of A. citricola against M. anisopliae more than the individual RNAi of GNBP-1 or Sgabd-2. Furthermore, a genetically engineered M. anisopliae expressing double-stranded RNA (dsSgabd-2) targeting Sgabd-2 in A. citricola successfully suppressed the expression of Sgabd-2 and demonstrated increased virulence against A. citricola. Our findings elucidated Sgabd-2 as a critical new antifungal immune gene and proposed a genetic engineering strategy to enhance the insecticidal virulence of entomogenous fungi through RNAi-mediated inhibition of pest immune genes.

Functional analysis of nuclear receptor genes in molting and metamorphosis of the cigarette beetle, Lasioderma serricorne

Nuclear receptors (NRs) are ligand-regulated transcription factors that are important for the normal growth and development of insects. However, systematic function analysis of NRs in the molting process of Lasioderma serricorne has not been reported. In this study, we identified and characterized 16 NR genes from L. serricorne. Spatiotemporal expression analysis revealed that six NRs were mainly expressed in 3-d-old 4th-instar larvae; five NRs were primarily expressed in 5-d-old adults and four NRs were predominately expressed in prepupae. All the NRs were highly expressed in epidermis, fat body and foregut. RNA interference (RNAi) experiments revealed that knockdown of 15 NRs disrupted the larva-pupa-adult transitions and caused 64.44-100 % mortality. Hematoxylin-eosin staining showed that depletion of 12 NRs prevented the formation of new cuticle and disrupted apolysis of old cuticle. Silencing of LsHR96, LsSVP and LsE78 led to newly formed cuticle that was thinner than the controls. The 20E titer and chitin content significantly decreased by 17.67-95.12 % after 15 NR dsRNA injection and the gene expression levels of 20E synthesis genes and chitin metabolism genes were significantly reduced. These results demonstrated that 15 NR genes are essential for normal molting and metamorphosis of L. serricorne by regulating 20E synthesis and chitin metabolism.

Alternative splicing of chitin deacetylase 2 regulates chitin and fatty acid metabolism in Asian citrus psyllid, Diaphorina citri

Chitin plays an important role in the development and molting of insects. The key genes involved in chitin metabolism were considered promising targets for pest control. In this study, two splice variants of chitin deacetylase 2 (CDA2) from Diaphorina citri were identified, including DcCDA2a and DcCDA2b. Bioinformatics analysis revealed that DcCDA2a and DcCDA2b encoded 550 and 544 amino acid residues with a signal peptide, respectively. Spatio-temporal expression patterns analysis showed that DcCDA2a and DcCDA2b were highly expressed in D. citri wing and nymph stages. Moreover, DcCDA2a and DcCDA2b expression levels were induced by 20-hydroxyecdysone (20E). Silencing DcCDA2a by RNA interference (RNAi) significantly disrupted the D. citri molting and increased D. citri mortality and malformation rate, whereas inhibition of DcCDA2b resulted in a semimolting phenotype. Furthermore, silencing DcCDA2a and DcCDA2b significantly suppressed D. citri chitin and fatty acid metabolism. Our results indicated that DcCDA2 might play crucial roles in regulating D. citri chitin and fatty acid metabolism, and it could be used as a potential target for controlling D. citri.

Expressions and functions of RR-1 cuticular protein genes in the integument of Mythimna separata

As the most outer layer between itself and the environment, integuments are necessary for insects with various important functions. Cuticular proteins (CPs) are the main components in integuments, while the functions of CP genes remain unknown in Mythimna separata (Walker), which is a devastating agricultural pest. In this study, 79 CP genes were identified from the transcriptomes of larval integuments, 57 of which were from the family containing conserved Rebers & Riddiford (R&R) consensus (CPR family). Amongst these CPRs, 44 genes belonged to the subfamily with RR-1 motif (RR-1 genes) and clustered into three clades, with the top 15 most abundant RR-1 genes identified based on fragments per kilobase per million mapped fragments (FPKM) values. RT-qPCR analysis showed that most of RR-1 genes such as MsCPR1-4 were highly expressed at larval stages and in their integuments. The expression levels of RR-1 genes were generally decreased at the beginning but increased at the late stage of molting process. RNAi was applied for six RR-1 genes, and MsCPR1-4 were knocked down significantly. Silence of MsCPR2 resulted in abnormal integument formed after molting, while knockdown of MsCPR3 and MsCPR4 led to failure of molting, respectively. No phenotype was obtained for the RNAi of MsCPR1. Therefore, the expression of RR-1 genes and their functions were analyzed in the development of integuments in M. separata, providing new insights of RR-1 genes and potential targets for the development of growth regulators and new insecticides for M. separata.

Cuticle protein gene LmCP8 is involved in the structural development of the ovipositor in the migratory locust Locusta migratoria

The ovipositor comprises the external genitalia of female insects, which plays an important role in the mating and ovipositing process of insects. However, it remains rudimentary of regional gene expression and physiological function in the ovipositor during structural development. Here, we analysed the basic structure and characteristics of the ovipositor in the migratory locust Locusta migratoria. RNA-seq analysis revealed the specialization of chitin metabolism, lipids synthesis and transport, tanning and cuticular protein genes in the ovipositor. Among them, two cuticle protein genes, LmCP8 and LmACP79, were identified, which are specifically expressed in the ovipositor. Functional analysis based on RNA interference showed that deficiency of LmCP8 affected the structural development of the ovipositor resulting in the retention of a large number of remaining unproduced oocysts in the ovary of the locusts. Our results provide a fundamental resource to investigate the structural development and physiological function of the ovipositor in L. migratoria.

RR-1 cuticular protein TcCPR69 is required for growth and metamorphosis in Tribolium castaneum

Cuticle is not only critical for protecting insects from noxious stimuli but is also involved in a variety of metabolic activities. Cuticular proteins (CPs) affect cuticle structure and mechanical properties during insect growth, reproduction, and environmental adaptation. Here, we describe the identification and characterization of a member of the RR-1 subfamily of CPs with an R&R consensus (CPR) in Tribolium castaneum (TcCPR69). Although it was previously reported to be highly expressed in the wings, we found that knocking down TcCPR69 by RNA interference (RNAi) did not cause obvious wing abnormalities but markedly disrupted the growth and metamorphosis of beetles with 100% cumulative mortality; additionally, the chitin content of the pharate adult was decreased and the new abdominal cuticle was significantly thinner before molting. TcCPR69 showed chitin-binding ability and the expression levels of key genes involved in chitin metabolism (trehalase [TcTRE], chitin synthase [TcCHSA and TcCHSB], and chitinase [TcCHT5 and TcCHT10]) were also decreased by TcCPR69 knockdown. TcCPR69 gene expression peaked shortly after molting and was increased 2.61 fold at 12 h after 20-hydroxyecdysone (20E) injection. This was reversed by RNAi of the ecdysone-related genes ecdysone receptor (TcECR) and fushi tarazu transcription factor 1 (TcFTZ-F1). These results indicate that TcCPR69 is positively regulated by 20E signaling to contribute to cuticle formation and maintain chitin accumulation during the growth and metamorphosis of beetles.

Silencing of Chitin-Binding Protein with PYPV-Rich Domain Impairs Cuticle and Wing Development in the Asian Citrus Psyllid, Diaphorina citri

Simple Summary

Molting is extremely important for insect growth and development, which is accompanied the degradation of old cuticle and synthesis of new cuticle. Chitin and proteins, as major components of insect cuticle, maintain the rigidity of the exoskeleton. The functions of chitin-binding proteins have not, to date, been characterized in Diaphorina citri. In the current study, we identified a cuticle protein (DcCP64) according to chitin column purification and LC-MS/MS analysis. Silencing of DcCP64 induced an abnormal phenotype and increased the permeability of the abdomen and wings. Additionally, the mortality and malformation rate significantly increased, and the molting rate decreased after inhibition of DcCP64. Transcriptome sequencing analysis revealed that up-regulated DEGs were mainly related to oxidative phosphorylation, whereas down-regulated DEGs were mainly involved in MAPK and FoxO signaling pathways. Our results provide a basis for further functional research on DcCP64 in D. citri.

Abstract

Chitin is a major component of the arthropod exoskeleton, always working together with chitin-binding proteins to maintain the functions of extracellular structures. In the present study, we identified a cuticle protein 64 from Diaphorina citri using a chitin-binding assay. Bioinformatics analysis revealed that DcCP64 contained eight conserved PYPV motifs but lacked a Rebers–Riddiford (R–R) consensus and other chitin-binding domains. RT-qPCR analysis suggested that DcCP64 had the highest expression level in the wing and fifth-instar nymph stage. Knockdown of DcCP64 by RNA interference (RNAi) resulted in a malformed-wing phenotype, higher mortality and decreased molting rate. Furthermore, transcriptomics analysis revealed that 1244 differentially expressed genes (DEGs) were up-regulated and 580 DEGs were down-regulated, compared with dsDcCP64 groups and dsGFP groups. KEGG enrichment analysis revealed that up-regulated DEGs were mainly related to oxidative phosphorylation, whereas down-regulated DEGs were mainly involved in the MAPK and FoxO signaling pathways. Moreover, inhibition of DcCP64 significantly affected the cuticle surface, and increased the permeability of the abdomen and wings. Further chitin- and cellulose-binding assay confirmed the chitin-binding properties of recombinant DcCP64 in vitro. These results indicate that DcCP64 might play an important role in the cuticle and wing development of D. citri.

Endocuticle is involved in caste differentiation of the lower termite

Caste differentiation in termites is one of the most conspicuous examples of facultative polyphenism in animals. It is clear that specific cuticular formation occurs in hard exocuticles during caste differentiation. However, the developmental pattern of the soft endocuticle in the differentiation pathways of castes is unknown. To reveal whether the endocuticle is involved in caste differentiation, we compared the exocuticle and endocuticle thickness of individuals in 2 pathways (nymph line and worker line) of caste differentiation in the termite Reticulitermes aculabialis. The endocuticle protein genes were identified by transcriptome analysis and the expression patterns of these genes were confirmed in caste differentiation. We found that the endocuticle structure showed dynamic changes in 2 pathways, and the first difference in endocuticle structure occurred after larvae differentiation bifurcated into workers and nymphs. The thinning of the endocuticle was a significant event from nymphs developing into alates with the thickest exocuticle and thinnest endocuticle. The thickest endocuticle layers were found in the heads of the workers and the ultrastructure of the endocuticle in the heads was more complex than that in the thorax-abdomens. Six endocuticle protein genes were identified and annotated as endocuticle structural glycoproteins SgAbd-2, SgAbd-9, and Abd-5. The expression levels of endocuticle protein genes changed dramatically during caste development and the expression levels in neotenic reproductives (secondary reproductives) were significantly higher than those in alates (primary reproductives). These results reveal the roles of endocuticles in caste differentiation and adaptation to the environment.

Insecticidal and synergistic activity of dsRNAs targeting buprofezin-specific genes against the small brown planthopper, Laodelphax striatellus

The small brown planthopper, Laodelphax striatellus, is a dangerous pest in rice fields. Although buprofezin has been used to control L. striatellus for more than a decade, the occurrence of buprofezin-resistant L. striatellus has been recently reported. To develop an alternative pest control strategy, comparative transcriptome analysis of buprofezin-treated and nontreated L. striatellus was performed to screen the buprofezin-specific target genes for RNA interference (RNAi) application. Among six genes downregulated in the buprofezin-treated L. striatellus, RNAi-based silencing of the lipophorin precursor, endocuticle structure glycoprotein, and chitin synthase significantly induced the lethality of L. striatellus in a concentration-dependent manner. In addition, a cocktail of double-stranded RNAs against these three genes showed synergistic effects with buprofezin. These results provide RNAi-based effective approaches to control L. striatellus as well as an efficient method to identify novel target genes for RNAi application.

RNA interference of tyrosine hydroxylase caused rapid mortality by impairing cuticle formation in Nilaparvata lugens (Hemiptera: Delphacidae)

BACKGROUND

The application of RNA interference (RNAi) technique in controlling agricultural insect pests has been receiving much attention since the discovery of RNAi. The brown planthopper (BPH) Nilaparvata lugens, a notorious pest of rice, has evolved a high level of resistance to many kinds of insecticides. Tyrosine hydroxylase (Th) is an indispensable survival gene in holometabolous insects, playing key roles in cuticle tanning and immunity. In this study, we investigated whether Th could be used as a potential target in controlling N. lugens.

RESULTS

Here, we demonstrated that NlTh had a periodical expression pattern during molting with the highest level observed in epidermis. Dysfunction of NlTH by dsNlTh microinjection or 3-IT feeding similarly caused rapid death of N. lugens. Compared with dsGFP control BPHs, dsNlTh injected BPHs (i) had cuticle pigmentation and sclerotizaton defects; (ii) had less endocuticle lamella in tergum integument; (iii) showed higher mortality during the molting process as a result of defective cuticle shedding; (iv) showed feeding disorders indicated by a low number of probe wound dots on rice; (v) had more vulnerable cuticle.

CONCLUSION

This study demonstrated that TH orthologues play a conservative and crucial role for exocuticle tanning in both holometabolous and hemimetabolous insects, and NlTh could be targeted for RNAi-mediated BPH control. The rapid lethal phenotype of NlTH dysfunction BPHs partly induced by cuticle formation defects. © 2020 Society of Chemical Industry.