JNK pathway plays a key role in the immune system of the pea aphid and is regulated by microRNA-184

Morphotype-Specific Antifungal Defense in Cacopsylla chinensis Arises from Metabolic and Immune Network Restructuring

Pear psylla (Cacopsylla chinensis), a major pear tree pest widely distributed in China, is increasingly affecting the productivity of orchards. This species exhibits seasonal polyphenism with two distinct forms, namely, a summer form and a winter form. Through topically applying Beauveria bassiana conidial suspensions to the abdominal cuticle of C. chinensis, we demonstrated that the entomopathogenic fungus B. bassiana exhibits significant yet phenotypically divergent virulence against these two forms. Using PacBio SMRT sequencing and Illumina RNA-seq, we analyzed transcriptomic changes post-infection, revealing form-specific immune responses, with 18,232 and 5027 differentially expressed genes identified in summer- and winter-form pear psylla, respectively, and a total of 3715 DEGs shared between the two seasonal phenotypes. In summer-form individuals, B. bassiana infection disrupted oxidative phosphorylation and downregulated immune recognition genes, cellular immune-related genes, and signaling genes, along with the upregulation of the immune inhibitor serpin, indicating immunosuppression. Conversely, in winter-form individuals, immune-related genes and glycolytic rate-limiting enzymes were upregulated after infection, suggesting that the winter-form immune system normally responds to B. bassiana infection and supports efficient defense through metabolic reprogramming to fuel energy-demanding defenses. These findings advance our understanding of C. chinensis/B. bassiana interactions, providing a basis for elucidating immune regulation in seasonally polymorphic insects. The results also inform strategies to optimize B. bassiana-based biocontrol, contributing to sustainable pear psylla management.

The synthesis of nitric oxide regulated by JNK pathway in the pea aphid to defend against bacterial infection

Compared to other insects, the pea aphid Acyrthosiphon pisum exhibits limited immune responses, particularly due to the absence of many immune genes, including those encoding antimicrobial peptides and key components of the IMD pathway. Prior studies proved that the conserved signaling, Jun N-terminal kinase (JNK) pathway, plays a critical role in the immune system of the pea aphid, and nitric oxide synthase (NOS) is required for the pea aphid's defense against infections. Herein, using in vitro biochemical assays and in vivo bioassays, we demonstrated that the JNK pathway directly regulates the expression of NOS and that the JNK pathway-NOS-NO signal axis is efficient in defending against bacterial infections. The Toll pathway is instrumental for combating bacterial infections, and NO can activate the Toll pathway. The Toll pathway induced by NO regulates the expressions of ROS metabolism, lysosome, and phagocytosis-related genes. NO was identified as a crucial signaling molecule that facilitates communication between the JNK and Toll pathways.

miR-278-3p targets ATG16L1 to modulate autophagy and suppresses CLas proliferation in Diaphorina citri

The phloem-limited bacterium Candidatus Liberibacter asiaticus (CLas) is the primary cause of citrus Huanglongbing (HLB) and is transmitted by the Asian citrus psyllid, Diaphorina citri. MicroRNAs (miRNAs) are key posttranscriptional regulators involved in various biological processes, yet their role in D. citri's response to CLas infection remains unclear. In this study, we found that autophagy levels were significantly elevated in CLas-infected D. citri compared to non-infected individuals. Modulating autophagy influenced CLas titers, suggesting its role in pathogen suppression. Small RNA sequencing identified differentially expressed miRNAs, with miR-278-3p being significantly downregulated by 72.3%. Functional analyses revealed that miR-278-3p regulates autophagy by targeting ATG16L1. Inhibition of miR-278-3p increased autophagosome formation, whereas its overexpression suppressed autophagy. Dual-luciferase reporter assays confirmed miR-278-3p directly binds to the 3'UTR of ATG16L1, negatively regulating its expression. Notably, miR-278-3p inhibition reduced CLas titers by 48.7%, demonstrating its role in pathogen defense. These findings provide novel insights into the molecular mechanisms underlying insect-pathogen interactions and highlight the potential of miRNA-based strategies for controlling plant diseases transmitted by insect vectors. Understanding these regulatory pathways may lead to innovative pest and disease management approaches in agriculture.

Characterization of temporal expression of immune genes in female locust challenged by fungal pathogen, Aspergillus sp

Introduction

The innate immune system provides defense against invading pathogens in insects and mammals.

Methods

We conducted transcriptomic analyses of the locust Locusta migratoria under Aspergillus oryzae infection to clarify temporal variation in its molecular immune response.

Results

We found that fat body cells and hemocytes play different roles in the immune response of locusts to Aspergillus infection at different time points after inoculation, and melanization was the main process underlying the immune response of female locusts. Most pattern recognition receptors (PRR) genes were up-regulated in fat body cells and down-regulated in hemocytes from 24 h to 72 h after inoculation. This means that fat body cells, but not hemocytes, would be able to precisely recognize invading pathogens. Most serine protease inhibitors (SERPINs) genes and clip domain serine proteinase (CLIP) genes were up-regulated in fat body cells. However, most SERPINs were down-regulated in hemocytes, which indicated that serine proteinases may be inhibited to activate downstream reactions involving the prophenoloxidase (PPO), peroxidase (POD), and Toll pathways. Most lysozymes, PPOs, and peroxiredoxin (PRDX) are effectors that were up-regulated in fat body cells 24 h after inoculation but down-regulated 48 h and 72 h after inoculation. Similar patterns were observed for effectors in hemocytes, which indicates that locust immune genes expression was suppressed by A. oryzae 72 h after inoculation, and might result in the weak melanization of locusts in response to Aspergillus infection.

Discussion

Our findings enhance our understanding of insect-fungi interactions, as well as have implications for the development of more effective microbial control strategies for the management of locust populations.

JNK-TOR signaling mediates production of winged offspring induced by infection in the pea aphid, Acyrthosiphon pisum

Non-immune defenses against pathogens and parasites are of particular importance for animals that have incomplete immune systems, such as aphids. Production of winged offspring that are able to fly away from danger in response to infection is one of the non-immune defensing strategies. However, the signaling mediating winged offspring production induced by infection is largely unknown so far. In this study, we found that the pea aphids Acyrthosiphon pisum produced more winged offspring when they were challenged by Micrococcus luteus and Beauveria bassiana. The target of rapamycin (TOR) pathway was up-regulated after infections, and inhibition of TOR activity or knockdown of TOR expression resulted in fewer winged offspring produced by the infected aphids. Similarly, inhibition of Jun N-terminal kinase (JNK) or knockdown of JNK expression had same effect. We further provide evidence showing that JNK regulates the TOR pathway. Taken together, our study suggests the JNK-TOR signaling pathway mediates induction of winged offspring as a non-immune response to infection in aphids.

The JNK signalling pathway gene BmJun is involved in the regulation of egg quality and production in the silkworm, Bombyx mori

The Jun N-terminal kinase (JNK) signalling pathway has a key role in tissue remodelling during insect metamorphosis by regulating programmed cell death. However, multiple members of the JNK pathway in Lepidoptera remain uncharacterized. In this study, two key genes of the JNK pathway, BmJun and BmFos, were cloned from the silkworm Bombyx mori, a lepidopteran model insect, and their effects on reproductive development were investigated. BmJun and BmFos encode 239 and 380 amino acids, respectively. Both proteins have typical basic leucine zipper domains and form a BmJUN-BmFOS dimer activator protein to exert transcriptional regulation. During the wandering stage of silkworm development, interference in BmJun expression had no effect on pupation, whereas B. mori vitellogenin (BmVg) expression, which is essential for egg development, was suppressed in the fat body and egg laying was significantly reduced. Additionally, numerous eggs appeared shrivelled and deformed, suggesting that they were nutritionally stunted. Inhibition of the JNK pathway caused abnormal pupal metamorphosis, an increase in shrivelled, unfertilized eggs, a decrease in fat body synthesis, and accumulation of BmVg in the ovaries of female B. mori. The results indicated that BmJUN and BmFOS can form an AP-1 dimer. Interfering with BmJun or inhibiting the phosphorylation of BmJUN leads to a reduction in the synthesis of BmVg in the fat body and its accumulation in the ovaries, thereby affecting the quality and production of the progeny eggs. These findings suggest that regulating Jun in the JNK pathway could be a potential way to inhibit female reproduction in Lepidoptera.

The miRNA-275 Targeting RpABCG23L is Involved in Pyrethroid Resistance in the Bird Cherry-Oat Aphid, a Serious Agricultural Pest

Rhopalosiphum padi is a global agricultural pest which had developed resistance to different insecticides. The ATP-binding cassette (ABC) transporter plays an important role in insecticide resistance. However, ABC transporters' role and regulatory mechanism in mediating R. padi 's response to pyrethroids are unclear. In this study, we found that RpABCG23L was significantly overexpressed in the pyrethroid-resistant strains of R. padi. Knockdown of RpABCG23L significantly increased the susceptibility of R. padi to lambda-cyhalothrin and bifenthrin. Luciferase reporter gene analysis showed that miR-275 binds to the RpABCG23L coding region and down-regulates its expression. Injection of miR-275 mimics significantly reduced RpABCG23L expression and increased R. padi susceptibility to lambda-cyhalothrin and bifenthrin, while miR-275 inhibitor injection enhanced RpABCG23L expression and increased tolerance to both insecticides. The results provide a theoretical basis for understanding the mechanism of miRNA-mediated pyrethroid resistance, and open up a new way for the development of miRNA-based biopesticides.

Developmental Expression Patterns of miRNA in Mythimna separata Walker (Lepidotera: Noctuidae)

BACKGROUND/OBJECTIVES

miRNAs are a family of single-stranded non-coding RNAs that regulate gene expression by targeting messenger RNAs (mRNAs) for suppression, with an average length of 22 nt. The oriental armyworm, Mythimna separata Walker, is a pest insect with long-distance migratory capability, which causes severe loss of grains and pastures in Eastern Asia, Southeastern Asia, and Oceania. This study aims to elucidate the post-transcriptional regulatory mechanisms of miRNAs in the development of this pest.

METHODS

We carried out small RNA sequencing on samples from eggs, third instar larvae, pre-pupae, pupae, and adults.

RESULTS

A total of 400 miRNAs were identified, among which 40 were known and 360 were novel miRNAs. Dynamic trend analysis of miRNAs revealed that 199 miRNAs were highly expressed in eggs (profile 12), while 173 miRNAs were highly expressed in both eggs and pupae (profile 13). The results of differential expression analysis of miRNAs (DEmiR) revealed that 75 miRNAs were significantly more abundant in eggs compared to other developmental stages. Furthermore, more up-regulated miRNAs were observed than down-regulated miRNAs in adults relative to 3rd instar larvae, pre-pupae, and pupae. The core genes for miRNA biosynthesis-Pasha, Dicer1, and Ago1-were highly expressed in eggs but poorly expressed in 3rd instar larvae. KEGG enrichment analyses indicated that several genes in the pentose and glucuronate interconversion pathway, as well as the fructose and mannose metabolism pathway, were regulated by DEmiRs.

CONCLUSIONS

DEmiRNAs targeted most genes of M. separata, resulting in a complex miRNA-mRNA regulation mode.

Innate Immunity in Insects: The Lights and Shadows of Phenoloxidase System Activation

Melanogenesis and melanin deposition are processes essential for the effective immune response of insects to various invaders. Phenoloxidase (PO), produced in specialized cells as an inactive precursor prophenoloxidase (proPO), is the key enzyme for melanin formation. The precursor is activated via limited proteolysis by a dedicated serine proteinase, which is the final element in the cascade of serine proteinases (SPs) that make up the PO system. Melanogenesis provides different cytotoxic molecules active in fighting infections, as well as melanin, which is important for sequestration of invaders. However, since the cytotoxic reactive compounds generated during melanization also pose a threat to host cells, strict control of the PO system is necessary for host self-protection. Different pathogens and parasites influence the PO system and melanization through various strategies, which allow them to survive and develop in the host insect body. In this review, we characterize "the lights and shadows" of PO system activation, indicating, on one hand, its advantages as an efficient and effective mechanism of the insect immune response and, on the other hand, the dangers for the insect host associated with the improper functioning of this system and selected strategies for regulating its activity by entomopathogenic organisms.

Epigenetic Regulation in Insect-Microbe Interactions

Insects have evolved diverse interactions with a variety of microbes, such as pathogenic fungi, bacteria, and viruses. The immune responses of insect hosts, along with the dynamic infection process of microbes in response to the changing host environment and defenses, require rapid and fine-tuned regulation of gene expression programs. Epigenetic mechanisms, including DNA methylation, histone modifications, and noncoding RNA regulation, play important roles in regulating the expression of genes involved in insect immunity and microbial pathogenicity. This review highlights recent discoveries and insights into epigenetic regulatory mechanisms that modulate insect-microbe interactions. A deeper understanding of these regulatory mechanisms underlying insect-microbe interactions holds promise for the development of novel strategies for biological control of insect pests and mitigation of vector-borne diseases.

Research progress of aphid immunity system: Potential effective target for green pest management

Due to the absence of acquired immunity, insects primarily rely on their innate immune system to resist pathogenic microorganisms and parasitoids in natural habitats. This innate immune system can be classified into cellular immunity and humoral immunity. Cellular immunity is mediated by hemocytes, which perform phagocytosis, aggregation, and encapsulation to fight against invaders, whereas the humoral immunity primarily activates the immune signaling pathways and induces the generation of immune effectors. Existing studies have revealed that the hemipteran aphids lack some crucial immune genes compared to other insect species, indicating the different immune mechanisms in aphids. The current review summarizes the adverse impacts of pathogenic microorganisms and parasitoids on aphids, introduces the cellular and humoral immune systems in insects, and analyzes the differences between aphids and other insect species. Furthermore, our review also discussed the existing prospects and challenges in aphid immunity research, and proposed the potential application of immune genes in green pest management.

Single von Willebrand factor C-domain protein-2 confers immune defense against bacterial infections in the silkworm, Bombyx mori

Single-domain von Willebrand factor type C proteins (SVWCs), primarily found in arthropods, responds to infections caused by various pathogens. Three SVWCs have been identified in the silkworm and BmSVWC2 might play a crucial role in the immune system. However, the regulatory mechanism of BmSVWC2 remains largely unknown. This study aimed to investigate the biochemical functions of BmSVWC2 in the immune system of B. mori comprehensively. Phylogenetic analysis revealed that BmSVWC1, BmSVWC3, and BmSVWC2 were distributed in diverse groups, suggesting distinct biochemical functions. The mRNA and protein levels of BmSVWC2 increased significantly in response to bacterial infection. BmSVWC2 exhibited clear binding activity to the polysaccharide pathogen-associated molecular patterns of bacteria and fungi, enhancing bacterial clearance in vivo but not in vitro. RNA-sequencing assays of the fat body and hemocytes showed that numerous immune genes were markedly up-regulated with higher level of BmSVWC2, primarily affecting recognition, signaling, and response production of the Toll and immune deficiency (IMD) signaling pathways. This led to the production of various antimicrobial peptides and significant antibacterial activities in the hemolymph. BmSVWC2 up-regulated phagocytosis-related genes in the fat body and hemocytes, and phagocytosis assays confirmed that BmSVWC2 improved the phagocytic ability of hemocytes against bacteria. Additionally, BmSVWC2 induced the expression of nitric oxide synthetase (NOS) in the fat body, and bioassays confirmed that BmSVWC2 increased NOS activity in the fat body and hemolymph, resulting in nitric oxide accumulation. However, BmSVWC2 did not affect phenoloxidase activity, despite it caused differential expression of a few serine proteases and serine protease inhibitors. Co-immunoprecipitation and mass spectrometry assays showed that BmSVWC2 interacted with 30 K proteins, such as 30 K protein 2, 30 K pBmHPC-19, 30 K 19G1-like, 30 K protein 8, 30 K protein 7, 30 K pBmHPC-23, and low molecular mass lipoprotein 4-like. Our study provides a comprehensive characterization of BmSVWC2 and elucidates the mechanism underlying its regulation of immune responses activation.

Morphological and functional characterization of circulating hemocytes in Tribolium castaneum larvae

Hemocytes are pivotal in the immune response of insects against invasive pathogens. However, our knowledge of hemocyte types and their specific function in Tribolium castaneum, an increasingly important Coleoptera model insect in various research fields, remains limited. Presently, a combination of morphological criteria and dye-staining properties were used to characterize hemocyte types from T. castaneum larvae, and 4 distinct types were identified: granulocytes, oenocytoids, plasmatocytes and prohemocytes. Following different immune challenges, the total hemocyte counts declined rapidly in the initial phase (at 2 h), then increased over time (at 4 and 6 h) and eventually returned to the naive state by 24 h post-injection. Notably, the morphology of granulocytes underwent dramatic changes, characterized by an expansion of the surface area and an increased production of pseudopods, and with the number of granulocytes rising significantly through mitotic division. Granulocytes and plasmatocytes, the main hemocyte types in T. castaneum larvae, can phagocytose bacteria or latex beads injected into the larval hemolymph in vivo. Furthermore, these hemocytes participate in the encapsulation and melanization processes in vitro, forming capsules to encapsulate and melanize nickel-nitrilotriacetic acid (Ni-NTA) beads. This study provides the first comprehensive characterization of circulating hemocytes in T. castaneum larvae, offering valuable insights into cell-mediated immunity in response to bacterial infection and the injection of latex beads. These results deepen our understanding of the cellular response mechanisms in T. castaneum larvae and lay a solid foundation for subsequent investigations of the involvement of T. castaneum hemocytes in combating pathogens.

Identification and function of microRNAs in hemipteran pests: A review

Hemiptera is one of the most significant orders of insect pests, including whiteflies, true bugs, aphids, planthoppers, psyllids, and so forth, which have led to substantial economic losses in agricultural industries and have significantly affected food yields through their ability to suck the phloem sap of crops and transmit numerous bacterial and viral pathogens. Therefore, explorations of pest-specific, eco-friendly and easy-to-adopt technologies for hemipteran pest control are urgently needed. To the best of our knowledge, microRNAs (miRNAs), which are endogenous non-coding small RNAs approximately 22 nucleotides in length, are involved in regulating gene expression via the direct recognition and binding of the 3'-untranslated region (3'-UTR) of target messenger RNAs (mRNAs) or by acting as a center of a competitive endogenous RNA (ceRNA) network at the post-transcriptional level. This review systematically outlines the characterization and functional investigation of the miRNA biogenesis pathway in hemipteran pests, such as whiteflies, true bugs, aphids and planthoppers. In addition, we explored the results of small RNA sequencing and functional observations of miRNAs in these pests, and the results suggest that the numerous miRNAs obtained and annotated via high-throughput sequencing technology and bioinformatic analyses contribute to molting development, fitness, wing polyphenism, symbiont interactions and insecticide resistance in hemipteran pests. Finally, we summarize current advances and propose a framework for future research to extend the current data and address potential limitations in the investigation and application of hemipteran miRNAs.

Functional regulation of microRNA-184 in the replication and infection of Autographa californica multiple nucleopolyhedrovirus

MicroRNAs (miRNAs) represent a class of short, non-coding RNAs that are widely acknowledged as crucial participants in virus-host interactions. MiR-184, a highly conserved and abundant miRNA in insects, has yet to be extensively studied for its involvement in baculovirus infection. In this study, we investigated how miR-184 affects the infection and replication of Autographa californica multiple nucleopolyhedrovirus (AcMNPV). The results indicated that after AcMNPV infection, there was an initial increase in the expression of miR-184 within 24 h, followed by a subsequent decrease. MiR-184 can inhibit AcMNPV's DNA replication and budded virus production by directly targeting four viral genes, namely ie1, ac66, p49, and lef9. Moreover, suppressing miR-184 expression enhanced the insecticidal efficacy of AcMNPV against Spodoptera exigua larvae and markedly elevated the host ATPase gene expressions. These findings showed that miR-184 had a substantial impact on the interactions between baculoviruses and insects, presenting a prospective candidate for developing highly effective miRNA-based biopesticides.

Utilizing Star Polycation Nanocarrier for the Delivery of miR-184 Agomir and Its Impact on the Life History Traits of the English Grain Aphid, Sitobion avenae

The investigation of genetics-based biopesticides has become a central focus in pesticide studies due to their inherent advantages, including species specificity, environmental safety, and a wide range of target genes. In this study, a mixture of miR-184 agomir and nanomaterial star polycation (SPc) was used to treat the nymphs of the English grain aphid, Sitobion avenae (F.). The life parameters of the aphids at various developmental stages were analyzed using an age-stage two-sex life table to assess the effect of miR-184 agomir on the experimental population. The results indicated that miR-184 agomir had a significant negative effect on four key life parameters, including the intrinsic rate of increase, the finite rate of increase, the net rate of increase, and the mean generation time. The population prediction revealed a substantial reduction (91.81% and 95.88%) in the population size of S. avenae at 60 d after treatment with miR-184 agomir, compared to the control groups. Our findings suggest that the miR-184 agomir has the potential to reduce the survival rate and mean longevity of S. avenae, highlighting its potential as a promising candidate for the development of an effective genetics-based biopesticide.

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway contributes to the defense against bacterial infection in the pea aphid

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling is activated by infections of bacteria, fungi, viruses and parasites and mediated cellular and humoral immune responses. In the pea aphid Acyrthosiphon pisum little is known about the function of JAK/STAT signaling in its immune system. In this study, we first showed that expression of genes in the JAK/STAT signaling, including the receptors Domeless1/2, Janus kinase (JAK) and transcriptional factor Stat92E, is up-regulated upon bacteria Escherichia coli and Staphylococcus aureus and fungus Beauveria bassiana infections. After knockdown of expression of these genes by means of dsRNA injection, the aphids harbored more bacteria and suffered more death after infected with E. coli and S. aureus, but showed no significant change after B. bassiana infection. Our study suggests the JAK/STAT signaling contributes to the defense against bacterial infection in the pea aphid.

A C-type lectin (CTL2) mediated both humoral and cellular immunity against bacterial infection in Tribolium castaneum

C-type lectins (CTLs) play essential roles in humoral and cellular immune responses of invertebrates. Previous studies have demonstrated the involvement of CTLs in the humoral immunity of Tribolium castaneum, a worldwide pest in stored products. However, the function of CTLs in cellular immunity remains unclear. Here, we identified a CTL gene located on chromosome X and designated it as CTL2 (TcCTL2) from T. castaneum. It encodes a protein of 305 amino acids with a secretion signal peptide and a carbohydrate-recognition domain. TcCTL2 was mainly expressed in the early pupae and primarily distributed in the hemocytes in the late larvae. It was significantly upregulated after larvae were infected with Escherichia coli or Staphylococcus aureus, while knockdown of TcCTL2 exacerbates larval mortality and bacterial colonization after infection. The purified recombinant TcCTL2 (rTcCTL2) can bind to pathogen-associated molecular patterns and microbes and promote hemocyte-mediated encapsulation, melanization and phagocytosis in vitro. rTcCTL2 also induced bacterial agglutination in a Ca2+-dependent manner. Knockdown of TcCTL2 drastically suppressed encapsulation, melanization, and phagocytosis. Furthermore, silencing of TcCTL2 followed by bacterial infection significantly decreased the expression of transcription factors in Toll and IMD pathways, antimicrobial peptides, and prophenoloxidases and phenoloxidase activity. These results unveiled that TcCTL2 mediates both humoral and cellular immunity to promote bacterial clearance and protect T. castaneum from infectious microbes, which will deepen the understanding of the interaction between CTLs and innate immunity in T. castaneum and permit the optimization of pest control strategies by a combination of RNAi technology and bacterial infection.

Genome-wide analysis of Panonychus citri microRNAs with a focus on potential insecticidal activity of 4 microRNAs to eggs and nymphs

Panonychus citri McGregor (Acari: Tetranychidae), a destructive citrus pest, causes considerable annual economic losses due to its short lifespan and rapid resistance development. MicroRNA (miRNA)-induced RNA interference is a promising approach for pest control because of endogenous regulation of pest growth and development. To search for miRNAs with potential insecticidal activity in P. citri, genome-wide analysis of miRNAs at different developmental stages was conducted, resulting in the identification of 136 miRNAs, including 73 known and 63 novel miRNAs. A total of 17 isomiRNAs and 12 duplicated miRNAs were characterized. MiR-1 and miR-252-5p were identified as reference miRNAs for P. citri and Tetranychus urticae. Based on differential expression analysis, treatments with miR-let-7a and miR-315 mimics and the miR-let-7a antagomir significantly reduced the egg hatch rate and resulted in abnormal egg development. Overexpression or downregulation of miR-34-5p and miR-305-5p through feeding significantly decreased the adult eclosion rate and caused molting defects. The 4 miRNAs, miR-let-7a, miR-315, miR-34-5p, and miR-305-5p, had important regulatory functions and insecticidal properties in egg hatching and adult eclosion. In general, these data advance our understanding of miRNAs in mite biology, which can assist future studies on insect-specific miRNA-based green pest control technology.

MicroRNA PC-5p-3991_515 mediates triflumezopyrim susceptibility in the small brown planthopper through regulating the post-transcriptional expression of P450 CYP417A2

BACKGROUND

Cytochrome P450 monooxygenases (P450s) are recognized as a major contributor to metabolic resistance in insects to most insecticides, through gene overexpressions and protein mutations. MicroRNA (miRNA), an important post-transcriptional regulator, has been reported to promote insecticide resistance by mediating the expression of detoxification enzyme genes.

RESULTS

In the present study, we reported that a novel microRNA PC-5p-3991_515 was involved in the post-transcriptional regulation of CYP417A2 and mediated the triflumezopyrim susceptibility in the small brown planthopper (SBPH), Laodelphax striatellus (Fallén). The tissue expression profiles showed that CYP417A2 was highly expressed in fat body. CYP417A2 was significantly up-regulated at 12, 36, 60, 84 and 108 h after the triflumezopyrim treatment. RNA interference (RNAi) against CYP417A2 significantly increased triflumezopyrim susceptibility in SBPH. According to the prediction by miRanda and TargetScan software, three miRNAs were indicated to bind to CYP417A2. However, when oversupply of agomir, only two miRNAs, PC-3p-625_4405 and PC-5p-3991_515, significantly increased the susceptibility to triflumezopyrim and decreased CYP417A2 levels. Furthermore, PC-5p-3991_515 was confirmed to be involved in the post-transcriptional regulation of CYP417A2 by dual luciferase reporter assay. Meanwhile, PC-5p-3991_515 was co-localized with CYP417A2 in the midgut in situ hybridization.

CONCLUSION

Our findings revealed that the novel microRNA, PC-5p-3991_515, post-transcriptionally regulated CYP417A2 expression, which then mediated the triflumezopyrim susceptibility in SBPH. © 2023 Society of Chemical Industry.

MicroRNA Targets PAP1 to Mediate Melanization in Plutella xylostella (Linnaeus) Infected by Metarhizium anisopliae

MicroRNAs (miRNAs) play a pivotal role in important biological processes by regulating post-transcriptional gene expression and exhibit differential expression patterns during development, immune responses, and stress challenges. The diamondback moth causes significant economic damage to crops worldwide. Despite substantial advancements in understanding the molecular biology of this pest, our knowledge regarding the role of miRNAs in regulating key immunity-related genes remains limited. In this study, we leveraged whole transcriptome resequencing data from Plutella xylostella infected with Metarhizium anisopliae to identify specific miRNAs targeting the prophenoloxidase-activating protease1 (PAP1) gene and regulate phenoloxidase (PO) cascade during melanization. Seven miRNAs (pxy-miR-375-5p, pxy-miR-4448-3p, pxy-miR-279a-3p, pxy-miR-3286-3p, pxy-miR-965-5p, pxy-miR-8799-3p, and pxy-miR-14b-5p) were screened. Luciferase reporter assays confirmed that pxy-miR-279a-3p binds to the open reading frame (ORF) and pxy-miR-965-5p to the 3' untranslated region (3' UTR) of PAP1. Our experiments demonstrated that a pxy-miR-965-5p mimic significantly reduced PAP1 expression in P. xylostella larvae, suppressed PO activity, and increased larval mortality rate. Conversely, the injection of pxy-miR-965-5p inhibitor could increase PAP1 expression and PO activity while decreasing larval mortality rate. Furthermore, we identified four LncRNAs (MSTRG.32910.1, MSTRG.7100.1, MSTRG.6802.1, and MSTRG.22113.1) that potentially interact with pxy-miR-965-5p. Interference assays using antisense oligonucleotides (ASOs) revealed that silencing MSTRG.7100.1 and MSTRG.22113.1 increased the expression of pxy-miR-965-5p. These findings shed light on the potential role of pxy-miR-965-5p in the immune response of P. xylostella to M. anisopliae infection and provide a theoretical basis for biological control strategies targeting the immune system of this pest.

Identification and characteristic analysis of an extracellular signal-regulated kinase from Ostrinia furnacalis Guenée

The extracellular signal-regulated kinase (ERK) pathway, a critical genetic determinant, controls diverse physiological functions, including innate immunity, development, and stress response. In the current study, a full-length cDNA (1592bp) encoding the ERK gene (OfERK) was cloned from Ostrinia furnacalis Guenée (GenBank accession number: MF797866). The open reading frame of the OfERK gene encoded 364 amino acids and shared 96.43%-98.08% amino acid identities with other insect mitogen-activated protein kinases. For spatiotemporal analysis of the expression pattern, OfERK exhibited a significant peak expression on the 3rd day of the pupa stage and showed the highest expression in hemocytes specifically. Indirect immunofluorescence assays and immuno-electron microscopy revealed a wide distribution of the OfERK protein in hemocytes and epidermis. Moreover, the results demonstrated that the Bt Cry1Ab-activated toxin significantly induces the expression of OfERK. Other genes related to immune response, development, and stress response exhibited dynamic changes in expression after Cry1Ab oral treatment. The expression of OfERK was downregulated through RNA interference, and the correlation of its expression with other related genes was verified using quantitative real-time polymerase chain reaction. Our study provides valuable insights into the regulatory mechanism of ERK in insects for future studies.

A secreted phospholipase A2 (BmsPLA2 ) regulates melanization of immunity through BmDDC in the silkworm Bombyx mori

Insect immune-associated phospholipase A2 (PLA2 ) is an important target of pathogen invasion. Melanization, an effective defense response, has significant correlations with other immune responses to coordinate immune attack against invaders. However, the effect of PLA2 on melanization has not yet been reported in insects or other arthropods. In this work, we cloned a PLA2 gene (BmsPLA2 ), and its protein had characteristic features of secreted PLA2 (sPLA2 ). After injection of bacteria, BmsPLA2 expression and sPLA2 activity in hemolymph significantly increased. BmsPLA2 fluorescence was transferred from the cytoplasm to the cell membranes of circulating hemocytes. These results indicated that BmsPLA2 was related to hemolymph immunity in silkworms. Interestingly, reducing BmsPLA2 by RNA interference decreased melanosis (melanistic hemocytes) levels in vivo and in vitro, while BmsPLA2 overexpression had the opposite effect. The larval survival and melanization rate in the hemocoel both slowed depending on the PLA2 inhibitor dosage. These results demonstrated that BmsPLA2 plays a role in melanization during the immune process of silkworms. Surprisingly, the level of BmDDC matched the degree of melanization in various observations. BmDDC expression showed a significant increase, with the peak occurring later than that of BmsPLA2 after injection of bacteria, implying that BmsPLA2 was activated prior to BmDDC. Moreover, the alteration of BmsPLA2 by RNA interference or overexpression led to altered BmDDC levels. These results suggested that BmsPLA2 regulates the melanization response in silkworms through BmDDC. Our study proposes a new regulatory mechanism of the melanization response and new directions for understanding the complex immune networks of insects.

Advances in the extracellular signal-regulated kinase signaling pathway in silkworms, Bombyx mori (Lepidoptera)

Signaling pathways regulate the transmission of signals during organism growth and development, promoting the smooth and accurate completion of numerous physiological and biochemical reactions. The extracellular signal-regulated kinase (ERK) signaling pathway is an essential pathway involved in regulating various physiological processes, such as cell proliferation, differentiation, adhesion, migration, and more. This pathway also contributes to several important physiological processes in silkworms, including protein synthesis, reproduction, and immune defense against pathogens. Organizing related studies on the ERK signaling pathway in silkworms can provide a better understanding of its mechanism in Lepidopterans and develop a theoretical foundation for improving cocoon production and new strategies for pest biological control.

Integrated analysis of miRNA profiles and gut bacterial changes in Altica viridicyanea following antibiotic treatment

The gut bacteria involves in insect homeostasis by playing essential roles in host physiology, metabolism, innate immunity, and so forth. microRNAs (miRNAs) are endogenous small noncoding RNAs that posttranscriptionally regulate gene expression to affect immune or metabolic processes in insects. For several non-model insects, the available knowledge on the relationship between changes in the gut bacteria and miRNA profiles is limited. In this study, we investigated the gut bacterial diversity, composition, and function from Altica viridicyanea feeding on normal- and antibiotic-treated host plants using 16S rRNA amplicon sequencing; antibiotics have been shown to affect the body weight and development time in A. viridicyanea, suggesting that the gut bacteria of the normal sample were more diverse and abundant than those of the antibiotic-fed group, and most of them were involved in various physical functions by enrichment analysis. Furthermore, we executed small RNA transcriptome sequencing using the two experimental groups to obtain numerous sRNAs, such as piRNAs, siRNAs, and known and novel miRNAs, by data mapping and quality control, and furthermore, a total of 224 miRNAs were identified as significantly differentially expressed miRNAs, of which some DEMs and their target genes participated in immune- and metabolism-related pathways based on GO and KEGG annotation. Besides, regarding the regulatory roles of miRNA and target genes, a interaction network of DEM-target gene pairs from eight immune- or metabolism-related signaling pathways were constructed. Finally, we discovered that DEMs from above pathways were significantly positively or negatively correlated with gut bacterial alterations following antibiotic treatment. Collectively, the observations of this study expand our understanding of how the disturbance of gut bacteria affects miRNA profiles in A. viridicyanea and provide new valuable resources from extreme ranges for future studies on the adaptive evolution in insects.

Insect-pathogen crosstalk and the cellular-molecular mechanisms of insect immunity: uncovering the underlying signaling pathways and immune regulatory function of non-coding RNAs

Multicellular organisms are constantly subjected to pathogens that might be harmful. Although insects lack an adaptive immune system, they possess highly effective anti-infective mechanisms. Bacterial phagocytosis and parasite encapsulation are some forms of cellular responses. Insects often defend themselves against infections through a humoral response. This phenomenon includes the secretion of antimicrobial peptides into the hemolymph. Specific receptors for detecting infection are required for the recognition of foreign pathogens such as the proteins that recognize glucans and peptidoglycans, together referred to as PGRPs and βGRPs. Activation of these receptors leads to the stimulation of signaling pathways which further activates the genes encoding for antimicrobial peptides. Some instances of such pathways are the JAK-STAT, Imd, and Toll. The host immune response that frequently accompanies infections has, however, been circumvented by diseases, which may have assisted insects evolve their own complicated immune systems. The role of ncRNAs in insect immunology has been discussed in several notable studies and reviews. This paper examines the most recent research on the immune regulatory function of ncRNAs during insect-pathogen crosstalk, including insect- and pathogen-encoded miRNAs and lncRNAs, and provides an overview of the important insect signaling pathways and effector mechanisms activated by diverse pathogen invaders.

The Effects of Diet on the Immune Responses of the Oriental Armyworm Mythimna separata

Nutrients can greatly affect host immune defenses against infection. Possessing a simple immune system, insects have been widely used as models to address the relationships between nutrition and immunity. The effects of high versus low protein-to-carbohydrate ratio (P:C) diets on insect immune responses vary in different studies. To reveal the dietary manipulation of immune responses in the polyphagous agricultural pest oriental armyworm, we examined immune gene expression, phenoloxidase (PO) activity, and phagocytosis to investigate the immune traits of bacteria-challenged oriental armyworms, which were fed different P:C ratio diets. We found the oriental armyworms that were fed a 35:7 (P:C) diet showed higher phenoloxidase (PO) activity and stronger melanization, and those reared on a 28:14 (P:C) diet showed higher antimicrobial activity. However, different P:C diets had no apparent effect on the hemocyte number and phagocytosis. These results overall indicate that high P:C diets differently optimize humoral immune defense responses in oriental armyworms, i.e., PO-mediated melanization and antimicrobial peptide synthesis in response to bacteria challenge.

Colonization Resistance of Symbionts in Their Insect Hosts

The symbiotic microbiome is critical in promoting insect resistance against colonization by exogenous microorganisms. The mechanisms by which symbionts contribute to the host's immune capacity is referred to as colonization resistance. Symbionts can protect insects from exogenous pathogens through a variety of mechanisms, including upregulating the expression of host immune-related genes, producing antimicrobial substances, and competitively excluding pathogens. Concordantly, insects have evolved fine-tuned regulatory mechanisms to avoid overactive immune responses against symbionts or specialized cells to harbor symbionts. Alternatively, some symbionts have evolved special adaptations, such as the formation of biofilms to increase their tolerance to host immune responses. Here, we provide a review of the mechanisms about colonization resistance of symbionts in their insect hosts. Adaptations of symbionts and their insect hosts that may maintain such symbiotic relationships, and the significance of such relationships in the coevolution of symbiotic systems are also discussed to provide insights into the in-depth study of the contribution of symbionts to host physiology and behavior.

Expression Profile, Regulatory Network, and Putative Role of microRNAs in the Developmental Process of Asian Honey Bee Larval Guts

MiRNAs, as a kind of key regulators in gene expression, play vital roles in numerous life activities from cellular proliferation and differentiation to development and immunity. However, little is known about the regulatory manner of miRNAs in the development of Asian honey bee (Apis cerana) guts. Here, on basis of our previously gained high-quality transcriptome data, transcriptome-wide identification of miRNAs in the larval guts of Apis cerana cerana was conducted, followed by investigation of the miRNAs' differential expression profile during the gut development. In addition to the regulatory network, the potential function of differentially expressed miRNAs (DEmiRNAs) was further analyzed. In total, 330, 351, and 321 miRNAs were identified in the 4-, 5-, and 6-day-old larval guts, respectively; among these, 257 miRNAs were shared, while 38, 51, and 36 ones were specifically expressed. Sequences of six miRNAs were confirmed by stem-loop RT-PCR and Sanger sequencing. Additionally, in the "Ac4 vs. Ac5" comparison group, there were seven up-regulated and eight down-regulated miRNAs; these DEmiRNAs could target 5041 mRNAs, involving a series of GO terms and KEGG pathways associated with growth and development, such as cellular process, cell part, Wnt, and Hippo. Comparatively, four up-regulated and six down-regulated miRNAs detected in the "Ac5 vs. Ac6" comparison group and the targets were associated with diverse development-related terms and pathways, including cell, organelle, Notch and Wnt. Intriguingly, it was noticed that miR-6001-y presented a continuous up-regulation trend across the developmental process of larval guts, implying that miR-6001-y may be a potential essential modulator in the development process of larval guts. Further investigation indicated that 43 targets in the "Ac4 vs. Ac5" comparison group and 31 targets in the "Ac5 vs. Ac6" comparison group were engaged in several crucial development-associated signaling pathways such as Wnt, Hippo, and Notch. Ultimately, the expression trends of five randomly selected DEmiRNAs were verified using RT-qPCR. These results demonstrated that dynamic expression and structural alteration of miRNAs were accompanied by the development of A. c. cerana larval guts, and DEmiRNAs were likely to participate in the modulation of growth as well as development of larval guts by affecting several critical pathways via regulation of the expression of target genes. Our data offer a basis for elucidating the developmental mechanism underlying Asian honey bee larval guts.

A microRNA, PC-5p-30_205949, regulates triflumezopyrim susceptibility in Laodelphax striatellus (Fallén) by targeting CYP419A1 and ABCG23

MicroRNAs (miRNAs) are known to be important post-transcriptional regulators of gene expression and have been shown to be associated with insecticide resistance in insects. In this research, we show that a miRNA, PC-5p-30_205949, is involved in triflumezopyrim susceptibility via regulating expressive abundance of cytochrome P450 CYP419A1 and ATP-binding cassette transporters ABCG23 in the small brown planthopper (SBPH), Laodelphax striatellus (Fallén). Triflumezopyrim treatment significantly reduced the abundance of PC-5p-30_205949, feeding of agomir-PC-5p-30_205949 significantly increased the sensitivity of SBPH to triflumezopyrim, and its spatiotemporal expression profiles showed that PC-5p-30_205949 were expressed at all developmental stages and were highly expressed in head tissue. By software prediction and dual luciferase reporter assay, the target genes of PC-5p-30_205949 were identified as two detoxification metabolism genes CYP419A1 and ABCG23. The relative expressions of CYP419A1 and ABCG23 were significantly up-regulated after 24 h, 48 h and 72 h with triflumezopyrim exposure. CYP419A1 was highly expressed in the 4th-instar nymphs and male adults, with the highest expression level in fat body. ABCG23 was highly expressed in female adults, and had the highest expression in head. Furthermore, silencing of CYP419A1 and ABCG23 by RNA interference significantly increased the mortality of SBPH to triflumezopyrim, and molecular docking showed that CYP419A1 and ABCG23 could stably bind to triflumezopyrim with binding free energies of -171.5622 and - 103.3402 kcal mol^-1, respectively. These results suggest that SBPH has a strategy to enhance the resistance to triflumezopyrim by attenuating the expression of PC-5P-30_205949, thereby activating the detoxification metabolic pathway by targeting CYP419A1 and ABCG23.

Nitric oxide synthase is required for the pea aphid's defence against bacterial infection

Compared to other insects, the pea aphid Acyrthosiphon pisum has a reduced immune system with an absence of genes coding for a lot of immunity-related molecules. Notably, nitric oxide synthase (NOS), which catalyses the synthesis of nitric oxide (NO), is present in the pea aphid. However, the role of NO in the immune system of pea aphid remains unclear. In this study, we explored the role of NO in the defence of the pea aphid against bacterial infections and found that the NOS gene of the pea aphid responded to an immune challenge, with the expression of ApNOS observably upregulated after bacterial infections. Knockdown of ApNOS using RNA interference or inhibition of NOS activity increased the number of live bacterial cells in aphids and the mortality of aphids after bacterial infection. Conversely, the increase in NO level in aphids using NO donor inhibited the bacterial growth, increased the survival of bacteria-infected aphids, and upregulated immune genes, such as Toll pathway and phagocytosis related genes. Thus, NO promotes immune responses and plays an important role in the immune system of pea aphid.

Eucalyptol antagonized the apoptosis and immune dysfunction of grass carp hepatocytes induced by tetrabromobisphenol A by regulating ROS/ASK1/JNK pathway

Tetrabromobisphenol A (TBBPA) is a common environmental pollutant which has multi-organ toxicity to mammals. Eucalyptol (EUC) has super antioxidant biological activity. However, in this experimental study, we probed into the mechanism of toxic of TBBPA exposure on Grass carp hepatocytes (L8824 cells) and the antagonistic impact of EUC on TBBPA. We treated L8824 cells with 8 μg/ml TBBPA and/or 20 μM EUC for 24 h in this test research. The experiment results suggested that TBBPA exposure induced elevated levels of reactive oxygen species (ROS), led to oxidative stress, decreased SOD and CAT activities, decreased GSH and T-AOC contents, exacerbated MDA accumulation, activated ASK1/JNK signaling pathway, and further increased the contents of mitochondrial dependent apoptosis pathway related indicators (Cyt-C, Bax, Caspase 9, Caspase 3), while Bcl-2 expression decreased. In addition, TBBPA exposure induced increased expression of TNF-α, IL-6, IL-1β, and decreased expression of IL-2, IFN-γ, Hepcidin, β-defensin, LEAP2. The oxidative stress level, ASK1/JNK signal pathway expression level, apoptosis ratio and cellular immune function of cells exposed to EUC alone did not change significantly. Combined exposure of TBBPA and EUC significantly reduced the proportion of apoptosis and restored cellular immune function. Therefore, these results suggest that EUC can effectively antagonize TBBPA-induced apoptosis and immune dysfunction of L8824 cells by regulating ROS/ASK1/JNK signaling pathway.

c-Jun regulates flotillin 2 transcription to benefit viral accumulation in insect vectors

The c-Jun N-terminal kinase (JNK) signaling pathway plays a critical role in viral infection in host cells. In addition to triggering immune reactions against pathogens, the JNK signaling pathway has also been found to benefit viral infection. Our previous work showed that JNK activation facilitated rice stripe virus (RSV) accumulation in the insect vector small brown planthopper, but the underlying mechanisms remain elusive. Here, we revealed a link between JNK activation and the transcriptional upregulation of the plasma membrane protein flotillin 2, which mediates RSV cell entry. c-Jun, a downstream substrate of JNKs, was identified as a transcription factor that targets the promoter of flotillin 2 at three binding sites. Phosphorylated c-Jun, especially at the serine 63 site, promoted the transcriptional activity of c-Jun on flotillin 2. JNK activation or inhibition affected c-Jun phosphorylation status and flotillin 2 expression. In the midguts of planthoppers, RSV infection significantly increased flotillin 2 expression and the phosphorylation level of JNKs and c-Jun. Manipulation of JNK status impacted viral acquisition in midgut cells. These findings reveal a new regulatory mechanism of the JNK signaling pathway and shed light on the virus-supportive effect of this pathway.

MicroRNAs reshape the immunity of insects in response to bacterial infection

The interaction between bacteria and insects can significantly impact a wide range of different areas because bacteria and insects are widely distributed around the globe. The bacterial-insect interactions have the potential to directly affect human health since insects are vectors for disease transmission, and their interactions can also have economic consequences. In addition, they have been linked to high mortality rates in economically important insects, resulting in substantial economic losses. MicroRNAs (miRNAs) are types of non-coding RNAs involved in regulating gene expression post-transcriptionally. The length of miRNAs ranges from 19 to 22 nucleotides. MiRNAs, in addition to their ability to exhibit dynamic expression patterns, have a diverse range of targets. This enables them to govern various physiological activities in insects, like innate immune responses. Increasing evidence suggests that miRNAs have a crucial biological role in bacterial infection by influencing immune responses and other mechanisms for resistance. This review focuses on some of the most recent and exciting discoveries made in recent years, including the correlation between the dysregulation of miRNA expression in the context of bacterial infection and the progression of the infection. Furthermore, it describes how they profoundly impact the immune responses of the host by targeting the Toll, IMD, and JNK signaling pathways. It also emphasizes the biological function of miRNAs in regulating immune responses in insects. Finally, it also discusses current knowledge gaps about the function of miRNAs in insect immunity, in addition to areas that require more research in the future.

Identification and profiling of Sogatella furcifera microRNAs and their potential roles in regulating the developmental transitions of nymph-adult

Sogatella furcifera is one of the most serious insect pests that affect rice in Asia. One class of small RNAs (sRNAs; ~22 nt long) is miRNAs, which participate in various biological processes by regulating the expression of target genes in a spatiotemporal manner. However, the role of miRNAs in nymph-to-adult transition in S. furcifera remains unknown. In this study, we sequenced sRNA libraries of S. furcifera prepared from individuals at three different developmental stages (pre-moult, moulting and early adult). A total of 253 miRNAs (134 known and 119 novel) were identified, of which 12 were differentially expressed during the nymph-to-adult developmental transition. Moreover, Real time quantitative PCR (RT-qPCR) analysis revealed that all 12 miRNAs were differentially expressed among five different nymph tissues and 14 different developmental stages (first to fifth instar nymphs and 1-day-old adults). Injection of miR-2a-2 mimic/antagomir and miR-305-5p-1 mimic/antagomir into 1-day-old fifth instar nymphs significantly increased the mortality rate. In addition, a defective moulting phenotype was observed in nymphs injected with miR-2a-2 and miR-305-5p-1, suggesting that these miRNAs are involved in S. furcifera nymph-adult transition. In conclusion, these results reveal the function of critical miRNAs in S. furcifera nymph-adult transition, and also provide novel potential targets of insecticides for the long-term sustainable management of S. furcifera.

Cotton leaf curl Multan virus differentially regulates innate antiviral immunity of whitefly (Bemisia tabaci) vector to promote cryptic species-dependent virus acquisition

Begomoviruses represent the largest group of economically important, highly pathogenic, DNA plant viruses that contribute a substantial amount of global crop disease burden. The exclusive transmission of begomoviruses by whiteflies (Bemisia tabaci) requires them to interact and efficiently manipulate host responses at physiological, biological and molecular scales. However, the molecular mechanisms underlying complex begomovirus-whitefly interactions that consequently substantiate efficient virus transmission largely remain unknown. Previously, we found that whitefly Asia II 7 cryptic species can efficiently transmit cotton leaf curl Multan virus (CLCuMuV) while MEAM1 cryptic species is a poor carrier and incompetent vector of CLCuMuV. To investigate the potential mechanism/s that facilitate the higher acquisition of CLCuMuV by its whitefly vector (Asia II 7) and to identify novel whitefly proteins that putatively interact with CLCuMuV-AV1 (coat protein), we employed yeast two-hybrid system, bioinformatics, bimolecular fluorescence complementation, RNA interference, RT-qPCR and bioassays. We identified a total of 21 Asia II 7 proteins putatively interacting with CLCuMuV-AV1. Further analyses by molecular docking, Y2H and BiFC experiments validated the interaction between a whitefly innate immunity-related protein (BTB/POZ) and viral AV1 (coat protein). Gene transcription analysis showed that the viral infection significantly suppressed the transcription of BTB/POZ and enhanced the accumulation of CLCuMuV in Asia II 7, but not in MEAM1 cryptic species. In contrast to MEAM1, the targeted knock-down of BTB/POZ substantially reduced the ability of Asia II 7 to acquire and accumulate CLCuMuV. Additionally, antiviral immune signaling pathways (Toll, Imd, Jnk and Jak/STAT) were significantly suppressed following viral infection of Asia II 7 whiteflies. Taken together, the begomovirus CLCuMuV potentiates efficient virus accumulation in its vector B. tabaci Asia II 7 by targeting and suppressing the transcription of an innate immunity-related BTB/POZ gene and other antiviral immune responses in a cryptic species-specific manner.

The IMD pathway in Hemipteran: A comparative analysis and discussion

The evolutionary patterns of the genes in the IMD pathway in hemipterans were characterized and compared. The hemipteran insects were clustered into two groups. One group that encompasses whitefly, plant lice, and scale insect partially lacks the IMD pathway and all antimicrobial peptide (AMP) genes, with the vast majority of IMD pathway and all AMP genes being absent in aphids. The reasons for the absence of the IMD pathway and AMP genes in hemipterans were analyzed based on aphids, in terms of fitness costs. In case of limited resources, aphids have to make a trade-off between the necessary costs such as clean food sources, the essential amino acids supplied by primary bacterial symbionts for survival, nutrients and/or protections against stress provided by secondary symbionts, and the high reproductive capacity, and the costs that do not increase the fitness. Obviously, aphids have to abandon the strong immune system, especially the AMPs and IMD pathway which is mainly against Gram-negative bacteria. The common ground shared with aphids may be the reason for the absence of the IMD pathway and AMP genes in other hemipteran insects.

The immune deficiency and c-Jun N-terminal kinase pathways drive the functional integration of the immune and circulatory systems of mosquitoes

The immune and circulatory systems of animals are functionally integrated. In mammals, the spleen and lymph nodes filter and destroy microbes circulating in the blood and lymph, respectively. In insects, immune cells that surround the heart valves (ostia), called periostial haemocytes, destroy pathogens in the areas of the body that experience the swiftest haemolymph (blood) flow. An infection recruits additional periostial haemocytes, amplifying heart-associated immune responses. Although the structural mechanics of periostial haemocyte aggregation have been defined, the genetic factors that regulate this process remain less understood. Here, we conducted RNA sequencing in the African malaria mosquito, Anopheles gambiae, and discovered that an infection upregulates multiple components of the immune deficiency (IMD) and c-Jun N-terminal kinase (JNK) pathways in the heart with periostial haemocytes. This upregulation is greater in the heart with periostial haemocytes than in the circulating haemocytes or the entire abdomen. RNA interference-based knockdown then showed that the IMD and JNK pathways drive periostial haemocyte aggregation and alter phagocytosis and melanization on the heart, thereby demonstrating that these pathways regulate the functional integration between the immune and circulatory systems. Understanding how insects fight infection lays the foundation for novel strategies that could protect beneficial insects and harm detrimental ones.

Early-Stage Defense Mechanism of the Cotton Aphid Aphis gossypii Against Infection With the Insect-Killing Fungus Beauveria bassiana JEF-544

Aphis gossypii, commonly known as the cotton aphid, is a widely distributed pest of agricultural crops and acts as a vector for many serious plant viruses. Cotton aphid shows high resistance to chemical insecticides due to rapid rates of genetic diversity as a result of its short life cycle, seasonal migration, and host alteration. As an alternative, entomopathogenic fungi can be used to control cotton aphids in an environmentally sound manner. However, little is known about how cotton aphids respond to fungal infection. In this work, a new Beauveria bassiana strain JEF-544 (Bb JEF-544) was selected and isolated through bioassays with high virulence against cotton aphid. Early response of cotton aphid to Bb JEF-544 infection was analyzed at the transcriptome level. Infected aphids were collected two days after treatment at 25% lethal time (LT25), and total RNA of non-infected and Bb JEF-544-infected aphids was independently subjected to sequencing. Infected aphids showed significant up-regulation of the insect hormone biosynthesis pathway. Bursicon (Burs) and crustacean cardioactive peptide (CCAP) receptors involved in molting along with ecdysone synthesis were also strongly up-regulated in the aphid response to the fungal infection. In the immune response, melanization in the hemocoel was significantly up-regulated, while phagocytosis was less actively transcribed. In conclusion, cotton aphids protect themselves from Bb JEF-544 infection by activating the immune response including melanization and insect molting hormones to shed infected cuticles. In addition to describing the initial stages of Bb JEF-544 infection at the transcriptome level, this work provides potential treatment targets and insight into how fungal isolates can effectively be used to control this serious aphid species.

The Aedes aegypti siRNA pathway mediates broad-spectrum defense against human pathogenic viruses and modulates antibacterial and antifungal defenses

The mosquito's innate immune system defends against a variety of pathogens, and the conserved siRNA pathway plays a central role in the control of viral infections. Here, we show that transgenic overexpression of Dicer2 (Dcr2) or R2d2 resulted in an accumulation of 21-nucleotide viral sequences that was accompanied by a significant suppression of dengue virus (DENV), Zika virus (ZIKV), and chikungunya virus (CHIKV) replication, thus indicating the broad-spectrum antiviral response mediated by the siRNA pathway that can be applied for the development of novel arbovirus control strategies. Interestingly, overexpression of Dcr2 or R2d2 regulated the mRNA abundance of a variety of antimicrobial immune genes, pointing to additional functions of DCR2 and R2D2 as well as cross-talk between the siRNA pathway and other immune pathways. Accordingly, transgenic overexpression of Dcr2 or R2d2 resulted in a lesser proliferation of the midgut microbiota and increased resistance to bacterial and fungal infections.

Advances in the Immune Regulatory Role of Non-Coding RNAs (miRNAs and lncRNAs) in Insect-Pathogen Interactions

Insects are by far the most abundant and diverse living organisms on earth and are frequently prone to microbial attacks. In other to counteract and overcome microbial invasions, insects have in an evolutionary way conserved and developed immune defense mechanisms such as Toll, immune deficiency (Imd), and JAK/STAT signaling pathways leading to the expression of antimicrobial peptides. These pathways have accessory immune effector mechanisms, such as phagocytosis, encapsulation, melanization, nodulation, RNA interference (RNAi), lysis, autophagy, and apoptosis. However, pathogens evolved strategies that circumvent host immune response following infections, which may have helped insects further sophisticate their immune response mechanisms. The involvement of ncRNAs in insect immunity is undeniable, and several excellent studies or reviews have investigated and described their roles in various insects. However, the functional analyses of ncRNAs in insects upon pathogen attacks are not exhaustive as novel ncRNAs are being increasingly discovered in those organisms. This article gives an overview of the main insect signaling pathways and effector mechanisms activated by pathogen invaders and summarizes the latest findings of the immune modulation role of both insect- and pathogen-encoded ncRNAs, especially miRNAs and lncRNAs during insect–pathogen crosstalk.

Hosting certain facultative symbionts modulates the phenoloxidase activity and immune response of the pea aphid Acyrthosiphon pisum

The pea aphid Acyrthosiphon pisum hosts different facultative symbionts (FS) which provide it with various benefits, such as tolerance to heat or protection against natural enemies (e.g., fungi, parasitoid wasps). Here, we investigated whether and how the presence of certain FS could affect phenoloxidase (PO) activity, a key component of insect innate immunity, under normal and stressed conditions. For this, we used clones of A. pisum of different genetic backgrounds (LL01, YR2 and T3-8V1) lacking FS or harboring one or two (Regiella insecticola, Hamiltonella defensa, Serratia symbiotica + Rickettsiella viridis). Gene expression and proteomics analyses of the aphid hemolymph indicated that the two A. pisum POs, PPO1 and PPO2, are expressed and translated into proteins. The level of PPO genes expression as well as the amount of PPO proteins and phenoloxidase activity in the hemolymph depended on both the aphid genotype and FS species. In particular, H. defensa and R. insecticola, but not S. symbiotica + R. viridis, caused a sharp decrease in PO activity by interfering with both transcription and translation. The microinjection of different types of stressors (yeast, Escherichia coli, latex beads) in the YR2 lines hosting different symbionts affected the survival rate of aphids and, in most cases, also decreased the expression of PPO genes after 24 h. The amount and activity of PPO proteins varied according to the type of FS and stressor, without clear corresponding changes in gene expression. These data demonstrate that the presence of certain FS influences an important component of pea aphid immunity.

Characterization and functional analysis of a Relish gene from the Asian corn borer, Ostrinia furnacalis (Guenée)

Pathogen-induced host immune responses reduce the efficacy of pathogens used to control pests. However, compared to the well-deciphered immunity system of Drosophila melanogaster, the immunity system of agricultural pests is largely unconfirmed through functional analysis. Beginning to unveil mechanisms of transcription regulation of immune genes in the Asian corn borer, Ostrinia furnacalis, we cloned the complementary DNA (cDNA) of a transcription factor Relish by rapid amplification of cDNA ends. The 3164 bp cDNA, designated Of-Relish, encodes a 956-residue protein. Bioinformatic analysis showed that Of-Relish had a Rel homology domain, a predicted cleavage site between Q⁴⁰⁹ and L⁴¹⁰ , six ankyrin repeats, and a death domain. The response of Of-Relish expression to the Gram-negative bacteria Pseudomonas aeruginosa was sooner and stronger than to the Gram-positive Micrococcus luteus. The antimicrobial peptide genes Attacin and Gloverin had similar expression patterns in response to the infections. Knockdown of Of-Relish led to a decrease in Attacin and Gloverin messenger RNA levels, suggesting that Attacin and Gloverin were regulated by Of-Relish. Together, the results suggested that Of-Relish is a key component of the IMD pathway in O. furnacalis, involved in defense against P. aeruginosa through activation of Attacin and Gloverin.

Immune properties of invertebrate phenoloxidases

Melanin production from different types of phenoloxidases (POs) confers immunity from a variety of pathogens ranging from viruses and microorganisms to parasites. The arthropod proPO expresses a variety of activities including cytokine, opsonin and microbiocidal activities independent of and even without melanin production. Proteolytic processing of proPO and its activating enzyme gives rise to several peptide fragments with a variety of separate activities in a process reminiscent of vertebrate complement system activation although proPO bears no sequence similarity to vertebrate complement factors. Pathogens influence proPO activation and thereby what types of immune effects that will be produced. An increasing number of specialised pathogens - from parasites to viruses - have been identified who can synthesise compounds specifically aimed at the proPO-system. In invertebrates outside the arthropods phylogenetically unrelated POs are participating in melanization reactions obviously aimed at intruders and/or aberrant tissues.

Two atypical gram-negative bacteria-binding proteins are involved in the antibacterial response in the pea aphid (Acyrthosiphon pisum)

The activation of immune pathways is triggered by the recognition of pathogens by pattern recognition receptors (PRRs). Gram-negative bacteria-binding proteins (GNBPs)/β-1,3-glucan recognition proteins (βGRPs) are a conserved family of PRRs in insects. Two GNBPs are predicted in the genome database of pea aphids; however, little is known about their functions in the aphid immune system. Here, we show that pea aphid GNBPs possess domain architectures and sequence features distinct from those of typical GNBPs/βGRPs and that their expression is induced by bacterial infection. Knockdown of their expression by dsRNA resulted in lower phenoloxidase activity, higher bacterial loads and higher mortality in aphids after infection. Our data suggest that these two atypical GNBPs are involved in the antibacterial response in the pea aphid, likely acting as PRRs in the prophenoloxidase pathway.

Triple RNA-Seq characterizes aphid gene expression in response to infection with unequally virulent strains of the endosymbiont Hamiltonella defensa

Background

Secondary endosymbionts of aphids provide benefits to their hosts, but also impose costs such as reduced lifespan and reproductive output. The aphid Aphis fabae is host to different strains of the secondary endosymbiont Hamiltonella defensa, which encode different putative toxins. These strains have very different phenotypes: They reach different densities in the host, and the costs and benefits (protection against parasitoid wasps) they confer to the host vary strongly.

Results

We used RNA-Seq to generate hypotheses on why four of these strains inflict such different costs to A. fabae. We found different H. defensa strains to cause strain-specific changes in aphid gene expression, but little effect of H. defensa on gene expression of the primary endosymbiont, Buchnera aphidicola. The highly costly and over-replicating H. defensa strain H85 was associated with strongly reduced aphid expression of hemocytin, a marker of hemocytes in Drosophila. The closely related strain H15 was associated with downregulation of ubiquitin-related modifier 1, which is related to nutrient-sensing and oxidative stress in other organisms. Strain H402 was associated with strong differential regulation of a set of hypothetical proteins, the majority of which were only differentially regulated in presence of H402.

Conclusions

Overall, our results suggest that costs of different strains of H. defensa are likely caused by different mechanisms, and that these costs are imposed by interacting with the host rather than the host’s obligatory endosymbiont B. aphidicola.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07742-8.

Regulatory roles of microRNAs in insect pests: prospective targets for insect pest control

At the post-transcriptional level, microRNAs (miRNAs) play an important role in the regulation of gene expression, thereby influencing the outcome of many biological processes in insects, such as development, reproduction, metamorphosis, immunity, and insecticide resistance. The alteration of miRNA expression by mimic/agomir or inhibitor/antagomir via injection/feeding can lead to pest developmental abnormalities, death, or reduced pesticide resistance, indicating that miRNAs are potential targets for pest control. This review provides an overview of recent advances in understanding the regulatory roles of miRNA in agricultural and public health insect pest, and further highlights the potential of miRNAs as prospective targets in pest control.

Scavenger receptor B1 mediates phagocytosis and the antimicrobial peptide pathway in the endoparasitic wasp Micropilits mediator

Scavenger receptors (SRs) are a family of pattern recognition receptors (PRRs) in the immune system. They are required for phagocytosis and act as co-receptors of Toll-like receptors to regulate immune signaling pathways in the fight against pathogens. Little is known about the function of SRs in insects. Here, we reported on a member of the SR family from the parasitic wasp Micropilits mediator (designated MmSR-B1) that is responsive to bacterial infection. The recombinant extracellular CD36 domain of MmSR-B1 produced in Escherichia coli cells is capable of binding to peptidoglycans and bacterial cells, causing agglutination of bacteria. Furthermore, we demonstrated that double-stranded RNA-mediated knockdown of MmSR-B1 impedes hemocyte phagocytosis and downregulates the expression of antimicrobial peptide (AMP) genes defensins and hymenoptaecins. Knockdown of MmSR-B1 led to increased death of the wasps when challenged by bacteria. Our study suggests that MmSR-B1 mediates phagocytosis and the production of AMPs in M. mediator wasps.

JNK signaling as a target for anticancer therapy

The JNKs are members of mitogen-activated protein kinases (MAPK) which regulate many physiological processes including inflammatory responses, macrophages, cell proliferation, differentiation, survival, and death. It is increasingly clear that the continuous activation of JNKs has a role in cancer development and progression. Therefore, JNKs represent attractive oncogenic targets for cancer therapy using small molecule kinase inhibitors. Studies showed that the two major JNK proteins JNK1 and JNK2 have opposite functions in different types of cancers, which need more specification in the design of JNK inhibitors. Some of ATP- competitive and ATP non-competitive inhibitors have been developed and widely used in vitro, but this type of inhibitors lack selectivity and inhibits phosphorylation of all JNK substrates and may lead to cellular toxicity. In this review, we summarized and discussed the strategies of JNK binding inhibitors and the role of JNK signaling in the pathogenesis of different solid and hematological malignancies.