Insects defend against fungal infection by employing microRNAs to silence virulence-related genes

Immunoregulatory mechanisms and cross-kingdom bacteriostatic effects of microRNAs in crustacean

MicroRNAs (miRNAs) are crucial regulators of gene expression, which contribute to immune response regulation in various organisms, including crustaceans. To investigate the immunoregulatory roles of miRNAs in Portunus trituberculatus, a comparative miRNAomic analysis of Vibrio parahaemolyticus infection was carried out. Through comparative miRNAomic analysis, we identified 17 differentially expressed miRNAs (DE-miRNAs), of which 12 were upregulated. Subsequently, miRNA-mRNA regulatory network analysis revealed that the DE-miRNAs were enriched in immune-related signaling pathways. Within the miRNA-mRNA regulatory network, miRNA novel0045 was identified as a crucial regulator of the tumor necrosis factor (TNF) pathway via targeting the TNF receptor-associated factor 6 gene. This result was corroborated by our RNA interference assay, confirming the significance of miRNA novel0045 in resistance to V. parahaemolyticus infection. Moreover, miRNA novel0294 was noted to possess cross-kingdom regulatory potential, translocating into bacterial cells and directly inhibiting V. parahaemolyticus proliferation. We validated this finding through fluorescence labeling and confocal microscopy, confirming effective internalization and presence of miRNA within bacterial. These results expand the current understanding of miRNA-mediated immune responses in crustaceans, highlighting the roles of miRNAs in host immune defense and cross-kingdom regulatory function in bacterial infection suppression, and have potential implications in the development of RNA-based antimicrobial strategies.

miR-11903a modulates CLIPB9-mediated pathogen defense and longevity in Aedes aegypti

Arthropod melanization is a crucial defense mechanism mediated by a complex cascade of CLIP domain serine proteases (CLIPs). In this study, it was confirmed that microRNA-11903a (miR-11903a) targets Aedes-CLIPB9 (AeCLIPB9) by bioinformatics prediction and dual-luciferase reporter assays. Following intrathoracic injection of miR-11903a agomir and antagomir, Real-time quantitative polymerase chain reaction confirmed that AeCLIPB9 is negatively regulated by miR-11903a. Spatiotemporal expression analysis revealed that miR-11903a is most abundant in 4th instar larvae, followed by pupae and adults, and highly expressed in the wings, head, and midgut of female adults. Following pathogen infection, AeCLIPB9 and miR-11903a exhibited opposite expression trends, indicating their potential roles in mosquito innate immunity. To further investigate the relationship between AeCLIPB9 and miR-11903a, double-strand CLIPB9 was synthesized and RNA interference was performed. Seven-d survival assays revealed that both AeCLIPB9 and miR-11903a were crucial immune factors in fighting pathogens. Finally, longevity assays demonstrated that miR-11903a influenced mosquito lifespan.

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.

Discovery and characterization of a novel Lepidoptera-specific antimicrobial peptide from the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Antimicrobial peptides (AMPs) are critical components of innate immunity in diverse organisms, including plants, vertebrates, and insects. This study identified and characterized a novel Lepidoptera-specific AMP, named lepidoptin, from the invasive pest Spodoptera frugiperda (Lepidoptera: Noctuidae). Lepidoptin is a 116-amino acid protein containing a signal peptide and a novel β-sandwich domain that is distinct from previously reported AMPs. Temporal and spatial expression analyses revealed a significant upregulation of the lepidoptin gene in vivo and in cultured SF9 cells in response to pathogens. Molecular docking analysis identified a specific binding cavity. Enzyme-linked immunosorbent assay and binding assays confirmed that lepidoptin can bind to pathogen-associated molecular patterns, bacteria, and fungi. Recombinant lepidoptin exhibited potent antibacterial activity by inducing bacterial agglutination, inhibiting bacterial growth, increasing bacterial membrane permeability, and preventing biofilm formation. Lepidoptin also showed antifungal activity against the entomopathogenic fungus Beauveria bassiana by inhibiting spore germination, increasing fungal cell permeability, and increasing reactive oxygen species. Injection of recombinant lepidoptin into S. frugiperda larvae increased survival after B. bassiana infection, whereas knockdown of lepidoptin by RNA interference decreased larval survival. In addition, lepidoptin showed antimicrobial activity against the plant pathogen Fusarium graminearum by inhibiting spore germination and alleviating disease symptoms in wheat seedlings and cherry tomatoes. This study demonstrates the remarkable dual functionality of lepidoptin in enhancing S. frugiperda immunity and controlling plant pathogens, making it a promising candidate for biocontrol strategies in both pest management and plant disease prevention.

The conserved role of miR-2 and novel miR-109 in the increase in fecundity of Diaphorina citri induced by symbiotic bacteria and pathogenic fungi

Infection with pathogens can increase the fecundity and other fitness-related traits of insect vectors for their own advantage. Our previous research has reported the pivotal role of DcKr-h1 in the fecundity improvement of Diaphorina citri induced by the bacterium, "Candidatus Liberibacter asiaticus" (CLas), and the fungus, Cordyceps fumosorosea (Cf). However, the posttranscriptional regulation of this process remains poorly understood. Given the significance of miRNAs in gene regulation, we delved into their roles in shaping phenotypes and their underlying molecular mechanisms. Our results indicated that two miRNAs, miR-2 and novel-miR-109, jointly inhibited DcKr-h1 expression by binding to its 3' untranslated region (UTR). In the D. citri-CLas interaction, the expression levels of miR-2 and novel-miR-109 in the ovaries of CLas-positive psyllids were lower compared to CLas-negative individuals. Overexpression of miR-2 or novel-miR-109 significantly decreased fecundity and CLas titer in ovaries and caused reproductive defects reminiscent of DcKr-h1 knockdown. Similarly, in the D. citri-Cf interaction, the levels of miR-2 and novel-miR-109 markedly decreased in the ovaries. Upregulation of miR-2 or novel-miR-109 also resulted in reduced fecundity and ovary defects similar to those caused by DcKr-h1 silencing. Moreover, feeding antagomir-2 or antagomir-109 partially rescued the defective phenotypes caused by DcKr-h1 silencing in both model systems, and miR-2 and novel-miR-109 were repressed by juvenile hormone (JH) and regulated the genes associated with egg development. This study shows a conserved regulatory mechanism, whereby JH suppresses the expression of miR-2 and novel-miR-109 which, together with JH-induced transcription of DcKr-h1, increases female fecundity induced by both symbiotic bacteria and pathogenic fungi.

IMPORTANCE

Infection with pathogens can increase the fecundity and other fitness-related traits of insect vectors for their own advantage. Our previous research has reported that DcKr-h1 plays a critical role in the increase in fecundity of Diaphorina citri induced by the bacterium, "Candidatus Liberibacter asiaticus" (CLas) and the fungus, Cordyceps fumosorosea (Cf). However, the posttranscriptional regulation of this process remains poorly understood. Given the significance of miRNAs in gene regulation, we delved into their roles in shaping phenotypes and their underlying molecular mechanisms. Our results indicated that two miRNAs, miR-2 and novel-miR-109, jointly inhibited DcKr-h1 expression by binding to its 3' untranslated region (UTR). In both D. citri-CLas and D. citri-Cf interactions, the increased juvenile hormone (JH) titer and reduced abundance of miR-2 and novel-miR-109 ensure high levels of DcKr-h1 expression, consequently stimulating ovarian development and enhancing fecundity. These observations provide evidence that miR-2 and miR-109 are crucial players in the JH-dependent increase in fecundity in psyllids induced by infection with different pathogens.

Transgenic overexpression of bmo-miR-6498-5p increases resistance to Nosema bombycis in the silkworm, Bombyx mori

Microsporidia are unfriendly microorganisms, and their infections cause considerable damage to economically or environmentally important insects like silkworms and honeybees. Thus, the identification of measures to improve host resistance to microsporidia infections is critically needed. Here, an overexpressed miR-6498-5p transgenic silkworm line was constructed. Importantly, the survival rates and median lethal doses of the transgenic line were clearly higher after infection with Nosema bombycis. H&E staining and RT-qPCR analyses revealed an inhibitory effect on the proliferation of N. bombycis in the transgenic larvae. Metabolomics analysis further revealed the presence of 56 differential metabolites between the two lines. KEGG analysis of these 56 metabolites found that they were involved in various amino acid and vitamin metabolism pathways. Notably, VB6 metabolism was enriched among the metabolites, and the pathway was well known for its involvement in the synthesis, interconversion, and degradation of amino acids. These suggest that miR-6498-5p modifies parasitic environments to inhibit the proliferation of N. bombycis by affecting the host amino acid metabolism. These results demonstrate the potential of microRNAs as biomolecules that can promote resistance to microsporidia and provide new insights and a new approach to generate microsporidia-resistant biological materials.IMPORTANCEMicrosporidia have an extremely wide host range and are capable of infecting a wide variety of insects and vertebrates, including humans, and their lethality to multiple species often poses significant environmental management challenge. Here, we successfully constructed a microsporidium-resistant line in the silkworm, based on the overexpression of miR-6498-5p. Our results strongly support the hypothesis that miR-6498-5p efficiently suppresses the proliferation of Nosema bombycis by regulating the host VB6 metabolism, a key pathway for enzymes involved in amino acid transport and protein metabolism. Our study provides new insights for understanding host anti-pathogen defenses toward microsporidia.

An iron-binding protein of entomopathogenic fungus suppresses the proliferation of host symbiotic bacteria

BACKGROUND

Entomopathogenic fungal infection-induced dysbiosis of host microbiota offers a window into understanding the complex interactions between pathogenic fungi and host symbionts. Such insights are critical for enhancing the efficacy of mycoinsecticides. However, the utilization of these interactions in pest control remains largely unexplored.

RESULTS

Here, we found that infection by the host-specialist fungus Metarhizium acridum alters the composition of the symbiotic microbiota and increases the dominance of some bacterial symbionts in locusts. Meanwhile, M. acridum also effectively limits the overgrowth of the predominant bacteria. Comparative transcriptomic screening revealed that the fungus upregulates the production of MaCFEM1, an iron-binding protein, in the presence of bacteria. This protein sequesters iron, thereby limiting its availability. Functionally, overexpression of MaCFEM1 in the fungus induces iron deprivation, which significantly suppresses bacterial growth. Conversely, MaCFEM1 knockout relieves the restriction on bacterial iron availability, resulting in iron reallocation. Upon ΔMaCFEM1 infection, some host bacterial symbionts proliferate uncontrollably, turning into opportunistic pathogens and significantly accelerating host death.

CONCLUSIONS

This study elucidates the critical role of pathogenic fungal-dominated iron allocation in mediating the shift of host microbes from symbiosis to pathogenicity. It also highlights a unique biocontrol strategy that jointly exploits pathogenic fungi and bacterial symbionts to increase host mortality. Video Abstract.

Engineering Entomopathogenic Fungi Using Thermal-Responsive Polymer to Boost Their Resilience against Abiotic Stresses

Entomopathogenic fungi offer an ecologically sustainable and highly effective alternative to chemical pesticides for managing plant pests. However, the efficacy of mycoinsecticides in pest control suffers from environmental abiotic stresses, such as solar UV radiation and temperature fluctuations, which seriously hinder their practical application in the field. Herein, we discovered that the synthetic amphiphilic thermal-responsive polymers are able to significantly enhance the resistance of Metarhizium robertsii conidia against thermal and UV irradiation stresses. The thermosensitive polymers with extremely low cytotoxicity and good biocompatibility can be engineered onto the M. robertsii conidia surface by anchoring hydrophobic alkyl chains. Further investigations revealed that polymer supplementation remarkably augmented the capacity for penetration and the virulence of M. robertsii under heat and UV stresses. Notably, broad-spectrum entomopathogenic fungi can be protected by the polymers. The molecular mechanism was elucidated through exploring RNA sequencing and in vivo/vitro enzyme activity assays. This work provides a novel avenue for fortifying the resilience of entomopathogenic fungi, potentially advancing their practical application as biopesticides.

Recombinant Beauveria bassiana expressing Bacillus thuringiensis toxin Cyt1Aa: a promising approach for enhancing Aedes mosquito control

The entomopathogenic fungus Beauveria bassiana provides an eco-friendly substitute to chemical insecticides for mosquito control. Nevertheless, its widespread application has been hindered by its comparatively slow efficacy in eliminating mosquitoes. To augment the potency of B. bassiana against Aedes mosquitoes, a novel recombinant strain, Bb-Cyt1Aa, was developed by incorporating the Bacillus thuringiensis toxin gene Cyt1Aa into B. bassiana. The virulence of Bb-Cyt1Aa was evaluated against Aedes aegypti and Aedes albopictus using insect bioassays. Compared to the wild-type (WT) strain, the median lethal time (LT50) for A. aegypti larvae infected with Bb-Cyt1Aa decreased by 33.3% at a concentration of 1 × 108 conidia/mL and by 22.2% at 1 × 107 conidia/mL. The LT50 for A. aegypti adults infected with Bb-Cyt1Aa through conidia ingestion was reduced by 37.5% at 1 × 108 conidia/mL and by 33.3% at 1 × 107 conidia/mL. Likewise, the LT50 for A. aegypti adults infected with Bb-Cyt1Aa through cuticle contact decreased by 33.3% and 30.8% at the same concentrations, respectively. Furthermore, the Bb-Cyt1Aa strain also demonstrated increased toxicity against both larval and adult A. albopictus, when compared to the WT strain. In conclusion, our study demonstrated that the expression of B. thuringiensis toxin Cyt1Aa in B. bassiana enhanced its virulence against Aedes mosquitoes. This suggests that B. bassiana expressing Cyt1Aa has potential value for use in mosquito control.

IMPORTANCE

Beauveria bassiana is a naturally occurring fungus that can be utilized as a bioinsecticide against mosquitoes. Cyt1Aa is a delta-endotoxin protein produced by Bacillus thuringiensis that exhibits specific and potent insecticidal activity against mosquitoes. In our study, the expression of this toxin Cyt1Aa in B. bassiana enhances the virulence of B. bassiana against Aedes aegypti and Aedes albopictus, thereby increasing their effectiveness in killing mosquitoes. This novel strain can be used alongside chemical insecticides to reduce dependence on harmful chemicals, thereby minimizing negative impacts on the environment and human health. Additionally, the potential resistance of B. bassiana against mosquitoes in the future could be overcome by acquiring novel combinations of exogenous toxin genes. The presence of B. bassiana that expresses Cyt1Aa is of significant importance in mosquito control as it enhances genetic diversity, creates novel virulent strains, and contributes to the development of safer and more sustainable methods of mosquito control.

Cross-kingdom RNA interference mediated by insect salivary microRNAs may suppress plant immunity

Communication between insects and plants relies on the exchange of bioactive molecules that traverse the species interface. Although proteinic effectors have been extensively studied, our knowledge of other molecules involved in this process remains limited. In this study, we investigate the role of salivary microRNAs (miRNAs) from the rice planthopper Nilaparvata lugens in suppressing plant immunity. A total of three miRNAs were confirmed to be secreted into host plants during insect feeding. Notably, the sequence-conserved miR-7-5P is specifically expressed in the salivary glands of N. lugens and is secreted into saliva, distinguishing it significantly from homologues found in other insects. Silencing miR-7-5P negatively affects N. lugens feeding on rice plants, but not on artificial diets. The impaired feeding performance of miR-7-5P-silenced insects can be rescued by transgenic plants overexpressing miR-7-5P. Through target prediction and experimental testing, we demonstrate that miR-7-5P targets multiple plant genes, including the immune-associated bZIP transcription factor 43 (OsbZIP43). Infestation of rice plants by miR-7-5P-silenced insects leads to the increased expression of OsbZIP43, while the presence of miR-7-5P counteracts this upregulation effect. Furthermore, overexpressing OsbZIP43 confers plant resistance against insects which can be subverted by miR-7-5P. Our findings suggest a mechanism by which herbivorous insects have evolved salivary miRNAs to suppress plant immunity, expanding our understanding of cross-kingdom RNA interference between interacting organisms.

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.

The accumulation of modular serine protease mediated by a novel circRNA sponging miRNA increases Aedes aegypti immunity to fungus

BACKGROUND

Mosquitoes transmit many infectious diseases that affect human health. The fungus Beauveria bassiana is a biological pesticide that is pathogenic to mosquitoes but harmless to the environment.

RESULTS

We found a microRNA (miRNA) that can modulate the antifungal immunity of Aedes aegypti by inhibiting its cognate serine protease. Fungal infection can induce the expression of modular serine protease (ModSP), and ModSP knockdown mosquitoes were more sensitive to B. bassiana infection. The novel miRNA-novel-53 is linked to antifungal immune response and was greatly diminished in infected mosquitoes. The miRNA-novel-53 could bind to the coding sequences of ModSP and impede its expression. Double fluorescence in situ hybridization (FISH) showed that this inhibition occurred in the cytoplasm. The amount of miRNA-novel-53 increased after miRNA agomir injection. This resulted in a significant decrease in ModSP transcript and a significant increase in mortality after fungal infection. An opposite effect was produced after antagomir injection. The miRNA-novel-53 was also knocked out using CRISPR-Cas9, which increased mosquito resistance to the fungus B. bassiana. Moreover, mosquito novel-circ-930 can affect ModSP mRNA by interacting with miRNA-novel-53 during transfection with siRNA or overexpression plasmid.

CONCLUSIONS

Novel-circ-930 affects the expression level of ModSP by a novel-circ-930/miRNA-novel-53/ModSP mechanism to modulate antifungal immunity, revealing new information on innate immunity in insects.

Changes in the gut bacterial community affect miRNA profiles in Riptortus pedestris under different rearing conditions

Insects possess complex and dynamic gut microbial system, which contributes to host nutrient absorption, reproduction, energy metabolism, and protection against stress. However, there are limited data on interactions of host-gut bacterial microbiota through miRNA (microRNA) regulation in a significant pest, Riptortus pedestris. Here, we performed the 16S rRNA amplicon sequencing and small RNA sequencing from the R. pedestris gut under three environmental conditions and antibiotic treatment, suggesting that we obtained a large amount of reads by assembly, filtration and quality control. The 16S rRNA amplicon sequencing results showed that the abundance and diversity of gut bacterial microbiota were significantly changed between antibiotic treatment and other groups, and they are involved in metabolism and biosynthesis-related function based on functional prediction. Furthermore, we identified different numbers of differentially expressed unigenes (DEGs) and differentially expressed miRNAs (DEMs) based on high-quality mappable reads, which were enriched in various immune-related pathways, including Toll-like receptor, RIG-I-like receptor, NOD-like receptor, JAK/STAT, PI3K/Akt, NF-κB, MAPK signaling pathways, and so forth, using GO and KEGG enrichment analysis. Later on, the identified miRNAs and their target genes in the R. pedestris gut were predicted and randomly selected to construct an interaction network. Finally, our study indicated that alterations in the gut bacterial microbiota are significantly positively or negatively associated with DEMs of the Toll/Imd signaling pathway with Pearson correlation analysis. Taken together, the results of our study lay the foundation for further deeply understanding the interactions between the gut microbiota and immune responses in R. pedestris through miRNA regulation, and provide the new basis for pest management in hemipteran pests.

Immunological responses and gut microbial shifts in Phthorimaea absoluta exposed to Metarhizium anisopliae isolates under different temperature regimes

The invasive tomato leaf miner, Phthorimaea absoluta, is conventionally controlled through chemical insecticides. However, the rise of insecticide resistance has necessitated sustainable and eco-friendly alternatives. Entomopathogenic fungi (EPF) have shown potential due to their ability to overcome resistance and have minimal impact on non-target organisms. Despite this potential, the precise physiological mechanisms by which EPF acts on insect pests remain poorly understood. To attain a comprehensive understanding of the complex physiological processes that drive the successful control of P. absoluta adults through EPF, we investigated the impacts of different Metarhizium anisopliae isolates (ICIPE 665, ICIPE 20, ICIPE 18) on the pest's survival, cellular immune responses, and gut microbiota under varying temperatures. The study unveiled that ICIPE 18 caused the highest mortality rate among P. absoluta moths, while ICIPE 20 exhibited the highest significant reduction in total hemocyte counts after 10 days at 25°C. Moreover, both isolates elicited notable shifts in P. absoluta's gut microbiota. Our findings revealed that ICIPE 18 and ICIPE 20 compromised the pest's defense and physiological functions, demonstrating their potential as biocontrol agents against P. absoluta in tomato production systems.

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.

Recent Advancements in Pathogenic Mechanisms, Applications and Strategies for Entomopathogenic Fungi in Mosquito Biocontrol

Fungal diseases are widespread among insects and play a crucial role in naturally regulating insect populations. Mosquitoes, known as vectors for numerous infectious diseases, pose a significant threat to human health. Entomopathogenic fungi (EPF) have emerged as highly promising alternative agents to chemical mosquitocides for controlling mosquitoes at all stages of their life cycle due to their unique infection pathway through direct contact with the insect's cuticle. In recent years, significant advancements have been made in understanding the infection pathways and pathogenic mechanisms of EPF against mosquitoes. Various strategies involving the use of EPF alone or combinations with other approaches have been employed to target mosquitoes at various developmental stages. Moreover, the application of genetic technologies in fungi has opened up new avenues for enhancing the mosquitocidal efficacy of EPF. This review presents a comprehensive summary of recent advancements in our understanding the pathogenic mechanisms of EPF, their applications in mosquito management, and the combination of EPF with other approaches and employment of transgenic technologies. The biosafety concerns associated with their use and the corresponding approaches are also discussed. The recent progress suggests that EPF have the potential to serve as a future biorational tool for controlling mosquito vectors.

CRISPR/Cas9-mediated gene editing of the let-7 seed sequence improves silk yield in the silkworm, Bombyx mori

Body size and silk protein synthesis ability are two crucial aspects of artificial selection in silkworm breeding; however, the role of genes in both pathways remains unknown. To determine whether let-7 microRNA could regulate larval development and silk gland growth simultaneously, we designed a guide RNA to edit let-7 using the CRISPR/Cas9 system. The indels predominantly appeared in the let-7 seed region, and the vast majority of the mutations were small-fragment deletions. Loss of let-7 function prolonged the fifth larval period, and substantially increased body weight during the wandering stage, but it resulted in developmental arrest during the pupal-moth transition. let-7 systemic knock down promoted silk gland growth and increased silk yield by >50 %, with efficiency significantly higher than in tissue-specific edited individuals. Hormone signaling and cell cycle pathway genes were activated in different patterns in the body and silk gland, implying that let-7 may regulate different target genes to play role in tissue growth. In summary, we first report that conditional knock down let-7 promoting the simultaneous growth of body and silk gland, greatly improve silk yield in the silkworm.

Transcriptomics Reveals the Killing Mechanism by Which Entomopathogenic Fungi Manipulate the RNA Expression Profiles of Termites and Provides Inspiration for Green Pest Management

As chemical pesticides have caused serious environmental pollution, fungus-based biological control has become a developing alternative to chemical control. Here, we aimed to determine the molecular mechanism underlying how Metarhizium anisopliae facilitated invasive infection. We found that the fungus increased its virulence by downregulating glutathione S-transferase (GST) and superoxide dismutase (SOD) throughout termite bodies. Among 13 fungus-induced microRNAs throughout termite bodies, miR-7885-5p and miR-252b upregulation significantly downregulated several mRNAs in response to toxic substances to increase the fungal virulence [e.g., phosphoenolpyruvate carboxykinase (GTP) and heat shock protein homologue SSE1]. In addition, nanodelivered small interfering RNA of GST and SOD and miR-7885-5p and miR-252b mimics increased the virulence of the fungus. These findings provide new insights into the killing mechanism of entomopathogens and their utilization of the host miRNA machinery to reduce host defenses, laying the groundwork to enhance virulence of biocontrol agents for green pest management.

Novel development of Lecanicillium lecanii-based granules as a platform against malarial vector Anopheles culicifacies

Mosquitoes are infectious vectors for a wide range of pathogens and parasites thereby transmitting several diseases including malaria, dengue, Zika, Japanese encephalitis and chikungunya which pose a major public health concern. Mostly synthetic insecticides are usually applied as a primary control strategy to manage vector-borne diseases. However excessive and non-judicious usage of such chemically derived insecticides has led to serious environmental and health issues owing to their biomagnification ability and increased toxicity towards non-target organisms. In this context, many such bioactive compounds originating from entomopathogenic microbes serve as an alternative strategy and environmentally benign tool for vector control. In the present paper, the entomopathogenic fungus, Lecanicillium lecanii (LL) was processed to make the granules. Developed 4% LL granules have been characterized using the technique of Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The developed formulation was also subjected to an accelerated temperature study at 40 °C and was found to be stable for 3 months. Further, GCMS of the L. lecanii was also performed to screen the potential biomolecules present. The developed formulation was found to be lethal against Anopheles culicifacies with an LC₅₀ value of 11.836 µg/mL. The findings from SEM and histopathology also substantiated the mortality effects. Further, the SEM EDX (energy dispersive X-ray) studies revealed that the treated larvae have lower nitrogen content which is correlated to a lower level of chitin whereas the control ones has higher chitin content and healthy membranes. The developed LL granule formulation exhibited high toxicity against Anopheles mosquitoes. The granule formulations can be used as an effective biocontrol strategy against malaria-causing mosquitoes.

Fungal Effectoromics: A World in Constant Evolution

Effectors are small, secreted molecules that mediate the establishment of interactions in nature. While some concepts of effector biology have stood the test of time, this area of study is ever-evolving as new effectors and associated characteristics are being revealed. In the present review, the different characteristics that underly effector classifications are discussed, contrasting past and present knowledge regarding these molecules to foster a more comprehensive understanding of effectors for the reader. Research gaps in effector identification and perspectives for effector application in plant disease management are also presented, with a focus on fungal effectors in the plant-microbe interaction and interactions beyond the plant host. In summary, the review provides an amenable yet thorough introduction to fungal effector biology, presenting noteworthy examples of effectors and effector studies that have shaped our present understanding of the field.

Microbial Effectors: Key Determinants in Plant Health and Disease

Effectors are small, secreted molecules that alter host cell structure and function, thereby facilitating infection or triggering a defense response. Effectoromics studies have focused on effectors in plant-pathogen interactions, where their contributions to virulence are determined in the plant host, i.e., whether the effector induces resistance or susceptibility to plant disease. Effector molecules from plant pathogenic microorganisms such as fungi, oomycetes and bacteria are major disease determinants. Interestingly, the effectors of non-pathogenic plant organisms such as endophytes display similar functions but have different outcomes for plant health. Endophyte effectors commonly aid in the establishment of mutualistic interactions with the plant and contribute to plant health through the induction of systemic resistance against pathogens, while pathogenic effectors mainly debilitate the plant's immune response, resulting in the establishment of disease. Effectors of plant pathogens as well as plant endophytes are tools to be considered in effectoromics for the development of novel strategies for disease management. This review aims to present effectors in their roles as promotors of health or disease for the plant host.

Laboratory evaluation of the compatibility of Beauveria bassiana with the egg parasitoid Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) for joint application against the oriental fruit moth Grapholita molesta (Lepidoptera: Tortricidae)

BACKGROUND

The entomopathogenic fungus Beauveria bassiana and the egg parasitoid Trichogramma dendrolimi can both contribute to biological control of the global fruit borer Grapholita molesta. To derive insights for optimizing their combined application in augmentation programs, we assayed fungal pathogenicity to both G. molesta (eggs, larvae and adults) and adult parasitoids, and assessed wasp acquisition and transmission of fungal spores following their emergence from B. bassiana-treated host eggs.

RESULTS

Concentrations of 10⁸ conidia mL^-1 of B. bassiana and higher caused virtually complete mortality of G. molesta larvae, but less than 30% mortality of eggs, and female moths surviving treatments had reduced fecundity. More than 80% of adult T. dendrolimi survived B. bassiana treatments of 10⁷ conidia mL^-1 , and more than 60% survived 10⁹ conidia mL^-1 , with surviving females achieving reproductive success equivalent to controls. Parasitoid females preferred healthy eggs over B. bassiana-infected ones in choice tests; wasps emerging from treated eggs carried about 10⁴ conidia each and contributed an additional 11% host mortality in trials combining both agents.

CONCLUSION

Our results indicate that combined applications of B. bassiana and T. dendrolimi can have complimentary impacts on G. molesta, the wasps compensating for low fungal pathogenicity to eggs and their progeny potentially aiding in subsequent disease transmission. Although foraging wasps tended to avoid infected eggs, negative interactions between the two agents might be further mitigated by timing B. bassiana applications from late instar larva to early moth stage, and T. dendrolimi releases several days later to coincide with peak oviposition periods. © 2022 Society of Chemical Industry.

Hermetia illucens L. larvae-associated intestinal microbes reduce the transmission risk of zoonotic pathogens in pig manure

Black soldier fly (BSF) larvae are considered a promising biological reactor to convert organic waste and reduce the impact of zoonotic pathogens on the environment. We analysed the effects of BSF larvae on Staphylococcus aureus and Salmonella spp. populations in pig manure (PM), which showed that BSF larvae can significantly reduce the counts of the associated S. aureus and Salmonella spp. Then, using a sterile BSF larval system, we validated the function of BSF larval intestinal microbiota in vivo to suppress pathogens, and lastly, we isolated eight bacterial strains from the BSF larval gut that inhibit S. aureus. Results indicated that functional microbes are essential for BSF larvae to antagonise S. aureus. Moreover, the analysis results of the relationship between the intestinal microbiota and S. aureus and Salmonella spp. showed that Myroides, Tissierella, Oblitimonas, Paenalcalignes, Terrisporobacter, Clostridium, Fastidiosipila, Pseudomonas, Ignatzschineria, Savagea, Moheibacter and Sphingobacterium were negatively correlated with S. aureus and Salmonella. Overall, these results suggested that the potential ability of BSF larvae to inhibit S. aureus and Salmonella spp. present in PM is accomplished primarily by gut‐associated microorganisms.

A Novel MicroRNA and the Target Gene TAB2 Can Regulate the Process of Sucking Blood in and the Spawn Rate of Hyalomma asiaticum (Acari: Ixodidae) Ticks

Ticks are blood-sucking parasites that are harmful to humans and animals. MicroRNAs are a class of conserved small noncoding RNAs that play regulatory roles in the expression of many genes at the posttranscriptional level. Here, a novel miRNA (nov-miR-17) was identified from a small RNA data library of Hyalomma asiaticum by next-generation sequencing. PCR was used to obtain precursor nov-miR-17 by RACE using mature loop primers. The secondary structure was predicted with UNAFold. The interaction of nov-miR-17 with its target gene TAB2 was predicted using RNAhybrid software and identified in vitro by luciferase assays. Moreover, the interaction was confirmed in vivo by phenotype rescue experiments in which dsTAB2 was used for RNA interference (RNAi) and an antagomir of nov-miR-17 was used for miRNA silencing. The expression levels of nov-miR-17 and TAB2 in ticks at different developmental stages and the expression of nov-miR-17 in different tissues were analyzed by real-time qPCR. All data were analyzed using GraphPad Prism version 5. Results: The results showed that TAB2 was a target gene of nov-miR-17. When the blood-sucking process of larval, nymph and adult ticks was prolonged, the expression of nov-miR-17 was decreased, and TAB2 expression was increased. However, the level of nov-miR-17 in the midgut of engorged ticks was highest at all stages. Therefore, nov-miR-17 plays an important role in the blood-sucking process. The overexpression of nov-miR-17 indicated that this miRNA affected the engorged weight (P < 0.001) and spawn rate (P < 0.001) of female ticks. RNAi of TAB2 also had the same effect. dsRNA not only impacted the weight (P < 0.01) but also reduced the spawn rate (P < 0.001) of the ticks. Furthermore, significant recovery was observed in nov-miR-17-silenced ticks after TAB2 silencing by RNAi. nov-miR-17 silencing by antagomir not only impacted the engorged weight of the female ticks (P < 0.001) but also the number of days that the females needed to progress from engorgement to spawning (P < 0.001). The study showed that nov-miR-17, as a new miRNA, plays an important role along with its target gene TAB2 in the blood-sucking and spawning processes in female ticks.

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.

Regulatory Roles of Histone Modifications in Filamentous Fungal Pathogens

Filamentous fungal pathogens have evolved diverse strategies to infect a variety of hosts including plants and insects. The dynamic infection process requires rapid and fine-tuning regulation of fungal gene expression programs in response to the changing host environment and defenses. Therefore, transcriptional reprogramming of fungal pathogens is critical for fungal development and pathogenicity. Histone post-translational modification, one of the main mechanisms of epigenetic regulation, has been shown to play an important role in the regulation of gene expressions, and is involved in, e.g., fungal development, infection-related morphogenesis, environmental stress responses, biosynthesis of secondary metabolites, and pathogenicity. This review highlights recent findings and insights into regulatory mechanisms of histone methylation and acetylation in fungal development and pathogenicity, as well as their roles in modulating pathogenic fungi-host interactions.

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.

Analysis of the Humoral Immunal Response Transcriptome of Ectropis obliqua Infected by Beauveria bassiana

Simple Summary

Ectropis obliqua is a destructive leaf-eating pest that is widely distributed in China’s tea gardens. This pest shows remarkable resistance against multiple insecticides. As an environmentally friendly entomopathogen, Beauveria bassiana has been widely used to prevent agricultural pest infestations. However, the molecular mechanism of B. bassiana against E. obliqua remains unclear. We firstly isolated and identified a highly virulent B. bassiana strain. Using a transcriptome, we analyzed the differences of immune gene expression levels in fat bodies and hemocytes of E. obliqua that were infected by the B. bassiana, which provide molecular insights into the insect–pathogen interaction.

Abstract

Ectropis obliqua is a destructive masticatory pest in China’s tea gardens. Beauveria bassiana as microbial insecticides can effectively control E. obliqua larvae; however, the immune response of this insect infected by B. bassiana are largely unknown. Here, after isolating a highly virulent strain of B. bassiana from E. obliqua, the changes in gene expression among different tissues, including hemocytes and fat bodies, of E. obliqua larvae infected by the entomopathogen were investigated using transcriptome sequencing. A total of 5877 co-expressed differentially expressed genes (DEGs) were identified in hemocytes and fat bodies, of which 5826 were up-regulated in hemocytes and 5784 were up-regulated in fat bodies. We identified 249 immunity-related genes, including pattern recognition receptors, immune effectors, signal modulators, and members of immune pathways. A quantitative real-time PCR analysis confirmed that several pattern recognition receptors were upregulated in hemocytes and fat bodies; however, others were downregulated. The investigated immune effectors (ATT and PPO-1) were suppressed. The results showed that there were tissue differences in the expression of immune genes. This study provides a large number of immunity-related gene sequences from E. obliqua after being infected by B. bassiana, furthering the understanding of the molecular mechanisms of E. obliqua defenses against B. bassiana.