Emerging strategies for RNA interference (RNAi) applications in insects

Biosafety aspects of RNAi-based pests control

While the overuse of classical chemical pesticides has had a detrimental impact on the environment and human health, the discovery of RNA interference (RNAi) offered the opportunity to develop new and sustainable approaches for pest management. RNAi is a naturally occurring regulation and defense mechanism that can be exploited to effectively protect crops by silencing key genes affecting the growth, development, behavior or fecundity of pests. However, as with all technologies, there is a range of potential risks and challenges associated with the application of RNAi, such as dsRNA stability, the potential for off-target effects, the safety of non-target organisms, and other application challenges. A better understanding of the molecular mechanisms involved in RNAi and in-depth discussion and analysis of these associated safety risks, is required to limit or mitigate potential adverse effects. © 2024 Society of Chemical Industry.

Impact of the Transboundary Interference Inhibitor on RNAi and the Baculovirus Expression System in Insect Cells

RNA interference inhibitors were initially discovered in plant viruses, representing a unique mechanism employed by these viruses to counteract host RNA interference. This mechanism has found extensive applications in plant disease resistance breeding and other fields; however, the impact of such interference inhibitors on insect cell RNA interference remains largely unknown. In this study, we screened three distinct interference inhibitors from plant and mammal viruses that act through different mechanisms and systematically investigated their effects on the insect cell cycle and baculovirus infection period at various time intervals. Our findings demonstrated that the viral suppressors of RNA silencing (VSRs) derived from plant and mammal viruses significantly attenuated the RNA interference effect in insect cells, as evidenced by reduced apoptosis rates, altered gene regulation patterns in cells, enhanced expression of exogenous proteins, and improved production efficiency of recombinant virus progeny. Further investigations revealed that the early expression of VSRs yielded superior results compared with late expression during RNA interference processes. Additionally, our results indicated that dsRNA-binding inhibition exhibited more pronounced effects than other modes of action employed by these interference inhibitors. The outcomes presented herein provide novel insights into enhancing defense mechanisms within insect cells using plant and mammal single-stranded RNA virus-derived interference inhibitors and have potential implications for expanding the scope of transformation within insect cell expression systems.

Response of the mosquito immune system and symbiotic bacteria to pathogen infection

Mosquitoes are the deadliest animal in the word, transmitting a variety of insect-borne infectious diseases, such as malaria, dengue fever, yellow fever, and Zika, causing more deaths than any other vector-borne pathogen. Moreover, in the absence of effective drugs and vaccines to prevent and treat insect-borne diseases, mosquito control is particularly important as the primary measure. In recent decades, due to the gradual increase in mosquito resistance, increasing attention has fallen on the mechanisms and effects associated with pathogen infection. This review provides an overview of mosquito innate immune mechanisms in terms of physical and physiological barriers, pattern recognition receptors, signalling pathways, and cellular and humoral immunity, as well as the antipathogenic effects of mosquito symbiotic bacteria. This review contributes to an in-depth understanding of the interaction process between mosquitoes and pathogens and provides a theoretical basis for biological defence strategies against mosquito-borne infectious diseases.

Rolling circle transcription: A new system to produce RNA microspheres for improving RNAi efficiency in an agriculturally important lepidopteran pest (Mythimna separate)

We applied a new RNA interference (RNAi) system using rolling circle transcription (RCT) technology to generate RNA microspheres (RMS) for targeting two key chitin synthetic pathway genes [chitin synthase A (CHSA), chitin synthase B (CHSB)] in the larvae of the oriental armyworm (Mythimna separate), a RNAi-unsusceptible agriculturally important lepidopteran pest. Feeding the third-instar larvae with the RMS-CHSA- or RMS-CHSB-treated corn leaf discs suppressed the expression of CHSA by 81.7% or CHSB by 88.1%, respectively, at 72 h. The silencing of CHSA consequently affected the larval development, including the reduced body weight (54.0%) and length (41.3%), as evaluated on the 7th day, and caused significant larval mortalities (51.1%) as evaluated on the 14th day. Similar results were obtained with the larvae fed RMS-CHSB. We also compared RNAi efficiencies among different strategies: 1) two multi-target RMS [i.e., RMS-(CHSA + CHSB), RMS-CHSA + RMS-CHSB], and 2) multi-target RMS and single-target RMS (i.e., either RMS-CHSA or RMS-CHSB) and found no significant differences in RNAi efficiency. By using Cy3-labeled RMS, we confirmed that RMS can be rapidly internalized into Sf9 cells (<6 h). The rapid cellular uptake of RMS accompanied with significant RNAi efficiency through larval feeding suggests that the RCT-based RNAi system can be readily applied to study the gene functions and further developed as bio-pesticides for insect pest management. Additionally, our new RNAi system takes the advantage of the microRNA (miRNA)-mediated RNAi pathway using miRNA duplexes generated in vivo from the RMS by the target insect. The system can be used for RNAi in a wide range of insect species, including lepidopteran insects which often exhibit extremely low RNAi efficiency using other RNAi approaches.

Climate change reshaping plant-fungal interaction

Plant diseases pose a severe threat to modern agriculture, necessitating effective and lasting control solutions. Environmental factors significantly shape plant ecology. Human-induced greenhouse gas emissions have led to global temperature rise, impacting various aspects, including carbon dioxide (CO2) concentration, temperature, ozone (O3), and ultraviolet-B, all of which influence plant diseases. Altered pathogen ranges can accelerate disease transmission. This review explores environmental effects on plant diseases, with climate change affecting fungal biogeography, disease incidence, and severity, as well as agricultural production. Moreover, we have discussed how climate change influences pathogen development, host-fungal interactions, the emergence of new races of fungi, and the dissemination of emerging fungal diseases across the globe. The discussion about environment-mediated impact on pattern-triggered immunity (PTI), effector-triggered immunity (ETI), and RNA interference (RNAi) is also part of this review. In conclusion, the review underscores the critical importance of understanding how climate change is reshaping plant-fungal interactions. It highlights the need for continuous research efforts to elucidate the mechanisms driving these changes and their ecological consequences. As the global climate continues to evolve, it is imperative to develop innovative strategies for mitigating the adverse effects of fungal pathogens on plant health and food security.

Novel compounds ZK-PI-5 and ZK-PI-9 regulate the reproduction of Spodoptera frugiperda (Lepidoptera: Noctuidae), with insecticide potential

Trehalase inhibitors prevent trehalase from breaking down trehalose to provide energy. Chitinase inhibitors inhibit chitinase activity affecting insect growth and development. This is an important tool for the investigation of regulation of trehalose metabolism and chitin metabolism in insect reproduction. There are few studies on trehalase or chitinase inhibitors' regulation of insect reproduction. In this study, ZK-PI-5 and ZK-PI-9 were shown to have a significant inhibitory effect on the trehalase, and ZK-PI-9 significantly inhibited chitinase activity in female pupae. We investigated the reproduction regulation of Spodoptera frugiperda using these new inhibitors and evaluated their potential as new insecticides. Compounds ZK-PI-5 and ZK-PI-9 were injected into the female pupae, and the control group was injected with solvent (2% DMSO). The results showed that the emergence failure rate for pupae treated with inhibitors increased dramatically and aberrant phenotypes such as difficulty in wings spreading occurred. The oviposition period and longevity of female adults in the treated group were significantly shorter than those in the control group, and the ovaries developed more slowly and shrank earlier. The egg hatching rate was significantly reduced by treatment with the inhibitor. These results showed that the two new compounds had a significant impact on the physiological indicators related to reproduction of S. frugiperda, and have pest control potential. This study investigated the effect of trehalase and chitin inhibitors on insect reproduction and should promote the development of green and efficient insecticides.

PxRdl2 dsRNA increased the insecticidal activities of GABAR-targeting compounds against Plutella xylostella

The utilization of RNA interference (RNAi) for pest management has garnered global interest. The bioassay results suggested the knockout of the PxRdl2 gene significantly increased the insecticidal activities of the γ-aminobutyric acid receptor (GABAR)-targeting compounds (fipronil, two pyrazoloquinazolines, and two isoxazolines), thereby presenting a viable target gene for RNAi-mediated pest control. Consequently, we suggest enhancing the insecticidal activities of GABAR-targeting compounds by knockdown the transcript level of PxRdl2. Furthermore, PxRdl2 dsRNA was expressed in HT115 Escherichia coli to reduce costs and protect dsRNA against degradation. In comparison to in vitro synthesized dsRNA, the recombinant bacteria (ds-B) exhibited superior interference efficiency and greater stability when exposed to UV irradiation. Collectively, our results provide a strategy for insecticide spray that combines synergistically with insecticidal activities by suppressing PxRdl2 using ds-B and may be beneficial for reducing the usage of insecticide and slowing pest resistance.

An oral dsRNA delivery system based on chitosan induces G protein-coupled receptor kinase 2 gene silencing for Apolygus lucorum control

RNA interference (RNAi) is recognized as a new and environmentally friendly pest control strategy due to its high specificity. However, the RNAi efficiency is relatively low in many sucking insect pests, such as Apolygus lucorum. Therefore, there is an urgent need to develop new and effective ways of dsRNA delivery. Bacterially expressed or T7 synthesized dsRNA targeting a G Protein-Coupled Receptor Kinase 2 gene was mixed with chitosan in a 1:2 ratio by mass. The size of the chitosan/dsRNA nanoparticles was 69 ± 12 nm, and the TEM and AFM images showed typical spherical or ellipsoidal structures. The chitosan nanoparticles protected the dsRNA from nuclease activity, and pH and temperature-dependent degradation, and the fluorescently-tagged nanoparticles were found to be stable on the surface of green bean plants (48 h) (Phaseolus vulgaris) and were absorbed by midgut epithelial cells and transported to hemolymph. Once fed to the A. lucorum nymph, chitosan/dsRNA could effectively inhibit the expression of the G protein-coupled receptor kinase 2 gene (70%), and led to significantly increase mortality (50%), reduced weight (26.54%) and a prolonged developmental period (8.04%). The feeding-based and chitosan-mediated dsRNA delivery method could be a new strategy for A. lucorum management, providing an effective tool for gene silencing of piercing-sucking insects.

Knockdown of Dcr1 and Dcr2 limits the lethal effect of C-factor in Chilo suppressalis

Dicer is a highly conserved ribonuclease in evolution. It belongs to the RNase III family and can specifically recognize and cleave double-stranded RNA (dsRNA). In this study, the genome and transcriptome of Chilo suppressalis were analyzed, and it was found that there were two members in the Dicer family, named Dcr1 and Dcr2. The dsRNAs of Dcr1 and Dcr2 genes were synthesized and fed to C. suppressalis larvae. The C-factor of C. suppressalis was selected as the marker gene. The results showed that both Dcr1 and Dcr2 genes were significantly knocked down. The larval mortality was significantly reduced by 43.50% (p < 0.05) after feeding on dsC-factor and dsDcr1. The transcription levels of C-factor genes were significantly increased by 33.95% (p < 0.05) and 32.94% (p < 0.05) when the larvae fed with dsDcr2 + dsC-factor for 72 h and 96 h, respectively. Furthermore, the mortality was significantly decreased by 79% (p < 0.05) after feeding dsC-factor and dsDcr2. These findings imply that Dcr1 can decrease the lethal effect of C-factor gene but cannot affect its RNAi efficiency and Dcr2 can decrease the lethal effect of C-factor gene by inhibiting RNAi efficiency.

Potential inhibitory effects of compounds ZK-PI-5 and ZK-PI-9 on trehalose and chitin metabolism in Spodoptera frugiperda (J. E. Smith)

Introduction:Spodoptera frugiperda is an omnivorous agricultural pest which is great dangerous for grain output.

Methods: In order to investigate the effects of potential trehalase inhibitors, ZK-PI-5 and ZK-PI-9, on the growth and development of S. frugiperda, and to identify new avenues for S. frugiperda control, we measured the content of the trehalose, glucose, glycogen and chitin, enzyme activity, and gene expression levels in trehalose and chitin metabolism of S. frugiperda. Besides, their growth and development were also observed.

Results: The results showed that ZK-PI-9 significantly reduced trehalase activity and ZK-PI-5 significantly reduced membraned-bound trehalase activity. Moreover, ZK-PI-5 inhibited the expression of SfTRE2, SfCHS2, and SfCHT, thus affecting the chitin metabolism. In addition, the mortality of S. frugiperda in pupal stage and eclosion stage increased significantly after treatment with ZK-PI-5 and ZK-PI-9, which affected their development stage and caused death phenotype (abnormal pupation and difficulty in breaking pupa).

Discussion: These results have provided a theoretical basis for the application of trehalase inhibitors in the control of agricultural pests to promote future global grain yield.

Plant Viruses of Agricultural Importance: Current and Future Perspectives of Virus Disease Management Strategies

Plant viruses cause significant losses in agricultural crops worldwide, affecting the yield and quality of agricultural products. The emergence of novel viruses or variants through genetic evolution and spillover from reservoir host species, changes in agricultural practices, mixed infections with disease synergism, and impacts from global warming pose continuous challenges for the management of epidemics resulting from emerging plant virus diseases. This review describes some of the most devastating virus diseases plus select virus diseases with regional importance in agriculturally important crops that have caused significant yield losses. The lack of curative measures for plant virus infections prompts the use of risk-reducing measures for managing plant virus diseases. These measures include exclusion, avoidance, and eradication techniques, along with vector management practices. The use of sensitive, high throughput, and user-friendly diagnostic methods is crucial for defining preventive and management strategies against plant viruses. The advent of next-generation sequencing technologies has great potential for detecting unknown viruses in quarantine samples. The deployment of genetic resistance in crop plants is an effective and desirable method of managing virus diseases. Several dominant and recessive resistance genes have been used to manage virus diseases in crops. Recently, RNA-based technologies such as dsRNA- and siRNA-based RNA interference, microRNA, and CRISPR/Cas9 provide transgenic and nontransgenic approaches for developing virus-resistant crop plants. Importantly, the topical application of dsRNA, hairpin RNA, and artificial microRNA and trans-active siRNA molecules on plants has the potential to develop GMO-free virus disease management methods. However, the long-term efficacy and acceptance of these new technologies, especially transgenic methods, remain to be established.

The role of polyplexes in developing a green sustainable approach in agriculture

Rise in global population has increased the food demands and thus the competition among farmers to produce more and more. In the race to obtain higher productivity, farmers have resorted to injudicious farming practices that include the reckless use of nitrogenous fertilizers and intensive cropping on farmlands. Such practices have paved the path for large scale infestations of crops and plants by pests thus affecting the plant productivity and crop vigour. There are several traditional techniques to control pest infestations in plants such as the use of chemical or bio-pesticides, and integrated pest management practices which face several drawbacks. Delivery of gene/nucleic acid in plants through genetic engineering approaches is a more sustainable and effective method of protection against pests. The technology of RNA interference (RNAi) provides a sustainable solution to counter pest control problems faced by other traditional techniques. The RNAi technique involves delivery of dsDNA/dsRNA or other forms of nucleic acids into target organisms thereby bringing about gene silencing. However, RNAi is also limited to its use because of their susceptibility to degradation wherein the use of cationic polymers can provide a tangible solution. Cationic polymers form stable complexes with the nucleic acids known as "polyplexes", which may be attributed to their high positive charge densities thus protecting the exogenous nucleic acids from extracellular degradation. The current paper focuses on the utility of nucleic acids as a sustainable tool for pest control in crops and the use of cationic polymers for the efficient delivery of nucleic acids in pests thus protecting the plant from infestations.

Functional Role of AsAP in the Reproduction of Adelphocoris suturalis (Hemiptera: Miridae)

Adelphocoris suturalis Jakovlev (Hemiptera: Miridae) is an omnivorous agricultural pest that has severe economic impacts on a diverse range of agricultural crops. Although the targeted disruption of reproductive development among insects has been proposed as a novel control strategy for pest species, the current understanding of the physiology and molecular mechanisms of A. suturalis reproduction is very limited. In this study, we isolated a putative A. suturalisaspartic protease (AsAP) gene that is highly expressed in the fat body and ovaries of sexually mature females. The double-stranded RNA (dsRNA)-mediated knockdown of AsAP suppressed ovarian development and negatively impacted female fertility, which suggested that it plays an essential role in A. suturalis reproduction. The results of this study could help to expand our understanding of A. suturalis reproductive development and have the potential to facilitate the development of effective strategies for the better control of this pest species.

Development of RNAi Methods for the Mormon Cricket, Anabrus simplex (Orthoptera: Tettigoniidae)

Mormon crickets are a major rangeland pest in the western United States and are currently managed by targeted applications of non-specific chemical insecticides, which can potentially have negative effects on the environment. In this study, we took the first steps toward developing RNAi methods for Mormon crickets as a potential alternative to traditional broad-spectrum insecticides. To design an effective RNAi-based insecticide, we first generated a de novo transcriptome for the Mormon cricket and developed dsRNAs that could silence the expression of seven housekeeping genes. We then characterized the RNAi efficiencies and time-course of knockdown using these dsRNAs, and assessed their ability to induce mortality. We have demonstrated that it is possible to elicit RNAi responses in the Mormon cricket by injection, but knockdown efficiencies and the time course of RNAi response varied according to target genes and tissue types. We also show that one of the reasons for the poor knockdown efficiencies could be the presence of dsRNA-degrading enzymes in the hemolymph. RNAi silencing is possible in Mormon cricket, but more work needs to be done before it can be effectively used as a population management method.

RNA meets toxicology: efficacy indicators from the experimental design of RNAi studies for insect pest management

RNA interference (RNAi) selectively targets genes and silences their expression in vivo, causing developmental defects, mortality and altered behavior. Consequently, RNAi has emerged as a promising research area for insect pest management. However, it is not yet a viable alternative over conventional pesticides despite several theoretical advantages in safety and specificity. As a first step toward a more standardized approach, a machine learning algorithm was used to identify factors that predict trial efficacy. Current research on RNAi for pest management is highly variable and relatively unstandardized. The applied random forest model was able to reliably predict mortality ranges based on bioassay parameters with 72.6% accuracy. Response time and target gene were the most important variables in the model, followed by applied dose, double-stranded RNA (dsRNA) construct size and target species, further supported by generalized linear mixed effect modeling. Our results identified informative trends, supporting the idea that basic principles of toxicology apply to RNAi bioassays and provide initial guidelines standardizing future research similar to studies of traditional insecticides. We advocate for training that integrates genetic, organismal, and toxicological approaches to accelerate the development of RNAi as an effective tool for pest management. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Double-Strand RNA (dsRNA) Delivery Methods in Insects: Diaphorina citri

RNAi is a gene-silencing mechanism conserved in the vast majority of eukaryotes. It is widely used to study gene function in animals due to the ease of eliciting gene knockdown. Beyond research applications, RNAi technology based on exogenous dsRNA is a promising candidate for next generation insect pest control. An advantage of using RNAi is that design of dsRNA essentially requires only the sequence of the target gene. The greatest challenge, however, is dsRNA delivery for large-scale insect control. Delivery methods that have widely been used are oral, injection, or via soaking. Unfortunately, each insect presents its own challenges owing to the differences in the presence of dsRNA degrading enzymes, cellular uptake efficiency, expression of core RNAi machinery, the nature of the target gene, the concentration and persistence of the dsRNA, as well as the particular way of feeding of each insect, which together cause variations in the efficiency of RNAi. In this chapter, a protocol for the synthetic production of dsRNA is described along with three methods for delivery that have been successful in one of the more problematic insects, Diaphorina citri.

Methods for Delivery of dsRNAs for Agricultural Pest Control: The Case of Lepidopteran Pests

RNA interference (RNAi) is a natural mechanism of gene regulation, highly conserved in eukaryotes. Since the elucidation of the gene silencing mechanism, RNAi became an important tool used in insect reverse genetics. The demonstration of effective target-gene silencing by ingestion of double-stranded RNA (dsRNA) produced by transgenic plants indicated the RNAi potential to be used in insect pest management, particularly in agriculture. However, the efficiency of gene silencing by RNAi in insects may vary according to the target taxa, and lepidopteran species have been shown to be quite recalcitrant to RNAi. Developing transgenic plants is a time-consuming and labor-intensive process, so alternative oral delivery systems are required to develop and optimize RNAi settings, such as selecting an efficient target gene, and dsRNA design, length, and stability, among other features. We have developed delivery systems to evaluate dsRNAs to silence genes from two important lepidopteran crop pests of tomato (Solanum lycopersicum) and sugarcane (Saccharum × officinarum): Tuta absoluta (Meyrick), the South American Tomato Pinworm, and Diatraea saccharalis (Fabricius), the Sugarcane Borer, respectively. The protocol described here can be used in similar species and includes (a) direct oral delivery by droplets containing dsRNA; (b) oral delivery by tomato leaflets that absorbed dsRNA solution; (c) delivery by Escherichia coli expressing dsRNA; and (d) delivery by transgenic plants expressing dsRNA.

Transplastomic Tomato Plants Expressing Insect-Specific Double-Stranded RNAs: A Protocol Based on Biolistic Transformation

Expressing insecticidal double-stranded RNA (dsRNA) molecules in plant plastids is a novel approach for in planta production of dsRNA that has enormous potential for developing improved plant-mediated RNA interference (RNAi) strategies for insect pest control. In this chapter, we describe the design of a transformation vector containing an expression cassette which can be used to stably transform plastids of tomato plants for production and accumulation of dsRNA . Such dsRNA can trigger the mechanisms of RNAi in pest insects and selectively suppress the expression of target genes, resulting in lethality. We also describe a protocol for detection of full-length dsRNA molecules in plastids using an RT-PCR-based method.

The overexpression of insect endogenous microRNA in transgenic rice inhibits the pupation of Chilo suppressalis and Cnaphalocrocis medinalis

BACKGROUND

Chilo suppressalis and Cnaphalocrocis medinalis are destructive rice pests co-occurring in major rice-growing areas in China. RNA interference (RNAi)-based insect-resistant genetically engineered (IRGE) crops provide a promising approach for pest management by suppressing gene expression or translation. A microRNA (miRNA)-mediated IRGE rice line expressing endogenous Chilo suppressalis miRNA Csu-novel-260, showing significant resistance against Chilo suppressalis, provides an attractive control strategy for Chilo suppressalis by suppressing the expression of the disembodied (dib) gene expression. However, whether this transgenic line also shows the resistance against Cnaphalocrocis medinalis remains unknown.

RESULTS

A spatiotemporal expression analysis of Csu-novel-260 in the transgenic rice line was performed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) to determine the paddy field pest exposure dose. In diet feeding assays, a chemically synthesized Csu-novel-260 agomir at 200 fmol g^-1 significantly inhibited Chilo suppressalis pupation. However, larval development, survival and pupal weight were not significantly affected. Additionally, the transgenic line significantly affected Cnaphalocrocis medinalis pupation but not larval survival. The qRT-PCR showed that Csdib and Cmdib expression levels were significantly suppressed when the two pests fed on the transgenic line. Additionally, the transgenic line significantly decreased Cry1C-resistant and Cry1C-susceptible Chilo suppressalis larval survival in detached rice tissue feeding assays, indicating that Cry1C-resistant Chilo suppressalis was not cross-resistant to Csu-novel-260 expressed in miRNA-mediated IRGE rice.

CONCLUSION

Our study demonstrated that miRNA-mediated IRGE rice significantly inhibited Chilo suppressalis and Cnaphalocrocis medinalis pupation. The results provide a new viewpoint for the application of RNAi-based plants and the inspiration for environmental risk assessment.

Coleopteran-specific StaufenC functions like Drosophila melanogaster Loquacious-PD in dsRNA processing

In Drosophila melanogaster, PD isoform of the double-stranded RNA binding protein (dsRBP) Loquacious (Loqs-PD) facilitates dsRNA cleavage to siRNA by Dicer-2. StaufenC (StauC) was discovered as a coleopteran-specific dsRBP required for dsRNA processing in coleopteran insects. Here, we show that StauC is essential for the high RNAi efficiency observed in coleopterans. Knockdown of StauC but not the homologs of Loqs-PD and R2D2 evoked a long-lasting insensitivity to RNAi in the coleopteran cell line, Ledp-SL1. The dsRNA insensitivity induced by StauC knockdown could not be overcome merely by an increase in dose or time of exposure to dsRNA or expression of Loquacious or R2D2. Furthermore, StauC but not Loqs and R2D2 are required for processing of dsRNA into siRNA. StauC overexpression also partly restored the impaired RNAi caused by the knockdown of Loqs-PD in D. melanogaster Kc cells. However, StauC was unable to compensate for the loss-of-the function of Dcr-2 or R2D2. Overall, these data suggest that StauC functions like Lops-PD in processing dsRNA to siRNA.

Biotic stress triggered small RNA and RNAi defense response in plants

The yield of crops is largely affected by different types of biotic stresses. To minimize the damage, crop plants adapted themselves to overcome the stress conditions through gene expression reprogramming at transcriptional and post-transcriptional levels. With a better knowledge of plants' responses in adverse environments, new methodologies and strategies have been applied to develop better stress-tolerant plants. In this manner, small RNAs (micro RNA and small-interfering RNA) are reported to play a central role to combat biotic stresses in plants. Depending upon the stress stimuli, these small RNAs can up or down regulate the genes expression, that indicate their potential role in overcoming the stress. These stress-induced small RNAs may reduce the expression of the target gene(s) that might negatively influence plants' response to the adverse conditions. Contrariwise, miRNA, a class of small RNA, can downregulate its expression to upregulate the expression of the target gene(s), which might positively aid to the stress adaptation. Along with this, benefits of RNA interference (RNAi) have also been stated in functional genomic research on insects, fungi and plant pathogens. RNAi is involved in the safe transport of dsRNA to the targeted mRNA(s) in the biotic stress-causing agents (for example fungi and insects) and saves the plant from damage, which is a safer approach compared to use of chemical pesticides. The current review summarizes the role of small RNAs and the use of RNAi to save the plants from biotic stress conditions.

Assessing the Risks of Topically Applied dsRNA-Based Products to Non-target Arthropods

RNA interference (RNAi) is a powerful technology that offers new opportunities for pest control through silencing of genes that are essential for the survival of arthropod pests. The approach relies on sequence-specificity of applied double-stranded (ds) RNA that can be designed to have a very narrow spectrum of both the target gene product (RNA) as well as the target organism, and thus allowing highly targeted pest control. Successful RNAi has been reported from a number of arthropod species belonging to various orders. Pest control may be achieved by applying dsRNA as foliar sprays. One of the main concerns related to the use of dsRNA is adverse environmental effects particularly on valued non-target species. Arthropods form an important part of the biodiversity in agricultural landscapes and contribute important ecosystem services. Consequently, environmental risk assessment (ERA) for potential impacts that plant protection products may have on valued non-target arthropods is legally required prior to their placement on the market. We describe how problem formulation can be used to set the context and to develop plausible pathways on how the application of dsRNA-based products could harm valued non-target arthropod species, such as those contributing to biological pest control. The current knowledge regarding the exposure to and the hazard posed by dsRNA in spray products for non-target arthropods is reviewed and suggestions are provided on how to select the most suitable test species and to conduct laboratory-based toxicity studies that provide robust, reliable and interpretable results to support the ERA.

Improving RNAi efficiency for pest control in crop species

The application of RNAi promotes the development of novel approaches toward plant protection in a sustainable way. Genetically modified crops expressing dsRNA have been developed as commercial products with great potential in insect pest management. Alternatively, some nontransformative approaches, including foliar spray, irrigation and trunk injection, are favorable in actual utilization. In this review, we summarize the recent progress and successful cases of RNAi-based pest management strategy, explore essential implications and possibilities to improve RNAi efficiency by delivery of dsRNA through transformative and nontransformative approaches, and highlight the remaining challenges and important issues related to the application of this technology.

Omics applications: towards a sustainable protection of tomato

Transcriptome data and gene expression analysis have a huge potential in the study of multiple relationships involving plants, pathogens, and pests, including the interactions with beneficial microorganisms such as endophytes or other functional groups. Next-generation sequencing (NGS) and other recent long-read-based sequencing approaches (i.e., nanopore and others) provide unprecedented tools allowing the fast identification of plant information processing systems, in situ and in real time, fundamental for crop management and pest regulation. Other -omics approaches such as metagenomics and metatranscriptomics allow high-resolution insights on the rhizosphere ecology. They may highlight key factors affecting belowground biodiversity or processes, modulating the expression of stress-responsive pathways. The application of miRNAs and other small RNAs is a relatively new field of application, with enormous potential for the selective activation of defense pathways. However, limitations concerning the stability of the RNA molecules and their effective delivery must be overcome.

The Detection and Surveillance of Asian Citrus Psyllid (Diaphorina citri)-Associated Viruses in Florida Citrus Groves

The plant pathogenic bacterium Candidatus Liberibacter asiaticus (CLas), the causal agent of the citrus disease Huanglongbing (HLB), and its insect vector, the Asian citrus psyllid (ACP; Diaphorina citri), have been devastating the Florida citrus industry. To restore the competitive production presence of Florida in the worldwide citrus market, effective and sustainable control of HLB and the ACP needs to be identified. As alternatives for resistance-inducing insecticides, viruses are currently being considered for biological control of the ACP. To identify possible biological control candidates, we conducted one of the most comprehensive surveys of natural ACP populations in major citrus production regions spanning 21 counties in Florida. By optimizing PCRs and RT-PCRs, we were able to successfully detect and monitor the prevalence of five previously identified ACP-associated RNA and DNA viruses throughout Florida citrus groves, which include: Diaphorina citri-associated C virus (DcACV), Diaphorina citri flavi-like virus (DcFLV), Diaphorina citri densovirus (DcDNV), Diaphorina citri reovirus (DcRV), and Diaphorina citri picorna-like virus (DcPLV). Adult and nymph ACP populations from 21 of Florida's major citrus-producing counties were collected each month during approximately 18 consecutive months. RNA extracts used for these viral screens were also regionally combined and subjected to High Throughput Sequencing (HTS) to reveal a more comprehensive picture of known and unknown viruses in Florida ACP populations. We discovered that DcACV was the most prevalent ACP-associated virus throughout nymph and adult ACP populations in Florida, detected in more than 60% of all samples tested, followed by DcPLV and DcFLV. HTS allowed us to identify a novel ACP-associated reo-like virus and a picorna-like virus. The putative reo-like virus, tentatively named Diaphorina citri cimodo-like virus, was later surveyed and detected back in seasonal adult and nymph ACP samples collected in Florida during this study. HTS generated data also revealed that the most abundant virus in Florida ACP populations was Citrus tristeza virus (CTV), which is not an ACP-associated virus, suggesting persistent presence of CTV infection in citrus throughout Florida groves. Collectively, information obtained from our study may be able to help guide the direction of biotechnological pest control efforts involving a number of viruses that were detected for the first time in Florida ACP populations, including two newly identified ACP-associated viruses.

Mechanisms, Applications, and Challenges of Insect RNA Interference

The RNA interference (RNAi) triggered by short/small interfering RNA (siRNA) was discovered in nematodes and found to function in most living organisms. RNAi has been widely used as a research tool to study gene functions and has shown great potential for the development of novel pest management strategies. RNAi is highly efficient and systemic in coleopterans but highly variable or inefficient in many other insects. Differences in double-stranded RNA (dsRNA) degradation, cellular uptake, inter- and intracellular transports, processing of dsRNA to siRNA, and RNA-induced silencing complex formation influence RNAi efficiency. The basic dsRNA delivery methods include microinjection, feeding, and soaking. To improve dsRNA delivery, various new technologies, including cationic liposome-assisted, nanoparticle-enabled, symbiont-mediated, and plant-mediated deliveries, have been developed. Major challenges to widespread use of RNAi in insect pest management include variable RNAi efficiency among insects, lack of reliable dsRNA delivery methods, off-target and nontarget effects, and potential development of resistance in insect populations.

Detection of Plant Viruses and Disease Management: Relevance of Genetic Diversity and Evolution

Plant viruses cause considerable economic losses and are a threat for sustainable agriculture. The frequent emergence of new viral diseases is mainly due to international trade, climate change, and the ability of viruses for rapid evolution. Disease control is based on two strategies: i) immunization (genetic resistance obtained by plant breeding, plant transformation, cross-protection, or others), and ii) prophylaxis to restrain virus dispersion (using quarantine, certification, removal of infected plants, control of natural vectors, or other procedures). Disease management relies strongly on a fast and accurate identification of the causal agent. For known viruses, diagnosis consists in assigning a virus infecting a plant sample to a group of viruses sharing common characteristics, which is usually referred to as species. However, the specificity of diagnosis can also reach higher taxonomic levels, as genus or family, or lower levels, as strain or variant. Diagnostic procedures must be optimized for accuracy by detecting the maximum number of members within the group (sensitivity as the true positive rate) and distinguishing them from outgroup viruses (specificity as the true negative rate). This requires information on the genetic relationships within-group and with members of other groups. The influence of the genetic diversity of virus populations in diagnosis and disease management is well documented, but information on how to integrate the genetic diversity in the detection methods is still scarce. Here we review the techniques used for plant virus diagnosis and disease control, including characteristics such as accuracy, detection level, multiplexing, quantification, portability, and designability. The effect of genetic diversity and evolution of plant viruses in the design and performance of some detection and disease control techniques are also discussed. High-throughput or next-generation sequencing provides broad-spectrum and accurate identification of viruses enabling multiplex detection, quantification, and the discovery of new viruses. Likely, this technique will be the future standard in diagnostics as its cost will be dropping and becoming more affordable.

Bacteria-Mediated RNA Interference for Management of Plagiodera versicolora (Coleoptera: Chrysomelidae)

RNA interference (RNAi) has emerged as a novel and feasible strategy for pest management. Methods for cost-effective production and stable delivery of double-stranded RNA (dsRNA) to the target insects are crucial for the wide application of RNAi for pest control. In this study, we tested the expression of dsRNA in RNaseIII-deficient Escherichia coli HT115 which was then fed to Plagiodera versicolora larvae, an insect pest of Salicaceae plants worldwide. By targeting six potential genes, including actin (ACT), signal recognition particle protein 54k (SRP54), heat shock protein 70 (HSC70), shibire (SHI), cactus (CACT), and soluble N-ethylmaleimide-sensitive fusion attachment proteins (SNAP), we found that feeding bacteria-expressed dsRNA successfully triggered the silencing of the five target genes tested and the suppression of ACT and SRP54 genes caused significant mortality. Our results suggest that the oral delivery of bacteria-expressed dsRNA is a potential alternative for the control of P. versicolora, and that ACT and SRP54 genes are the potent targets.

Knockout of the HaREase Gene Improves the Stability of dsRNA and Increases the Sensitivity of Helicoverpa armigera to Bacillus thuringiensis Toxin

Double-stranded RNA (dsRNA)-induced genes are usually related to RNA interference (RNAi) mechanisms and are involved in immune-related pathways. In a previous study, we found a lepidopteran-specific nuclease gene REase that was up-regulated by dsRNA and that affected RNAi efficiency in Asian corn borer (Ostrinia furnacalis). In this study, to verify the function of REase, the homologous gene HaREase in cotton bollworm (Helicoverpa armigera) was knocked out using CRISPR/Cas9 system. We found that the midgut epithelium structure was apparently not affected in the ΔHaREase mutant [Knock out (KO)]. Transcript sequencing results showed that most of the known insect immune-related genes were up-regulated in KO. When second instar larvae were fed artificial diet with Cry1Ac, a protoxin from Bacillus thuringiensis (Bt), in sublethal doses (2.5 or 4 μg/g), the growth rate of KO was repressed significantly. The dsRNA stability was also enhanced in midgut extraction of KO; however, RNAi efficiency was not obviously improved compared with the wild type (WT). The KO and WT were injected with dsEGFP (Enhanced green fluorescent protein) and subjected to transcriptome sequencing. The results showed that the expression levels of 14 nuclease genes were enhanced in KO after the dsRNA treatment. These findings revealed that HaREase expression level was not only related with dsRNA stability, but also with Bt resistance in cotton bollworm. When HaREase was knocked out, other immune- or nuclease-related genes were enhanced significantly. These results remind us that insect immune system is complex and pest control for cotton bollworm is an arduous task.

Targeting MIAT reduces apoptosis of cardiomyocytes after ischemia/reperfusion injury

This study aims to investigate the role of targeting lncRNA myocardial infarction-associated transcript (MIAT) in protection against hypoxia/reoxygenation (H/R) injury in H9c2 cells in vitro and myocardial ischemia/reperfusion (I/R) injury in vivo by regulating expression of NF-kB and p53 upregulated modulator of apoptosis (PUMA). H9C2 cells were infected with lentivirus expressing the short-hairpin RNA direct against human MIAT gene (Lv-MIAT shRNA) or lentivirus expressing scrambled control (Lv-NC shRNA) or PUMA siRNA or p65 siRNA or their control siRNA respectively. Then the H9c2 cells were infected with Lv-shRNA to 2 hours of hypoxia (H) and 24 hour of reoxygenation (R). 100 ul of Lv-MIAT shRNA (1 × 10⁸ PFU) or Lv-NC shRNA was transfected into mouse hearts, then the hearts were subjected to I/R (1h/72 h). We discovered targeting MIAT remarkably enhanced H9c2 cell viability, decreased H/R-induced cell apoptosis and LDH leakage and significantly decreased I/R-induced myocardial infarct size, reduced myocardial apoptosis and enhanced the heart function. Targeting MIAT downregulated p65 nuclear translocation, NF-κB activity and anti-apoptotic protein cleaved-caspase-3, Bax, and upregulated anti-apoptotic protein Bcl-2 induced by H/R or I/R. Our study suggests that targeting MIAT may protect against H9c2 cardiomyoblasts H/R injury or myocardial I/R injury via inhibition of cell apoptosis, mediated by NF-κB and PUMA signal pathway.

CRISPR/Cas9 Genome Editing Introduction and Optimization in the Non-model Insect Pyrrhocoris apterus

The CRISPR/Cas9 technique is widely used in experimentation with human cell lines as well as with other model systems, such as mice Mus musculus, zebrafish Danio reiro, and the fruit fly Drosophila melanogaster. However, publications describing the use of CRISPR/Cas9 for genome editing in non-model organisms, including non-model insects, are scarce. The introduction of this relatively new method presents many problems even for experienced researchers, especially with the lack of procedures to tackle issues concerning the efficiency of mutant generation. Here we present a protocol for efficient genome editing in the non-model insect species Pyrrhocoris apterus. We collected data from several independent trials that targeted several genes using the CRISPR/Cas9 system and determined that several crucial optimization steps led to a remarkably increased efficiency of mutant production. The main steps are as follows: the timing of embryo injection, the use of the heteroduplex mobility assay as a screening method, in vivo testing of sgRNA efficiency, and G0 germline mosaicism screening. The timing and the method of egg injections used here need to be optimized for other species, but other here-described optimization solutions can be applied immediately for genome editing in other insect species.

RNA Interference in the Tobacco Hornworm, Manduca sexta, Using Plastid-Encoded Long Double-Stranded RNA

RNA interference (RNAi) is a promising method for controlling pest insects by silencing the expression of vital insect genes to interfere with development and physiology; however, certain insect Orders are resistant to this process. In this study, we set out to test the ability of in planta-expressed dsRNA synthesized within the plastids to silence gene expression in an insect recalcitrant to RNAi, the lepidopteran species, Manduca sexta (tobacco hornworm). Using the Manduca vacuolar-type H+ ATPase subunit A (v-ATPaseA) gene as the target, we first evaluated RNAi efficiency of two dsRNA products of different lengths by directly feeding the in vitro-synthesized dsRNAs to M. sexta larvae. We found that a long dsRNA of 2222 bp was the most effective in inducing lethality and silencing the v-ATPaseA gene, when delivered orally in a water droplet. We further transformed the plastid genome of the M. sexta host plant, Nicotiana tabacum, to produce this long dsRNA in its plastids and performed bioassays with M. sexta larvae on the transplastomic plants. In the tested insects, the plastid-derived dsRNA had no effect on larval survival and no statistically significant effect on expression of the v-ATPaseA gene was observed. Comparison of the absolute quantities of the dsRNA present in transplastomic leaf tissue for v-ATPaseA and a control gene, GFP, of a shorter size, revealed a lower concentration for the long dsRNA product compared to the short control product. We suggest that stability and length of the dsRNA may have influenced the quantities produced in the plastids, resulting in inefficient RNAi in the tested insects. Our results imply that many factors dictate the effectiveness of in planta RNAi, including a likely trade-off effect as increasing the dsRNA product length may be countered by a reduction in the amount of dsRNA produced and accumulated in the plastids.

Management of Pest Insects and Plant Diseases by Non-Transformative RNAi

Since the discovery of RNA interference (RNAi), scientists have made significant progress towards the development of this unique technology for crop protection. The RNAi mechanism works at the mRNA level by exploiting a sequence-dependent mode of action with high target specificity due to the design of complementary dsRNA molecules, allowing growers to target pests more precisely compared to conventional agrochemicals. The delivery of RNAi through transgenic plants is now a reality with some products currently in the market. Conversely, it is also expected that more RNA-based products reach the market as non-transformative alternatives. For instance, topically applied dsRNA/siRNA (SIGS - Spray Induced Gene Silencing) has attracted attention due to its feasibility and low cost compared to transgenic plants. Once on the leaf surface, dsRNAs can move directly to target pest cells (e.g., insects or pathogens) or can be taken up indirectly by plant cells to then be transferred into the pest cells. Water-soluble formulations containing pesticidal dsRNA provide alternatives, especially in some cases where plant transformation is not possible or takes years and cost millions to be developed (e.g., perennial crops). The ever-growing understanding of the RNAi mechanism and its limitations has allowed scientists to develop non-transgenic approaches such as trunk injection, soaking, and irrigation. While the technology has been considered promising for pest management, some issues such as RNAi efficiency, dsRNA degradation, environmental risk assessments, and resistance evolution still need to be addressed. Here, our main goal is to review some possible strategies for non-transgenic delivery systems, addressing important issues related to the use of this technology.

RNA interference-based antiviral immune response against the salivary gland hypertrophy virus in Glossina pallidipes

Background

Glossina pallidipes salivary gland hypertrophy virus (GpSGHV; Hytrosaviridae) is a non-occluded dsDNA virus that specifically infects the adult stages of the hematophagous tsetse flies (Glossina species, Diptera: Glossinidae). GpSGHV infections are usually asymptomatic, but unknown factors can result to a switch to acute symptomatic infection, which is characterized by the salivary gland hypertrophy (SGH) syndrome associated with decreased fecundity that can ultimately lead to a colony collapse. It is uncertain how GpSGHV is maintained amongst Glossina spp. populations but RNA interference (RNAi) machinery, a conserved antiviral defense in insects, is hypothesized to be amongst the host’s mechanisms to maintain the GpSGHV in asymptomatic (persistent or latent) infection state. Here, we investigated the involvement of RNAi during GpSGHV infections by comparing the expression of three key RNAi machinery genes, Dicer (DCR), Argonaute (AGO) and Drosha, in artificially virus injected, asymptomatic and symptomatic infected G. pallidipes flies compared to PBS injected (controls) individuals. We further assessed the impact of AGO2 knockdown on virus infection by RT-qPCR quantification of four selected GpSGHV genes, i.e. odv-e66, dnapol, maltodextrin glycosyltransferase (a tegument gene) and SGHV091 (a capsid gene).

Results

We show that in response to hemocoelic injections of GpSGHV into G. pallidipes flies, increased virus replication was accompanied by significant upregulation of the expression of three RNAi key genes; AGO1, AGO2 and DCR2, and a moderate increase in the expression of Drosha post injection compared to the PBS-injected controls. Furthermore, compared to asymptomatically infected individuals, symptomatic flies showed significant downregulation of AGO1, AGO2 and Drosha, but a moderate increase in the expression of DCR2. Compared to the controls, knockdown of AGO2 did not have a significant impact on virus infection in the flies as evidenced by unaltered transcript levels of the selected GpSGHV genes.

Conclusion

The upregulation of the expression of the RNAi genes implicate involvement of this machinery in controlling GpSGHV infections and the establishment of symptomatic GpSGHV infections in Glossina. These findings provide a strategic foundation to understand GpSGHV infections and to control latent (asymptomatic) infections in Glossina spp. and thereby control SGHVs in insect production facilities.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1298-1) contains supplementary material, which is available to authorized users.

Characterization and expression profiling of microRNAs in response to plant feeding in two host-plant strains of the lepidopteran pest Spodoptera frugiperda

Background

A change in the environment may impair development or survival of living organisms leading them to adapt to the change. The resulting adaptation trait may reverse, or become fixed in the population leading to evolution of species. Deciphering the molecular basis of adaptive traits can thus give evolutionary clues. In phytophagous insects, a change in host-plant range can lead to emergence of new species. Among them, Spodoptera frugiperda is a major agricultural lepidopteran pest consisting of two host-plant strains having diverged 3 MA, based on mitochondrial markers. In this paper, we address the role of microRNAs, important gene expression regulators, in response to host-plant change and in adaptive evolution.

Results

Using small RNA sequencing, we characterized miRNA repertoires of the corn (C) and rice (R) strains of S. frugiperda, expressed during larval development on two different host-plants, corn and rice, in the frame of reciprocal transplant experiments. We provide evidence for 76 and 68 known miRNAs in C and R strains and 139 and 171 novel miRNAs. Based on read counts analysis, 34 of the microRNAs were differentially expressed in the C strain larvae fed on rice as compared to the C strain larvae fed on corn. Twenty one were differentially expressed on rice compared to corn in R strain. Nine were differentially expressed in the R strain compared to C strain when reared on corn. A similar ratio of microRNAs was differentially expressed between strains on rice. We could validate experimentally by QPCR, variation in expression of the most differentially expressed candidates. We used bioinformatics methods to determine the target mRNAs of known microRNAs. Comparison with the mRNA expression profile during similar reciprocal transplant experiment revealed potential mRNA targets of these host-plant regulated miRNAs.

Conclusions

In the current study, we performed the first systematic analysis of miRNAs in Lepidopteran pests feeding on host-plants. We identified a set of the differentially expressed miRNAs that respond to the plant diet, or differ constitutively between the two host plant strains. Among the latter, the ones that are also deregulated in response to host-plant are molecular candidates underlying a complex adaptive trait.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5119-6) contains supplementary material, which is available to authorized users.

Prediction of effective RNA interference targets and pathway-related genes in lepidopteran insects by RNA sequencing analysis

When using RNA interference (RNAi) to study gene functions in Lepidoptera insects, we discovered that some genes could not be suppressed; instead, their expression levels could be up-regulated by double-stranded RNA (dsRNA). To predict which genes could be easily silenced, we treated the Asian corn borer (Ostrinia furnacalis) with dsGFP (green fluorescent protein) and dsMLP (muscle lim protein). A transcriptome sequence analysis was conducted using the cDNAs 6 h after treatment with dsRNA. The results indicated that 160 genes were up-regulated and 44 genes were down-regulated by the two dsRNAs. Then, 50 co-up-regulated, 25 co-down-regulated and 43 unaffected genes were selected to determine their RNAi responses. All the 25 down-regulated genes were knocked down by their corresponding dsRNA. However, several of the up-regulated and unaffected genes were up-regulated when treated with their corresponding dsRNAs instead of being knocked down. The genes up-regulated by the dsGFP treatment may be involved in insect immune responses or the RNAi pathway. When the immune-related genes were excluded, only seven genes were induced by dsGFP, including ago-2 and dicer-2. These results not only provide a reference for efficient RNAi target predications, but also provide some potential RNAi pathway-related genes for further study.

Plant-mediated RNAi silences midgut-expressed genes in congeneric lepidopteran insects in nature

BACKGROUND

Plant-mediated RNAi (PMRi) silencing of insect genes has enormous potential for crop protection, but whether it works robustly under field conditions, particularly with lepidopteran pests, remains controversial. Wild tobacco Nicotiana attenuata and cultivated tobacco (N. tabacum) (Solanaceae) is attacked by two closely related specialist herbivores Manduca sexta and M. quinquemaculata (Lepidoptera, Sphingidae). When M. sexta larvae attack transgenic N. attenuata plants expressing double-stranded RNA(dsRNA) targeting M. sexta's midgut-expressed genes, the nicotine-ingestion induced cytochrome P450 monooxygenase (invert repeat (ir)CYP6B46-plants) and the lyciumoside-IV-ingestion induced β-glucosidase1 (irBG1-plants), these larval genes which are important for the larvae's response to ingested host toxins, are strongly silenced.

RESULTS

Here we show that the PMRi procedure also silences the homologous genes in native M. quinquemaculata larvae feeding on irCYP6B46 and irBG1-transgenic N. attenuata plants in nature. The PMRi lines shared 98 and 96% sequence similarity with M. quinquemaculata homologous coding sequences, and CYP6B46 and BG1 transcripts were reduced by ca. 90 and 80%, without reducing the transcripts of the larvae's most similar, potential off-target genes.

CONCLUSIONS

We conclude that the PMRi procedure can robustly and specifically silence genes in native congeneric insects that share sufficient sequence similarity and with the careful selection of targets, might protect crops from attack by congeneric-groups of insect pests.

Viral Delivery of dsRNA for Control of Insect Agricultural Pests and Vectors of Human Disease: Prospects and Challenges

RNAi is applied as a new and safe method for pest control in agriculture but efficiency and specificity of delivery of dsRNA trigger remains a critical issue. Various agents have been proposed to augment dsRNA delivery, such as engineered micro-organisms and synthetic nanoparticles, but the use of viruses has received relatively little attention. Here we present a critical view of the potential of the use of recombinant viruses for efficient and specific delivery of dsRNA. First of all, it requires the availability of plasmid-based reverse genetics systems for virus production, of which an overview is presented. For RNA viruses, their application seems to be straightforward since dsRNA is produced as an intermediate molecule during viral replication, but DNA viruses also have potential through the production of RNA hairpins after transcription. However, application of recombinant virus for dsRNA delivery may not be straightforward in many cases, since viruses can encode RNAi suppressors, and virus-induced silencing effects can be determined by the properties of the encoded RNAi suppressor. An alternative is virus-like particles that retain the efficiency and specificity determinants of natural virions but have encapsidated non-replicating RNA. Finally, the use of viruses raises important safety issues which need to be addressed before application can proceed.

Macrophages in Invertebrates: From Insects and Crustaceans to Marine Bivalves

Macrophages are critical components of the antimicrobial response. The recent explosion of knowledge on the evolutionary, genetic, and biochemical aspects of the interaction between macrophages and microbes has renewed scientific interest in macrophages. The conservation of immune components or mechanisms between organisms during the evolutionary process allows us to elucidate antimicrobial mechanisms or discover new immune functions through the study of basal-branching organisms, such as invertebrates. As a result, immunity in non-vertebrates has attracted the attention of researchers in the last few decades. In this review, we summarize what is presently known about macrophage-like cells in various invertebrate species.

Host-Derived Artificial MicroRNA as an Alternative Method to Improve Soybean Resistance to Soybean Cyst Nematode

The soybean cyst nematode (SCN), Heterodera glycines, is one of the most important pests limiting soybean production worldwide. Novel approaches to managing this pest have focused on gene silencing of target nematode sequences using RNA interference (RNAi). With the discovery of endogenous microRNAs as a mode of gene regulation in plants, artificial microRNA (amiRNA) methods have become an alternative method for gene silencing, with the advantage that they can lead to more specific silencing of target genes than traditional RNAi vectors. To explore the application of amiRNAs for improving soybean resistance to SCN, three nematode genes (designated as J15, J20, and J23) were targeted using amiRNA vectors. The transgenic soybean hairy roots, transformed independently with these three amiRNA vectors, showed significant reductions in SCN population densities in bioassays. Expression of the targeted genes within SCN eggs were downregulated in populations feeding on transgenic hairy roots. Our results provide evidence that host-derived amiRNA methods have great potential to improve soybean resistance to SCN. This approach should also limit undesirable phenotypes associated with off-target effects, which is an important consideration for commercialization of transgenic crops.

RNAi Efficiency, Systemic Properties, and Novel Delivery Methods for Pest Insect Control: What We Know So Far

In recent years, the research on the potential of using RNA interference (RNAi) to suppress crop pests has made an outstanding growth. However, given the variability of RNAi efficiency that is observed in many insects, the development of novel approaches toward insect pest management using RNAi requires first to unravel factors behind the efficiency of dsRNA-mediated gene silencing. In this review, we explore essential implications and possibilities to increase RNAi efficiency by delivery of dsRNA through non-transformative methods. We discuss factors influencing the RNAi mechanism in insects and systemic properties of dsRNA. Finally, novel strategies to deliver dsRNA are discussed, including delivery by symbionts, plant viruses, trunk injections, root soaking, and transplastomic plants.

Recombinant fungal entomopathogen RNAi target insect gene

RNA interference (RNAi) technology is considered as an alternative for control of pests. However, RNAi has not been used in field conditions yet, since delivering exogenous ds/siRNA to target pests is very difficult. The laboratory methods of introducing the ds/siRNA into insects through feeding, micro feeding / dripping and injecting cannot be used in fields. Transgenic crop is perhaps the most effective application of RNAi for pest control, but it needs long-time basic researches in order to reduce the cost and evaluate the safety. Therefore, transgenic microbe is maybe a better choice. Entomopathogenic fungi generally invade the host insects through cuticle like chemical insecticides contact insect to control sucking sap pests. Isaria fumosorosea is a common fungal entomopathogen in whitefly, Bemisia tabaci. We constructed a recombinant strain of I. fumosorosea expressing specific dsRNA of whitefly's TLR7 gene. It could silence the TLR7 gene and improve the virulence against whitefly. Transgenic fungal entomopathogen has shown great potential to attain the application of RNAi technology for pests control in fields. In the future, the research interests should be focused on the selection of susceptible target pests and their vital genes, and optimizing the methods for screening genes and recombinants as well.

Vector-Borne Bacterial Plant Pathogens: Interactions with Hemipteran Insects and Plants

Hemipteran insects are devastating pests of crops due to their wide host range, rapid reproduction, and ability to transmit numerous plant-infecting pathogens as vectors. While the field of plant-virus-vector interactions has flourished in recent years, plant-bacteria-vector interactions remain poorly understood. Leafhoppers and psyllids are by far the most important vectors of bacterial pathogens, yet there are still significant gaps in our understanding of their feeding behavior, salivary secretions, and plant responses as compared to important viral vectors, such as whiteflies and aphids. Even with an incomplete understanding of plant-bacteria-vector interactions, some common themes have emerged: (1) all known vector-borne bacteria share the ability to propagate in the plant and insect host; (2) particular hemipteran families appear to be incapable of transmitting vector-borne bacteria; (3) all known vector-borne bacteria have highly reduced genomes and coding capacity, resulting in host-dependence; and (4) vector-borne bacteria encode proteins that are essential for colonization of specific hosts, though only a few types of proteins have been investigated. Here, we review the current knowledge on important vector-borne bacterial pathogens, including Xylella fastidiosa, Spiroplasma spp., Liberibacter spp., and 'Candidatus Phytoplasma spp.'. We then highlight recent approaches used in the study of vector-borne bacteria. Finally, we discuss the application of this knowledge for control and future directions that will need to be addressed in the field of vector-plant-bacteria interactions.