CRISPR/Cas9-mediated targeted gene mutagenesis in Spodoptera litura

Multi-omics analysis reveal the fall armyworm Spodoptera frugiperda tolerate high temperature by mediating chitin-related genes

Climate change facilitates the rapid invasion of agricultural pests, threatening global food security. The fall armyworm Spodoptera frugiperda is a highly polyphagous migratory pest tolerant to high temperatures, allowing its proliferation in harsh thermal environments. We aimed to demonstrate mechanisms of its high-temperature tolerance, particularly transcriptional and metabolic regulation, which are poorly understood. To achieve the aim, we examined the impact and mechanism of heat events on S. frugiperda by using multiple approaches: ecological measurements, transcriptomics, metabolomics, RNAi, and CRISPR/Cas9 technology. We observed that several physiological indices (larval survival rate, larval period, pupation rate, pupal weight, eclosion rate, and average fecundity) decreased as the temperature increased, with the 32 °C treatment displaying a significant difference from the control group at 26 °C. Significantly upregulated expression of genes encoding endochitinase and chitin deacetylase was observed in the chitin-binding, extracellular region, and carbohydrate metabolic process GO terms of hemolymph, fat body, and brain, exhibiting a tissue-specific pattern. Significantly enriched pathways (e.g., cutin, suberin, and wax biosynthesis; oxidative phosphorylation and cofactor biosynthesis; diverse amino acid biosynthesis and degradation; carbon metabolism; and energy metabolism), all of which are essential for S. frugiperda larvae to tolerate temperature, were found in metabolites that were expressed differently. Successful RNA interference targeting of the three chitin-related genes reduced gene expression levels and larval survival rate. Knockout of the endochitinase gene by using the CRISPR/Cas9 system significantly reduced the relative gene expression and increased sensitivity to high-temperature exposure. On the basis of our findings, theoretical foundations for understanding the high-temperature tolerance of S. frugiperda populations and latent genetic control strategies were established.

Genome editing: A novel approach to manage insect vectors of plant viruses

Insect vectors significantly threaten global agriculture by transmitting numerous plant viruses. Various measures, from conventional insecticides to genetic engineering, are used to mitigate this threat. However, none provide complete resistance. Therefore, researchers are looking for novel control options. In recent years with the advancements in genomic technologies, genomes and transcriptomes of various insect vectors have been generated. However, the lack of knowledge about gene functions hinders the development of novel strategies to restrict virus spread. RNA interference (RNAi) is widely used to elucidate gene functions, but its variable efficacy hampers its use in managing insect vectors and plant viruses. Genome editing has the potential to overcome these challenges and has been extensively used in various insect pest species. This review summarizes the progress and potential of genome editing in plant virus vectors and its application as a functional genomic tool to elucidate virus-vector interactions. We also discuss the major challenges associated with editing genes of interest in insect vectors.

Disruption of Spodoptera exigua serine protease 2 (Ser2) results in male sterility by CRISPR/Cas9 technology

BACKGROUND

Sperm development and behavior present promising targets for environmentally safer, target-specific biorational control strategies. Serine protease in seminal fluid proteins plays a crucial role in the post-mating reproductive processes of lepidopteran pest insects. The serine protease 2 has been identified as the initiatorin of the seminal fluid protein in Lepidoptera, and its loss of function leads to male sterility. Nevertheless, the genetic pattern of this gene mutation and the impacts of various mutant genotypes on the hatchability of the eggs of pests remain unclear.

RESULTS

This study focused on the cloning of Spodoptera exigua serine protease 2 (SeSer2), which is specifically expressed in male moths. The open reading frame of SeSer2 consists of 843 nucleotides, encoding 280 amino acids with structural characteristics typical of serine proteases in the S1 family. To validate the functional role of SeSer2 in the fertility of S. exigua, a targeted ~3574-bp deletion of SeSer2 was introduced using the CRISPR/Cas9 genome editing system, leading to premature truncation of the SeSer2 protein. The SeSer2 mutation had no significant impact on the growth and development of individuals of either sex. However, disruption of SeSer2 resulted in heritable male sterility. Although females mated with SeSer2-/- (SeSer2 knockout homozygote) males laid eggs normally, these eggs failed to hatch. SeSer2+/- (SeSer2 knockout heterozygote) male moths crossed with female moths produced viable offspring, indicating the gene's recessive role in egg hatching.

CONCLUSION

These findings strongly support the conclusion that the Ser2 gene is essential for male reproductive success in diverse lepidopterans. Targeting the Ser2 gene holds promise as a foundational element of a novel pest control strategy. © 2024 Society of Chemical Industry.

Comparative analysis of testicular fusion in Spodoptera litura (cutworm) and Bombyx mori (silkworm): Histological and transcriptomic insights

Spodoptera litura commonly known as the cutworm, is among the most destructive lepidopteran pests affecting over 120 plants species. The powerful destructive nature of this lepidopteran is attributable to its high reproductive capacity. The testicular fusion that occurs during metamorphosis from larvae to pupa in S.litura positively influences the reproductive success of the offspring. In contrast, Bombyx mori, the silkworm, retains separate testes throughout its life and does not undergo this fusion process. Microscopic examination reveals that during testicular fusion in S.litura, the peritoneal sheath becomes thinner and more translucent, whereas in B.mori, the analogous region thickens. The outer basement membrane in S.litura exhibits fractures, discontinuity, and uneven thickness accompanied by a significant presence of cellular secretions, large cell size, increased vesicles, liquid droplets, and a proliferation of rough endoplasmic reticulum and mitochondria. In contrast, the testicular peritoneal sheath of B.mori at comparable developmental stage exhibits minimal change. Comparative transcriptomic analysis of the testicular peritoneal sheath reveals a substantial difference in gene expression between the two species. The disparity in differential expressed genes (DEGs) is linked to an enrichment of numerous transcription factors, intracellular signaling pathways involving Ca2+ and GTPase, as well as intracellular protein transport and signaling pathways. Meanwhile, structural proteins including actin, chitin-binding proteins, membrane protein fractions, cell adhesion, extracellular matrix proteins are predominantly identified. Moreover, the study highlights the enrichment of endopeptidases, serine proteases, proteolytic enzymes and matrix metalloproteins, which may play a role in the degradation of the outer membrane. Five transcription factors-Slforkhead, Slproline, Slcyclic, Slsilk, and SlD-ETS were identified, and their expression pattern were confirmed by qRT-PCR. they are candidates for participating in the regulation of testicular fusion. Our findings underscore significant morphological and trancriptomic variation in the testicular peritoneal sheath of S.litura compared to the silkworm, with substantial changes at the transcriptomic level coinciding with testicular fusion. The research provides valuable clues for understanding the complex mechanisms underlying this unique phenomenon in insects.

Efficient DIPA-CRISPR-mediated knockout of an eye pigment gene in the white-backed planthopper, Sogatella furcifera

Although CRISPR/Cas9 has been widely used in insect gene editing, the need for the microinjection of preblastoderm embryos can preclude the technique being used in insect species with eggs that are small, have hard shells, and/or are difficult to collect and maintain outside of their normal environment. Such is the case with Sogatella furcifera, the white-backed planthopper (WBPH), a significant pest of Oryza sativa (rice) that oviposits inside rice stems. Egg extraction from the stem runs the risk of mechanical damage and hatching is heavily influenced by the micro-environment of the rice stem. To bypass these issues, we targeted embryos prior to oviposition via direct parental (DIPA)-CRISPR, in which Cas9 and single-guide RNAs (sgRNAs) for the WBPH eye pigment gene tryptophan 2,3-dioxygenase were injected into the hemocoel of adult females. Females at varying numbers of days posteclosion were evaluated to determine at what stage their oocyte might be most capable of taking up the gene-editing components. An evaluation of the offspring indicated that the highest G0 gene-edited efficacy (56.7%) occurred in females injected 2 d posteclosion, and that those mutations were heritably transmitted to the G1 generation. This study demonstrates the potential utility of DIPA-CRISPR for future gene-editing studies in non-model insect species and can facilitate the development of novel pest management applications.

CRISPR/Cas9-mediated genome editing technique to control fall armyworm (Spodoptera frugiperda) in crop plants with special reference to maize

Fall Armyworm imposes a major risk to agricultural losses. Insecticides have historically been used to manage its infestations, but it eventually becomes resistant to them. To combat the pest, a more recent strategy based on the use of transgenic maize that expresses Bt proteins such as Cry1F from the bacteria has been used. Nonetheless, there have been numerous reports of Cry1F maize resistance in FAW populations. Nowadays, the more effective and less time-consuming genome editing method known as CRISPR/Cas9 technology has gradually supplanted these various breeding techniques. This method successfully edits the genomes of various insects, including Spodoptera frugiperda. On the other hand, this new technique can change an insect's DNA to overcome its tolerance to specific insecticides or to generate a gene drive. The production of plant cultivars resistant to fall armyworms holds great potential for the sustainable management of this pest, given the swift advancement of CRISPR/Cas9 technology and its varied uses. Thus, this review article discussed and critically assessed the use of CRISPR/Cas9 genome-editing technology in long-term fall armyworm pest management. However, this review study focuses primarily on the mechanism of the CRISPR-Cas9 system in both crop plants and insects for FAW management.

Strategies for mitigation of pesticides from the environment through alternative approaches: A review of recent developments and future prospects

Chemical-based peticides are having negative impacts on both the healths of human beings and plants as well. The World Health Organisation (WHO), reported that each year, >25 million individuals in poor nations are having acute pesticide poisoning cases along with 20,000 fatal injuries at global level. Normally, only ∼0.1% of the pesticide reaches to the intended targets, and rest amount is expected to come into the food chain/environment for a longer period of time. Therefore, it is crucial to reduce the amounts of pesticides present in the soil. Physical or chemical treatments are either expensive or incapable to do so. Hence, pesticide detoxification can be achieved through bioremediation/biotechnologies, including nano-based methodologies, integrated approaches etc. These are relatively affordable, efficient and environmentally sound methods. Therefore, alternate strategies like as advanced biotechnological tools like as CRISPR Cas system, RNAi and genetic engineering for development of insects and pest resistant plants which are directly involved in the development of disease- and pest-resistant plants and indirectly reduce the use of pesticides. Omics tools and multi omics approaches like metagenomics, genomics, transcriptomics, proteomics, and metabolomics for the efficient functional gene mining and their validation for bioremediation of pesticides also discussed from the literatures. Overall, the review focuses on the most recent advancements in bioremediation methods to lessen the effects of pesticides along with the role of microorganisms in pesticides elimination. Further, pesticide detection is also a big challenge which can be done by using HPLC, GC, SERS, and LSPR ELISA etc. which have also been described in this review.

CRISPR/Cas9 mediated mutagenesis of the major sex pheromone gene, acyl-CoA delta-9 desaturase (DES9) in Fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

The Fall armyworm, Spodoptera frugiperda is a significant global pest causing serious yield loss on several staple crops. In this regard, this pest defies several management approaches based on chemicals, Bt transgenics etc., requiring effective alternatives. Recently CRISPR/Cas9 mediated genome editing has opened up newer avenues to establish functions of various target genes before employing them for further application. The virgin female moths of S. frugiperda emit sex pheromones to draw conspecific males. Therefore, we have edited the key pheromone synthesis gene, fatty acyl-CoA Delta-9 desaturase (DES9) of the Indian population of S. frugiperda. In order to achieve a larger deletion of the DES9, we have designed two single guide RNA (sgRNA) in sense and antisense direction targeting the first exon instead of a single guide RNA. The sgRNA caused site-specific knockout with a larger deletion which impacted the mating. Crossing studies between wild male and mutant female resulted in no fecundity, while fecundity was normal when mutant male crossed with the wild female. This indicates that mating disruption is stronger in females where DES9 is mutated. The current work is the first of its kind to show that DES9 gene editing impacted the likelihood of mating in S. frugiperda.

CRISPR/Cas9: a cutting-edge solution for combatting the fall armyworm, Spodoptera frugiperda

The utilization of CRISPR/Cas9 in Spodoptera frugiperda, commonly known as fall armyworm, presents a groundbreaking avenue for pest management. With its ability to precisely modify the insect's genome, CRISPR/Cas9 offers innovative strategies to combat this destructive pest. The application of CRISPR/Cas9 in S. frugiperda holds immense potential. It enables the identification and functional analysis of key genes associated with its behavior, development, and insecticide resistance. This knowledge can unveil novel target sites for more effective and specific insecticides. Additionally, CRISPR/Cas9 can facilitate the development of population control methods by disrupting vital genes essential for survival. However, challenges such as off-target effects and the efficient delivery of CRISPR/Cas9 components remain. Addressing these obstacles is vital to ensure accurate and reliable results. Furthermore, ethical considerations, biosafety protocols, and regulatory frameworks must be integral to the adoption of this technology. Looking forward, CRISPR/Cas9-based gene drive systems hold the potential to promulgate desirable genetic traits within S. frugiperda populations, offering a sustainable and eco-friendly approach. This could curtail their reproductive capabilities or make them more susceptible to certain interventions. In conclusion, CRISPR/Cas9 presents a transformative platform for precise and targeted pest management in S. frugiperda. By deciphering the insect's genetic makeup and developing innovative strategies, we can mitigate the devastating impact of fall armyworm on agriculture while ensuring environmental sustainability.

Unveiling the Genetic Symphony: Harnessing CRISPR-Cas Genome Editing for Effective Insect Pest Management

Phytophagous insects pose a significant threat to global crop yield and food security. The need for increased agricultural output while reducing dependence on harmful synthetic insecticides necessitates the implementation of innovative methods. The utilization of CRISPR-Cas (Clustered regularly interspaced short palindromic repeats) technology to develop insect pest-resistant plants is believed to be a highly effective approach in reducing production expenses and enhancing the profitability of farms. Insect genome research provides vital insights into gene functions, allowing for a better knowledge of insect biology, adaptability, and the development of targeted pest management and disease prevention measures. The CRISPR-Cas gene editing technique has the capability to modify the DNA of insects, either to trigger a gene drive or to overcome their resistance to specific insecticides. The advancements in CRISPR technology and its various applications have shown potential in developing insect-resistant varieties of plants and other strategies for effective pest management through a sustainable approach. This could have significant consequences for ensuring food security. This approach involves using genome editing to create modified insects or crop plants. The article critically analyzed and discussed the potential and challenges associated with exploring and utilizing CRISPR-Cas technology for reducing insect pest pressure in crop plants.

Advancements and prospects of CRISPR/Cas9 technologies for abiotic and biotic stresses in sugar beet

Sugar beet is a crop with high sucrose content, known for sugar production and recently being considered as an emerging raw material for bioethanol production. This crop is also utilized as cattle feed, mainly when animal green fodder is scarce. Bioethanol and hydrogen gas production from this crop is an essential source of clean energy. Environmental stresses (abiotic/biotic) severely affect the productivity of this crop. Over the past few decades, the molecular mechanisms of biotic and abiotic stress responses in sugar beet have been investigated using next-generation sequencing, gene editing/silencing, and over-expression approaches. This information can be efficiently utilized through CRISPR/Cas 9 technology to mitigate the effects of abiotic and biotic stresses in sugar beet cultivation. This review highlights the potential use of CRISPR/Cas 9 technology for abiotic and biotic stress management in sugar beet. Beet genes known to be involved in response to alkaline, cold, and heavy metal stresses can be precisely modified via CRISPR/Cas 9 technology for enhancing sugar beet's resilience to abiotic stresses with minimal off-target effects. Similarly, CRISPR/Cas 9 technology can help generate insect-resistant sugar beet varieties by targeting susceptibility-related genes, whereas incorporating Cry1Ab and Cry1C genes may provide defense against lepidopteron insects. Overall, CRISPR/Cas 9 technology may help enhance sugar beet's adaptability to challenging environments, ensuring sustainable, high-yield production.

CRISPR/Cas9 mediated editing of pheromone biosynthesis activating neuropeptide (PBAN) gene disrupts mating in the Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

The Fall armyworm, Spodoptera frugiperda, is a globally important invasive pest, primarily on corn, causing severe yield loss. Overuse of synthetic chemicals has caused significant ecological harm, and in many instances control has failed. Therefore, developing efficient, environmentally friendly substitutes for sustainable management of this pest is of high priority. CRISPR/Cas9-mediated gene editing causes site-specific mutations that typically result in loss-of-function of the target gene. In this regard, identifying key genes that govern the reproduction of S. frugiperda and finding ways to introduce mutations in the key genes is very important for successfully managing this pest. In this study, the pheromone biosynthesis activator neuropeptide (PBAN) gene of S. frugiperda was cloned and tested for its function via a loss-of-function approach using CRISPR/Cas9. Ribonucleoprotein (RNP) complex (single guide RNA (sgRNA) targeting the PBAN gene + Cas9 protein) was validated through in vitro restriction assay followed by embryonic microinjection into the G0 stage for in vivo editing of the target gene. Specific suppression of PBAN by CRISPR/Cas9 in females significantly affected mating. Mating studies between wild males and mutant females resulted in no fecundity. This was in contrast to when mutant males were crossed with wild females, which resulted in reduced fecundity. These results suggest that mating disruption is more robust where PBAN is edited in females. The behavioural bioassay using an olfactometer revealed that mutant females were less attractive to wild males compared to wild females. This study is the first of its kind, supporting CRISPR/Cas9 mediating editing of the PBAN gene disrupting mating in S. frugiperda. Understanding the potential use of these molecular techniques may help develop novel management strategies that target other key functional genes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03798-3.

Natural Coumarin Shows Toxicity to Spodoptera litura by Inhibiting Detoxification Enzymes and Glycometabolism

Coumarin and its derivatives are plant-derived compounds that exhibit potent insecticidal properties. In this study, we found that natural coumarin significantly inhibited the growth and development of Spodoptera litura larvae through toxicological assay. By transcriptomic sequencing, 80 and 45 differentially expressed genes (DEGs) related to detoxification were identified from 0 to 24 h and 24 to 48 h in S. litura after coumarin treatment, respectively. Enzyme activity analysis showed that CYP450 and acetylcholinesterase (AChE) activities significantly decreased at 48 h after coumarin treatment, while glutathione S-transferases (GST) activity increased at 24 h. Silencing of SlCYP324A16 gene by RNA interference significantly increased S. litura larval mortality and decreased individual weight after treatment with coumarin. Additionally, the expression levels of DEGs involved in glycolysis and tricarboxylic acid (TCA) cycle were inhibited at 24 h after coumarin treatment, while their expression levels were upregulated at 48 h. Furthermore, metabonomics analysis identified 391 differential metabolites involved in purine metabolism, amino acid metabolism, and TCA cycle from 0 to 24 h after treated with coumarin and 352 differential metabolites associated with ATP-binding cassette (ABC) transporters and amino acid metabolism. These results provide an in-depth understanding of the toxicological mechanism of coumarin on S. litura.

Co-CRISPR: A valuable toolkit for mutation enrichment in the gene editing of Spodoptera frugiperda

The CRISPR/Cas9 system has been successfully applied in dozens of diverse species; although the screening of successful CRISPR/Cas9 editing events remains particularly laborious, especially for those that occur at relatively low frequency. Recently, a co-CRISPR strategy was proved to enrich the desired CRISPR events. Here, the co-CRISPR strategy was developed in the Fall armyworm, Spodoptera frugiperda, with kynurenine 3-monooxygenase gene (kmo) as a marker. The kmo mosaics induced by single-guide RNAs (sgRNAs)/Cas9 displayed the darker green color phenotype in larvae, compared with wild type (brown), and mosaic-eye adults were significantly acquired from the mosaic larvae group. In the kmo knockout strain, no significant difference was observed in larval development and adult reproduction. Acetylcholinesterase 2 (ace2) and Wnt1 were selected as target genes to construct the co-CRISPR strategy using kmo marker. By co-injection of kmo and ace2 sgRNAs, the mutant efficiency of ace2 was significantly increased in the kmo mosaic (larvae or adults) groups. Similarly, more malformed pupae with Wnt1 mutations were observed in the darker green larvae group. Taken together, these results demonstrated that kmo was a suitable visible marker gene for the application and extension of co-CRISPR strategy in Fall armyworm. Using darker green color in larvae or mosaic-eye in adults from kmo knockout as a marker, the mutant efficiency of a target gene could be enriched in a Fall armyworm group consisting of marked individuals. The co-CRISPR strategy is helpful for gene function studies by the knockout technique with no or lethal phenotypes.

CRISPR Cas9 mediated knockout of sex determination pathway genes in Aedes aegypti

The vector role of Aedes aegypti for viral diseases including dengue and dengue hemorrhagic fever makes it imperative for its proper control. Despite various adopted control strategies, genetic control measures have been recently focused against this vector. CRISPR Cas9 system is a recent and most efficient gene editing tool to target the sex determination pathway genes in Ae. aegypti. In the present study, CRISPR Cas9 system was used to knockout Ae. aegypti doublesex (Aaedsx) and Ae. aegypti sexlethal (AaeSxl) genes in Ae. aegypti embryos. The injection mixes with Cas9 protein (333 ng ul^-1) and gRNAs (each at 100 ng ul^-1) were injected into eggs. Injected eggs were allowed to hatch at 26 ± 1°C, 60 ± 10% RH. The survival and mortality rate was recorded in knockout Aaedsx and AaeSxl. The results revealed that knockout produced low survival and high mortality. A significant percentage of eggs (38.33%) did not hatch as compared to control groups (P value 0.00). Highest larval mortality (11.66%) was found in the knockout of Aaedsx female isoform, whereas, the emergence of only male adults also showed that the knockout of Aaedsx (female isoform) does not produce male lethality. The survival (3.33%) of knockout for AaeSxl eggs to the normal adults suggested further study to investigate AaeSxl as an efficient upstream of Aaedsx to target for sex transformation in Ae. aegypti mosquitoes.

A brief review on oryzacystatin: a potent phytocystatin for crop management

Phytocystatins are a type of proteinase inhibitor which are extensively studied for their specific inhibitory action against cysteine protease enzymes (CP) of insects and pathogens. Oryzacystatins (OC), a phytocystatin from rice inhibits CP in a reversible manner with its conserved tripartite wedge. OCs have important role in plant innate defense mechanism through phytohormonal signalling pathways. OC are induced in response to both biotic and abiotic stress conditions and are used to develop transgenic plants exhibiting resistance against stress conditions. In this review, we focus on the structure and mechanism of action of oryzacystatins, their possible role in plant physiology, biotic and abiotic stress tolerance mechanism in plants and their potential application strategies for future crop management studies.

CRISPR/Cas9-Mediated genomic knock out of tyrosine hydroxylase and yellow genes in cricket Gryllus bimaculatus

Gryllus bimaculatus is an emerging model organism in various fields of biology such as behavior, neurology, physiology and genetics. Recently, application of reverse genetics provides an opportunity of understanding the functional genomics and manipulating gene regulation networks with specific physiological response in G. bimaculatus. By using CRISPR/Cas9 system in G. bimaculatus, we present an efficient knockdown of Tyrosine hydroxylase (TH) and yellow-y, which are involved in insect melanin and catecholamine-biosynthesis pathway. As an enzyme catalyzing the conversion of tyrosine to 3,4-dihydroxyphenylalanine, TH confines the first step reaction in the pathway. Yellow protein (dopachrome conversion enzyme, DCE) is also involved in the melanin biosynthetic pathway. The regulation system and molecular mechanism of melanin biogenesis in the pigmentation and their physiological functions in G. bimaculatus hasn't been well defined by far for lacking of in vivo models. Deletion and insertion of nucleotides in target sites of both TH and Yellow are detected in both F0 individuals and the inheritable F1 progenies. We confirm that TH and yellow-y are down-regulated in mutants by quantitative real-time PCR analysis. Compared with the control group, mutations of TH and yellow-y genes result in defects in pigmentation. Most F0 nymphs with mutations of TH gene die by the first instar, and the only adult had significant defects in the wings and legs. However, we could not get any homozygotes of TH mutants for all the F2 die by the first instar. Therefore, TH gene is very important for the growth and development of G. bimaculatus. When the yellow-y gene is knocked out, 71.43% of G. bimaculatus are light brown, with a slight mosaic on the abdomen. The yellow-y gene can be inherited stably through hybridization experiment with no obvious phenotype except lighter cuticular color. The present loss of function study indicates the essential roles of TH and yellow in pigmentation, and TH possesses profound and extensive effects of dopamine synthesis in embryonic development in G. bimaculatus.

CRISPR-Cas Genome Editing for Insect Pest Stress Management in Crop Plants

Global crop yield and food security are being threatened by phytophagous insects. Innovative methods are required to increase agricultural output while reducing reliance on hazardous synthetic insecticides. Using the revolutionary CRISPR-Cas technology to develop insect-resistant plants appears to be highly efficient at lowering production costs and increasing farm profitability. The genomes of both a model insect, Drosophila melanogaster, and major phytophagous insect genera, viz. Spodoptera, Helicoverpa, Nilaparvata, Locusta, Tribolium, Agrotis, etc., were successfully edited by the CRISPR-Cas toolkits. This new method, however, has the ability to alter an insect’s DNA in order to either induce a gene drive or overcome an insect’s tolerance to certain insecticides. The rapid progress in the methodologies of CRISPR technology and their diverse applications show a high promise in the development of insect-resistant plant varieties or other strategies for the sustainable management of insect pests to ensure food security. This paper reviewed and critically discussed the use of CRISPR-Cas genome-editing technology in long-term insect pest management. The emphasis of this review was on the prospective uses of the CRISPR-Cas system for insect stress management in crop production through the creation of genome-edited crop plants or insects. The potential and the difficulties of using CRISPR-Cas technology to reduce pest stress in crop plants were critically examined and discussed.

CRISPR/Cas9 for Insect Pests Management: A Comprehensive Review of Advances and Applications

Insect pests impose a serious threat to agricultural productivity. Initially, for pest management, several breeding approaches were applied which have now been gradually replaced by genome editing (GE) strategies as they are more efficient and less laborious. CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeat/CRISPR-associated system) was discovered as an adaptive immune system of bacteria and with the scientific advancements, it has been improvised into a revolutionary genome editing technique. Due to its specificity and easy handling, CRISPR/Cas9-based genome editing has been applied to a wide range of organisms for various research purposes. For pest control, diverse approaches have been applied utilizing CRISPR/Cas9-like systems, thereby making the pests susceptible to various insecticides, compromising the reproductive fitness of the pest, hindering the metamorphosis of the pest, and there have been many other benefits. This article reviews the efficiency of CRISPR/Cas9 and proposes potential research ideas for CRISPR/Cas9-based integrated pest management. CRISPR/Cas9 technology has been successfully applied to several insect pest species. However, there is no review available which thoroughly summarizes the application of the technique in insect genome editing for pest control. Further, authors have highlighted the advancements in CRISPR/Cas9 research and have discussed its future possibilities in pest management.

A detailed landscape of CRISPR-Cas-mediated plant disease and pest management

Genome editing technology has rapidly evolved to knock-out genes, create targeted genetic variation, install precise insertion/deletion and single nucleotide changes, and perform large-scale alteration. The flexible and multipurpose editing technologies have started playing a substantial role in the field of plant disease management. CRISPR-Cas has reduced many limitations of earlier technologies and emerged as a versatile toolbox for genome manipulation. This review summarizes the phenomenal progress of the use of the CRISPR toolkit in the field of plant pathology. CRISPR-Cas toolbox aids in the basic studies on host-pathogen interaction, in identifying virulence genes in pathogens, deciphering resistance and susceptibility factors in host plants, and engineering host genome for developing resistance. We extensively reviewed the successful genome editing applications for host plant resistance against a wide range of biotic factors, including viruses, fungi, oomycetes, bacteria, nematodes, insect pests, and parasitic plants. Recent use of CRISPR-Cas gene drive to suppress the population of pathogens and pests has also been discussed. Furthermore, we highlight exciting new uses of the CRISPR-Cas system as diagnostic tools, which rapidly detect pathogenic microorganism. This comprehensive yet concise review discusses innumerable strategies to reduce the burden of crop protection.

Melanin Synthesis Pathway Interruption: CRISPR/Cas9-mediated Knockout of dopa decarboxylase (DDC) in Harmonia axyridis (Coleoptera: Coccinellidae)

CRISPR/Cas9 technology is a very powerful genome editing tool and has been used in many insect species for functional genomics studies through targeted gene mutagenesis. Here, we successfully established CRISPR/Cas9 research platform in Asian multi-colored ladybird beetle, Harmonia axyridis, an important natural enemy in biological control. In this study, one pivotal gene dopa decarboxylase (DDC) in melanin synthesis was targeted by CRISPR/Cas9 to generate mutants in H. axyridis by CRISPR/Cas9 technology. Our results showed that injection of single guide RNA of the DDC and Cas9 protein into preblastoderm eggs induced one insertion and four deletion (indels) mutant H. axyridis. Mutations of HaDDC gene generated 25% mutant rate with melanin missing phenotype in larva, pupa,l and adult stage. The predation ability of the fourth instar larvae has no significant difference between wild (control) and mutant H. axyridis (G0), while these mutant fourth instar larvae had longer developmental period than that of the wild type. Consequently, the total predation of the fourth instar larvae was significantly increased in H. axyridis mutants comparing with the wild type. These results indicated that the success of CRISPR/Cas9 gene editing in H. axyridis. The gene editing platform in H. axyridis would facilitate the gene function research and promote special strain of predatory ladybird beetle generation.

CRISPR/Cas9-mediated Serine protease 2 disruption induces male sterility in Spodoptera litura

Male fertility is essential for reproduction and population growth in animals. Many factors affect male fertility, such as courtship behavior, sperm quantity, and sperm motility, among others. Seminal Fluid Proteins (SFPs) are vital components of seminal fluid in the male ejaculate, which affect male fertility, sperm activation, and female ovulation. However, the knowledge of SFPs is insufficient; the function of many SFPs remains unknown, and most described functions were mainly characterized in Drosophila or other laboratory models. Here, we focus on the Serine protease 2 (Ser2) gene in the lepidopteran pest Spodoptera litura. The Ser2 gene was specifically expressed in male adults. Disruption of the Ser2 gene mediated by CRISPR/Cas9 induced male sterility but females remained fertile. PCR-based detection of the next-generation mutants showed that male sterility was stably inherited. The qRT-PCR analysis of SlSer2 mutants showed that motor protein family genes and structural protein family genes were down-regulated, while protein modification family genes were up-regulated, suggesting that SlSer2 may be involved in sperm movement and activity. These results demonstrate that Ser2 is an important component of SFPs in seminal fluid and was identified for a useful sterile gene for pest control that may lead to new control strategies for lepidopteran insect pests such as S. litura.

CRISPR/Cas9 mediates efficient site-specific mutagenesis of the odorant receptor co-receptor (Orco) in the malaria vector Anopheles sinensis

BACKGROUND

Anopheles sinensis is the most widely distributed mosquito species and is the main transmitter of Plasmodium vivax malaria in China. Most previous research has focused on the mechanistic understanding of biological processes in An. sinensis and novel ways of interrupting malaria transmission. However, the development of functional genomics and genetics-based vector control strategies against An. sinensis remain limited because of insufficient site-specific genome editing tools.

RESULTS

We report the first successful application of the CRISPR/Cas9 mediated knock-in for highly efficient, site-specific mutagenesis in An. sinensis. The EGFP marker gene driven by the 3 × P3 promoter was precisely integrated into the odorant receptor co-receptor (Orco) by direct injections of Cas9 protein, double-stranded DNA donor, and Orco-gRNA. We achieved a mutation rate of 3.77%, similar to rates in other mosquito species. Precise knock-in at the intended locus was confirmed by polymerase chain reaction (PCR) amplification and sequencing. The Orco mutation severely impaired mosquito sensitivity to some odors and their ability to locate and discriminate a human host.

CONCLUSION

Orco was confirmed as a key mediator of multiple olfactory-driven behaviors in the An. sinensis life cycle, highlighting the importance of Orco as a key molecular target for malaria control. The results also demonstrated that CRISPR/Cas9 was a simple and highly efficient genome editing technique for An. sinensis and could be used to develop genetic control tools for this vector. © 2022 Society of Chemical Industry.

Masculinizer and Doublesex as Key Factors Regulate Sexual Dimorphism in Ostrinia furnacalis

Simple Summary

In animals, sexually dimorphic traits are ubiquitous and play vital roles in reproduction, courtship, and environmental adaptation, especially in insects. In this study, we used the CRISPR/Cas9 genome editing system to generate somatic mutations of the Masculinizer (Masc) and doublesex (dsx) genes in the sex determination pathway of Ostrinia furnacalis. The OfMasc and Ofdsx genes are structural orthologs of the key sex regulation factors in Bombyx mori. Mutation of the OfMasc and Ofdsx genes induced abnormal external genitalia, adult sterility, and sex reversal of sexually dimorphic traits including wing pigmentation, gene expression patterns, and dsx sex-specific splicing. These results demonstrate that the Masc and dsx genes are conserved factors in sexually dimorphic traits, and therefore represent potential target genes in the effort to control O. furnacalis and other lepidopteran pests.

Abstract

Sex determination is an important and traditional biological process. In Lepidoptera, Masculinizer (Masc) and doublesex (dsx) are the essential genes for sex determination and play critical roles in sexual differentiation and development. The functions of Masc and dsx have been characterized in several model insect species. However, the molecular mechanism and sex determination functions of Masc and dsx in Ostrinia furnacalis, an agricultural pest, are still unknown. Here, we successfully used the CRISPR/Cas9 genome editing system to knock out OfMasc and Ofdsx. Mutation of OfMasc induced male external genital defects and sterility. Disruptions of the Ofdsx common region caused sex-specific defects in the external genitals and adult sterility. In addition, we found that OfMasc and Ofdsx can regulate the pigmentation genes that control wing pigmentation patterns. These results demonstrate that OfMasc and Ofdsx play key roles in the sex determination of O. furnacalis, and suggest novel genetic control approaches for the management of pests, including O. furnacalis.

Biotechnological Approaches for Host Plant Resistance to Insect Pests

Annually, the cost of insect pest control in agriculture crosses billions of dollars around the world. Until recently, broad-spectrum synthetic pesticides were considered as the most effective means of pest control in agriculture. However, over the years, the overreliance on pesticides has caused adverse effects on beneficial insects, human health and the environment, and has led to the development of pesticide resistant insects. There is a critical need for the development of alternative pest management strategies aiming for minimum use of pesticides and conservation of natural enemies for maintaining the ecological balance of the environment. Host plant resistance plays a vital role in integrated pest management but the development of insect-resistant varieties through conventional ways of host plant resistance takes time, and is challenging as it involves many quantitative traits positioned at various loci. Biotechnological approaches such as gene editing, gene transformation, marker-assisted selection etc. in this direction have recently opened up a new era of insect control options. These could contribute towards about exploring a much wider array of novel insecticidal genes that would otherwise be beyond the scope of conventional breeding. Biotechnological interventions can alter the gene expression level and pattern as well as the development of transgenic varieties with insecticidal genes and can improve pest management by providing access to novel molecules. This review will discuss the emerging biotechnological tools available to develop insect-resistant engineered crop genotypes with a better ability to resist the attack of insect pests.

First Report on CRISPR/Cas9-Based Genome Editing in the Destructive Invasive Pest Tuta Absoluta (Meyrick) (Lepidoptera: Gelechiidae)

The tomato leaf miner Tuta absoluta (Meyrick) is one of the world’s most destructive pests of tomato, and because of its severe economic impacts, as well as the development of pesticide resistance, the species has been intensively studied, especially in regard to the identification of targets for T. absoluta control. However, functional genomic studies of T. absoluta have been constrained by a lack of effective genetic tools. Therefore, the aim of the present study was to develop a CRISPR/Cas9 zygote microinjection protocol for generating heritable mutations in T. absoluta, using the ommochrome synthesis gene cinnabar as an easily evaluated target gene. The injection of fertilised eggs with Cas9 protein and four sgRNAs, which targeted cinnabar exon 3, resulted in a mutagenesis rate of 31.9% for eggs reaching adulthood, and cinnabar mutagenesis resulted in either red or mosaic eye colour phenotypes. As such, this study is the first to report a complete and detailed CRISPR/Cas9 workflow for the efficient genome editing of the globally important invasive pest T. absoluta. The application of this robust genome-editing tool to T. absoluta will greatly facilitate the discovery of suitable RNAi control targets and the subsequent development of novel control strategies.

CRISPR/Cas9-Mediated Mutagenesis of Abdominal-A and Ultrabithorax in the Asian Corn Borer, Ostrinia furnacalis

Simple Summary

Homeotic genes encode transcription factors that coordinated the anatomical structure formation during the early embryonic development of organisms. In this study, we functionally characterized two homeotic genes, Abdominal-A (Abd-A) and Ultrabithorax (Ubx), in the Asian corn borer, Ostrinia furnacalis (a maize pest that has devastated the Asia-Pacific region) by using a CRISPR/Cas9 genome editing system. Our results show that the mutagenesis of OfAbd-A and OfUbx led to severe morphological defects in O. furnacalis, which included fused segments and segmental twist during the larval stage, and hollowed and incision-like segments during the pupal stage in OfAbd-A mutants, as well as defects in the wing-pad development in pupal and adult OfUbx mutants. Overall, knocking out Abd-A and Ubx in O. furnacalis resulted in the embryonic lethality to, and pleiotropic impact on, other homeotic genes. This study not only confirms the conserved body planning functions in OfAbd-A and OfUbx, but it also strengthens the control implications of these homeotic genes for lepidopteran pests.

Abstract

(1) Background: Abdominal-A (Abd-A) and Ultrabithorax (Ubx) are homeotic genes that determine the identity and morphology of the thorax and abdomen in insects. The Asian corn borer, Ostrinia furnacalis (Guenée) (Lepidoptera: Pyralidae), is a devastating maize pest throughout Asia, the Western Pacific, and Australia. Building on previous knowledge, we hypothesized that the knockout of Abd-A and Ubx would disrupt the abdominal body planning in O. furnacalis. (2) Methods: CRISPR/Cas9-targeted mutagenesis was employed to decipher the functions of these homeotic genes. (3) Results: Knockout insects demonstrated classical homeotic transformations. Specifically, the mutagenesis of OfAbd-A resulted in: (1) Fused segments and segmental twist during the larval stage; (2) Embryonic lethality; and (3) The pleiotropic upregulation of other homeotic genes, including Lab, Pd, Dfd, Antp, and Abd-B. The mutagenesis of OfUbx led to: (1) Severe defects in the wing pads, which limited the ability of the adults to fly and mate; (2) Female sterility; and (3) The pleiotropic upregulation of other homeotic genes, including Dfd, Abd-B, and Wnt1. (4) Conclusions: These combined results not only support our hypothesis, but they also strengthen the potential of using homeotic genes as molecular targets for the genetic control of this global insect pest.

Evaluating the pesticidal impact of plant protease inhibitors: lethal weaponry in the co-evolutionary battle

In the arsenal of plant defense, protease inhibitors (PIs) are well-designed defensive products to counter field pests. PIs are produced in plant tissues by means of 'stable defense metabolite' and triggered on demand as the perception of the signal and well established as a part of plant active defense. PIs have been utilized for approximately four decades, initially as a gene-alone approach that was later replaced by multiple gene pyramiding/gene stacking due to insect adaptability towards the PI alone. By considering the adaptive responses of the pest to the single insecticidal gene, the concept of gene pyramiding gained continuous appreciation for the development of transgenic crops to deal with co-evolving pests. Gene pyramiding approaches are executed to bypass the insect's adaptive responses against PIs. Stacking PIs with additional insecticidal proteins, plastid engineering, recombinant proteinase inhibitors, RNAi-based methods and CRISPR/Cas9-mediated genome editing are the advanced tools and methods for next-generation pest management. Undoubtedly, the domain associated with the mechanism of PIs in the course of plant-pest interactions will occupy a central role for the advancement of more efficient and sustainable pest control strategies. © 2021 Society of Chemical Industry.

Metabolic-based insecticide resistance mechanism and ecofriendly approaches for controlling of beet armyworm Spodoptera exigua: a review

The beet army worm, Spodoptera exigua, is a widely distributed polyphagous pest of economically important crops worldwide. The management of this pest insect continues to face many challenges. Despite synthetic chemicals posing a serious threat to the environment, these remain the conventional approach for controlling S. exigua in the field. An over-reliance on chemical control has not only led to selection for resistance to insecticides and to a reduction of natural enemies, but has also polluted various components of ecosystem. Given these increasing pressures on the ecosystem, there is a need to implement integrated pest management (IPM) approaches exploiting a wider range of tools (biotechnological approaches, microbial control, biological control, cultural control, and use of host plant resistance) for an alternative to chemical control. The IPM approach can not only reduce the hazard of chemical residues in the environment and associated health problems, but may also provide best strategies to control insect pests. This review synthesizes published information on insecticide resistance of S. exigua and explores alternative IPM approaches to control S. exigua.

A cytorhabdovirus-based expression vector in Nilaparvata lugens, Laodelphax striatellus, and Sogatella furcifera

The brown planthopper (BPH, Nilaparvata lugens), the small brown planthopper (SBPH, Laodelphax striatellus), and the white-backed planthopper (WBPH, Sogatella furcifera) are problematic insect pests and cause severe yield losses through phloem sap-sucking and virus transmission. Barley yellow striate mosaic virus (BYSMV), a plant cytorhabdovirus, has been developed as versatile expression platforms in SBPHs and cereal plants. However, bio-safe overexpression vectors based on recombinant BYSMV (rBYSMV) remain to be developed and applied to the three kinds of planthoppers. Here, we found that rBYSMV was able to infect SBPHs, BPHs and WBPHs through microinjection with crude extracts from rBYSMV-infected barley leaves. To ensure bio-safety of the rBYSMV vectors, we generated an rBYSMV mutant by deleting the accessory protein P3, a putative viral movement protein. As expected, the resulting mutant abolished viral systemic infection in barley plants but had no effects on BYSMV infectivity in insect vectors. Subsequently, we used the modified rBYSMV vector to overexpress iron transport peptide (ITP) in the three kinds of planthoppers and revealed the potential functions of ITP. Overall, our results provide bio-safe overexpression platforms to facilitate functional genomics studies of planthoppers.

CRISPR/Cas9 in lepidopteran insects: Progress, application and prospects

Clustered regularly spaced short palindrome repeats (CRISPR) structure family forms the acquired immune system in bacteria and archaea. Recent advances in CRISPR/Cas genome editing as derived from prokaryotes, confirmed the characteristics of robustness, high target specificity and programmability, and also revolutionized the insect sciences field. The successful application of CRISPR in a wide variety of lepidopteran insects, with a high genetic diversity, provided opportunities to explore gene functions, insect modification and pest control. In this review, we present a detailed overview on the recent progress of CRISPR in lepidopteran insects, and described the basic principles of the system and its application. Major interest is on wing development, pigmentation, mating, reproduction, sex determination, metamorphosis, resistance and silkworm breeding innovation. Finally, we outlined the limitations of CRISPR/Cas system and discussed its application prospects in lepidopteran insects.

Genome and transcriptome analysis of the beet armyworm Spodoptera exigua reveals targets for pest control

The genus Spodoptera (Lepidoptera: Noctuidae) includes some of the most infamous insect pests of cultivated plants including Spodoptera frugiperda, Spodoptera litura, and Spodoptera exigua. To effectively develop targeted pest control strategies for diverse Spodoptera species, genomic resources are highly desired. To this aim, we provide the genome assembly and developmental transcriptome comprising all major life stages of S. exigua, the beet armyworm. Spodoptera exigua is a polyphagous herbivore that can feed on > 130 host plants, including several economically important crops. The 419 Mb beet armyworm genome was sequenced from a female S. exigua pupa. Using a hybrid genome sequencing approach (Nanopore long-read data and Illumina short read), a high-quality genome assembly was achieved (N50 = 1.1 Mb). An official gene set (18,477 transcripts) was generated by automatic annotation and by using transcriptomic RNA-seq datasets of 18 S. exigua samples as supporting evidence. In-depth analyses of developmental stage-specific expression combined with gene tree analyses of identified homologous genes across Lepidoptera genomes revealed four potential genes of interest (three of them Spodoptera-specific) upregulated during first- and third-instar larval stages for targeted pest-outbreak management. The beet armyworm genome sequence and developmental transcriptome covering all major developmental stages provide critical insights into the biology of this devastating polyphagous insect pest species worldwide. In addition, comparative genomic analyses across Lepidoptera significantly advance our knowledge to further control other invasive Spodoptera species and reveals potential lineage-specific target genes for pest control strategies.

Genome editing for resistance against plant pests and pathogens

The conventional breeding of crops struggles to keep up with increasing food needs and ever-adapting pests and pathogens. Global climate changes have imposed another layer of complexity to biological systems, increasing the challenge to obtain improved crop cultivars. These dictate the development and application of novel technologies, like genome editing (GE), that assist targeted and fast breeding programs in crops, with enhanced resistance to pests and pathogens. GE does not require crossings, hence avoiding the introduction of undesirable traits through linkage in elite varieties, speeding up the whole breeding process. Additionally, GE technologies can improve plant protection by directly targeting plant susceptibility (S) genes or virulence factors of pests and pathogens, either through the direct edition of the pest genome or by adding the GE machinery to the plant genome or to microorganisms functioning as biocontrol agents (BCAs). Over the years, GE technology has been continuously evolving and more so with the development of CRISPR/Cas. Here we review the latest advancements of GE to improve plant protection, focusing on CRISPR/Cas-based genome edition of crops and pests and pathogens. We discuss how other technologies, such as host-induced gene silencing (HIGS) and the use of BCAs could benefit from CRISPR/Cas to accelerate the development of green strategies to promote a sustainable agriculture in the future.

Chromosome-level genome reference and genome editing of the tea geometrid

The tea geometrid is a destructive insect pest on tea plants, which seriously affects tea production in terms of both yield and quality and causes severe economic losses. The tea geometrid also provides an important study system to address the ecological adaptive mechanisms underlying its unique host plant adaptation and protective resemblance. In this study, we fully sequenced and de novo assembled the reference genome of the tea geometrid, Ectropis grisescens, using long sequencing reads. We presented a highly continuous, near-complete genome reference (787.4 Mb; scaffold N50: 26.9 Mb), along with the annotation of 18,746 protein-coding genes and 53.3% repeat contents. Importantly, we successfully placed 97.8% of the assembly in 31 chromosomes based on Hi-C interactions and characterized the sex chromosome based on sex-biased sequencing coverage. Multiple quality-control assays and chromosome-scale synteny with the model species all supported the high quality of the presented genome reference. We focused biological annotations on gene families related to the host plant adaptation and camouflage in the tea geometrid and performed comparisons with other representative lepidopteran species. Important findings include the E. grisescens-specific expansion of CYP6 P450 genes that might be involved in metabolism of tea defensive chemicals and unexpected massive expansion of gustatory receptor gene families that suggests potential polyphagy for this tea pest. Furthermore, we developed an efficient genome editing system based on CRISPR/Cas9 technology and successfully implement mutagenesis of a Hox gene in the tea geometrid. Our study provides key genomic resources both for exploring unique mechanisms underlying the ecological adaptation of tea geometrids and for developing environment-friendly strategies for tea pest management.

Cytotoxicity against human breast carcinoma cells of silver nanoparticles biosynthesized using Capsosiphon fulvescens extract

Targeting cancer cells with small nanoparticles is a novel and promising approach to cancer therapy. Breast cancer is the most common cancer afflicting women worldwide. In the present study, silver nanoparticles (AgNPs) were synthesized using the aqueous extract of the marine alga Capsosiphon (C.) fulvescens, and the cytotoxicity and anti-cancer activities of the nanoparticles against MCF-7 breast cancer cells were analyzed. Nanoparticle formation was confirmed by solution color change and UV-Vis spectroscopy. The size and distribution of the C. fulvescens-biosynthesized silver nanoparticles (CfAgNPs) were then examined using various analytical methods; the particle size was around 20-22 nm and spherical in shape with no agglomeration. Cytotoxicity analysis revealed that the inhibitory concentration (IC₅₀) of CfAgNPs was 50 μg/ml. MCF-7 cell viability decreased with increasing concentrations of CfAgNPs. MCF-7 cells were evaluated for morphological changes before and after treatment with the CfAgNPs; cells treated with C. fulvescens aqueous algal extract (without CfAgNPs) showed irregular confluent aggregates with round polygonal cells, similar to the untreated control. Tamoxifen- (TMX) and CfAgNPs-treated cells show significant morphological changes. An apoptosis study was conducted using 4',6-diamidino-2-phenylindole (DAPI) staining, in which CfAgNP-treated MCF-7 cells generated bright blue fluorescence and shortened, disjointed chromatin was evident; control cells displayed less bright fluorescence. Flow cytometry analysis revealed that the percentage of cells in late apoptosis was high following treatment with TMX (77.2%) and CfAgNP (74.6%). A novel anti-cancer agent, developed by generating silver nanoparticles from C. fulvescens extract, showed strong cytotoxic activity against MCF-7 cells.

Functional conservation and diversification of yellow-y in lepidopteran insects

The diverse colors and patterns found in Lepidoptera are important for success of these species. Similar to the wings of adult butterflies, lepidopteran larvae exhibit diverse color variations to adapt to their habitats. Compared with butterfly wings, however, less attention has been paid to larval body colorations and patterns. In the present study, we focus on the yellow-y gene, which participates in the melanin synthesis pathway. We conducted CRISPR/Cas9-mediated targeted mutagenesis of yellow-y in the tobacco cutworm Spodoptera litura. We analyzed the role of S. litura yellow-y in pigmentation by morphological observation and discovered that yellow-y is necessary for normal black pigmentation in S. litura. We also showed species- and tissue-specific requirements of yellow-y in pigmentation in comparison with those of Bombyx mori yellow-y mutants. Furthermore, we found that almost none of the yellow-y mutant embryos hatched unaided. We provide evidence that S. litura yellow-y has a novel important function in egg hatching, in addition to pigmentation. The present study will enable a greater understanding of the functions and diversification of the yellow-y gene in insects.

Disruption of the ovarian serine protease (Osp) gene causes female sterility in Bombyx mori and Spodoptera litura

BACKGROUND

Precise regulation of oogenesis is crucial to female reproduction. Seventy percent of pests belong to lepidopteran species, so it would be interesting to explore the highly conserved genes involved in oogenesis that do not affect growth and development in the lepidopteran model, Bombyx mori. This can provide potential target genes for pest control and promote the development of insect sterility technology.

RESULTS

In lepidopteran species, ovarian serine protease (Osp), which encodes a member of the serine protease family, is essential for oogenesis. In this study, we used transgenic CRISPR/Cas9 technology to obtain Osp mutants in the model lepidopteran insect Bombyx mori and in the lepidopteran agricultural pest Spodoptera litura. Sequence analysis of mutants revealed an array of deletions in Osp loci in both species. We found that the deletion of Osp resulted in female sterility, whereas male fertility was not affected. Although B. mori and S. litura mutant females mated normally, they laid fewer eggs than wild-type females and eggs did not hatch.

CONCLUSION

Osp is crucial for female reproductive success in two species of Lepidoptera. As the Osp gene is highly conserved in insect species, this gene is a potential molecular target for genetic-based pest management. © 2019 Society of Chemical Industry.

Protease inhibitors: recent advancement in its usage as a potential biocontrol agent for insect pest management

Plant-derived protease inhibitors (PIs) are a promising defensin for crop improvement and insect pest management. Although agronomist made significant efforts in utilizing PIs for managing insect pests, the potentials of PIs are still obscured. Insect ability to compensate nutrient starvation induced by dietary PI feeding using different strategies, that is, overexpression of PI-sensitive protease, expression of PI-insensitive proteases, degradation of PI, has made this innumerable collection of PIs worthless. A practical challenge for agronomist is to identify potent PI candidates, to limit insect compensatory responses and to elucidate insect compensatory and resistance mechanisms activated upon herbivory. This knowledge could be further efficiently utilized to identify potential targets for RNAi-mediated pest control. These vital genes of insects could be functionally annotated using the advanced gene-editing technique, CRISPR/Cas9. Contemporary research is exploiting different in silico and modern molecular biology techniques to utilize PIs in controlling insect pests efficiently. This review is structured to update recent advancements in this field, along with its chronological background.

The C-type lectin IML-10 promotes hemocytic encapsulation by enhancing aggregation of hemocytes in the Asian corn borer Ostrinia furnacalis

C-type lectins participate in hemocytic encapsulation as pattern recognition receptors; however, the molecular mechanisms underlying their function remain unknown. In this study, we determined that the encapsulation-promoting function of a C-type lectin, IML-10, may be related to its interaction with hemocytes in the agricultural pest Ostrinia furnacalis. IML-10 possesses two carbohydrate-recognition domains (CRDs) containing EPN and QPD motifs with 4 and 6 conserved cysteine residues, respectively. IML-10 was found to mainly be secreted by the fat body into the larval plasma, and its expression was induced by Sephadex A-25 beads. Anti-IML-10 antibodies inhibited encapsulation-promoting function of IML-10 in the larval plasma. The encapsulation rate of Sephadex A-25 beads decreased from approximately 90%-30% when expression of IML-10 in O. furnacalis larvae was inhibited by RNAi. Moreover, the Sephadex bead-encapsulating ability of hemocytes decreased to almost zero in O. furnacalis larvae with IML-10 knocked out by CRISPR/Cas9, with IML-10 expression clearly decreasing compared to that of the control. Similar to the larval plasma, recombinant IML-10 promoted Sephadex bead encapsulation by hemocytes. Immunohistochemistry analysis showed that IML-10 was able to bind to the surface of both granulocytes and plasmatocytes but not to Sephadex beads as foreign objects. Furthermore, recombinant IML-10 promoted hemocyte aggregation but not adhesion. Therefore, we speculate that IML-10 binds to the surface of hemocytes to promote their aggregation and further improve their encapsulation capacity. These results contribute to clarifying the function of insect C-type lectins in encapsulation.

Bringing immersive science to undergraduate laboratory courses using CRISPR gene knockouts in frogs and butterflies

The use of CRISPR/Cas9 for gene editing offers new opportunities for biology students to perform genuine research exploring the gene-to-phenotype relationship. It is important to introduce the next generation of scientists, health practitioners and other members of society to the technical and ethical aspects of gene editing. Here, we share our experience leading hands-on undergraduate laboratory classes, where students formulate hypotheses regarding the roles of candidate genes involved in development, perform loss-of-function experiments using programmable nucleases and analyze the phenotypic effects of mosaic mutant animals. This is enabled by the use of the amphibian Xenopus laevis and the butterfly Vanessa cardui, two organisms that reliably yield hundreds of large and freshly fertilized eggs in a scalable manner. Frogs and butterflies also present opportunities to teach key biological concepts about gene regulation and development. To complement these practical aspects, we describe learning activities aimed at equipping students with a broad understanding of genome editing techniques, their application in fundamental and translational research, and the bioethical challenges they raise. Overall, our work supports the introduction of CRISPR technology into undergraduate classrooms and, when coupled with classroom undergraduate research experiences, enables hypothesis-driven research by undergraduates.

First report on CRISPR/Cas9-targeted mutagenesis in the Colorado potato beetle, Leptinotarsa decemlineata

Leptinotarsa decemlineata (Say), commonly known as the Colorado potato beetle (CPB), is an agricultural important pest for potatoes and other solanaceous plants. The CRISPR/Cas system is an efficient genome editing technology, which could be exploited to study the biology of CPB and possibly also lead to the development of better environmentally friendly pest management strategies. However, the use of CRISPR/Cas9 has been limited to only a few model insects. Here, for the first time, a CRISPR/Cas9 protocol for mutagenesis studies in CPB was developed. A gene with a clear phenotype such as the vestigial gene (vest), known to be involved in wing development in other insect species, was selected as a good indicator for the knockout study. First, vest was functionally characterized in CPB by using RNAi technology for knockdown studies. Once the expected deformed wing phenotypes were observed, a CRISPR/Cas9 work flow was established for mutagenesis in CPB. By co-injecting the Cas9 protein and a vest-guide RNA into 539 CPB eggs of <1 h old, sixty-two successfully developed to adults, among which mutation in the vest loci was confirmed in 5 of the 18 wingless CPBs (29% phenotypic mutation efficiency). The mutation in vest resulted in a clear phenotype in the CPBs, which developed to adulthood with no hindwing and elytron formed. Altogether, this study provides for the first time a useful methodology involving the use of the CRISPR/Cas9 system for mutagenesis studies in one of the most important pest insects.

Mutation of the seminal protease gene, serine protease 2, results in male sterility in diverse lepidopterans

Sterile insect technology (SIT) is an environmentally friendly method for pest control. As part of our efforts to develop a strategy that results in engineered male-sterile strains with minimum effects on viability and mating competition, we used CRISPR/Cas9 technology to disrupt Ser2, which encodes a seminal fluid protein, in the model lepidopteran insect, Bombyx mori, and an important agricultural pest, Plutella xylostella. Disruption of Ser2 resulted in dominant heritable male sterility. Wild-type females mated with Ser2-deficient males laid eggs normally, but the eggs did not hatch. We detected no differences in other reproductive behaviors in the mutant males. These results support the conclusion that Ser2 gene is necessary for male reproductive success in diverse lepidopterans. Targeting Ser2 gene has the potential to form the basis for a new strategy for pest control.

The Masc gene product controls masculinization in the black cutworm, Agrotis ipsilon

Sex determination has been studied in the model lepidopteran species Bombyx mori, but it remains poorly understood in lepidopteran pests. In the present study, we identified and characterized the Masculinizer (Masc) gene in a Noctuidae pest species, Agrotis ipsilon. Sequence analysis revealed that AiMasc encodes a protein of 658 amino acids that has two CCCH-type zinc finger domains and two conserved cysteine residues (Cys-277 and Cys-280). We assessed the masculinizing activity of AiMasc in BmN cells and found that AiMasc induced expression of the male-specific doublesex isoform. Disruption of Masc via clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) in A. ipsilon caused abnormalities in abdominal segments and external genitalia, resulting in male-specific sterility. These results suggest that Masc participates in the process of sex determination in A. ipsilon. Successful identification of sex-determination gene in a pest species may enable the development of novel genetic approaches for pest control.

Identification and functional characterization of doublesex gene in the testis of Spodoptera litura

Fusion of the testis occurs in most Lepidoptera insects, including Spodoptera litura, an important polyphagous pest. Testicular fusion in S. litura is advantageous for male reproduction, and the molecular mechanism of fusion remains unknown. Doublesex influences the formation of genitalia, the behavior of courtship, and sexually dimorphic traits in fruit-fly and silkworm, and is essential for sexual differentiation. However, its purpose in the testis of S. litura remains unknown. The doublesex gene of S. litura (Sldsx) has male-specific Sldsx^M and female-specific Sldsx^F isoforms, and exhibits a higher expression level in the male testis. At the testicular fusion stage (L6D6), Sldsx attained the highest expression compared to the pre-fusion and post-fusion periods. Moreover, Sldsx had a higher expression in the peritoneal sheaths of testis than that of germ cells in the follicle. CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/Cas9) was applied to S. litura to determine the role of Sldsx. A mixture of single guide RNA messenger RNA and Cas9 protein (300 ng/μL each) was injected into eggs within 2 h following oviposition. CRISPR/Cas9 successfully induced genomic mutagenesis of Sldsx at G₀ generation. The mutant males had smaller testis surrounded by less tracheae. Moreover, the mutant males had abnormal external genitalia and could not finish mating with wild-type females. Additionally, testes were fused for almost all mutant males. The results showed that Sldsx was not related to testicular fusion, and is required for both testis development and the formation and function of external genitalia in S. litura. The main roles of doublesex on the male are similar to other insects.

CRISPR/Cas9-mediated ebony knockout results in puparium melanism in Spodoptera litura

Insect body pigmentation and coloration are critical to adaption to the environment. To explore the mechanisms that drive pigmentation, we used the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) genome editing system to target the ebony gene in the non-model insect Spodoptera litura. Ebony is crucial to melanin synthesis in insects. By directly injecting Cas9 messenger RNA and ebony-specific guide RNAs into S. litura embryos, we successfully induced a typical ebony-deficient phenotype of deep coloration of the puparium and induction of melanin formation during the pupal stage. Polymerase chain reaction-based genotype analysis demonstrated that various mutations had occurred at the sites targeted in ebony. Our study clearly demonstrates the function of ebony in the puparium coloration and also provides a potentially useful marker gene for functional studies in S. litura as well as other lepidopteran pests.

CRISPR Disruption of BmOvo Resulted in the Failure of Emergence and Affected the Wing and Gonad Development in the Silkworm Bombyx mori

The domesticated silkworm is an economically important insect that is widely used as a lepidopteran insect model. Although somatic sex determination in the silkworm is well characterized, germline sex determination is not. Here, we used the transgenic-based CRISPR/Cas9 genome editing system to study the function of the Ovo gene in Bombyx mori. BmOvo is the homolog of a factor important in germline sex determination in Drosophila melanogaster. BmOvo mutants had abnormally shaped eggs that were disordered in the ovarioles, and gonad development was abnormal. Interestingly, wing discs and wings did not develop properly, and most of the mutants failed to eclose. Gene expression analyses by qRT-PCR showed that BmOvo gene was highly expressed in the wing disc and epidermis. Genes involved in the WNT signaling pathway and wing development genes BmWCP10 and BmE74 were downregulated in the BmOvo mutants when compared with wild-type animals. These results demonstrate that the BmOvo gene product plays an important role in wing metamorphosis. Thus, this study provides new insights into the multiple functions of BmOvo beyond germline sex determination.

Disruption of sex-specific doublesex exons results in male- and female-specific defects in the black cutworm, Agrotis ipsilon

BACKGROUND

Doublesex (dsx), the downstream gene in the insect sex-determination pathway, is a key regulator of sexually dimorphic development and behavior across a variety of insects. Manipulating expression of dsx could be useful in the genetic control of insects. However, information on the sex-specific function of dsx in non-model insects is lacking.

RESULTS

In this work, we isolated a dsx homolog, which is alternatively spliced into six female-specific and one male-specific isoforms, from an important agricultural pest, the black cutworm, Agrotis ipsilon. Studies on the expression of sex-specific Aidsx mRNA during embryonic development showed that the sixth hour post oviposition is the key stage for sex determination in A. ipsilon. Functional analysis of Aidsx was conducted using a CRISPR/Cas9 system targeting female- and male-specific Aidsx exons. Disruptions of sex-specific Aidsx exons resulted in sex-specific, sexually dimorphic defects in external genitals, gonads and antennae, and expression of sex-specific genes as well as production of offspring in both sexes.

CONCLUSION

Our results not only demonstrate that dsx is a key player determining A. ipsilon sexually dimorphic traits, but also provide a potential method for the genetic control of this pest. © 2018 Society of Chemical Industry.

Improving plant-resistance to insect-pests and pathogens: The new opportunities through targeted genome editing

The advantages of high input agriculture are fading away due to degenerating soil health and adverse effects of climate change. Safeguarding crop yields in the changing environment and dynamics of pest and pathogens, has posed new challenges to global agriculture. Thus, integration of new technologies in crop improvement has been imperative for achieving the breeding objectives in faster ways. Recently, enormous potential of genome editing through engineered nucleases has been demonstrated in plants. Continuous refinements of the genome editing tools have increased depth and breadth of their applications. So far, genome editing has been demonstrated in more than fifty plant species. These include model species like Arabidopsis, as well as important crops like rice, wheat, maize etc. Particularly, CRISPR/Cas9 based two component genome editing system has been facile with wider applicability. Potential of genome editing has unfurled enormous possibilities for engineering diverse agronomic traits including durable resistance against insect-pests and pathogens. Novel propositions of developing insect and pathogen resistant crops by genome editing include altering the effector-target interaction, knocking out of host-susceptibility genes, engineering synthetic immune receptor eliciting broad spectrum resistance, uncoupling of antagonistic action of defense hormones etc. Alternatively, modification of insect genomes has been used either to create gene drive or to counteract resistance to various insecticides. The distinct advantage of genome editing system is that it can knock out specific target region in the genome without leaving the unwanted vector backbone. In this article, we have reviewed the novel opportunities offered by the genome editing technologies for developing insect and pathogen resistant crop-types, their future prospects and anticipated challenges.

CRISPR/Cas9 mediated knockout of the abdominal-A homeotic gene in fall armyworm moth (Spodoptera frugiperda)

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is an important pest of maize in the Americas and has recently been introduced into Africa. Fall armyworm populations have developed resistance to control strategies that depend on insecticides and transgenic plants expressing Bacillus thuringiensis toxins. The study of various resistance mechanisms at the molecular level and the development novel control strategies have been hampered by a lack of functional genomic tools such as gene editing in this pest. In the current study, we explored the possibility of using the CRISPR/Cas9 system to modify the genome of FAW. We first identified and characterized the abdominal-A (Sfabd-A) gene of FAW. Sfabd-A single guide RNA (sgRNA) and Cas9 protein were then injected into 244 embryos of FAW. Sixty-two embryos injected with Sfabd-A sgRNA hatched. Of these hatched embryos, twelve developed into larvae that displayed typical aba-A mutant phenotypes such as fused segments. Of the twelve mutant larvae, three and five eventually developed into female and male moths, respectively. Most mutant moths were sterile, and one female produced a few unviable eggs when it was outcrossed to a wild-type male. Genotyping of 20 unhatched Sfabd-A sgRNA-injected embryos and 42 moths that developed from Sfabd-A sgRNA-injected embryos showed that 100% of the unhatched embryos and 50% of the moths contained indel mutations at the Sfabd-A genomic locus near the guide RNA target site. These results suggest that the CRISPR/Cas9 system is highly efficient in editing FAW genome. Importantly, this gene editing technology can be used to validate gene function to facilitate an understanding of the resistance mechanism and lead to the development of novel pest management approaches.