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BACKGROUND: Vitellogenin (Vg), known as the yolk protein precursor for oocyte development in female insects, can be secreted to plant host from salivary glands of hemipterans, including rice leafhopper Recilia dorsalis. The aim of this study was to investigate the function of salivary‐secreted Vg of R. dorsalis (RdVg) in rice host. We propose that RdVg possibly regulates the rice defense against insects, benefiting R. dorsalis feeding. RESULTS: RdVg was released into rice phloem along with saliva during R. dorsalis feeding. Knocking down RdVg increased the level of H2O2 and improved H2O2 metabolism in rice plants, making it difficult for R. dorsalis to feed. The transient expression or overexpression of the lipoprotein N‐terminal domain of RdVg (RdVg2) significantly reduced hydrogen peroxide (H2O2) metabolism in plants. This suggests that salivary‐secreted RdVg acts as an effector suppressing the H2O2 burst in rice plants, and RdVg2 is the key domain. RdVg2 could interact with rice sulfite oxidase (OsSO), which catalyzes the oxidation of SO32− and produces H2O2. Exposure of rice plants to R. dorsalis, overexpression of RdVg2 or knocking out OsSO reduced OsSO accumulation and SO32− oxidation, benefiting R. dorsalis feeding. However overexpression of OsSO increased SO32− oxidation and H2O2 metabolism, inhibiting R. dorsalis feeding. CONCLUSION: RdVg inhibits H2O2 generation via suppressing OsSO accumulation, ultimately benefiting R. dorsalis feeding. These findings identify RdVg as an effector that suppresses plant defense to insects, and provide insights into the function of salivary‐secreted Vg in other Hemiptera insects. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

SUMMARY Plants are attacked by various insect herbivores. Upon attack‐triggered biosynthesis of the phytohormone jasmonates (JAs), the JA receptor CORONATINE INSENSITIVE 1 recruits the JA‐ZIM domain (JAZ) repressors for ubiquitination, releases the MYC‐MYB transcription factor (TF) complexes, and enhances glucosinolates (GSs) biosynthesis to promote defense against insects in Arabidopsis. However, the negative regulation of JA‐regulated defense remains largely unclear. Here, we found that Arabidopsis IVa bHLH TFs bHLH19 and bHLH20 interacted with JAZs. The bhlh19/20 mutations enhanced defense against the insects Spodoptera frugiperda and S. exigua, while their overexpression inhibited defense. bHLH19/20 repressed defense via at least two layers of regulation: first, bHLH19/20 interacted with the members MYC2/3/4/5 and MYB34/51/122 of MYC‐MYB complexes, and inhibited the interaction/transcription activity of MYC2‐MYB34; second, bHLH19/20 activated the RNA level of nitrile‐specifier protein 1, which converts GSs into the less toxic nitriles. bhlh19/20 exhibited no penalty in JA‐regulated growth inhibition. Collectively, our findings reveal the molecular mechanism for negatively regulating JA‐mediated defense against insects in Arabidopsis without growth penalty by the pair of bHLH19/20 TFs. [ABSTRACT FROM AUTHOR]

The article in Integrative Zoology discusses the immune evasion mechanisms of microbial pathogens, focusing on how the entomopathogenic fungus Metarhizium robertsii inhibits cellular encapsulation in Bombyx mori. Researchers found that destruxin A (DA) synthesized by M. robertsii targets hemocytin, a protein involved in insect immune responses. The study sheds light on the interplay between pathogens and insect immune defenses, offering insights into potential pest control strategies and cellular defense mechanisms. The research was supported by the National Natural Science Foundation of China and Suzhou Medical College of Soochow University. [Extracted from the article]

The construction of a plant rhizosphere system enriched with beneficial microbes (BMs) can efficiently help plants defend against phytophagous insects. However, our comprehensive understanding of this approach is still incomplete. In this review, we methodically analyzed the progress made over the last decade, identifying both challenges and opportunities. The main methods for developing a BMs‐enriched rhizosphere system include inoculating exogenous BMs into plants, amending the existing soil microbiomes with amendments, and utilizing plants to shape the soil microbiomes. BMs can assist plants in suppressing phytophagous insects across many orders, including 13 Lepidoptera, seven Homoptera, five Hemiptera, five Coleoptera, four Diptera, and one Thysanoptera species by inducing plant systemic resistance, enhancing plant tolerance, augmenting plant secondary metabolite production, and directly suppressing herbivores. Context‐dependent factors such as abiotic and biotic conditions, as well as the response of insect herbivores, can affect the outcomes of BM‐assisted plant defense. Several challenges and opportunities have emerged, including the development of synthetic microbial communities for herbivore control, the integration of biosensors for effectiveness assessment, the confirmation of BM targets for phytophagous insect defense, and the regulation of outcomes via smart farming with artificial intelligence. This study offers valuable insights for developing a BM‐enriched rhizosphere system within an integrated pest management approach. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The review comprehensively explores factors influencing enzyme activities in insects and their implications in defense against toxicants. It encompasses a diverse array of enzymes involved in metabolizing synthetic chemicals, emphasizing their dynamic regulation. Key factors affecting enzyme activities, such as external and internal influences, are discussed, shedding light on the intricate regulatory mechanisms. The inhibitory effects of various compounds on insect GST activity are thoroughly examined, providing insights into potential avenues for insect control. The implications of insect defenses against toxicants are elucidated, emphasizing the complexity of plant–insect interactions. The review delves into the evolutionary adaptations of insects to plant defense mechanisms, highlighting the role of enzymes like thioglucosidase and myrosinase in detoxifying glucosinolates. The co-evolutionary dynamics between insects and plants, particularly in the Brassicaceae family, are explored, underscoring the intricate biochemical strategies employed by both parties. Additionally, the review addresses the challenges associated with developing pest-resistant crop plants through traditional breeding or genetic engineering. It discusses the need for a nuanced approach, considering the adaptability of insects to various toxicants and the potential drawbacks of repeated exposures. The success of chemical plant defenses, particularly monoterpene synthesis in pine trees, is noted, along with the distinctive biodegradability of plant metabolites. The review provides a thorough examination of the mechanisms underlying insect responses to toxic plant metabolites, offering valuable insights into the dynamic interplay between insects and plants. It suggests potential targets for insect control programs and highlights the importance of understanding the co-evolutionary processes that shape these interactions. [ABSTRACT FROM AUTHOR]

Background: Plants have evolved various defense mechanisms against insect herbivores, including the formation of physical barriers, the synthesis of toxic metabolites, and the activation of phytohormone responses. Although plant-associated microbiota influence plant growth and health, whether they play a role in plant defense against insect pests in natural ecosystems is unknown. Results: Here, we show that leaves of beetle-damaged weeping willow (Salix babylonica) trees are more resistant to the leaf beetle Plagiodera versicolora (Coleoptera) than those of undamaged leaves. Bacterial community transplantation experiments demonstrated that plant-associated microbiota from the beetle-damaged willow contribute to the resistance of the beetle-damaged willow to P. versicolora. Analysis of the composition and abundance of the microbiome revealed that Pseudomonas spp. is significantly enriched in the phyllosphere, roots, and rhizosphere soil of beetle-damaged willows relative to undamaged willows. From a total of 49 Pseudomonas strains isolated from willows and rhizosphere soil, we identified seven novel Pseudomonas strains that are toxic to P. versicolora. Moreover, re-inoculation of a synthetic microbial community (SynCom) with these Pseudomonas strains enhances willow resistance to P. versicolora. Conclusions: Collectively, our data reveal that willows can exploit specific entomopathogenic bacteria to enhance defense against P. versicolora, suggesting that there is a complex interplay among plants, insects, and plant-associated microbiota in natural ecosystems. 5putw3esi-W9k4EYdexs12 Video Abstract [ABSTRACT FROM AUTHOR]

The F-box protein Coronatine Insensitive (COI) is a receptor for the jasmonic acid signaling pathway in plants. To investigate the functions of the 6 maize (Zea mays) COI proteins (COI1a, COI1b, COI1c, COI1d, COI2a, and COI2b), we generated single, double, and quadruple loss-of-function mutants. The pollen of the coi2a coi2b double mutant was inviable. The coi1 quadruple mutant (coi1-4x) exhibited shorter internodes, decreased photosynthesis, leaf discoloration, microelement deficiencies, and accumulation of DWARF8 and/or DWARF9, 2 DELLA family proteins that repress the gibberellic acid (GA) signaling pathway. Coexpression of COI and DELLA in Nicotiana benthamiana showed that the COI proteins trigger proteasome-dependent DELLA degradation. Many genes that are downregulated in the coi1-4x mutant are GA-inducible. In addition, most of the proteins encoded by the downregulated genes are predicted to be bundle sheath- or mesophyll-enriched, including those encoding C4-specific photosynthetic enzymes. Heterologous expression of maize Coi genes in N. benthamiana showed that COI2a is nucleus-localized and interacts with maize jasmonate zinc-finger inflorescence meristem domain (JAZ) proteins, the canonical COI repressor partners. However, maize COI1a and COI1c showed only partial nuclear localization and reduced binding efficiency to the tested JAZ proteins. Together, these results show the divergent functions of the 6 COI proteins in regulating maize growth and defense pathways. Hormonal regulation of maize stalk height is influenced by 4 members of a gene family that has similarity to genes previously associated with insect defense induction in numerous other plant species. [ABSTRACT FROM AUTHOR]

Insects are established models for understanding host-pathogen interactions and innate immune mechanisms. The innate immune system in insects is highly efficient in recognizing and opposing pathogens that cause detrimental effects during infection. The cuticular layer which covers the superficial layer of the insect body participates in host defense and wound healing by inducing innate immune responses. Previous studies have started to address the involvement of cuticular genes in conferring resistance to insect pathogens, particularly those that infect by disrupting the insect cuticle. For example, the cuticular gene Transglutaminase (TG) in Drosophila melanogaster plays a structural role in cuticle formation and blood coagulation and also possesses immune properties against pathogenic infection. However, more information is becoming available about the immune function of other cuticular gene families in insects. In this review, we aim to highlight the recent advances in insect cuticular immunity and address the necessity of pursuing further research to fill the existing gaps in this important field of insect immunology. This information will lead to novel strategies for the efficient management of agricultural insect pests and vectors of plant and human disease. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides (AMPs) in insects are endogenous peptides that are effector components of the innate defense system of the insect. AMPs may serve as antimicrobial agents because of their small molecular weight and broad‐spectrum antimicrobial activity. In this study, we performed transcriptome analysis of cigarette beetle (Lasioderma serricorne) larvae, parasitized by the ectoparasitic wasp, Anisopteromalus calandrae. Several AMP genes were significantly upregulated following A. calandrae parasitism, postulating the hypothesis that the parasitization enhanced the host's resistance against pathogenic microorganisms through the regulation of host AMP genes. Specifically, 3 AMP genes (LsDef1, LsDef2, and LsCole) were significantly upregulated and we studied their immune function in L. serricorne. Immune challenge and functional analysis showed that LsCole was responsible for the immune response against Gram‐negative and Gram‐positive bacteria, while LsDef1 and LsDef2 were involved in insect defense against Gram‐positive bacteria. Purified recombinant LsCole exhibited antimicrobial activities against the Gram‐negative bacterium Escherichia coli and the Gram‐positive bacterium Staphylococcus aureus. LsDef2 showed an antibacterial effect against S. aureus. LsCole and LsDef2 exhibited antibiofilm activity against S. aureus. The 2 AMPs disrupted cell membranes and caused leakage of S. aureus cell contents. The results indicated that the 3 AMPs in L. serricorne are involved in the innate immunity of this pest insect. These AMPs may have potential as antimicrobial agents for bacterial infection chemotherapy. Hence, data are discussed in relation to new control strategies with greater biosafety against pest insects with use of microbial biocontrol agents in combination with RNA interference against the insect's defensive AMP genes. [ABSTRACT FROM AUTHOR]

The relationship between plants and insects has always been a hot research topic for ecologists. In order to understand the current research and development status of the relationship between plants and insects in China, we took the literature on the relationship between plants and insects published on CNKI from 2002 to 2021 as data sources, using bibliometric methods and software, such as Excel and VOSviewer, to conduct statistical analysis on the annual number of papers published, authors, institutions, journals and keywords. The results showed that the number of published papers were the least in 2002, and then the number of annual papers increased rapidly, reaching a peak in 2006, and the largest number of papers was in 2020, with an overall upward trend. From the perspective of the main authors, most authors published less than 5 papers, and only 24 authors published 5 or more papers. Chinese Academy of Sciences, Chinese Academy of Agricultural Sciences and Zhejiang University were leading scientific research institutions in this field. Judging from the source journals, Chinese Journal of Applied Entomology, Acta Entomologica Sinica, Chinese Bulletin of Entomology and Journal of Environmental Entomology had the largest number of publications, which were more favored by researchers. From the research hotspots, domestic scholars mainly focused on the selection of host plants by insects and the defense of plants against insects in the research on the relationship between plants and insects. In a word, the current research on the relationship between plants and insects had been published in domestic journals in a relatively small number and the research direction was relatively concentrated. It was expected that more researchers should publish the latest scientific research results in domestic journals to promote the development of this field. [ABSTRACT FROM AUTHOR]

Throughout evolution, arboviruses have developed various strategies to counteract the host's innate immune defenses to maintain persistent transmission. Recent studies have shown that, in addition to bacteria and fungi, the innate Toll-Dorsal immune system also plays an essential role in preventing viral infections in invertebrates. However, whether the classical Toll immune pathway is involved in maintaining the homeostatic process to ensure the persistent and propagative transmission of arboviruses in insect vectors remain unclear. In this study, we revealed that the transcription factor Dorsal is actively involved in the antiviral defense of an insect vector (Laodelphax striatellus) by regulating the target gene, zinc finger protein 708 (LsZN708), which mediates downstream immune-related effectors against infection with the plant virus (Rice stripe virus, RSV). In contrast, an antidefense strategy involving the use of the nonstructural-protein (NS4) to antagonize host antiviral defense through competitive binding to Dorsal from the MSK2 kinase was employed by RSV; this competitive binding inhibited Dorsal phosphorylation and reduced the antiviral response of the host insect. Our study revealed the molecular mechanism through which Toll-Dorsal-ZN708 mediates the maintenance of an arbovirus homeostasis in insect vectors. Specifically, ZN708 is a newly documented zinc finger protein targeted by Dorsal that mediates the downstream antiviral response. This study will contribute to our understanding of the successful transmission and spread of arboviruses in plant or invertebrate hosts. [ABSTRACT FROM AUTHOR]

Coevolution of hosts and their parasites has shaped heterogeneity of effector hemocyte types, providing immune defense reactions with variable effectiveness. In this work, we characterize hemocytes of Drosophila willistoni, a species that has evolved a cellular immune system with extensive variation and a high degree of plasticity. Monoclonal antibodies were raised and used in indirect immunofluorescence experiments to characterize hemocyte subpopulations, follow their functional features and differentiation. Pagocytosis and parasitization assays were used to determine the functional characteristics of hemocyte types. Samples were visualized using confocal and epifluorescence microscopy. We identified a new multinucleated giant hemocyte (MGH) type, which differentiates in the course of the cellular immune response to parasitoids. These cells differentiate in the circulation through nuclear division and cell fusion, and can also be derived from the central hematopoietic organ, the lymph gland. They have a binary function as they take up bacteria by phagocytosis and are involved in the encapsulation and elimination of the parasitoid. Here, we show that, in response to large foreign particles, such as parasitoids, MGHs differentiate, have a binary function and contribute to a highly effective cellular immune response, similar to the foreign body giant cells of vertebrates. [ABSTRACT FROM AUTHOR]

The midgut, a vital component of the digestive system in arthropods, serves as an interface between ingested food and the insect’s physiology, playing a pivotal role in nutrient absorption and immune defense mechanisms. Distinct cell types, including columnar, enteroendocrine, goblet and regenerative cells, comprise the midgut in insects and contribute to its robust immune response. Enterocytes/ columnar cells, the primary absorptive cells, facilitate the immune response through enzyme secretions, while regenerative cells play a crucial role in maintaining midgut integrity by continuously replenishing damaged cells and maintaining the continuity of the immune defense. The peritrophic membrane is vital to the insect’s innate immunity, shielding the midgut from pathogens and abrasive food particles. Midgut juice, a mixture of digestive enzymes and antimicrobial factors, further contributes to the insect’s immune defense, helping the insect to combat invading pathogens and regulate the midgut microbial community. The cutting-edge single-cell transcriptomics also unveiled previously unrecognized subpopulations within the insect midgut cells and elucidated the striking similarities between the gastrointestinal tracts of insects and higher mammals. Understanding the intricate interplay between midgut cell types provides valuable insights into insect immunity. This review provides a solid foundation for unraveling the complex roles of the midgut, not only in digestion but also in immunity. Moreover, this review will discuss the novel immune strategies led by the midgut employed by insects to combat invading pathogens, ultimately contributing to the broader understanding of insect physiology and defense mechanisms. [ABSTRACT FROM AUTHOR]

Introduction: Wheat stem sawfly (WSS), Cephus cinctus Norton, is a major pest of common bread wheat (Triticum aestivum L.) and other cultivated cereals in North America. Planting of cultivars with solid stems has been the primary management strategy to prevent yield loss due to WSS infestation, however expression of this phenotype can vary depending on environmental conditions and solid stems hinder biological control of WSS via braconid parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck. In the hollow stems of oat (Avena sativa L.), WSS larvae experience 100% mortality before they reach late instars, but the mechanisms for this observed resistance have not been characterized. Objective: The objective of this study was to explore additional sources of resistance outside of the historic solid stem phenotype. Methods: Here, we use an untargeted metabolomics approach to examine the response of the metabolome of two cultivars of oat and four cultivars of spring wheat to infestation by WSS. Using liquid chromatography-mass spectrometry (LC-MS), differentially expressed metabolites were identified between oat and wheat which were associated with the phenylpropanoid pathway, phospholipid biosynthesis and signaling, the salicylic acid signaling pathway, indole-3-acetic acid (IAA) degradation, and biosynthesis of 1,4-benzoxazin-3-ones (Bxs). Several phospho-and galacto-lipids were found in higher abundance in oat, and with the exception of early stem solidness cultivar Conan, both species experienced a decrease in abundance once infested. In all wheat cultivars except Conan, an increase in abundance was observed for Bxs HMDBOA-glc and DIBOA-b-Dglucoside after infestation, indicating that this pathway is involved in wheat response to infestation in both solid and hollow stemmed cultivars. Differences between species in compounds involved in IAA biosynthesis, degradation and inactivation suggest that wheat may respond to infestation by inactivating IAA or altering the IAA pool in stem tissue. Conclusion: We propose that the species differences found here likely affect the survival of WSS larvae and may also be associated with differences in stem architecture at the molecular level. Our findings suggest pathways to focus on for future studies in elucidating plant response to WSS infestation. [ABSTRACT FROM AUTHOR]

Insects constitute approximately 75% of the world's recognized fauna, with the majority of species considered as pests. Entomopathogenic fungi (EPF) are parasitic microorganisms capable of efficiently infecting insects, rendering them potent biopesticides. In response to infections, insects have evolved diverse defense mechanisms, prompting EPF to develop a variety of strategies to overcome or circumvent host defenses. While the interaction mechanisms between EPF and insects is well established, recent findings underscore that their interplay is more intricate than previously thought, especially evident across different stages of EPF infection. This review primarily focuses on the interplay between EPF and the insect defense strategies, centered around three infection stages: (1) Early infection stage: involving the pre-contact detection and avoidance behavior of EPF in insects, along with the induction of behavioral responses upon contact with the host cuticle; (2) Penetration and intrahemolymph growth stage: involving the initiation of intricate cellular and humoral immune functions in insects, while symbiotic microbes can further contribute to host resistance; (3) Host insect's death stage: involving the ultimate confrontation between pathogens and insects. Infected insects strive to separate themselves from the healthy population, while pathogens rely on the infected insects to spread to new hosts. Also, we discuss a novel pest management strategy underlying the cooperation between EPF infection and disturbing the insect immune system. By enhancing our understanding of the intricate interplay between EPF and the insect, this review provides novel perspectives for EPFmediated pest management and developing effective fungal insecticides. [ABSTRACT FROM AUTHOR]

The gut is a crucial organ in insect defense against various pathogens and harmful substances in their environment and diet. Distinct insect gut compartments possess unique functionalities contributing to their physiological processes, including immunity. The insect gut's cellular composition is vital for cellular and humoral immunity. The peritrophic membrane, mucus layer, lumen, microvilli, and various gut cells provide essential support for activating and regulating immune defense mechanisms. These components also secrete molecules and enzymes that are imperative in physiological activities. Additionally, the gut microbiota initiates various signaling pathways and produces vitamins and minerals that help maintain gut homeostasis. Distinct immune signaling pathways are activated within the gut when insects ingest pathogens or hazardous materials. The pathway induced depends on the infection or pathogen type; include immune deficiency (imd), Toll, JAK/STAT, Duox-ROS, and JNK/FOXO regulatory pathways. These pathways produce different antimicrobial peptides (AMPs) and maintain gut homeostasis. Furthermore, various signaling mechanisms within gut cells regulate insect gut recovery following infection. Although some questions regarding insect gut immunity in different species require additional study, this review provides insights into the insect gut's structure and composition, commensal microorganism roles in Drosophila melanogaster and Tenebrio molitor life cycles, different signaling pathways involved in gut immune systems, and the insect gut post-infection recovery through various signaling mechanisms. [ABSTRACT FROM AUTHOR]

Background: As a member of the immunoglobulin superfamily, hemolins play a vital role in insect development and defense against pathogens. However, the innate immune response of hemolin to baculovirus infection varies among different insects. Methods and results: In this study, the hemolin-like gene from a Crambidae insect, Cnaphalocrocis medinalis, CmHem was cloned, and its role in insect development and baculovirus infection was analyzed. A 1,528 bp contig as potential hemolin-like gene of C. medinalis was reassembled from the transcriptome. Further, the complete hemolin sequence of C. medinalis (CmHem) was cloned and sequenced. The cDNA of CmHem was 1,515 bp in length and encoded 408 amino acids. The deduced amino acid of CmHem has relatively low identities (41.9-62.3%) to various insect hemolins. However, it contains four Ig domains similarity to other insect hemolins. The expression level of CmHem was the highest in eggs, followed by pupae and adults, and maintained a low expression level at larval stage. The synthesized siRNAs were injected into mature larvae, and the CmHem transcription decreased by 51.7%. Moreover, the abdominal somites of larvae became straightened, could not pupate normally, and then died. Infection with a baculovirus, C. medinalis granulovirus (CnmeGV), the expression levels of CmHem in the midgut and fat body of C. medinalis significantly increased at 12 and 24 h, respectively, and then soon returned to normal levels. Conclusions: Our results suggested that hemolin may be related to the metamorphosis of C. medinalis. Exposure to baculovirus induced the phased expression of hemolin gene in the midgut and fat body of C. medinalis, indicated that hemolin involved in the immune recognition of Crambidae insects to baculovirus. [ABSTRACT FROM AUTHOR]

Plants emit volatiles as signals to trigger broad physiological responses, including airborne defense (AD). Gong et al. (Nature 2023; 622: 139–145) recently reported the genetic framework of how plants use AD to combat aphids and viruses. The study elucidates the mutualistic relationships between aphids and the viruses they transmit, revealing the broad biological and ecological significance of AD. [ABSTRACT FROM AUTHOR]

Insects employ multifaceted strategies to combat invading fungi, with immunity being a promising mechanism. Immune pathways function in signal transduction and amplification, ultimately leading to the activation of antimicrobial peptides (AMPs). Although several studies have shown that immune pathways are responsible for defending against fungi, the roles of parasitoid immune pathways involved in antifungal responses remain unknown. In this study, we evaluated the roles of the Toll and IMD pathways of a pupal parasitoid, Pteromalus puparum (Hymenoptera: Pteromalidae), in fighting against Beauveria bassiana (Hypocreales: Cordycipitaceae). Successful colonization of B. bassiana on P. puparum adults was confirmed by scanning electron microscopy (SEM). AMPs were induced upon B. bassiana infection. The knockdown of key genes, PpTollA and PpIMD, in Toll and IMD signaling pathways, respectively, significantly compromised insect defense against fungal infection. The knockdown of either PpTollA or PpIMD in P. puparum dramatically promoted the proliferation of B. bassiana, resulting in a decreased survival rate and downregulated expression levels of AMPs against B. bassiana compared to controls. These data indicated that PpTollA and PpIMD participate in Toll and IMD-mediated activation of antifungal responses, respectively. In summary, this study has greatly broadened our knowledge of the parasitoid antifungal immunity against fungi. [ABSTRACT FROM AUTHOR]

The relationship between insect pathogenic fungi and their insect hosts is a classic example of a co-evolutionary arms race between pathogen and target host: parasites evolve towards mechanisms that increase their advantage over the host, and the host increasingly strengthens its defenses. The present review summarizes the literature data describing the direct and indirect role of lipids as an important defense mechanism during fungal infection. Insect defense mechanisms comprise anatomical and physiological barriers, and cellular and humoral response mechanisms. The entomopathogenic fungi have the unique ability to digest the insect cuticle by producing hydrolytic enzymes with chitin-, lipo- and proteolytic activity; besides the oral tract, cuticle pays the way for fungal entry within the host. The key factor in insect resistance to fungal infection is the presence of certain types of lipids (free fatty acids, waxes or hydrocarbons) which can promote or inhibit fungal attachment to cuticle, and might also have antifungal activity. Lipids are considered as an important source of energy, and as triglycerides are stored in the fat body, a structure analogous to the liver and adipose tissue in vertebrates. In addition, the fat body plays a key role in innate humoral immunity by producing a range of bactericidal proteins and polypeptides, one of which is lysozyme. Energy derived from lipid metabolism is used by hemocytes to migrate to the site of fungal infection, and for phagocytosis, nodulation and encapsulation. One polyunsaturated fatty acid, arachidonic acid, is used in the synthesis of eicosanoids, which play several crucial roles in insect physiology and immunology. Apolipoprotein III is important compound with antifungal activity, which can modulate insect cellular response and is considered as important signal molecule. [ABSTRACT FROM AUTHOR]

The chemical defense of insects is effective for avoiding predation, but may carry a cost in terms of life history traits. If chemical defenses require the resources and/or nutrients necessary for the larva or post-larval stages to survive, grow, and reproduce, there will be a trade-off between chemical defense and other traits, particularly in habitats where larvae are subjected to frequent predator attacks. The larvae of Osmylus hyalinatus McLachlan (Neuroptera: Osmylidae) are semiaquatic, inhabiting the edges of small streams and ponds, where they encounter multiple predators both on land and in water. Larvae of this species spray a hyaline liquid from an anal opening when disturbed. The liquid is stored in the posterior half of the hindgut. Daily stimulation of larvae to exhaust the stored liquid, thereby simulating repeated predator attacks, resulted in smaller adult body size at emergence than the control, but had little effect on the larval/pupal period, cocoon production (for predator avoidance of prepupae and pupae), reproductive potential, or chemical defense of adults in which prothoracic glands release a substance that smells unpleasant to predators. The lack of such effects is explained in part by adults gaining more resources through feeding than the larval stages, as well as nuptial gifts from males to females. The spraying liquids and silk used to spin cocoons are both discharged from an anal opening; therefore, a trade-off between these two materials is plausible and should be examined in the future. [ABSTRACT FROM AUTHOR]

Glucosinolates are secondary plant metabolites that are part of the plant's defense system against pathogens and pests and are activated via enzymatic degradation by thioglucoside glucohydrolases (myrosinases). Epithiospecifier proteins (ESPs) and nitrile-specifier proteins (NSPs) divert the myrosinase-catalyzed hydrolysis of a given glucosinolate to form epithionitrile and nitrile rather than isothiocyanate. However, the associated gene families have not been explored in Chinese cabbage. We identified three ESP and fifteen NSP genes randomly distributed on six chromosomes in Chinese cabbage. Based on a phylogenetic tree, the ESP and NSP gene family members were divided into four clades and had similar gene structure and motif composition of Brassica rapa epithiospecifier proteins (BrESPs) and B. rapa nitrile-specifier proteins (BrNSPs) in the same clade. We identified seven tandem duplicated events and eight pairs of segmentally duplicated genes. Synteny analysis showed that Chinese cabbage and Arabidopsis thaliana are closely related. We detected the proportion of various glucosinolate hydrolysates in Chinese cabbage and verified the function of BrESPs and BrNSPs in glucosinolate hydrolysis. Furthermore, we used quantitative RT-PCR to analyze the expression of BrESPs and BrNSPs and demonstrated that these genes responded to insect attack. Our findings provide novel insights into BrESPs and BrNSPs that can help further promote the regulation of glucosinolate hydrolysates by ESP and NSP to resist insect attack in Chinese cabbage. [ABSTRACT FROM AUTHOR]

Simple Summary: Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to biotic and abiotic stresses by participating in interplant communication. Because MeJA is hydrophobic and it can easily move between plant cells, it is considered a propagable form of JA, which can utilize this method to induce plant defenses. Pests are able to 'eavesdrop' on plant signal molecules as cues for activating the detoxification system to protect themselves from plant defenses, and insects have evolved a variety of mechanisms to metabolize, sequester, or detoxify plant toxins. Spodoptera litura is an omnivorous insect that damages a variety of crops worldwide. We analyzed the growth of S. litura and its detoxification ability against xanthotoxin after exposure to different concentrations of MeJA fumigation, and the effective role of MeJA in inducing insects' defense response to the toxin was studied. We demonstrated that MeJA is effective at inducing S. litura defense response by increasing its detoxifying enzyme activities, but the enhanced detoxifying ability could not overcome the strong toxins. Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to interbiotic and abiotic stresses by participating in interplant communication. Despite its function in interplant communication, the specific role of MeJA in insect defense responses is poorly understood. In this study, we found that carboxylesterase (CarE) activities, glutathione-S-transferase (GSTs) activities, and cytochrome mono-oxygenases (P450s) content increased more after the feeding of diets containing xanthotoxin, while larvae exposed to MeJA fumigation also showed higher enzyme activity in a dose-dependent manner: lower and medium concentrations of MeJA induced higher detoxification enzyme activities than higher concentrations of MeJA. Moreover, MeJA improved the growth of larvae fed on the control diet without toxins and diets with lower concentrations of xanthotoxin (0.05%); however, MeJA could not protect the larvae against higher concentrations of xanthotoxin (0.1%, 0.2%). In summary, we demonstrated that MeJA is effective at inducing S. litura defense response, but the enhanced detoxifying ability could not overcome the strong toxins. [ABSTRACT FROM AUTHOR]

The first enzyme, 1-Deoxy-D-xylulose-5-phosphate synthase (DXS), in the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway for isoprenoid precursor biosynthesis has been reported to function differently according to species. However, the current state of knowledge about this gene family in Toona ciliata is limited. The TcDXS gene family was identified from the whole genome of T. ciliata by firstly using bioinformatics analysis. Then, the phylogenetic tree was built and the promoter cis-elements were predicted. Six DXS genes were identified and divided into three groups, which had similar domains and gene structure. They are located on five different chromosomes and encode products that do not vary much in size. An analysis of the cis-acting elements revealed that TcDXS genes possessed light, abiotic stress, and hormone responsive elements. Ultimately, TcDXS1/2/5 was cloned for an in-depth analysis of their subcellular localization and expression patterns. The subcellular localization results of TcDXS1/2/5 showed that they were located in the chloroplast envelope membranes. Based on tissue-specific analyses, TcDXS1/2/5 had the highest expression in mature leaves. Under Hypsipyla robusta stress, their different expressions indicated that these genes may have insect-resistance functions. This research provides a theoretical basis for further functional verification of TcDXSs in the future, and a new concept for breeding pest-resistant T. ciliata. [ABSTRACT FROM AUTHOR]

Edible insects have the potential to become one of the major future foods. In fact, they can be considered cheap, highly nutritious, and healthy food sources. International agencies, such as the Food and Agriculture Organization (FAO), have focused their attention on the consumption of edible insects, in particular, regarding their nutritional value and possible biological, toxicological, and allergenic risks, wishing the development of analytical methods to verify the authenticity, quality, and safety of insect-based products. Edible insects are rich in proteins, fats, fiber, vitamins, and minerals but also seem to contain large amounts of polyphenols able to have a key role in specific bioactivities. Therefore, this review is an overview of the potential of edible insects as a source of bioactive compounds, such as polyphenols, that can be a function of diet but also related to insect chemical defense. Currently, insect phenolic compounds have mostly been assayed for their antioxidant bioactivity; however, they also exert other activities, such as anti-inflammatory and anticancer activity, antityrosinase, antigenotoxic, and pancreatic lipase inhibitory activities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Leaf-based artificial diets allow to study the effect of chemical defenses on insects. • Tomato defenses enhanced the lethality of a bacterial entomopathogen. • Over-accumulated plant metabolites were identified after elicitation of defenses. • Plant defense elicitors contribute to the action of Bacillus thuringiensis. In nature, insect herbivory exerts continuous selective pressure on plants that, in turn, have developed a wide array of constitutive and inducible defenses to fight against attackers. Since plant defenses may affect higher trophic levels, including entomopathogens, further research is required to understand how plant compounds influence insect-pathogens interactions and their implications for integrated pest management programs. Here, we evaluated the impact of tomato defenses on the lethality produced by the bacterial entomopathogen Bacillus thuringiensis (Bt) against second instar larvae of Spodoptera exigua. We first examined the effect of constitutive defenses from fifteen wild tomato species and forty cultivated varieties (Solanum lycopersicum) on S. exigua larval growth and susceptibility to Bt. The results showed larvae fed on wild tomato species had a reduced larval growth compared to larvae fed on cultivated varieties, whereas susceptibility to Bt was similar between both groups. We then selected six cultivated varieties, including those with high and low impacts on larval growth and Bt-induced mortality, to further explore the effect of inducible defenses. Elicitation of defenses by methyl jasmonate (MeJA) reduced larval growth and increased basal mortality. Additionally, when larvae were infected with Bt, MeJA treatment further increased their susceptibility to the entomopathogen. Metabolomic analysis confirmed a reprogramming of tomato leaf metabolism following MeJA elicitation, with an induced accumulation of bioactive compounds, such as saponins or flavonoids, known for their anti-herbivory properties in most tomato varieties. Overall, these data reveal that both constitutive and inducible tomato defenses not only protect the plant by directly affecting the insect pest but also enhance the efficacy of bacterial entomopathogens. [ABSTRACT FROM AUTHOR]

Over a long period of evolution, insects have developed unique intestinal defenses against invasion by foreign microorganisms, including physical defenses and immune responses. The physical defenses of the insect gut consist mainly of the peritrophic matrix (PM) and mucus layer, which are the first barriers to pathogens. Gut microbes also prevent the colonization of pathogens. Importantly, the immune-deficiency (Imd) pathways produce antimicrobial peptides to eliminate pathogens; mechanisms related to reactive oxygen species are another important pathway for insect intestinal immunity. The janus kinase/STAT signaling pathway is involved in intestinal immunity by producing bactericidal substances and regulating tissue repair. Melanization can produce many bactericidal active substances into the intestine; meanwhile, there are multiple responses in the intestine to fight against viral and parasitic infections. Furthermore, intestinal stem cells (ISCs) are also indispensable in intestinal immunity. Only the coordinated combination of the intestinal immune defense system and intestinal tissue renewal can effectively defend against pathogenic microorganisms. [ABSTRACT FROM AUTHOR]

Marine insects are constantly exposed to ultraviolet radiation. How the marine insect Hemiptera: Gerridae responds to UV stress and the molecular mechanisms underlying this adaptation are still unknown. This study analyzed the adaptability of marine insects that are constantly exposed to UV radiation by extracting anti-UV compounds produced by these marine insects. These marine insects have the ability to produce anti-UV B compounds and anti UV A compound with a high point of absorbance, because it is able to absorb UV-B (280 nm-320 nm) with the highest absorbance value at point 4 with a wavelength of 280 nm - 300 nm, and is also capable to absorb UV-A (320 nm - 400 nm) with the highest absorbance value at point 3.5 with a wavelength of 340 nm. [ABSTRACT FROM AUTHOR]

The phytohormones ethylene (ET) and jasmonate (JA) regulate plant development, growth, and defense responses; however, the molecular basis for their signaling crosstalk is unclear. Here, we show that JA‐ZIM‐domain (JAZ) proteins, which repress JA signaling, repress trichome initiation/branching and anthocyanin accumulation, and inhibit the transcriptional activity of the basic helix‐loop‐helix (bHLH)‐MYB members (GLABRA3 (GL3)‐GL1 and TRANSPARENT TESTA 8 (TT8)‐MYB75) of WD‐repeat/bHLH/MYB (WBM) complexes. The ET‐stabilized transcription factors ETHYLENE‐INSENSITIVE3 (EIN3) and EIN3‐LIKE1 (EIL1) were found to bind to several members of WBM complexes, including GL3, ENHANCER OF GLABRA3 (EGL3), TT8, GL1, MYB75, and TRANSPARENT TESTA GLABRA1 (TTG1). This binding repressed the transcriptional activity of the bHLH‐MYB proteins and inhibited anthocyanin accumulation, trichome formation, and defenses against insect herbivores while promoting root hair formation. Conversely, the JA‐activated bHLH members GL3, EGL3, and TT8 of WBM complexes were able to interact with and attenuate the transcriptional activity of EIN3/EIL1 at the HOOKLESS1 promoter, and their overexpression inhibited apical hook formation. Thus, this study demonstrates a molecular framework for signaling crosstalk between JA and ET in plant development, secondary metabolism, and defense responses. [ABSTRACT FROM AUTHOR]

(Z)–3–hexenol, a small gaseous molecule, is produced in plants under biotic stress and induces defense responses in neighboring plants. However, little is known about how (Z)–3–hexenol induces plant defense–related signaling. In this study, we uncovered how (Z)–3–hexenol treatment enhances plant resistance to insect attacks by increasing γ–aminobutyric acid (GABA) contents in Arabidopsis leaves. First, (Z)–3–hexenol increases the intracellular content of calcium as secondary messenger in Arabidopsis leaf mesophyll cells. Both intracellular and extracellular calcium stores regulate changes in calcium content. Then, CML8 and GAD4 transmit calcium signaling to affect (Z)–3–hexenol induced GABA content and plant resistance. Herein, CML8 interaction with GAD4 was examined via yeast two–hybrid assays, firefly luciferase complementation imaging, and GST pull–down assays. These results indicate that (Z)–3–hexenol treatment increased the GABA contents in Arabidopsis leaves based on CML8 and GAD4, thus increasing plant resistance to the insect Plutella xylostella. This study revealed the mechanism of activating plant insect defense induced by (Z)–3–hexenol, which guides the study of volatiles as biological pest control. • CML8 interacting with GAD4 depended on Ca2+ concentration leading to GABA accumulation in (Z)-3-hexenol regulation. [ABSTRACT FROM AUTHOR]

Plant sphingolipids are important membrane components and bioactive molecules in development and defense responses. However, the function of sphingolipids in plant defense, especially against herbivores, is not fully understood. Here, we report that Spodoptera exigua feeding affects sphingolipid metabolism in Arabidopsis, resulting in increased levels of sphingoid long-chain bases, ceramides, and hydroxyceramides. Insect-induced ceramide and hydroxyceramide accumulation is dependent on the jasmonate signaling pathway. Loss of the Arabidopsis alkaline ceramidase ACER increases ceramides and decreases long-chain base levels in plants; in this work, we found that loss of ACER enhances plant resistance to S. exigua and improves response to mechanical wounding. Moreover, acer-1 mutants exhibited more severe root-growth inhibition and higher anthocyanin accumulation than wild-type plants in response to methyl jasmonate treatment, indicating that loss of ACER increases sensitivity to jasmonate and that ACER functions in jasmonate-mediated root growth and secondary metabolism. Transcript levels of ACER were also negatively regulated by jasmonates, and this process involves the transcription factor MYC2. Thus, our findings reveal that ACER is involved in mediating jasmonate-related plant growth and defense and that jasmonates function in regulating the expression of ACER. [ABSTRACT FROM AUTHOR]

Melanization is an integral part of the insect defense system and is often induced by pathogen invasion. Phenoloxidases (POs) are critical enzymes that catalyze melanin formation. PO3 is associated with the antifungal response of the mosquito, Aedes aegypti, but the molecular mechanism of the prophenoloxidase-3 (PPO3) activation is unclear. Here we report that PPO3 cleavage activation is mediated by a clip-domain serine protease, CLIPB9. We purified recombinant CLIPB9 and found that it cleaved PPO3 and increased PO activity in the hemolymph. We then identified CLIPA14 (a serine protease homolog) by co-immunoprecipitation using anti-CLIPB9 antibody. After being cleaved by CLIPB9, Ae. aegypti CLIPA14 acted as a cofactor for PPO3 activation. In addition, dsRNA co-silencing of CLIPB9 and CLIPA14 genes reduced melanization after infection with the entomopathogen, Beauveria bassiana, making the adult mosquitoes more sensitive to fungal infection. These results illustrate the roles of CLIPB9 and CLIPA14 in the PPO activation pathway and revealed the complexity of the upstream serine protease network controlling melanization. [ABSTRACT FROM AUTHOR]

Some insects can be used as food, while others can affect the destruction of crops and the reduction of food reserves. The studies described in this article showed quantitative and qualitative changes in the composition of volatile compounds contained in adult Tenebrio molitor and Leptinotarsa decemlineata insects after applying insecticides. The samples were prepared by SPME and the final determinations were carried out by GC/MS. The volatile compounds that were present only in the insects after the application of insecticides (or in a larger quantities) could be due to the insecticides, as an insect defense response to these insecticides. For example, in adult T. molitor insects, the percentage of alkanes ranged from 38.63 to 59.05% (male), and from 38.89% to 60.20 (female), depending on the insecticide used and the time elapsed since its application. In contrast, in L. decemlineata, the percentage of alkanes ranged from 43.84 to 61.85% (female), and from 42.41 to 60.11% (male). The results of the present study can be useful in understanding the i defense strategies of insects against insecticides. [ABSTRACT FROM AUTHOR]

• Insect pathogens enter hosts through natural openings or epithelial barriers • Pathogen infection routes regulate the insect immune response • This information is critical for understanding the evolution of innate immunity Recent advances in insect-pathogen interactions have started to reveal the role of insect tissues and organs as natural infection routes for parasites and microbial pathogens. Here we summarize this information highlighting the micro- and macro-parasites that enter insects through distinct infection routes and link them to innate immune activity. We also examine whether the infection route determines the insect immune response and if the resulting immunological and physiological processes underpinning these different routes of infection are clearly distinct. Understanding how the infection route is associated with the robustness in insect host defense will help us identify conserved evolutionary and ecological patterns in order to design novel strategies for the management of destructive agricultural pests and disease vectors. [ABSTRACT FROM AUTHOR]

BACKGROUND: Fungal insecticides are notorious for slow kill action, an intrinsic trait that can be improved by the genetic engineering of an exogenous or endogenous virulence factor. However, transgenic insecticides expressing exogenous toxin and herbicide‐resistant marker genes may cause unexpected ecological risks and are hardly permitted for field release due to strict regulatory hurdles. It is necessary to improve biotechnology that can speed up fungal insect‐killing action and exclude ecological risk source. RESULTS: A markerless transformation system of Beauveria bassiana, a main source of wide‐spectrum fungal insecticides, was reconstructed based on the fungal uridine auxotrophy (Δura3). The system was applied for overexpression of the small cysteine‐free protein (120 amino acids) gene cfp previously characterized as a regulator of the fungal virulence and gene expression. Three cfp‐overexpressed strains showed much faster kill action to Galleria mellonella larvae than the parental wild‐type via normal cuticle infection but no change in vegetative growth and aerial condition. The faster kill action was achieved due to not only significant increases in conidial adherence to insect cuticle and total activity of secreted cuticle‐degrading Pr1 proteases and of antioxidant enzymes crucial for collapse of insect immune defense but acceleration of hemocoel localization, proliferation in vivo and host death from mummification. CONCLUSION: The markerless system is free of any foreign DNA fragment as a source of ecologic risk and provides a novel biotechnological approach to enhancing fungal insecticidal activity with non‐risky endogenous genes and striding over the regulatory hurdles. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Phenoloxidase (PO)–catalyzed melanization is a vital immune response in insects for defense against pathogen infection. This process is mediated by clip domain serine proteases and regulated by members of the serpin superfamily. We here revealed that the infection of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) significantly inhibited the PO activity in Ostrinia furnacalis hemolymph and induced the expression of O. furnacalis serpin–4. Addition of recombinant serpin-4 protein to O. furnacalis hemolymph resulted in a great increase of AcMNPV copies. Serpin-4 significantly suppressed the PO activity and the amidase activity in cleaving colorimetric substrate IEAR p NA (IEARase activity) of hemolymph. Further experiments indicated it formed covalent complexes with three serine proteases (SP1, SP13 and SP105) and prevented them from cleaving their cognate downstream proteases in vitro. Altogether, O. furnacalis melanization restricted AcMNPV replication and serpin-4 facilitated AcMNPV infection by inhibiting serine proteases, SP1, SP13, and SP105 which were all involved in the melanization response. [ABSTRACT FROM AUTHOR]

Silicon (Si) enhances rice resistance to various insect herbivores. However, the underlying mechanisms remain unclear. Whereas the salicylic acid (SA) signaling pathway plays a vital role in plant defense responses to sucking insects, its role in Si-enhanced rice resistance has not been investigated. Si transporter mutant OsLsi1 and mutants with antisense expression of ICS (as-ics) and NPR1 (as-npr1) in the SA pathway and their corresponding wild types (WT) were treated with and without Si to determine Si effects on rice resistance to brown planthopper (BPH), Nilaparvata lugens (Stål), as well as on SA accumulation, defense-related enzyme activity and gene expression. Si application significantly affected host preference of BPH, significantly reduced honeydew secretion and inhibited oviposition and hatch rate. Upon BPH infestation, SA content, transcript levels of BPH3, ICS1 and PAL4, and activities of POD, SOD, PPO and PAL were significantly higher in Si-treated than untreated plants. The defense responses were also faster. However, OsLsi1 mutant plants displayed higher susceptibility to BPH and minimal defense responses. Furthermore, simultaneous application of SA and Si in WT plants showed the highest resistance to BPH, but had no obvious effect on OsLsi1, antisense as-ics and as-npr1 plants. Our results suggest that Si enhances rice defense against the sucking insect BPH by defense priming and the Si-mediated priming involves SA signaling pathway. [ABSTRACT FROM AUTHOR]

Plants have evolved a series of inducible or constitutive defense mechanisms in response to herbivore attack. Constitutive plant defenses are morphological and biochemical traits of the plants themselves, regardless of the presence of herbivores. We bred an alfalfa variety (Caoyuan No.4) with high thrips resistance, but the mechanisms underlying Caoyuan No.4 resistance to thrips are not well understood. To explore the constitutive defense of Caoyuan No.4, the morphological and biochemical traits associated with constitutive defense to thrips in alfalfa were analyzed using a thrips-susceptible alfalfa accession (Caoyuan No.2) as a control. The results showed that Caoyuan No.4 had thicker palisade tissue and parenchyma tissue, wider collenchyma, phloem, cambium and lignin layer, and smaller epidermal cells and stomatal aperture compared to Caoyuan No.2. Moreover, Caoyuan No.4 showed more non-glandular trichomes in both leaves and stems, but less glandular trichomes and more wax in stems. In addition, the results of the widely targeted metabolomics analysis showed that metabolites related to flavonoid, isoflavonoid, flavone and flavonol biosynthesis, as well as cysteine and methionine metabolism, differed between CaoyuanNo.2 and Caoyuan No.4. These findings shed new light on the constitutive insect defense of plants associated with physical or biochemical traits and may provide convenient markers for breeding thrips-resistant alfalfa cultivars. [ABSTRACT FROM AUTHOR]

Microsporidia are obligate intracellular parasites able to infest specifically a large range of species, including insects. The knowledge about the biology of microsporidial infections remains confined to mostly descriptive studies, including molecular approaches such as transcriptomics or proteomics. Thus, functional data to understand insect host defenses are currently lacking. Here, we have undertaken a genetic analysis of known host defenses of the Drosophila melanogaster using an infection model whereby Tubulinosema ratisbonensis spores are directly injected in this insect. We find that phagocytosis does confer some protection in this infection model. In contrast, the systemic immune response, extracellular reactive oxygen species, thioester proteins, xenophagy, and intracellular antiviral response pathways do not appear to be involved in the resistance against this parasite. Unexpectedly, several genes such as PGRP-LE seem to promote this infection. The prophenol oxidases that mediate melanization have different functions; PPO1 presents a phenotype similar to that of PGRP-LE whereas that of PPO2 suggests a function in the resilience to infection. Similarly, eiger and Unpaired3 , which encode two cytokines secreted by hemocytes display a resilience phenotype with a strong susceptibility to T. ratisbonensis. [ABSTRACT FROM AUTHOR]

Key message: Comparative analysis of herbivory responsive miRNAs between pod borer susceptible C. cajan and its resistant Crop Wild Relative (CWR) C. scarabaeoides revealed miRNA-based regulation of defense genes and plant–insect interactions. Gram pod borer (Helicoverpa armigera) is one of most devastating pests of pigeon pea (Cajanus cajan) worldwide, responsible for huge losses in crop productivity. The lack of genes conferring resistance to pod borer in pigeon pea has proven to be a bottleneck for its improvement. One of its CWR, C. scarabaeoides has demonstrated resistance to this pest and can be exploited for developing pest resistant crop varieties. Differences in expression patterns of herbivory responsive microRNAs in the susceptible C. cajan and resistant C. scarabaeoides after different time duration of pod borer infestation (2 h, 8 h and 18 h) were identified, characterized and functionally validated to understand their role in insect defense response. A total of 462 conserved and 449 novel miRNAs and 273 conserved and 185 novel miRNAs, were identified in C. cajan and C. scarabaeoides, respectively. Among the identified miRNAs, 65, 68 and 65 miRNAs were found to be differentially expressing between the C. scarabaeoides and C. cajan libraries 2 h, 8 h and 18 h post infestation, respectively. These miRNAs were found to target genes involved in a number of pathways contributing to defense and acquired resistance in C. scarabaeoides against pod borer, indicating miRNA-based regulation of defense pathways. Expression patterns of eight of these miRNAs were validated by qRT-PCR. This study provides novel insights into the miRNA-mediated plant–insect interactions and the mechanisms of regulatory pathways involved in insect defense. These findings can be utilized for further exploring the mechanism of herbivore defense in plant systems. [ABSTRACT FROM AUTHOR]

The enzyme phenoloxidase (PO) plays an essential role in insect immune defense. Phenolic compounds sharing structural homology with PO substrates could act as substrate analogues, and may interfere with insect physiological process, thus, leading to their control. Herein, the bioinformatic molecular docking was used to predict the interaction of the crystal 3D structure of the insect Manduca sexta PO (PDB: 3HHS) with the antiseptic 4 hexylresorcinol (4‐Hr). The method was firstly validated using phenylthiourea (PTU) as reference ligand. Data demonstrated the ability of the 4‐Hr to bind to M. sexta PO with binding energy score ΔG = −372,285 Kcal/mol indicative of a plausible affinity to active site of the enzyme, nevertheless, the affinity of PTU was stronger with a binding energy of ΔG = −462.173 Kcal/mol. Furthermore, biochemical in vitro assays confirmed the behavior of 4‐Hr as substrate‐analog when binding to the active site of the insect PO leading to its competitive inhibition. This is the first report demonstrating the molecular bases of the usefulness of hexylresorcinol as a promising insecticide. Further investigations could emphasize synergistic effects of 4‐Hr with other insecticides in integrated pest management (IPM) programs. [ABSTRACT FROM AUTHOR]

The calcium (Ca2+) signaling is a crucial event during plant-herbivore interaction, which involves a transient change in cytosolic Ca2+ concentration, which is sensed by Ca2+-sensors, and the received message is transduced to downstream target proteins leading to appropriate defense response. Calmodulin-like proteins (CMLs) are calcium-sensing plant-specific proteins. Although CMLs have been identified in a few plants, they remained uncharacterized in leguminous crop plants. Therefore, a wide-range analysis of CMLs of soybean was performed, which identified 41 true CMLs with greater than 50% similarity with Arabidopsis CMLs. The phylogenetic study revealed their evolutionary relatedness with known CMLs. Further, the identification of conserved motifs, gene structure analysis, and identification of cis -acting elements strongly supported their identity as members of this family and their involvement in stress responses. Only a few Glycine max CMLs (GmCMLs) exhibited differential expression in different tissue types, and rest of them had minimal expression. Additionally, differential expression patterns of GmCMLs were observed during Spodoptera litura -feeding, wounding, and signaling compound treatments, indicating their role in plant defense. The three-dimensional structure prediction, identification of interactive domains, and docking with Ca2+ ions of S. litura -inducible GmCMLs, indicated their identity as calcium sensors. This study on the characterization of GmCMLs provided insights into their roles in calcium signaling and plant defense during herbivory. [ABSTRACT FROM AUTHOR]

There are drawbacks associated with current methods used to quantify insect predation. However, there has been relatively little effort to experimentally document the sources of biases associated with different methodologies. In this study, we investigated how methods used experimentally to quantify predation may influence insect antipredator defenses being observed, and thus alter the determination of the number of prey killed by predators, and potentially the conclusions reported in the study. We focused on acclimation period, which represents the time between the point at which a prey individual is made available, for example on a leaf, and when the experiment is initiated. In essence, this is the period of time during which an organism adjusts to the conditions that surround it before a treatment is imposed. We investigated if prey acclimation period on plants influences the antipredator behavior of larval Orgyia leucostigma (J.E. Smith) (Lepidoptera: Lymantriidae), and the number of prey killed in the laboratory by the predatory wasp Polistes fuscatus (Fabricius) (Hymenoptera: Vespidae). The results of this study provide evidence that acclimation time significantly affects the antipredator behavior observed and mortality of caterpillars exposed to predators. The majority of larvae allowed short acclimation periods did not drop in response to the attacks of wasps. These larvae suffered significantly higher mortality compared to caterpillars that were allowed to acclimate for longer periods of time. [ABSTRACT FROM AUTHOR]

Cyanogenic glucosides (CGs) play a key role in host-plant defense to insect feeding; however, the metabolic tradeoffs between synthesis of CGs and plant growth are not well understood. In this study, genetic mutants coupled with nondestructive phenotyping techniques were used to study the impact of the CG dhurrin on fall armyworm [Spodoptera frugiperda (J.E. Smith)] (FAW) feeding and plant growth in sorghum [Sorghum bicolor (L.) Moench]. A genetic mutation in CYP79A1 gene that disrupts dhurrin biosynthesis was used to develop sets of near-isogenic lines (NILs) with contrasting dhurrin contents in the Tx623 bmr6 genetic background. The NILs were evaluated for differences in plant growth and FAW feeding damage in replicated greenhouse and field trials. Greenhouse studies showed that dhurrin-free Tx623 bmr6 cyp79a1 plants grew more quickly than wild-type plants but were more susceptible to insect feeding based on changes in green plant area (GPA), total leaf area, and total dry weight over time. The NILs exhibited similar patterns of growth in field trials with significant differences in leaf area and dry weight of dhurrin-free plants between the infested and non-infested treatments. Taken together, these studies reveal a significant metabolic tradeoff between CG biosynthesis and plant growth in sorghum seedlings. Disruption of dhurrin biosynthesis produces plants with higher growth rates than wild-type plants but these plants have greater susceptibility to FAW feeding. [ABSTRACT FROM AUTHOR]

The sigma glutathione S‐transferases (GSTSs) are a class of cytosolic glutathione S transferases (GSTs) that play important roles in antioxidant defense in insects, but the mechanisms by which GSTSs contribute to antioxidant activity remain unclear. Here, we isolated a GSTS (GSTS6) from Tribolium castaneum and explored its function. Homology and phylogenetic analysis revealed that TcGSTS6 shared high identity with other evolutionarily conserved GSTSs. The recombinant TcGSTS6 protein had strong activity toward cumene hydroperoxide and 4‐hydroxynonenal but low activity toward the universal substrate 1‐chloro‐2,4‐dinitrobenzene. Exposure to various types of oxidative stress, including heat, cold, UV and pathogenic microbes, significantly induced TcGSTs6 expression, which indicates that it is involved in antioxidant defense. Knockdown TcGSTs6 by using RNA interference (RNAi) caused reduced antioxidant capacity, which was accomplished by cooperating with other antioxidant genes. Moreover, treatment with various insecticides such as phoxim, lambda‐cyhalothrin, dichlorvos and carbofuran revealed that TcGSTS6 plays an important role in insecticide detoxification. The RNAi results showed that TcGSTS6 is essential for embryogenesis in T. castaneum. Our study elucidates the mechanism by which a GSTS contributes to antioxidant activity and enhances our understanding of the functional diversity of GSTSs in insects. [ABSTRACT FROM AUTHOR]

As the major and abundant type of glucosinolates (GL) in plants, sinigrin has potential functions in promoting health and insect defense. The final step in the biosynthesis of sinigrin core structure is highly representative in GL compounds, which corresponds to the process from 3-methylthiopropyl ds-GL to 3-methylthiopropyl GL catalyzed by sulfotransferase (SOT). However, due to the lack of the crystallographic structure of SOT complexed with the 3-methylthiopropyl GL, little is known about this sulfonation process. Fortunately, the crystal structure of SOT 18 from Arabidopsis thaliana (AtSOT18) containing the substance (sinigrin) similar to 3-methylthiopropyl GL has been determined. To understand the enzymatic mechanism, we employed molecular dynamics (MD) simulation and quantum mechanics combined with molecular mechanics (QM/MM) methods to study the conversion from ds-sinigrin to sinigrin catalyzed by AtSOT18. The calculated results demonstrate that the reaction occurs through a concerted dissociative mechanism. Moreover, Lys93, Thr96, Thr97, Tyr130, His155, and two enzyme peptide chains (Pro92-Lys93 and Gln95-Thr96-Thr97) play a role in positioning the substrates and promoting the catalytic reaction by stabilizing the transition state geometry. Particularly, His155 acts as a catalytic base while Lys93 acts as a catalytic acid in the reaction process. The presently proposed concerted dissociative mechanism explains the role of AtSOT18 in sinigrin biosynthesis, and could be instructive for the study of GL biosynthesis catalyzed by other SOTs. [ABSTRACT FROM AUTHOR]

Thanatin is an antimicrobial peptide (AMP) generated by insects for defense against bacterial infections. In the present study, we performed cDNA cloning of thanatin and found the presence of multiple precursor proteins from the bean bug, Riptortus pedestris. The cDNA sequences encoded 38 precursor proteins, generating 13 thanatin isoforms. In the phylogenetic analysis, thanatin isoforms were categorized into two groups based on the presence of the membrane attack complex/perforin (MACPF) domain. In insect-bacterial symbiosis, specific substances are produced by the immune system of the host insect and are known to modulate the symbiont's population. Therefore, to determine the biological function of thanatin isoforms in symbiosis, the expression levels of three AMP genes were compared between aposymbiotic insects and symbiotic R. pedestris. The expression levels of the thanatin genes were significantly increased in the M4 crypt, a symbiotic organ, of symbiotic insects upon systemic bacterial injection. Further, synthetic thanatin isoforms exhibited antibacterial activity against gut-colonized Burkholderia symbionts rather than in vitro -cultured Burkholderia cells. Interestingly, the suppression of thanatin genes significantly increased the population of Burkholderia gut symbionts in the M4 crypt under systemic Escherichia coli K12 injection. Overgrown Burkholderia gut symbionts were observed in the hemolymph of host insects and exhibited insecticidal activity. Taken together, these results suggest that thanatin of R. pedestris is a host-derived symbiotic factor and an AMP that controls the population of gut-colonized Burkholderia symbionts. [ABSTRACT FROM AUTHOR]

Insects frequently confront different microbial assemblages. Bacteria inhabiting an insect gut are often commensal, but some can become pathogenic when the insect is compromised from different stressors. Herbivores are often confronted by various forms of plant resistance, but how defenses generate opportunistic microbial infections from residents in the gut are not well understood. In this study, we evaluated the pathogenic tendencies of Serratia isolated from the digestive system of healthy fall armyworm larvae (Spodopterafrugiperda) and how it interfaces with plant defenses. We initially selected Serratia strains that varied in their direct expression of virulence factors. Inoculation of the different isolates into the fall armyworm body cavity indicated differing levels of pathogenicity, with some strains exhibiting no effects while others causing mortality 24 h after injection. Oral inoculations of pathogens on larvae provided artificial diets caused marginal (< 7%) mortality. However, when insects were provided different maize genotypes, mortality from Serratia increased and was higher on plants exhibiting elevated levels of herbivore resistance (< 50% mortality). Maize defenses facilitated an initial invasion of pathogenic Serratia into the larval hemocoel¸ which was capable of overcoming insect antimicrobial defenses. Tomato and soybean further indicated elevated mortality due to Serratia compared to artificial diets and differences between plant genotypes. Our results indicate plants can facilitate the incipient emergence of pathobionts within gut of fall armyworm. The ability of resident gut bacteria to switch from a commensal to pathogenic lifestyle has significant ramifications for the host and is likely a broader phenomenon in multitrophic interactions facilitated by plant defenses. [ABSTRACT FROM AUTHOR]

All social insects defend their colony from predators, parasites, and pathogens. In Oster and Wilson's classic work, they posed one of the key paradoxes about defense in social insects: Given the universal necessity of defense, why then is there so much diversity in mechanisms? Ecological factors undoubtedly are important: Predation and usurpation have imposed strong selection on eusocial insects, and active defense by colonies is a ubiquitous feature of all social insects. The description of diverse insect groups with castes of sterile workers whose main duty is defense has broadened the purview of social evolution in insects, in particular with respect to caste and behavior. Defense is one of the central axes along which we can begin to organize and understand sociality in insects. With the establishment of social insect models such as the honey bee, new discoveries are emerging regarding the endocrine, neural, and gene regulatory mechanisms underlying defense in social insects. The mechanisms underlying morphological and behavioral defense traits may be shared across diverse groups, providing opportunities for identifying both conserved and novel mechanisms at work. Emerging themes highlight the context dependency of and interaction between factors that regulate defense in social insects. [ABSTRACT FROM AUTHOR]