High value-added application of a renewable bioresource as acaricide: Investigation the mechanism of action of scoparone against Tetranychus cinnabarinus

Recent Advances and Outlook of Benzopyran Derivatives in the Discovery of Agricultural Chemicals

Scaffold structures, new mechanisms of action, and targets present enormous challenges in the discovery of novel pesticides. The discovery of new scaffolds is the basis for the continuous development of modern agrochemicals. Identification of a good scaffold such as triazole, carbamate, methoxy acrylate, pyrazolamide, pyrido-pyrimidinone mesoionic, and bisamide often leads to the development of a new series of pesticides. In addition, pesticides with the same target, including the inhibitors of succinate dehydrogenase (SDH), oxysterol-binding-protein, and p-hydroxyphenyl pyruvate dioxygenase (HPPD), may have the same or similar scaffold structure. Recent years have witnessed significant progress in the discovery of new pesticides using natural products as scaffolds or bridges. In recent years, there have been increasing reports on the application of natural benzopyran compounds in the discovery of new pesticides, especially osthole and coumarin. A systematic and comprehensive review of benzopyran active compounds in the discovery of new agricultural chemicals is helpful to promote the discussion and development of benzopyran active compounds. Therefore, this work systematically reviewed the research and application of benzopyran derivatives in the discovery of agricultural chemicals, summarized the antiviral, herbicidal, antibacterial, fungicidal, insecticidal, nematicidal and acaricidal activities of benzopyran active compounds, and discussed the structural-activity relationship and mechanism of action. In addition, some active fragments were recommended to further optimize the chemical structure of benzopyran active compounds based on reference information.

Functional analysis of a down-regulated transcription factor-SoxNeuroA gene involved in the acaricidal mechanism of scopoletin against spider mites

BACKGROUND

Insight into the mode of action of plant-derived acaricides will help in the development of sustainable control strategies for mite pests. Scopoletin, a promising plant-derived bioactive compound, displays prominent acaricidal activity against Tetranychus cinnabarinus. The transcription factor SoxNeuroA plays a vital role in maintaining calcium ion (Ca2+ ) homeostasis. Down-regulation of SoxNeuroA gene expression occurs in scopoletin-exposed mites, but the functional role of this gene remains unknown.

RESULTS

A SoxNeuroA gene from T. cinnabarinus (TcSoxNeuroA) was first cloned and identified. Reverse transcription polymerase chain reaction (RT-PCR), quantitative real-time polymerase chain reaction (qPCR), and Western blotting assays all confirmed that the gene expression and protein levels of TcSoxNeuroA were significantly reduced under scopoletin exposure. Furthermore, RNA interference silencing of the weakly expressed SoxNeuroA gene significantly enhanced the susceptibility of mites to scopoletin, suggesting that the acaricidal mechanism of scopoletin was mediated by the weakly expressed SoxNeuroA gene. Additionally, yeast one-hybrid (Y1H) and dual-luciferase reporter assays revealed that TcSoxNeuroA was a repressor of Orai1 Ca2+ channel gene transcription, and the key binding sequence was ATCAAAG (positions -361 to -368 of the Orai1 promoter). Importantly, site-directed mutagenesis and microscale thermophoresis assays further indicated that ASP185, ARG189, and LYS217, which were key predicted hydrogen-bonding sites in the molecular docking model, may be the vital binding sites for scopoletin in TcSoxNeuroA.

CONCLUSION

These results demonstrate that the acaricidal mechanism of scopoletin involves inhibition of the transcription factor SoxNeuroA, thus inducing the activation of the Orai1 Ca2+ channel, eventually leading to Ca2+ overload and lethality. Elucidation of the transcription factor-targeted mechanism for this potent plant-derived acaricide has vital implications for the design of next-generation green acaricides with novel targets. © 2023 Society of Chemical Industry.

Chitosan/dsRNA polyplex nanoparticles advance environmental RNA interference efficiency through activating clathrin-dependent endocytosis

Chitosan, as a promising gene nanocarrier for enhancing RNA interference (RNAi) efficiency, displays tremendous application prospects in addressing dsRNA delivery concerns. However, the molecular mechanism of chitosan/dsRNA polyplex nanoparticles (PNs) for advancing dsRNA delivery efficiency remains largely unknown. Here, chitosan/dsRNA PNs were prepared by an electrostatic attraction method. The results showed that the chitosan/dsRNA PNs significantly advance stability, and cellular uptake efficiency of dsRNA, and RNAi efficiency. RNA-Seq and qPCR assays further revealed that chitosan/dsRNA PNs upregulated the key clathrin heavy chain (CHC) gene for activating clathrin-dependent endocytosis (CDE) pathway. Additionally, inhibition of CDE hindered the robust RNAi responses of chitosan/dsRNA PNs using an inhibitor (chlorpromazine) and an RNAi-of-RNAi strategy. Ultimately, microscale thermophoresis assay confirmed that chitosan/dsRNA PNs directly bound to CHC protein, which was a core component in CDE, to advance RNAi efficiency. To our knowledge, our findings firstly illuminate the molecular mechanism how chitosan nanoparticles-based RNAi deliver dsRNA for enhancing RNAi efficiency. Above mechanism will advance the extensive utilization of nanocarrier-based RNAi in pest management and gene delivery.

Development of Sustainable Insecticide Candidates for Protecting Pollinators: Insight into the Bioactivities, Selective Mechanism of Action and QSAR of Natural Coumarin Derivatives against Aphids

Plants employ abundant toxic secondary metabolites to withstand insect attack, while pollinators can tolerate some natural defensive compounds. Coumarins, as promising green alternatives to chemical insecticides, possess wide application prospects in the crop protection field. Herein, the bioactivities of 30 natural coumarin derivatives against Aphis gossypii were assessed and revealed that 6-methylcoumarin exhibited potent aphicidal activity against aphids but displayed no toxicity to honeybees. Additionally, using biochemical, bioinformatic, and molecular assays, we confirmed that the action mode of 6-methylcoumarin against aphids was by inhibiting acetylcholinesterase (AChE). Meanwhile, functional assays revealed that the difference in action site, which located in Lys585 in aphid AChE (equivalent to Val548 in honeybee AChE), was the principal reason for 6-methylcoumarin being toxic to aphids but safe to pollinators. This action site was further validated by mutagenesis data, which uncovered how 6-methylcoumarin was unique selective to the aphid over honeybee or mammalian AChE. Furthermore, a 2D-QSAR model was established, revealing that the central structural feature was H3m, which offers guidance for the future design of more potent coumarin compounds. This work provides a sustainable strategy to take advantage of coumarin analogues for pest management while protecting nontarget pollinators.

Feeding-induced plant metabolite responses to a phoretic gall mite, its carrier psyllid and both, after detachment

Phoresy is one of the most distinctive relationships between mites and insects, and the off-host interaction between phoretic mites and their carriers is the most critical factor sustaining the phoretic association. As phoretic associations commonly occur in temporary habitats, little is known about off-host interactions between phoronts and carriers. However, an off-host interaction has been reported, in which the plant-mediated competition between a phoretic gall mite, Aceria pallida, and its psyllid vector, Bactericera gobica, after detachment decreases leaf abscission caused by B. gobica and then directly facilitates their phoretic association. In this obligate phoresy, A. pallida seasonally attaches to B. gobica for overwinter survival and they share the same host plant, Lycium barbarum, during the growing season. It is unknown how the host plant responds to these two herbivores and what plant metabolites are involved in their interspecific interaction. Here, effects of A. pallida and B. gobica on the host plant's transcriptome and metabolome, and on enzymes involved in plant defence, at various infestation stages were studied by inoculating A. pallida and B. gobica either separately or simultaneously on leaves of L. barbarum. Our results showed that (a) A. pallida significantly promoted primary and secondary metabolite accumulation, (b) B. gobica markedly inhibited primary and secondary metabolite accumulation and had little influence on defence enzyme activity, and (c) under simultaneous A. pallida and B. gobica infestation, an intermediate response was predicted. These findings indicate that A. pallida and B. gobica have different effects on host plants, A. pallida inhibits B. gobica mainly by increasing the secondary metabolism of L. barbarum, whereas B. gobica inhibits A. pallida mainly by decreasing the primary metabolism of L. barbarum. In conjunction with our previous research, we speculate that this trade-off in host plant metabolite response between A. pallida and B. gobica after detachment promotes a stable phoretic association.

Contact Toxicity, Antifeedant Activity, and Oviposition Preference of Osthole against Agricultural Pests

Osthole, the dominant bioactive constituent in the Cnidium monnieri, has shown acute pesticidal activities. However, its detailed toxicity, antifeedant, and oviposition preference effects against agricultural pests have not been fully understood, limiting its practical use. This study aimed to investigate the contact toxicity, antifeedant activity, and oviposition preference of osthole against three agricultural pests (Tetranychus urticae, Myzus persicae, and Bactrocera dorsalis). Our results showed that the Cnidium monnieri (L.) Cusson (CMC) has a high osthole content of 11.4 mg/g. Osthole exhibited a higher level of acute toxicity against the T. urticae to four other coumarins found in CMC. It showed significant pesticidal activity against T. urticae and M. persicae first-instar nymphs and adults in a dose-dependent manner but not against B. dorsalis adults. Osthole exposure reduced the fecundity and prolonged the developmental time of the T. urticae and M. persicae. Leaf choice bioassays revealed potent antifeedant activity in the T. urticae and M. persicae. Furthermore, the female B. dorsalis showed a distinct preference for laying eggs in mango juice with 0.02 mg/mL osthole at 48 h, a preference that persisted at 96 h. These results provide valuable insights into the toxicity, repellent activity, and attractant activity of osthole, thereby providing valuable insights into its potential efficacy in pest control.

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.

Mediterranean Plants as Potential Source of Biopesticides: An Overview of Current Research and Future Trends

The development and implementation of safe natural alternatives to synthetic pesticides are urgent needs that will provide ecological solutions for the control of plant diseases, bacteria, viruses, nematodes, pests, and weeds to ensure the economic stability of farmers and food security, as well as protection of the environment and human health. Unambiguously, production of botanical pesticides will allow for the sustainable and efficient use of natural resources and finally decrease the use of chemical inputs and burden. This is further underlined by the strict regulations on pesticide residues in agricultural products and is in harmony with the Farm to Fork strategy, which aims to reduce pesticide use by 50% by 2030. Thus, the present work aims to compile the scientific knowledge of the last 5 years (2017-February 2023) regarding the Mediterranean plants that present biopesticidal effects. The literature review revealed 40 families of Mediterranean plants with at least one species that have been investigated as potential biopesticides. However, only six families had the highest number of species, and they were reviewed comprehensively in this study. Following a systematic approach, the extraction methods, chemical composition, biopesticidal activity, and commonly used assays for evaluating the antimicrobial, pesticidal, repellant, and herbicidal activity of plant extracts, as well as the toxicological and safety aspects of biopesticide formulation, are discussed in detail. Finally, the aspects that have not yet been investigated or are under-investigated and future perspectives are highlighted.

Biochemical characterisation of Cytochrome P450 oxidoreductase from the cattle tick, Rhipicephalus microplus, highlights potential new acaricide target

Management of the cattle tick, Rhipicephalus microplus, presents a challenge because some populations of this cosmopolitan and economically important ectoparasite are resistant to multiple classes of acaricides. Cytochrome P450 oxidoreductase (CPR) is part of the cytochrome P450 (CYP450) monooxygenases that are involved in metabolic resistance by their ability to detoxify acaricides. Inhibiting CPR, the sole redox partner that transfers electrons to CYP450s, could overcome this type of metabolic resistance. This report represents the biochemical characterisation of a CPR from ticks. Recombinant CPR of R. microplus (RmCPR), minus its N-terminal transmembrane domain, was produced in a bacterial expression system and subjected to biochemical analyses. RmCPR displayed a characteristic dual flavin oxidoreductase spectrum. Incubation with nicotinamide adenine dinucleotide phosphate (NADPH) lead to an increase in absorbance between 500 and 600 nm with a corresponding appearance of a peak absorbance at 340-350 nm indicating functional transfer of electrons between NADPH and the bound flavin cofactors. Using the pseudoredox partner, kinetic parameters for both cytochrome c and NADPH binding were calculated as 26.6 ± 11.4 µM and 7.03 ± 1.8 µM, respectively. The turnover, K_cat, for RmCPR for cytochrome c was calculated as 0.08 s^-1 which is significantly lower than the CPR homologues of other species. IC₅₀ (Half maximal Inhibitory Concentration) values obtained for the adenosine analogues 2', 5' ADP, 2'- AMP, NADP⁺and the reductase inhibitor diphenyliodonium were: 140, 82.2, 24.5, and 75.3 µM, respectively. Biochemically, RmCPR resembles CPRs of hematophagous arthropods more so than mammalian CPRs. These findings highlight the potential of RmCPR as a target for the rational design of safer and potent acaricides against R. microplus.

Molecular mechanism of plant elicitor daphnetin-carboxymethyl chitosan nanoparticles against Ralstonia solanacearum by activating plant system resistance

The exploration of biopolymer-based materials to avoid hazardous chemicals in agriculture has gained enormous importance for sustainable crop protection. Due to its good biocompatibility and water solubility, carboxymethyl chitosan (CMCS) has been widely applied as a pesticide carrier biomaterial. However, the mechanism by which carboxymethyl chitosan-grafted natural product nanoparticles induce tobacco systemic resistance against bacterial wilt remains largely unknown. In this study, water-soluble CMCS-grafted daphnetin (DA) nanoparticles (DA@CMCS-NPs) were successfully synthesized, characterized, and assessed for the first time. The grafting rate of DA in CMCS was 10.05 %, and the water solubility was increased. In addition, DA@CMCS-NPs significantly increased the activities of CAT, PPO and SOD defense enzymes, activated the expression of PR1 and NPR1, and suppressed the expression of JAZ3. DA@CMCS-NPs could induce immune responses against R. solanacearum in tobacco, including increases in defense enzymes and overexpression of pathogenesis-related (PR) proteins. The application of DA@CMCS-NPs effectively suppressed the development of tobacco bacterial wilt in pot experiments, and the control efficiency was as high as 74.23 %, 67.80 %, 61.67 % at 8, 10, and 12 days after inoculation. Additionally, DA@CMCS-NPs has excellent biosafety. Therefore, this study highlighted the application of DA@CMCS-NPs in manipulating tobacco to generate defense responses against R. solanacearum, which can be attributed to systemic resistance.

Betulin, Synthesized by PpCYP716A1, Is a Key Endogenous Defensive Metabolite of Peach against Aphids

Wild pest-resistant germplasms employ secondary metabolites to withstand insect attacks. A close wild relative of the cultivated peach, Prunus davidiana, displays strong resistance to green peach aphids by utilizing metabolites to cope with aphid infestation; however, the underlying mechanism of aphid resistance remains mostly unknown. Here, metabolomic analysis was performed to explore the changes in metabolite levels in P. davidiana after aphid infestation. The data revealed that betulin is a key defensive metabolite in peaches that protects against aphids and possesses potent aphidicidal activity. Further toxicity tests demonstrated that betulin was toxic to pests but not to beneficial insects. Additionally, transcriptomic and phylogenetic analyses revealed that the cytochrome P450 gene PpCYP716A1 was responsible for betulin synthesis─this finding was confirmed by the heterologous expression of this gene. This study revealed a strategy whereby plants harness defense metabolites to develop resistance to pests. These findings may facilitate controlling such pests.

The Insecticidal Efficacy and Physiological Action Mechanism of a Novel Agent GC16 against Tetranychus pueraricola (Acari: Tetranychidae)

Simple Summary

Spider mite is major pest in agriculture and have developed resistance to commonly used pesticides. Therefore, it is urgent to discover new pesticides to control the pest. In order to provide alternatives for its management, we evaluated the effectiveness of a new agent GC16 against the spider mite Tetranychus pueraricola. Then, we preliminarily revealed the its acaricidal mechanism of action based on the damage of cuticle and organelles of mites. We confirmed that GC16 has a good controlling effect on T. pueraricola and it is not harmful to Picromerus lewisi and Harmonia axyridis. Our research provides not only an alternative pesticide for the management of spider mites, but also guidance for the application of GC16 in sustainable agriculture.

Abstract

Chemical control plays a crucial role in pest management but has to face challenges due to insect resistance. It is important to discover alternatives to traditional pesticides. The spider mite Tetranychus pueraricola (Ehara & Gotoh) (Acari: Tetranychidae) is a major agricultural pest that causes severe damage to many crops. GC16 is a new agent that consists of a mixture of Calcium chloride (CaCl₂) and lecithin. To explore the acaricidal effects and mode of action of GC16 against T. pueraricola, bioassays, cryogenic scanning electron microscopy (cryo-SEM) and transmission electron microscopy (TEM) were performed. GC16 had lethal effects on the eggs, larvae, nymphs, and adults of T. pueraricola, caused the mites to dehydrate and inactivate, and inhibited the development of eggs. GC16 displayed contact toxicity rather than stomach toxicity through the synergistic effects of CaCl₂ with lecithin. Cryo-SEM analysis revealed that GC16 damaged T. pueraricola by disordering the array of the cuticle layer crest. Mitochondrial abnormalities were detected by TEM in mites treated by GC16. Overall, GC16 had the controlling efficacy on T. pueraricola by cuticle penetration and mitochondria dysfunction and had no effects on Picromerus lewisi and Harmonia axyridis, indicating that GC16 is likely a new eco-friendly acaricide.

Itol A May Affect the Growth and Development of Spodoptera frugiperda through Hijacking JHBP and Impeding JH Transport

Isoryanodane and ryanodane diterpenes have a carbon skeleton correlation in structures, and their natural product-oxidized diterpenes show antifeedant and insecticidal activities against Hemiptera and Lepidoptera. While ryanodine mainly acts on the ryanodine receptor (RyR), isoryanodane does not. In this study, we demonstrated that itol A, an isoryanodane diterpenoid, could significantly downregulate the expression level of juvenile hormone-binding protein (JHBP), which plays a vital role in JH transport. RNAi bioassay indicated that silencing the Spodoptera frugipreda JHBP (SfJHBP) gene decreased itol A activity, which confirmed the developmental phenotypic observation. Parallel reaction monitoring (PRM) further confirmed that itol A affected JHBP's expression abundance. Although JHBP is not proven as the direct or only target of itol A, we confirmed that itol A's action effect depends largely on JHBP and that JHBP is a potential target of itol A. We present foundational evidence that itol A inhibits the growth and development of Spodoptera frugiperda mainly through hijacking JHBP.