Genetic approaches to reducing losses of stored grain to insects and diseases

Role of CYP6MS subfamily enzymes in detoxification of Sitophilus zeamais after exposure to terpinen-4-ol and limonene

Food security is an important basis and guarantee to national safety, the loss caused by storage pests was a serious problem which affects the food security widely. Frequent application of chemical pesticides caused several critical crises including the development of resistance, pesticide residues, environmental pollution, and exposure risk to human or non-target organisms. The utilization of volatile components acts as a natural alternative for controlling storage pests has aroused extensive interest in recent years. It has been reported that terpinene-4-ol and limonene showed significant insecticidal activity against Sitophilus zeamais in our previous studies, which was evaluated to have strong influences to CYP450 genes. To determine the links and roles of related genes, we identified the SzCYP6MS subfamily genes which encoded a putative protein of 493 or 494 amino acids. Then, the expression of four CYP6MS subfamily genes were increased significantly under the fumigation stress by terpinen-4-ol and limonene, which was determined by the RT-qPCR analysis compared with non-fumigated colonies. In addition, we determined that RNAi-mediated CYP6MS genes knockdown significantly increased the sensitivity of S. zeamais to terpinen-4-ol and limonene, the mortality rates of insects with knocked down CYP6MS1, CYP6MS5, CYP6MS6, CYP6MS8, and CYP6MS9 genes increased by 25%, 25%, 16%, 17%, and 4% in terpinen-4-ol treatment groups and by 29%, 25%, 15%, 22%, and 3% in limonene treatment groups compared with that in the control groups, respectively. Finally, it was validated that CYP6MS5 exhibited the most stable binding with terpinen-4-ol that was similar to the result between CYP6MS8 and limonene which were verified by molecular docking analysis. In together, this study demonstrates the potential of terpinen-4-ol and limonene used as novel botanical pesticides to control storage pests, thereby reducing application of chemical pesticides and postponing resistance development.

Transcriptomic analysis of Sitophilus zeamais in response to limonene fumigation

BACKGROUND

Frequent application of chemical fumigants has contributed to the development of resistance in stored-product pests. Essential oils provide a novel and environmentally friendly alternative to conventional chemical pesticides. In this work, the fumigant activity of Taxodium 'zhongshansha' essential oil (TZEO) and main active components against Sitophilus zeamais were evaluated. In addition, the molecular mechanisms mediating the fumigant activity of limonene were assessed.

RESULTS

TZEO showed strong fumigant activity against Sitophilus zeamais, with a 50% lethal concentration (LC₅₀ ) of 22.90 μL L^-1 air in 24 h. The main components of TZEO were identified using gas chromatography-mass spectrometry, the main active ingredient (limonene) showed an LC₅₀ of 9.93 μL L^-1 air in 24 h which had a serious dose-time-effect. The LC₅₀ value of the positive control (aluminum phosphide) was 1.91 μL L^-1 . In total, 3982 up-regulated and 3067 down-regulated genes were sequenced in limonene-fumigated Sitophilus zeamais, the genes related to metabolic detoxification were significantly enriched. The mortality rate of 7 day-old Sitophilus zeamais adult mediated with knockdown of SzCYP6MS5 and SzCYP6MS6 raised up to 65.67% and 67.65% after fumigation with limonene in 24 h, respectively. The results showed that SzCYP6MS5 and SzCYP6MS6 are closely involved to the detoxification of limonene.

CONCLUSION

In this study, candidate genes affected by limonene treatment in Sitophilus zeamais were identified. These findings provided insights into the systemic metabolic response of Sitophilus zeamais to limonene and established a basis for the development of limonene as a botanical pesticide for the control of stored-product pests. © 2022 Society of Chemical Industry.

Inhibition constant and stability of tripeptide inhibitors of gut trypsin-like enzyme of the soybean pest Anticarsia gemmatalis

Insects overcome the action of natural protease inhibitors (PIs) due to evolutionary adaptations through endogenous proteolysis and reprogramming proteases. Insect adaptations complicate the formulation of IP-based crop protection products. However, small peptides designed based on the active site of enzymes have shown promising results that could change this scenario. GORE1 and GORE2 are designed tripeptides that reduce the survival of Anticarsia gemmatalis when ingested orally. In this article, the stability and ability of the peptides to bind trypsin-like enzymes of A. gemmatalis were evaluated by molecular dynamics (MD) simulations. The ability of the peptides to inhibit trypsin-like enzymes in vivo was compared with the SKTI protein by feeding A. gemmatalis larvae at different concentrations, followed by an inhibition persistence assay. During the MD simulation of enzyme-ligand complexes, both peptides showed a small variation of root-mean-square deviation and root-mean-square fluctuation, suggesting that these molecules reach equilibrium when forming a complex with the trypsin-like enzyme. Furthermore, both peptides form hydrogen bonds with substrate recognition sites of A. gemmatalis trypsin-like enzyme, with GORE2 having more interactions than GORE1. Larvae of A. gemmatalis exposed to the peptides and SKTI showed a similar reduction in proteolytic activity, but the persistence of inhibition of trypsin-like enzyme was longer in peptide-fed insects. Despite their size, the peptides exhibit important active and substrate binding site interactions, stability during complex formation, and steadiness effects in vivo. The results provide fundamental information for the development of mimetic molecules and help in decision-making for the selection of delivery methods for larger-scale experiments regarding similar molecules.

Genome-Wide Identification of the Long Noncoding RNAs of Tribolium castaneum in Response to Terpinen-4-ol Fumigation

Simple Summary

Long noncoding RNAs (lncRNAs) are important regulatory factors in multiple biological processes, including genomic imprinting, cancer, RNA interference, and protein translation. Several lncRNAs can respond to insecticides. However, lncRNA functions associated with terpinen-4-ol resistance in the red flour beetle (Tribolium castaneum) have not yet been identified. In previous work, we found terpinen-4-ol to have strong fumigation activity against store-product pests. As a pesticide from plants, terpinen-4-ol shows nearly no residual danger to the environment; however, resistance is inevitable if people use terpinen-4-ol immoderately. To avoid resistance to terpinen-4-ol occurring in the red flour beetle, we deeply sequenced and tried to find some lncRNAs that can regulate target mRNA expression to reduce terpinen-4-ol.

Abstract

Long noncoding RNAs (lncRNAs) are important regulatory factors in multiple biological processes, and several lncRNAs are known to respond to insecticides. However, the lncRNA functions that are associated with terpinen-4-ol resistance in the red flour beetle (Tribolium castaneum) have not yet been identified. In this study, we determined the differentially transcribed lncRNAs between fumigated and control experimental groups. In the six libraries that underwent RNA sequencing, 34,546 transcripts were identified, including 8267 novel lncRNAs, 4155 novel mRNAs, 1151 known lncRNAs, and 20,973 known mRNAs. Among these, we found that the expression of 1858 mRNAs and 1663 lncRNAs was significantly different in the fumigated group compared with the control group. Among the differentially transcribed lncRNAs, 453 were up-regulated and 1210 were down-regulated lncRNAs. In addition, we identified the regulatory function targets of the lncRNAs. Functionally, all lncRNAs and target genes associated with terpinen-4-ol metabolism were enriched in several metabolic pathways, like the ATP-binding cassette transporter, pentose interconversion, and glucuronate interconversion. To the best of our knowledge, this study represents the first global identification of lncRNAs and their potential association with terpinen-4-ol metabolism in the red flour beetle. These results will provide reference information for studies on the resistance to terpinen-4-ol and other essential oil compounds and chemical pesticides, as well as an understanding of other biological processes in T. castaneum.

Effect of the Addition of Different Vegetal Mixtures on the Nutritional, Functional, and Sensorial Properties of Snacks Based on Pseudocereals

Quick meals available in markets are popular among consumers. Generally, these products are not recognized as functional foods owing to nutrient-poor composition. In this study, energy snack bars were developed with different formulations, using puffed quinoa, amaranth, cacao liquor, and coconut oil, and the effects of the addition of commercial vegetal mixtures (VM) on nutritional and functional properties were assessed. VM addition showed significant effects on the protein, lipid, and fiber contents, phenolic compounds (PHC) content, and antioxidant activity of the snacks. The control snack showed higher levels of free and bound PHC. The oxygen radical absorbance capacity (ORAC) analyses recorded highest values of free PHC (9392.7 μmol TE/100 g dry weight) in PC65 (concentrate based on a combination of vegetal proteins), whereas the highest bound PHC levels of 47,087 and 46,531 μmol TE/100 g dry weight were observed in PC65 and the control snacks, respectively. Sensorial attributes assessment provided a high score on the hedonic scale, wherein panelists detected no differences among the samples. Altogether, the selection of non-conventional ingredients with high antioxidant activities emerged as a successful strategy to produce sensory acceptable meals.

Extending Plant Defense Theory to Seeds

Plant defense theory explores how plants invest in defenses against natural enemies but has focused primarily on the traits expressed by juvenile and mature plants. Here we describe the diverse ways in which seeds are chemically and physically defended. We suggest that through associations with other traits, seeds are likely to exhibit defense syndromes that reflect constraints or trade-offs imposed by selection to attract dispersers, enable effective dispersal, ensure appropriate timing of seed germination, and enhance seedling performance. We draw attention to seed and reproductive traits that are analogous to defense traits in mature plants and describe how the effectiveness of defenses is likely to differ at pre- and postdispersal stages. We also highlight recent insights into the mutualistic and antagonistic interactions between seeds and microbial communities, including fungi and endohyphal bacteria, that can influence seed survival in the soil and subsequent seedling vigor.

Modulation of Aleurone Peroxidases in Kernels of Insect-Resistant Maize (Zea mays L.; Pob84-C3R) After Mechanical and Insect Damage

Peroxidases (PODs) have many biological functions during the plant life cycle. In maize kernels, endosperm PODs have been identified as biochemical contributors to resistance against Sitophilus zeamais, but their identities have not been determined. In this study, we identified these PODs and determined whether their contributions are basal or inducible. Semi-purification and LC-MS/MS analyses showed that the protein ZmPrx35 is the predominant soluble endosperm POD from kernels of Pob84-C3R. Subsequent time-course analyses after mechanical damage showed that POD activity was regulated in a fluctuating kinetics pattern and that zmprx35 mRNA expression levels reflected this pattern. After 48 h of infestation with S. zeamais or Prostephanus truncatus, soluble endosperm POD activities were 1.38- or 0.85-fold, respectively. Under the same conditions, zmprx35 expression was induced 1.61-fold (S. zeamais infestation) and 1.17-fold (P. truncatus infestation). These findings suggest that ZmPrx35 contributes to the protective responses of aleurone cells against wounding and pest attacks, which could be enhanced/repressed by insect factors. Our data also provide evidence that the mechanisms of resistance of maize Pob84-C3R kernels toward the insect pests S. zeamais and P. truncatus are independent.

Mining maize diversity and improving its nutritional aspects within agro-food systems

Agro-food systems are undergoing rapid innovation in the world and the system's continuum is promoted at different scales with one of the main outcomes to improve nutrition of consumers. Consumer knowledge through educational outreach is important to food and nutrition security and consumer demands guide breeding efforts. Maize is an important part of food systems. It is a staple food and together with rice and wheat, they provide 60% of the world's caloric intake. In addition to being a major contributor to global food and nutrition security, maize forms an important part of the culinary culture in many areas of Africa, the Americas, and Asia. Maize genetics are being exploited to improve human nutrition with the ultimate outcome of improving overall health. By impacting the health of maize consumers, market opportunities will be opened for maize producers with unique genotypes. Although maize is a great source of macronutrients, it is also a source of many micronutrients and phytochemicals purported to confer health benefits. The process of biofortification through traditional plant breeding has increased the protein, provitamin A carotenoid, and zinc contents of maize. The objective of this paper is to review the innovations developed and promoted to improve the nutritional profiles of maize and outcomes of the maize agro-food system.

Occurrence of deoxynivalenol and zearalenone in brewing barley grains from Brazil

Barley (Hordeum vulgare L.) is an important cereal crop for food and represents one of the main ingredients in beer production. Considering the importance of barley and its derived products, the knowledge about the mycotoxin contamination in the barley production is essential in order to assess its safety. In this study, the levels of deoxynivalenol (DON) and zearalenone (ZEN) in brewing barley were determined using a LC-MS/MS method. A survey was conducted in 2015 to estimate the mycotoxin levels in these products (n = 76) from four crop regions in Brazil. The results showed high levels of DON and ZEN in the analyzed samples, with contamination levels of 94 and 73.6%, respectively. The mean levels of DON and ZEN ranged from 1700 to 7500 μg/kg and from 300 to 630 μg/kg, respectively. Barley samples from regions 1 and 2 presented higher levels of ZEN and DON, respectively, and those from region 4 presented lower levels of both. Co-occurrence of DON and ZEN was seen in the majority of the barley grain samples, and the mycotoxin content was above the maximum levels established by the Brazilian and European regulations.

Identification of B6T173 (ZmPrx35) as the prevailing peroxidase in highly insect-resistant maize (Zea mays, p84C3) kernels by activity-directed purification

Plant peroxidases (PODs) are involved in diverse physiological processes, including defense against pathogens and insects. Contrary to their biological importance, only very few plant PODs have been proven on protein level, because their low abundance makes them difficult to detect in standard proteomics work-flows. A statistically significant positive correlation between POD activity and post-harvest insect resistance has been found for maize (Zea mays, p84C3) kernels. In combining activity-directed protein purification, genomic and proteomic tools we found that protein B6T173 (ZmPrx35) is responsible for the majority of the POD activity of the kernel. We successfully produced recombinant ZmPrx35 protein in Escherichia coli and demonstrate both, in vitro activity and the presence of a haem (heme) cofactor of the enzyme. Our findings support the screening for insect resistant maize variants and the construction of genetically optimized maize plants.

Peroxidase activity in scutella of maize in association with anatomical changes during germination and grain storage

The embryo of the maize grain (Zea mays L.) is separated from the starchy endosperm by a fibrous structure, which is called the fibrous layer (FL). Using histochemical staining, it was determined that the FL is composed of collapsed cellular layers that contain phenols, neutral lipids, and 1,3-β-glucan. Due to its composition, the FL prevents free diffusion and separates the embryo from the endosperm during germination. Twenty-four hours after imbibition, the scutellum epidermis initiated a series of asynchronous spatial modifications, including cell growth, the perforation of cell walls, increased peroxidase activity in the apoplastic space, and elevated levels of superoxide, phenols, and other components that interact with the fibrous layer, enabling its transformation in addition to the free flow between compartments. During storage at high relative humidity levels, which leads to fast or slow deterioration depending on the temperature, the activity of phenol peroxidase in the scutellum was associated with a loss of vigor and reduced germination capacity when compared with low temperature and low relative humidity conditions. Such deterioration is associated with alterations in autofluorescent emissions from endogenous compounds in the scutellum, indicating changes in the microenvironment or in the differential proportions of epidermal and FL components.

Impact of cell wall composition on maize resistance to pests and diseases

In cereals, the primary cell wall is built of a skeleton of cellulosic microfibrils embedded in a matrix of hemicelluloses and smaller amounts of pectins, glycoproteins and hydroxycinnamates. Later, during secondary wall development, p-coumaryl, coniferyl and sinapyl alcohols are copolymerized to form mixed lignins. Several of these cell wall components show a determinative role in maize resistance to pest and diseases. However, defense mechanisms are very complex and vary among the same plant species, different tissues or even the same tissue at different developmental stages. Thus, it is important to highlight that the role of the cell wall components needs to be tested in diverse genotypes and specific tissues where the feeding or attacking by the pathogen takes place. Understanding the role of cell wall constituents as defense mechanisms may allow modifications of crops to withstand pests and diseases.

Activity-directed identification of maize kernel peroxidases associated with postharvest insect resistance

Maize grain peroxidases are associated with insect resistance. In this study we present an activity directed approach for the identification of peroxidases localized in different grain tissues. With drastically reduced proteomic effort we could identify different peroxidases for maize weevil susceptible and resistant genotypes of maize. Our strategy also allows for the identification of previously unknown plant peroxidases.

Demethyloleuropein and beta-glucosidase activity in olive fruits

Demethyloleuropein plays a major role in the defense mechanism of olive fruits. To understand how this molecule is metabolized during different stages of maturation of olive fruits, a biomolecular approach to identify the demethyloleuropein chemistry was employed. The beta-glucosidase activity in crude extracts was assayed spectrophotometrically using the chromogenic substrate p-nitrophenyl-beta-D-glucopyranoside. Demethyloleuropein was extracted and identified by HPLC-MS from both infected and uninfected olive fruits at different physiological stages. The release of more functionally relevant dialdehydes in uninfected fruits was investigated using ESIMS/ MS. In fruits harvested in October, the activity of beta-glucosidase was significantly enhanced in uninfected fruits when compared to the infected fruits. Quantitative differences in the demethyloleuropein content from uninfected fruits showed the highest values (5.09 mg/g) in October, whereas lower levels (4.44 mg/g) were found in infected fruits. The results demonstrated that demethyloleuropein derivatives could be influenced by beta-glucosidase activity to improve the quality of the olive products with the best dialdehyde nutraceutical content.

Delivery methods for peptide and protein toxins in insect control

Since the introduction of DDT in the 1940s, arthropod pest control has relied heavily upon chemical insecticides. However, the development of insect resistance, an increased awareness of the real and perceived environmental and health impacts of these chemicals, and the need for systems with a smaller environmental footprint has stimulated the search for new insecticidal compounds, novel molecular targets, and alternative control methods. In recent decades a variety of biocontrol methods employing peptidic or proteinaceous insect-specific toxins derived from microbes, plants and animals have been examined in the laboratory and field with varying results. Among the many interdependent factors involved with the production of a cost-effective pesticide--production expense, kill efficiency, environmental persistence, pest-specificity, pest resistance-development, public perception and ease of delivery--sprayable biopesticides have not yet found equal competitive footing with chemical counterparts. However, while protein/peptide-based biopesticides continue to have limitations, advances in the technology, particularly of genetically modified organisms as biopesticidal delivery systems, has continually progressed. This review highlights the varieties of delivery methods currently practiced, examining the strengths and weaknesses of each method.

Fighting the global pest problem: preface to the special Toxicon issue on insecticidal toxins and their potential for insect pest control

Arthropod pests are responsible for major crop devastation and are vectors for the transmission of new and re-emerging diseases in humans and livestock. Despite many years of effective control by conventional agrochemical insecticides, a number of factors are threatening the effectiveness and continued use of these agents. These include the development of insecticide resistance and use-cancellation or de-registration of some insecticides due to human health and environmental concerns. Several approaches are being investigated for the design of new (bio)pesticides. These include the development of transgenic plants and recombinant baculoviruses as delivery systems for a variety of insect-selective toxins. Additional approaches for the development of foliar sprays include the rational design of peptidomimetics based on the key residues of these toxins that interact with the insect target. This special issue provides an overview of these phyletically selective animal, plant and microbial toxins and their diverse mechanisms of action to paralyze or kill arthropods. In addition, it reviews their potential for biopesticide discovery and validation of novel insecticide targets and provides an overview of the strengths and weaknesses of biopesticides in the global control of arthropod pests.

Putative role of pith cell wall phenylpropanoids in Sesamia nonagrioides (Lepidoptera: Noctuidae) resistance

The stem borer Sesamia nonagrioides (Lefèbvre) is the most important insect pest that attacks maize, Zea mays L., in northwestern Spain. Host plant resistance to this borer was investigated in relation to the cell wall phenylpropanoids content in the pith. Eight inbred lines that differ in resistance were analyzed. Three major simple phenolic acids, p-coumaric, trans-ferulic, and cis-ferulic acids, and three isomers of diferulic acid, 8-5', 8-O-4', and 8-5'b (benzofuran form), were identified. The amount of all these compounds was correlated with the resistance level in the genotypes, with the resistant inbreds having the highest concentrations. The role of these compounds in cell wall fortification and lignification is well-documented, suggesting their possible intervention in S. nonagrioides resistance. Future studies that focus on these compounds could be useful to enhance S. nonagroides resistance.