Suppressing the activity of trehalase with validamycin disrupts the trehalose and chitin biosynthesis pathways in the rice brown planthopper, Nilaparvata lugens

Regulation of three novel pepper thiothiazolidinones on the fecundity of Spodoptera frugiperda

Spodoptera frugiperda has emerged as a major invasive pest worldwide. The utilization of chemical pesticides not only poses numerous ecological concerns but also fosters resistance in S. frugiperda. In this study, we designed and synthesized three novel thiothiazolidinone compounds (6a, 7b, and 7e) and incorporated innovative thiothiazolidinone structural elements into the piperine skeleton. Treatment with compounds 6a and 7e resulted in the blackening and agglomeration of oviduct eggs within the ovaries of certain female moths, impeding the release of normal eggs. The levels of vitellogenin and vitellogenin receptor, along with three trehalase inhibitors, exhibited a dynamic equilibrium state, leading to no discernible change in egg production but a notable increase in the generation of low-hatching-rate egg fragments. Compared with the injection of 2%DMSO, the eclosion rate of 6a injection was significantly decreased, as followed the spawning time and longevity were prolonged or significantly prolonged in the trehalase inhibitors of 6a, 7b, and 7e. We aimed to investigate the regulatory impacts of three new pepper thiothiazolidinone compounds on the reproduction of S. frugiperda, and to authenticate the efficacy of novel alginase inhibitors in inhibiting the reproduction of S. frugiperda. This research endeavors to aid in the identification of efficient and steadfast trehalase inhibitors, thereby expediting the research and development of potent biological pesticides.

Comparative transcriptome profiling of two pesticides, Acephate and Chlorantraniliprole in non-targeted insect model, Drosophila melanogaster

Acephate and chlorantraniliprole are two insecticides widely used in agricultural applications. Several studies were focused on the mode of action and related biological and cellular level expressions. However, the sub-lethal dose and related molecular expression level of acephate and chlorantraniliprole have not been evaluated or studied to the same degree. In this study, we investigated the sub-lethal toxicity of acephate and chlorantraniliprole in Drosophila melanogaster. The EC50 value was recorded with high difference, and is found to be 1.9 μg/ml and 0.029 μg/ml respectively for acephate and chlorantraniliprole, the difference is simply because of the different modes of action. The 1/5th EC50 concentration was selected for studying the pesticide induced transcriptomics in D. melanogaster. Both pesticides significantly altered the expression profile of several transcripts which are involved in proteolysis, detoxification, chromosome associated proteins and immune response genes and so on. The effect of both pesticides on D. melanogaster was further explored by screening the genes involved in toxicity, which were analyzed using, GO and KEGG pathways. The results revealed that the sub-lethal exposure of both pesticides caused significant changes in the global gene transcription profiles and each pesticide had their unique mode of alteration in the D. melanogaster.

Spraying double-stranded RNA targets UDP-N-acetylglucosamine pyrophosphorylase in the control of Nilaparvata lugens

The rice pest Nilaparvata lugens (the brown planthopper, BPH) has developed different levels of resistance to at least 11 chemical pesticides. RNAi technology has contributed to the development of environmentally friendly RNA biopesticides designed to reduce chemical use. Consequently, more precise targets need to be identified and characterized, and efficient dsRNA delivery methods are necessary for effective field pest control. In this study, a low off-target risk dsNlUAP fragment (166 bp) was designed in silico to minimize the potential adverse effects on non-target organisms. Knockdown of NlUAP via microinjection significantly decreased the content of UDP-N-acetylglucosamine and chitin, causing chitinous structural disorder and abnormal phenotypes in wing and body wall, reduced fertility, and resulted in pest mortality up to 100 %. Furthermore, dsNlUAP was loaded with ROPE@C, a chitosan-modified nanomaterial for spray application, which significantly downregulated the expression of NlUAP, led to 48.9 % pest mortality, and was confirmed to have no adverse effects on Cyrtorhinus lividipennis, an important natural enemy of BPH. These findings will contribute to the development of safer biopesticides for the control of N. lugens.

Identification and RNAi-based function analysis of trehalase family genes in Frankliniella occidentalis (Pergande)

BACKGROUND

Insects utilize trehalases (TREs) to regulate energy metabolism and chitin biosynthesis, which are essential for their growth, development, and reproduction. TREs can therefore be used as potential targets for future insecticide development. However, the roles of TREs in Frankliniella occidentalis (Pergande), a serious widespread agricultural pest, remain unclear.

RESULTS

Three TRE genes were identified in F. occidentalis and cloned, and their functions were then investigated via feeding RNA interference (RNAi) and virus-induced gene silencing (VIGS) assays. The results showed that silencing FoTRE1-1 or FoTRE1-2 significantly decreased expression levels of FoGFAT, FoPGM, FoUAP, and FoCHS, which are members of the chitin biosynthesis pathway. Silencing FoTRE1-1 or FoTRE2 significantly down-regulated FoPFK and FoPK, which are members of the energy metabolism pathway. These changes resulted in 2-fold decreases in glucose and glycogen content, 2-fold increases in trehalose content, and 1.5- to 2.0-fold decreases in chitinase activity. Furthermore, knocking down FoTRE1-1 or FoTRE1-2 resulted in deformed nymphs and pupae as a result of hindered molting. The VIGS assay for the three FoTREs revealed that FoTRE1-1 or FoTRE2 caused shortened ovarioles, and reduced egg-laying and hatching rates.

CONCLUSION

The results suggest that FoTRE1-1 and FoTRE1-2 play important roles in the growth and development of F. occidentalis, while FoTRE1-1 and FoTRE2 are essential for its reproduction. These three genes could be candidate targets for RNAi-based management and control of this destructive agricultural pest. © 2024 Society of Chemical Industry.

Impact of Three Thiazolidinone Compounds with Piperine Skeletons on Trehalase Activity and Development of Spodoptera frugiperda Larvae

Trehalases (TREs) are pivotal enzymes involved in insect development and reproduction, making them prime targets for pest control. We investigated the inhibitory effect of three thiazolidinones with piperine skeletons (6a, 7b, and 7e) on TRE activity and assessed their impact on the growth and development of the fall armyworm (FAW), Spodoptera frugiperda. The compounds were injected into FAW larvae, while the control group was treated with 2% DMSO solvent. All three compounds effectively inhibited TRE activity, resulting in a significant extension of the pupal development stage. Moreover, the treated larvae exhibited significantly decreased survival rates and a higher incidence of abnormal phenotypes related to growth and development compared to the control group. These results suggest that these TRE inhibitors affect the molting of larvae by regulating the chitin metabolism pathway, ultimately reducing their survival rates. Consequently, these compounds hold potential as environmentally friendly insecticides.

Toxicological, biochemical, and in silico investigations of three trehalase inhibitors for new ways to control aphids

Insect trehalases have been identified as promising new targets for pest control. These key enzymes are involved in trehalose hydrolysis and plays an important role in insect growth and development. In this contribution, plant and microbial compounds, namely validamycin A, amygdalin, and phloridzin, were evaluated for their effect, through trehalase inhibition, on Acyrthosiphon pisum aphid. The latter is part of the Aphididae family, main pests as phytovirus vectors and being very harmful for crops. Validamycin A was confirmed as an excellent trehalase inhibitor with an half maximal inhibitory concentration and inhibitor constant of 2.2 × 10-7 and 5 × 10-8 M, respectively, with a mortality rate of ~80% on a A. pisum population. Unlike validamycin A, the insect lethal efficacy of amygdalin and phloridzin did not correspond to their trehalase inhibition, probably due to their hydrolysis by insect β-glucosidases. Our docking studies showed that none of the three compounds can bind to the trehalase active site, unlike their hydrolyzed counterparts, that is, validoxylamine A, phloretin, and prunasin. Validoxylamine A would be by far the best trehalase binder, followed by phloretin and prunasin.

In vivo evaluation of the neurogenotoxic effects of exposure to validamycin A in neuroblasts of Drosophila melanogaster larval brain

Agriculture commonly utilizes crop protection products to tackle infestations from fungi, parasites, insects, and weeds. Validamycin A, an inhibitor of trehalase, possesses antibiotic and antifungal attributes. Epidemiological evidence has led to concerns regarding a potential link between pesticide usage and neurodegenerative diseases. The fruit fly, Drosophila melanogaster, has been recognized as a reliable model for genetic research due to its significant genetic similarities with mammals. Here, we propose to use D. melanogaster as an effective in vivo model system to investigate the genotoxic risks associated with exposure to validamycin A. In this study, we performed a neurotoxic evaluation of validamycin A in D. melanogaster larvae. Several endpoints were evaluated, including toxicity, intracellular oxidative stress (reactive oxygen species), intestinal damage, larval behavior (crawling behavior, light/dark sensitivity assay, and temperature sensitivity assay), locomotor (climbing) behavior, and neurogenotoxic effects (impaired DNA via Comet assay, enhanced by Endo III and formamidopyrimidine DNA glycosylase [FPG]). The results showed that exposure to validamycin A, especially at higher doses (1 and 2.5 mM), induced DNA impairment in neuroblasts as observed by Comet assay. Both larvae and adults exhibited behavioral changes and produced reactive oxygen species. Most importantly, this research represents a pioneering effort to report neurogenotoxicity data specifically in Drosophila larval neuroblasts, thus underscoring the importance of this species as a testing model in exploring the biological impacts of validamycin A. The in vivo findings from the experiments are a valuable and novel addition to the existing validamycin A neurogenotoxicity database.

Gene expression plasticity facilitates different host feeding in Ips sexdentatus (Coleoptera: Curculionidae: Scolytinae)

Host shift is ecologically advantageous and a crucial driver for herbivore insect speciation. Insects on the non-native host obtain enemy-free space and confront reduced competition, but they must adapt to survive. Such signatures of adaptations can often be detected at the gene expression level. It is astonishing how bark beetles cope with distinct chemical environments while feeding on various conifers. Hence, we aim to disentangle the six-toothed bark beetle (Ips sexdentatus) response against two different conifer defences upon host shift (Scots pine to Norway spruce). We conducted bioassay and metabolomic analysis followed by RNA-seq experiments to comprehend the beetle's ability to surpass two different terpene-based conifer defence systems. Beetle growth rate and fecundity were increased when reared exclusively on spruce logs (alternative host) compared to pine logs (native host). Comparative gene expression analysis identified differentially expressed genes (DEGs) related to digestion, detoxification, transporter activity, growth, signalling, and stress response in the spruce-feeding beetle gut. Transporter genes were highly abundant during spruce feeding, suggesting they could play a role in pumping a wide variety of endogenous and xenobiotic compounds or allelochemicals out. Trehalose transporter (TRET) is also up-regulated in the spruce-fed beetle gut to maintain homeostasis and stress tolerance. RT-qPCR and enzymatic assays further corroborated some of our findings. Taken together, the transcriptional plasticity of key physiological genes plays a crucial role after the host shift and provides vital clues for the adaptive potential of bark beetles on different conifer hosts.

The Bmtret1 Gene Family and Its Potential Role in Response to BmNPV Stress in Bombyx mori

Trehalose is a non-reducing disaccharide and participates in physiological activities such as organ formation, energy metabolism, and stress resistance in insects. The Bmtret1 gene family is mainly involved in in the sugar metabolism of silkworm. In the present study, phylogenetic analysis divided 21 Bmtret1 orthologs into three clades. These genes are equally distributed on the nine chromosomes. The cis-elements in the promoter regions of Bmtret1s indicated the possible function of Bmtret1s in response to hormones and environmental stimulus. The qPCR analysis showed the significantly different expression levels of Bmtret1s in different tissues and organs, indicating possible functional divergence. In addition, most Bmtret1s showed disturbed expression levels in response to silkworm nuclear polyhedrosis virus (BmNPV) stresses. Our results provide a clue for further functional dissection of the Tret1s in Bombyx mori and implicate them as potential regulators of antiviral responses.

VdPT1 Encoding a Neutral Trehalase of Verticillium dahliae Is Required for Growth and Virulence of the Pathogen

Verticillum dahliae is a soil-borne phytopathogenic fungus causing destructive Verticillium wilt disease. We previously found a trehalase-encoding gene (VdPT1) in V. dahliae being significantly up-regulated after sensing root exudates from a susceptible cotton variety. In this study, we characterized the function of VdPT1 in the growth and virulence of V. dahliae using its deletion-mutant strains. The VdPT1 deletion mutants (ΔVdPT1) displayed slow colony expansion and mycelial growth, reduced conidial production and germination rate, and decreased mycelial penetration ability and virulence on cotton, but exhibited enhanced stress resistance, suggesting that VdPT1 is involved in the growth, pathogenesis, and stress resistance of V. dahliae. Host-induced silencing of VdPT1 in cotton reduced fungal biomass and enhanced cotton resistance against V. dahliae. Comparative transcriptome analysis between wild-type and mutant identified 1480 up-regulated and 1650 down-regulated genes in the ΔVdPT1 strain. Several down-regulated genes encode plant cell wall-degrading enzymes required for full virulence of V. dahliae to cotton, and down-regulated genes related to carbon metabolism, DNA replication, and amino acid biosynthesis seemed to be responsible for the decreased growth of the ΔVdPT1 strain. In contrast, up-regulation of several genes related to glycerophospholipid metabolism in the ΔVdPT1 strain enhanced the stress resistance of the mutated strain.

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

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

Jinggangmycin stimulates reproduction and increases CHCs-dependent desiccation tolerance in Drosophila melanogaster

Jinggangmycin (JGM), an agricultural antibiotic compound, is mainly used against the rice sheath blight (RSB) Rhizoctonia solani. However, its application may lead to unexpected consequences in insects. In this study, the effects of JGM on the physiological parameters of Drosophila melanogaster were investigated. The results showed that 0.005 g/ml JGM exposure increased female daily egg production and extended the oviposition period, while there was no significant effect on reproduction at 0.016 g/ml. At the same time, desiccation tolerance increased in flies fed 0.005 g/ml JGM. The RT-qPCR results revealed that FAS1 and FAS3 expression were upregulated in 0.005 g/ml JGM treated flies. Consistently, the amount of CHCs accumulated on the cuticle surface increased upon JGM treatment at 0.005 g/ml. Moreover, RNAi for FAS3 decreased desiccation tolerance of JGM-treated flies. These results suggest that JGM affects fatty acid biosynthesis, which in turn enhances reproduction and desiccation tolerance in Drosophila.

Validamycin Inhibits the Synthesis and Metabolism of Trehalose and Chitin in the Oriental Fruit Fly, Bactrocera dorsalis (Hendel)

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a notorious invasive pest that has raised concerns worldwide. Validamycin has been demonstrated to be a very strong inhibitor against trehalase in a variety of organisms. However, whether validamycin can inhibit trehalase activity to suppress trehalose hydrolysis and affect any other relevant physiological pathways in B. dorsalis remains unknown. In this study, the effects of validamycin injection on the synthesis and metabolism of trehalose and chitin were evaluated. The results show that validamycin injection significantly affected trehalase activity and caused trehalose accumulation. In addition, the downstream pathways of trehalose hydrolysis, including the synthesis and metabolism of chitin, were also remarkably affected as the expressions of the key genes in these pathways were significantly regulated and the chitin contents were changed accordingly. Intriguingly, the upstream trehalose synthesis was also affected by validamycin injection due to the variations in the expression levels of key genes, especially BdTPPC1. Moreover, BdTPPC1 was predicted to have a binding affinity to validamycin, and the subsequent in vitro recombinant enzyme activity assay verified the inhibitory effect of validamycin on BdTPPC1 activity for the first time. These findings collectively indicate that validamycin can be considered as a promising potential insecticide for the management of B. dorsalis.

Roles of GFAT and PFK genes in energy metabolism of brown planthopper, Nilaparvata lugens

Glutamine:fructose-6-phosphate aminotransferases (GFATs) and phosphofructokinase (PFKs) are the principal rate-limiting enzymes involved in hexosamine biosynthesis pathway (HBP) and glycolysis pathway, respectively. In this study, the NlGFAT and NlPFK were knocked down through RNA interference (RNAi) in Nilaparvata lugens, the notorious brown planthopper (BPH), and the changes in energy metabolism were determined. Knockdown of either NlGFAT or NlPFK substantially reduced gene expression related to trehalose, glucose, and glycogen metabolism pathways. Moreover, trehalose content rose significantly at 72 h after dsGFAT injection, and glycogen content increased significantly at 48 h after injection. Glucose content remained unchanged throughout the experiment. Conversely, dsPFK injection did not significantly alter trehalose, but caused an extreme increase in glucose and glycogen content at 72 h after injection. The Knockdown of NlGFAT or NlPFK significantly downregulated the genes in the glycolytic pathway, as well as caused a considerable and significant decrease in pyruvate kinase (PK) activity after 48 h and 72 h of inhibition. After dsGFAT injection, most of genes in TCA cycle pathway were upregulated, but after dsNlPFK injection, they were downregulated. Correspondingly, ATP content substantially increased at 48 h after NlGFAT knockdown but decreased to an extreme extent by 72 h. In contrast, ATP content decreased significantly after NlPFK was knocked down and returned. The results have suggested the knockdown of either NlGFAT or NlPFK resulted in metabolism disorders in BPHs, highlighting the difference in the impact of those two enzyme genes on energy metabolism. Given their influence on BPHs energy metabolism, developing enzyme inhibitors or activators may provide a biological control for BPHs.

Chlorbenzuron caused growth arrest through interference of glycolysis and energy metabolism in Hyphantria cunea (Lepidoptera: Erebidae) larvae

Chlorbenzuron is a kind of benzoylphenylureas (BPUs), which plays a broad role in insect growth regulators (IGRs), with an inhibitory effect on chitin biosynthesis. However, BPUs how to regulate glycolysis and insect growth remains largely unclear. Here, we investigated the effects of chlorbenzuron on growth, nutritional indices, glycolysis, and carbohydrate homeostasis in Hyphantria cunea, a destructive and highly polyphagous forest pest, to elucidate the action mechanism of chlorbenzuron from the perspective of energy metabolism. The results showed that chlorbenzuron dramatically restrained the growth and nutritional indices of H. cunea larvae and resulted in lethality. Meanwhile, we confirmed that chlorbenzuron significantly decreased carbohydrate levels, adenosine triphosphate (ATP), and pyruvic acid (PA) in H. cunea larvae. Further studies indicated that chlorbenzuron caused a significant enhancement in the enzyme activities and mRNA expressions of hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK), resulting in increased glycolytic flux. Expressions of genes involved in the AMP-activated protein kinase (AMPK) signaling pathway were also upregulated. Moreover, chlorbenzuron had remarkable impacts on H. cunea larvae from the perspective of metabolite enrichment, including the tricarboxylic acid (TCA) cycle and glycolysis, indicating an energy metabolism disorder in larvae. The findings provide a novel insight into the molecular mechanism by which chlorbenzuron abnormally promotes glycolysis and eventually interferes with insect growth and nutritional indices.

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

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

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

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

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

Glycosylated quantum dots as fluorometric nanoprobes for trehalase

Trehalase is an important enzyme in the metabolic cascades of many organisms, catalysing the hydrolysis of the disaccharide trehalose. Herein we describe the first examples of fluorometric nanoprobes for detection of trehalase, based on trehalose-functionalised quantum dots (QDs). QDs cross-linked with trehalose form aggregates, which are released upon enzymatic cleavage of the trehalose glycosidic bond proportionally to the enzyme concentration, offering a unique and efficient approach for specific sensing of this biologically important enzyme.

The effect of chlorantraniliprole on the transcriptomic profile of Spodoptera frugiperda: a typical case analysis for the response of a newly invaded pest to an old insecticide

BACKGROUND

Chlorantraniliprole is a diamide insecticide widely used in China over the last 15 years. The fall armyworm (FAW), Spodoptera frugiperda, newly invaded China in 2019. The response of FAW to chlorantraniliprole deserves more attention, in the context of many destructive lepidopteran species are resistant to diamide insecticides and the patent on core chemical of chlorantraniliprole in China expired in August 2022.

METHODS AND RESULTS

This study investigated the response profile in larvae under chlorantraniliprole-induced (LC₅₀) stress using methods of bioassay, RNA-Seq and qPCR. We observed growth inhibition and lethal effects in FAW larvae, but at a relatively high LC₅₀ value compared to other several pests. Additionally, under chlorantraniliprole-induced stress, 3309 unigenes were found to be differentially expressed genes. The impacted genes included 137 encoding for detoxification enzymes, 29 encoding for cuticle proteins, and 20 key enzymes involved in the chitin metabolism, which all associated with metabolic resistance. Finally, we obtained the single nucleotide polymorphisms (SNPs) of two RyR genes, which are the target proteins for chlorantraniliprole. We also investigated the causes of the high LC₅₀ value in our FAW, which possibly related to the stabilized 4743 M on SNP frequency of RyR. These findings documented the genetic background of RyR of FAW and indicated that application of chlorantraniliprole has a high risk of controlling FAW in China.

CONCLUSION

In brief, our results provide a better understanding of the mechanisms of chlorantraniliprole toxicity and detoxification in FAW, and will aid in monitoring the development of resistant strains for a newly pest to an old insecticide.

Targeting Aedes aegypti Metabolism with Next-Generation Insecticides

Aedes aegypti is the primary vector of dengue virus (DENV), zika virus (ZIKV), and other emerging infectious diseases of concern. A key disease mitigation strategy is vector control, which relies heavily on the use of insecticides. The development of insecticide resistance poses a major threat to public health worldwide. Unfortunately, there is a limited number of chemical compounds available for vector control, and these chemicals can have off-target effects that harm invertebrate and vertebrate species. Fundamental basic science research is needed to identify novel molecular targets that can be exploited for vector control. Next-generation insecticides will have unique mechanisms of action that can be used in combination to limit selection of insecticide resistance. Further, molecular targets will be species-specific and limit off-target effects. Studies have shown that mosquitoes rely on key nutrients during multiple life cycle stages. Targeting metabolic pathways is a promising direction that can deprive mosquitoes of nutrition and interfere with development. Metabolic pathways are also important for the virus life cycle. Here, we review studies that reveal the importance of dietary and stored nutrients during mosquito development and infection and suggest strategies to identify next-generation insecticides with a focus on trehalase inhibitors.

Trehalose-6-phosphate phosphatases are involved in trehalose synthesis and metamorphosis in Bactrocera minax

Trehalose is the principal sugar circulating in the hemolymph of insects, and trehalose synthesis is catalyzed by trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP). Insect TPS is a fused enzyme containing both TPS domain and TPP domain. Thus, many insects do not possess TPP genes as TPSs have replaced the function of TPPs. However, TPPs are widely distributed across the dipteran insects, while the roles they play remain largely unknown. In this study, 3 TPP genes from notorious dipteran pest Bactrocera minax (BmiTPPB, BmiTPPC1, and BmiTPPC2) were identified and characterized. The different temporal-spatial expression patterns of 3 BmiTPPs implied that they exert different functions in B. minax. Recombinant BmiTPPs were heterologously expressed in yeast cells, and all purified proteins exhibited enzymatic activities, despite the remarkable disparity in performance between BmiTPPB and BmiTPPCs. RNA interference revealed that all BmiTPPs were successfully downregulated after double-stranded RNA injection, leading to decreased trehalose content and increased glucose content. Also, suppression of BmiTPPs significantly affected expression of downstream genes and increased the mortality and malformation rate. Collectively, these results indicated that all 3 BmiTPPs in B. minax are involved in trehalose synthesis and metamorphosis. Thus, these genes could be evaluated as insecticidal targets for managing B. minax, and even for other dipteran pests.

The uncommon function and mechanism of the common enzyme glyceraldehyde-3-phosphate dehydrogenase in the metamorphosis of Helicoverpa armigera

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis, is commonly used as an internal reference gene in humans, mice, and insects. However, the function of GAPDH in insect development, especially in metamorphosis, has not been reported. In the present study, Helicoverpa armigera and Spodoptera frugiperda ovarian cell lines (Sf9 cells) were used as materials to study the function and molecular mechanism of GAPDH in larval metamorphosis. The results showed that HaGAPDH was more closely related to GAPDH of S. frugiperda and Spodoptera litura. The transcript peaks of HaGAPDH in sixth instar larvae were 6L-3 (epidermal and midgut) and 6L-1 (fat body) days, and 20E and methoprene significantly upregulated the transcripts of HaGAPDH of larvae in qRT-PCR. HaGAPDH–GFP–His was specifically localized in mitochondria in Sf9 cells. Knockdown of HaGAPDH by RNA interference (RNAi) in sixth instar larvae resulted in weight loss, increased mortality, and decreases in the pupation rate and emergence rates. HaGAPDH is directly bound to soluble trehalase (HaTreh1) physically and under 20E treatment in yeast two-hybrid, coimmunoprecipitation, and colocalization experiments. In addition, knockdown of HaGAPDH increased the Treh1 activity, which in turn decreased the trehalose content but increased the glucose content in larvae. Therefore, these data demonstrated that GAPDH controlled the glucose content within the normal range to ensure glucose metabolism and metamorphosis by directly binding with HaTreh1.

Chitinase (CHI) of Spodoptera frugiperda affects molting development by regulating the metabolism of chitin and trehalose

Chitin is the main component of insect exoskeleton and midgut peritrophic membrane. Insect molting is the result of the balance and coordination of chitin synthesis and degradation in chitin metabolism under the action of hormones. In this study, a 678 bp dsRNA fragment was designed and synthesized according to the known CHI (Chitinase) sequence of Spodoptera frugiperda. It was injected into the larvae to observe the molting and development of S. frugiperda. At the same time, the activities of trehalase and chitinase, the contents of trehalose, chitin and other substances were detected, and the expression of related genes in the chitin synthesis pathway was determined. The results showed that CHI gene was highly expressed at the end of each instar, prepupa and pupal stage before molting; At 12 and 24 h after dsRNA injection of CHI gene of S. frugiperda, the expression of CHI gene decreased significantly, and the chitinase activity decreased significantly from 12 to 48 h. The expression of chitin synthase (CHSB) gene decreased significantly, and the chitin content increased significantly. Some larvae could not molt normally and complete development, leading to certain mortality. Secondly, after RNAi of CHI gene, the content of glucose and glycogen increased first and then decreased, while the content of trehalose decreased significantly or showed a downward trend. The activities of the two types of trehalase and the expression levels of trehalase genes decreased first and then increased, especially the trehalase activities increased significantly at 48 h after dsCHI injection. And trehalose-6-phosphate synthase (TPS), glutamine: fructose-6-phosphate amidotransferase (GFAT), UDP-N-acetylglucosamine pyrophosphorylases (UAP), hexokinase (HK), glucose-6-phosphate isomerase (G6PI) and phosphoacetylglucosamine mutase (PAGM) all decreased significantly at 24 h, and then increased or significantly increased at 48 h. These results indicated that when the expression of chitinase gene of S. frugiperda was inhibited, it affected the degradation of chitin in the old epidermis and the formation of new epidermis, and the content of chitin increased, which led to the failure of larvae to molt normally. Moreover, the chitin synthesis pathway and trehalose metabolism were also regulated. The relevant results provide a theoretical basis for screening target genes and developing green insecticides to control pests by using the chitin metabolism pathway.

E74 knockdown represses larval development and chitin synthesis in Hyphantria cunea

E74 is a key transcription factor induced by 20E, which plays a broad role in many physiological events during insect growth and development, including vitellogenesis, organ remodeling and new tissue formation, programmed cell death and metamorphosis. However, whether it is involved in regulating insect chitin biosynthesis remains largely unclear. Here, the E74 gene was identified for the first time from Hyphantria cunea, a notorious defoliator of forestry. Thereafter, the role of HcE74 in regulating growth, development and chitin synthesis in H. cunea larvae was evaluated. Bioinformatics analysis showed that HcE74 shared the highest identity (95.53%) with E74A of Spodoptera litura, which belonged to Ets superfamily. The results of RNAi bioassay showed that the larval mortality on 6 d after HcE74 knockdown was up to 51.11 ± 6.94%. Meanwhile, a distinct developmental deformity phenotype was found when HcE74 was silenced. These results indicated that HcE74 plays an important role in the development and molting of H. cunea larvae. Moreover, HcE74 knockdown also significantly decreased the expression of four key genes related to chitin synthesis, including glucose-6-phosphate isomerase (HcG6PI), UDP-N-acetylglucosamine pyrophosphorylase (HcUAP), chitin synthetase A (HcCHSA), and chitin synthetase B (HcCHSB). As a result, the content of chitin in midgut and epidermis decreased by 0.54- and 0.08-fold, respectively. Taken together, these results demonstrated that HcE74 not only plays a critical role in the growth and molting of H. cunea larvae, but also probably participates in the transcriptional regulation of genes involved in chitin biosynthesis.

Parasitoid Wasps Can Manipulate Host Trehalase to the Benefit of Their Offspring

Trehalase is an essential hydrolase of trehalose in insects. However, whether and how trehalase performs in the association of parasitoid wasps and their hosts still remains unknown. Here, the exact function of trehalase of the general cutworm Spodoptera litura after it was parasitized by its predominant endoparasitoid Meterous pulchricornis was elucidated. Two trehalase genes (SlTre1, SlTre2) were identified, and they were highly expressed five days after parasitization by M. pulchricornis. Then, we successfully silenced SlTre1 and SlTre2 in parasitized third instar S. litura larvae. The content of glucose, which is the hydrolysate of trehalose, was significantly decreased after silencing SlTres in parasitized S. litura larvae, and the activities of trehalase were also notably reduced. In addition, the cocoon weight, the emergence rate, proportion of normal adults, and the body size of parasitoid offsprings were significantly decreased in SlTre1- or SlTre2-silenced groups compared to the controls. These results implied that parasitization by parasitoids regulated the trehalase of host larvae to create a suitable nutritional environment for the parasitoid offspring. The present study broadens the knowledge of trehalase in the interaction between parasitoids and their hosts and is of benefit to biological control of S. litura acting by parasitoid wasps.

PxTret1-like Affects the Temperature Adaptability of a Cosmopolitan Pest by Altering Trehalose Tissue Distribution

Global warming poses new challenges for insects to adapt to higher temperatures. Trehalose is the main blood sugar in insects and plays an important role in energy metabolism and stress resistance. The transmembrane transport of trehalose mainly depends on the trehalose transporter (TRET1). Plutella xylostella (L.) is a worldwide agricultural pest; however, the effects of the trehalose transport mechanism and trehalose distribution in tissues on the development, reproduction and temperature adaptation of P. xylostella have yet to be reported. In this study, PxTret1-like was cloned and analyzed regarding its expression pattern. It was found that the expression of PxTret1-like was affected by ambient temperature. The knockout mutation of PxTret1-like was generated using a CRISPR/Cas9 system by targeted knockout. The trehalose content and trehalase activity of mutant P. xylostella increased at different developmental stages. The trehalose content increased in the fat body of the fourth-instar P. xylostella, and decreased in the hemolymph, and there was no significant change in glucose in the fat body and hemolymph. Mutant strains of P. xylostella showed a significantly reduced survival rate, fecundity and ability to withstand extreme temperatures. The results showed that PxTret1-like could affect the development, reproduction and temperature adaptability of P. xylostella by regulating the trehalose content in the fat body and hemolymph.

Validamycin treatment significantly inhibits the glycometabolism and chitin synthesis in the common cutworm, Spodoptera litura

Validamycin, as a broadly applied antibiotic, has been used to control rice sheath blight disease. Furthermore, validamycin was considered as an insecticide to control agricultural pests. Insight into the mechanism of validamycin's action on insects can provide molecular targets for the control of agricultural pests. In this study, a toxicological test analysis revealed that Spodoptera litura larval growth and development was significantly inhibited and the pupation rate was significantly reduced with the increase of the concentration of validamycin. According to the NMR-based metabolomic analysis, a total of 15 metabolites involved in glycolysis and tricarboxylic acid cycle (TCA) pathways were identified. Additionally, trehalase activities, glucose and chitin contents were significantly downregulated, but the trehalose content was upregulated after exposure to validamycin. Reverse transcription quantitative PCR analysis revealed that the expression level of genes involved in glycolysis, TCA and chitin synthesis were upregulated after treating with validamycin. Further chitin staining also confirmed that chitin content was downregulated at 12 h after validamycin treatment. Our results indicated that validamycin worked via two different molecular mechanisms, one through inhibiting glycometabolism and the other by inhibiting chitin synthesis in S. litura. The information lays a theoretical foundation for further control of S. litura.

Metformin-induced AMPK activation suppresses larval growth and molting probably by disrupting 20E synthesis and glycometabolism in fall webworm, Hyphantria cunea Drury

Metformin, considered to be a potent AMPK activator, is widely used for clinical therapy of cancer and diabetes due to its distinct function in regulating cell energy balance and body metabolism. However, the effect of metformin-induced AMPK activation on the growth and development of insects remains largely unknown. In the present study, we focused on the role of metformin in regulating the growth and development of Hyphantria cunea, a notorious defoliator in the forestry. Firstly, we obtained the complete coding sequences of HcAMPKα2, HcAMPKβ1, HcAMPKγ2 from H. cunea, which encoded a protein of 512, 281, and 680 amino acids respectively. Furthermore, the phylogenetic analysis revealed that these three subunits were highly homologous with the AMPK subunits from other lepidopteran species. According to the bioassay, we found metformin remarkably restrained the growth and development of H. cunea larvae, and caused molting delayed and body weight reduced. In addition, expressions of HcAMPKα2, HcAMPKβ1, and HcAMPKγ2 were upregulated 3.30-, 5.93- and 5.92-folds at 24 h after treatment, confirming that metformin activated AMPK signaling at the transcriptional level in H. cunea larvae. Conversely, the expressions of two vital Halloween genes (HcCYP306A1 and HcCYP314A1) in the 20E synthesis pathway were remarkably suppressed by metformin. Thus, we presumed that metformin delayed larval molting probably by impeding 20E synthesis in the H. cunea larvae. Finally, we found that metformin accelerated glycogen breakdown, elevated in vivo trehalose level, promoted chitin synthesis, and upregulated transcriptions of the genes in chitin synthesis pathway. Taken together, the findings provide a new insight into the molecular mechanisms by which AMPK regulates carbohydrate metabolism and chitin synthesis in insects.

The vital hormone 20-hydroxyecdysone controls ATP production by upregulating binding of trehalase 1 with ATP synthase subunit α in Helicoverpa armigera

Trehalose is the major “blood sugar” of insects and it plays a crucial role in energy supply and as a stress protectant. The hydrolysis of trehalose occurs only under the enzymatic control of trehalase (Treh), which plays important roles in growth and development, energy supply, chitin biosynthesis, and abiotic stress responses. Previous reports have revealed that the vital hormone 20-hydroxyecdysone (20E) regulates Treh, but the detailed mechanism underlying 20E regulating Treh remains unclear. In this study, we investigated the function of HaTreh1 in Helicoverpa armigera larvae. The results showed that the transcript levels and enzymatic activity of HaTreh1 were elevated during molting and metamorphosis stages in the epidermis, midgut, and fat body, and that 20E upregulated the transcript levels of HaTreh1 through the classical nuclear receptor complex EcR-B1/USP1. HaTreh1 is a mitochondria protein. We also found that knockdown of HaTreh1 in the fifth- or sixth-instar larvae resulted in weight loss and increased mortality. Yeast two-hybrid, coimmunoprecipitation, and glutathione-S-transferase (GST) pull-down experiments demonstrated that HaTreh1 bound with ATP synthase subunit alpha (HaATPs-α) and that this binding increased under 20E treatment. In addition, 20E enhanced the transcript level of HaATPs-α and ATP content. Finally, the knockdown of HaTreh1 or HaATPs-α decreased the induction effect of 20E on ATP content. Altogether, these findings demonstrate that 20E controls ATP production by up-regulating the binding of HaTreh1 to HaATPs-α in H. armigera.

Integrated transcriptome sequencing and RNA interference reveals molecular changes in Diaphorina citri after exposure to validamycin

Validamycin has been widely used as a specific competitive inhibitor of trehalase. In our previous research, validamycin significantly inhibited trehalase activity and chitin synthesis in Diaphorina citri, resulting in abnormal phenotypes. However, the mechanism of validamycin's action on D. citri remains unclear. Here, using a comparative transcriptome analysis, 464 differentially expressed genes (DEGs) in D. citri were identified after validamycin treatment. A Gene Ontology enrichment analysis revealed that these DEGs were mainly involved in "small molecule process", "structural molecule activity" and "transition metal ion binding". DEGs involved in chitin metabolism, cuticle synthesis and insecticide detoxification were validated by reverse transcription quantitative polymerase chain reaction. The RNA interference of D. citri chitinase-like protein ENO3 and D. citri cuticle protein 7 genes significantly affected D. citri molting. Moreover, the recombinant chitinase-like protein ENO3 exhibited a chitin-binding property, and an antimicrobial activity against Bacillus subtilis. This study provides a first insight into the molecular changes in D. citri after exposure to validamycin and identifies two effective RNA interference targets for D. citri control.

Trehalase inhibition by validamycin A may be a promising target to design new fungicides and insecticides

The introduction of insecticides and fungicides in agriculture has improved crop yields and, consequently, the quality of life for many people, especially in what is widely considered as the 'first world'. However, the indiscriminate use of dangerous chemical insecticides has led to pest resistance, human and animal poisoning and environmental pollution. Biochemical and genetic evidence concludes that the non-reducing disaccharide trehalose plays an essential role in the pathobiology of many insects and fungi. Both organisms share identical pathway for trehalose biosynthesis (the TPS/TPP pathway), while a high degree of homology in their trehalose hydrolysis capacity (trehalase activities) has also been demonstrated. In the search for new, effective and environmentally sustainable compounds, a set of trehalase inhibitors has emerged as a potentially interesting antifungal and insecticidal target. In particular, the trehalose analogue, Validamycin A, which has a strong inhibitory effect on several trehalases, has been successfully introduced for the treatment of various diseases caused by insects and fungi. Herein, we review the main features of the specific interaction between Validamycin A and trehalase as well as the expected advantages of the applications based on trehalase inhibition as insecticides and fungicides. © 2021 Society of Chemical Industry.

Optimizing Efficient RNAi-Mediated Control of Hemipteran Pests (Psyllids, Leafhoppers, Whitefly): Modified Pyrimidines in dsRNA Triggers

The advantages from exogenously applied RNAi biopesticides have yet to be realized in through commercialization due to inconsistent activity of the dsRNA trigger, and the activity level of RNAi suppression. This has prompted research on improving delivery methods for applying exogenous dsRNA into plants and insects for the management of pests and pathogens. Another aspect to improve RNAi activity is the incorporation of modified 2′-F pyrimidine nucleotides into the dsRNA trigger. Modified dsRNA incorporating 32–55% of the 2′-F- nucleotides produced improved RNAi activity that increased insect mortality by 12–35% greater than non-modified dsRNA triggers of the same sequence. These results were repeatable across multiple Hemiptera: the Asian citrus psyllid (Diaphorina citri, Liviidae); whitefly (Bemisia tabaci, Aleyroididae); and the glassy-winged sharpshooter (Homalodisca vitripennis, Cicadellidae). Studies using siRNA with modified 2′-F- pyrimidines in mammalian cells show they improved resistance to degradation from nucleases, plus result in greater RNAi activity, due to increase concentrations and improved binding affinity to the mRNA target. Successful RNAi biopesticides of the future will be able to increase RNAi repeatability in the field, by incorporating modifications of the dsRNA, such as 2′-F- pyrimidines, that will improve delivery after applied to fruit trees or crop plants, with increased activity after ingestion by insects. Costs of RNA modification have decreased significantly over the past few years such that biopesticides can now compete on pricing with commercial chemical products.

Combined Transcriptomic Analysis and RNA Interference Reveal the Effects of Methoxyfenozide on Ecdysone Signaling Pathway of Spodoptera exigua

Spodoptera exigua is a worldwide pest afflicting edible vegetables and has developed varying levels of resistance to insecticides. Methoxyfenozide (MET), an ecdysteroid agonist, is effective against lepidopteran pests such as S. exigua. However, the mechanism of MET to S. exigua remains unclear. In this study, we analyzed the expression patterns of genes related to the ecdysone signaling pathway in transcriptome data treated with sublethal doses of MET and analyzed how expression levels of key genes affect the toxicity of MET on S. exigua. Our results demonstrated that 2639 genes were up-regulated and 2512 genes were down-regulated in S. exigua treated with LC₃₀ of MET. Of these, 15 genes were involved in the ecdysone signaling pathway. qPCR results demonstrated that ecdysone receptor A (EcRA) expression levels significantly increased in S. exigua when treated with different doses of MET, and that the RNAi-mediated silencing of EcRA significantly increased mortality to 55.43% at 72 h when L3 S. exigua larvae were exposed to MET at the LC₃₀ dose. Additionally, knocking down EcRA suppressed the most genes expressed in the ecdysone signaling pathway. The combination of MET and dsEcRA affected the expression of E74 and enhanced the expression of TREA. These results demonstrate that the adverse effects of sublethal MET disturb the ecdysone signaling pathway in S. exigua, and EcRA is closely related to MET toxic effect. This study increases our collective understanding of the mechanisms of MET in insect pests.

Comparative genomic analysis of azasugar biosynthesis

Azasugars are monosaccharide analogs in which the ring oxygen is replaced with a nitrogen atom. These well-known glycosidase inhibitors are of interest as therapeutics, yet several aspects of azasugars remain unknown including their distribution, structural diversity, and chemical ecology. The hallmark signature of bacterial azasugar biosynthesis is a three gene cluster (3GC) coding for aminotransferase, phosphatase, and dehydrogenase enzymes. Using the bioinformatics platform Enzyme Similarity Tool (EST), we identified hundreds of putative three gene clusters coding for azasugar production in microbial species. In the course of this work, we also report a consensus sequence for the aminotransferase involved in azasugar biosynthesis as being: SGNXFRXXXFPNXXXXXXXLXVPXPYCXRC. Most clusters are found in Bacillus and Streptomyces species which typically inhabit soil and the rhizosphere, but some clusters are found with diverse species representation such as Photorhabdus and Xenorhabdus which are symbiotic with entomopathogenic nematodes; the human skin commensal Cutibacterium acnes, and the marine Bacillus rugosus SPB7, a symbiont to the sea sponge Spongia officinalis. This pan-taxonomic survey of the azasugar 3GC signature may lead to the identification of new azasugar producers, facilitate studies of their natural functions, and lead to new potential therapeutics.

Characterization and functional analysis of chitinase family genes involved in nymph-adult transition of Sogatella furcifera

Chitinase degrades chitin in the old epidermis or peritrophic matrix of insects, which ensures normal development and metamorphosis. In our previous work, we comprehensively studied the function of SfCht7 in Sogatella furcifera. However, the number and function of chitinase genes in S. furcifera remain unknown. Here, we identified 12 full-length chitinase transcripts from S. furcifera, which included nine chitinase (Cht), two imaginal disc growth factor (IDGF), and one endo-β-N-acetylglucosaminidase (ENGase) genes. Expression analysis results revealed that the expression levels of eight genes (SfCht3, SfCht5, SfCht6-1, SfCht6-2, SfCht7, SfCht8, SfCht10, and SfIDGF2) with similar transcript levels peaked prior to molting of each nymph and were highly expressed in the integument. Based on RNA interference (RNAi), description of the functions of each chitinase gene indicated that the silencing of SfCht5, SfCht10, and SfIDGF2 led to molting defects and lethality. RNAi inhibited the expressions of SfCht5, SfCht7, SfCht10, and SfIDGF2, which led to downregulated expressions of chitin synthase 1 (SfCHS1, SfCHS1a, and SfCHS1b) and four chitin deacetylase genes (SfCDA1, SfCDA2, SfCDA3, and SfCDA4), and caused a change in the expression level of two trehalase genes (TRE1 and TRE2). Furthermore, silencing of SfCht7 induced a significant decrease in the expression levels of three wing development-related genes (SfWG, SfDpp, and SfHh). In conclusion, SfCht5, SfCht7, SfCht10, and SfIDGF2 play vital roles in nymph-adult transition and are involved in the regulation of chitin metabolism, and SfCht7 is also involved in wing development; therefore, these genes are potential targets for control of S. furcifera.

The fitness advantages of bistrifluron resistance related to chitin synthase A in Spodoptera litura (Fab.) (Noctuidae: Lepidoptera)

BACKGROUND

Spodoptera litura is one of the major agricultural pests in China, and it has developed serious resistance to many traditional chemical insecticides. In the present study, the bistrifluron-resistant (Bis-SEL) strain accompanied by a higher oviposition, 113.8-fold RR compared to the bistrifluron-susceptible (Bis-UNSEL) strain, was obtained by bidirectional screening. A comparison of their gonad coefficiency and genes related to oviposition or resistance was used to elucidate the resurgence mechanism.

RESULTS

The ovarian index, oviposition, and potential egg production in the Bis-SEL strain of female adults were significantly higher than those in the Bis-UNSEL strain, and the length of ovariole in the Bis-SEL strain was also significantly elongated. The protein contents of vitellogenin (Vg) and vitellogenin receptor (VgR) in the Bis-UNSEL strain were lower than those in the Bis-SEL strain, consistent with their gene expressions levels, and there was a significantly positive linear correlation between Vg and VgR protein contents, further confirming that resistant strains have high reproductive fitness. Moreover, the chitin synthase A in the Bis-SEL strain was clearly up-regulated, and a mutation (H866Y) near the QRRRW in the catalytic domain caused a rise in the hydrogen bond between UDP-GlcNAc and chitin synthase, and its chitin content was higher than that in the Bis-UNSEL strain. Nevertheless, the sensitivity of the Bis-SEL strain to bistrifluron was significantly recovered when it was knocked down though RNA interference.

CONCLUSION

The fitness advantages of bistrifluron resistance may be related to the up-regulation and mution of chitin synthase A. © 2021 Society of Chemical Industry.

Inhibition of trehalase affects the trehalose and chitin metabolism pathways in Diaphorina citri (Hemiptera: Psyllidae)

The Asian citrus psyllid, Diaphorina citri is the principal vector of huanglongbing, which transmits Candidatus Liberibacter asiaticus. Trehalase is a key enzyme involved in trehalose hydrolysis and plays an important role in insect growth and development. The specific functions of this enzyme in D. citri have not been determined. In this study, three trehalase genes (DcTre1-1, DcTre1-2, and DcTre2) were identified based on the D. citri genome database. Bioinformatic analysis showed that DcTre1-1 and DcTre1-2 are related to soluble trehalase, whereas DcTre2 is associated with membrane-bound trehalase. Spatiotemporal expression analysis indicated that DcTre1-1 and DcTre1-2 had the highest expression levels in the head and wing, respectively, and DcTre2 had high expression levels in the fat body. Furthermore, DcTre1-1 and DcTre1-2 expression levels were induced by 20-hydroxyecdysone and juvenile hormone Ⅲ, but DcTre2 was unaffected. The expression levels of DcTre1-1, DcTre1-2, and DcTre2 were significantly upregulated, which resulted in high mortality after treatment with validamycin. Trehalase activities and glucose contents were downregulated, but the trehalose content increased after treatment with validamycin. In addition, the expression levels of chitin metabolism-related genes significantly decreased at 24 and 48 h after treatment with validamycin. Furthermore, silencing of DcTre1-1, DcTre1-2, and DcTre2 reduced the expression levels of chitin metabolism-related genes and led to a malformed phenotype of D. citri. These results indicate that D. citri trehalase plays an essential role in regulating chitin metabolism and provides a new target for control of D. citri.

Cloning, Characterization, and RNA Interference Effect of the UDP-N-Acetylglucosamine Pyrophosphorylase Gene in Cnaphalocrocis medinalis

The rice leaf folder, Cnaphalocrocis medinalis is a major pest of rice and is difficult to control. UDP-N-acetylglucosamine pyrophosphorylase (UAP) is a key enzyme in the chitin synthesis pathway in insects. In this study, the UAP gene from C. medinalis (CmUAP) was cloned and characterized. The cDNA of CmUAP is 1788 bp in length, containing an open reading frame of 1464 nucleotides that encodes 487 amino acids. Homology and phylogenetic analyses of the predicted protein indicated that CmUAP shared 91.79%, 87.89%, and 82.75% identities with UAPs of Glyphodes pyloalis, Ostrinia furnacalis, and Heortia vitessoides, respectively. Expression pattern analyses by droplet digital PCR demonstrated that CmUAP was expressed at all developmental stages and in 12 tissues of C. medinalis adults. Silencing of CmUAP by injection of double-stranded RNA specific to CmUAP caused death, slow growth, reduced feeding and excretion, and weight loss in C. medinalis larvae; meanwhile, severe developmental disorders were observed. The findings suggest that CmUAP is essential for the growth and development of C. medinalis, and that targeting the CmUAP gene through RNAi technology can be used for biological control of this insect.

GFAT and PFK genes show contrasting regulation of chitin metabolism in Nilaparvata lugens

Glutamine:fructose-6-phosphate aminotransferase (GFAT) and phosphofructokinase (PFK) are enzymes related to chitin metabolism. RNA interference (RNAi) technology was used to explore the role of these two enzyme genes in chitin metabolism. In this study, we found that GFAT and PFK were highly expressed in the wing bud of Nilaparvata lugens and were increased significantly during molting. RNAi of GFAT and PFK both caused severe malformation rates and mortality rates in N. lugens. GFAT inhibition also downregulated GFAT, GNPNA, PGM1, PGM2, UAP, CHS1, CHS1a, CHS1b, Cht1-10, and ENGase. PFK inhibition significantly downregulated GFAT; upregulated GNPNA, PGM2, UAP, Cht2-4, Cht6-7 at 48 h and then downregulated them at 72 h; upregulated Cht5, Cht8, Cht10, and ENGase; downregulated Cht9 at 48 h and then upregulated it at 72 h; and upregulated CHS1, CHS1a, and CHS1b. In conclusion, GFAT and PFK regulated chitin degradation and remodeling by regulating the expression of genes related to the chitin metabolism and exert opposite effects on these genes. These results may be beneficial to develop new chitin synthesis inhibitors for pest control.

RNA interference of trehalose-6-phosphate synthase and trehalase genes regulates chitin metabolism in two color morphs of Acyrthosiphon pisum Harris

Trehalose-6-phosphate synthase (TPS) and trehalase (TRE) directly regulate trehalose metabolism and indirectly regulate chitin metabolism in insects. Real-time quantitative PCR (RT-qPCR) and RNA interference (RNAi) were used to detect the expressions and functions of the ApTPS and ApTRE genes. Abnormal phenotypes were found after RNAi of ApTRE in the Acyrthosiphon pisum. The molting deformities were observed in two color morphs, while wing deformities were only observed in the red morphs. The RNAi of ApTPS significantly down-regulated the expression of chitin metabolism-related genes, UDP-N-acetyglucosamine pyrophosphorylase (ApUAP), chitin synthase 2 (Apchs-2), Chitinase 2, 5 (ApCht2, 5), endo-beta-N-acetylglucosaminidase (ApENGase) and chitin deacetylase (ApCDA) genes at 24 h and 48 h; The RNAi of ApTRE significantly down-regulated the expression of ApUAP, ApCht1, 2, 8 and ApCDA at 24 h and 48 h, and up-regulated the expression of glucose-6-phosphate isomerase (ApGPI) and Knickkopf protein (ApKNK) genes at 48 h. The RNAi of ApTRE and ApTPS not only altered the expression of chitin metabolism-related genes but also decreased the content of chitin. These results demonstrated that ApTPS and ApTRE can regulate the chitin metabolism, deepen our understanding of the biological functions, and provide a foundation for better understanding the molecular mechanism of insect metamorphosis.

Regulatory Functions of Nilaparvata lugens GSK-3 in Energy and Chitin Metabolism

Glucose metabolism is a biologically important metabolic process. Glycogen synthase kinase (GSK-3) is a key enzyme located in the middle of the sugar metabolism pathway that can regulate the energy metabolism process in the body through insulin signaling. This paper mainly explores the regulatory effect of glycogen synthase kinase on the metabolism of glycogen and trehalose in the brown planthopper (Nilaparvata lugens) by RNA interference. In this paper, microinjection of the target double-stranded GSK-3 (dsGSK-3) effectively inhibited the expression of target genes in N. lugens. GSK-3 gene silencing can effectively inhibit the expression of target genes (glycogen phosphorylase gene, glycogen synthase gene, trehalose-6-phosphate synthase 1 gene, and trehalose-6-phosphate synthase 2 gene) in N. lugens and trehalase activity, thereby reducing glycogen and glucose content, increasing trehalose content, and regulating insect trehalose balance. GSK-3 can regulate the genes chitin synthase gene and glucose-6-phosphate isomerase gene involved in the chitin biosynthetic pathway of N. lugens. GSK-3 gene silencing can inhibit the synthesis of chitin N. lugens, resulting in abnormal phenotypes and increased mortality. These results indicated that a low expression of GSK-3 in N. lugens can regulate the metabolism of glycogen and trehalose through the insulin signal pathway and energy metabolism pathway, and can regulate the biosynthesis of chitin, which affects molting and wing formation. The relevant research results will help us to more comprehensively explore the molecular mechanism of the regulation of energy and chitin metabolism of insect glycogen synthase kinases in species such as N. lugens.

Roles of the PTP61F Gene in Regulating Energy Metabolism of Tribolium castaneum (Coleoptera: Tenebrionidae)

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator in the insulin signaling pathway. It belongs to a class of non-receptor phosphatases of protein tyrosine phosphatase and can catalyze the dephosphorylation of tyrosine to regulate cell differentiation, growth, and metabolism. However, few studies have focused on the role of PTP1B in regulating energy metabolism of insects. In this study, we investigated the expression profiles and the functions of a PTP1B gene (designated TcPTP61F) in the red flour beetle Tribolium castaneum. Quantitative real-time PCR analyzed showed that TcPTP61F was highly expressed in the pupal and adult stages. In adult tissues, TcPTP61F was prominently expressed in the tarsus and head. RNA interference-mediated silencing of TcPTP61F reduced the expression of eight genes in trehalose metabolic and glycolytic pathways. TcPTP61F depletion also caused a significant change in the distribution of trehalose, glucose, and glycogen. Additionally, knockdown of TcPTP61F inhibited the pyruvate kinase (PK) activity and significantly decreased the adenosine triphosphate (ATP) level. The results suggest that TcPTP61F is indispensible for trehalose and energy metabolism of T. castaneum.

Validamycin A Delays Development and Prevents Flight in Aedes aegypti (Diptera: Culicidae)

Trehalose is a disaccharide that is the major sugar found in insect hemolymph fluid. Trehalose provides energy, and promotes growth, metamorphosis, stress recovery, chitin synthesis, and insect flight. The hydrolysis of trehalose is under the enzymatic control of the enzyme trehalase. Trehalase is critical to the role of trehalose in insect physiology, and is required for the regulation of metabolism and glucose generation. Trehalase inhibitors represent a novel class of insecticides that have not been fully developed. Here, we tested the ability of trehalose analogues to function as larvacides or adulticides in an important disease vector-Aedes aegypti. We show that validamycin A, but not 5-thiotrehalose, delays larval and pupal development and prevents flight of adult mosquitoes. Larval mosquitoes treated with validamycin A were hypoglycemic and pupae had increased levels of trehalose. Treatment also skewed the sex ratio toward male mosquitoes. These data reveal that validamycin A is a mosquito adulticide that can impair normal development of an important disease vector.

The Inhibitory Effect of Validamycin A on Aspergillus flavus

Aspergillus flavus is one of the most common isolates from patients with fungal infections. Aspergillus infection is usually treated with antifungal agents, but side effects of these agents are common. Trehalase is an essential enzyme involved in fungal metabolism, and the trehalase inhibitor, validamycin A, has been used to prevent fungal infections in agricultural products. In this study, we observed that validamycin A significantly increased trehalose levels in A. flavus conidia and delayed germination, including decreased fungal adherence. In addition, validamycin A and amphotericin B showed a combinatorial effect on A. flavus ATCC204304 and clinical isolates with high minimum inhibitory concentrations (MICs) of amphotericin B using checkerboard assays. We observed that validamycin A and amphotericin B had a synergistic effect on A. flavus strains resistant to amphotericin B. The MICs in the combination of validamycin A and amphotericin B were at 0.125 μg/mL and 2 μg/mL, respectively. The FICI of validamycin A and amphotericin B of these clinical isolates was about 0.25-0.28 with synergistic effects. No drug cytotoxicity was observed in human bronchial epithelial cells treated with validamycin A using LDH-cytotoxicity assays. In conclusion, this study demonstrated that validamycin A inhibited the growth of A. flavus and delayed conidial germination. Furthermore, the combined effect of validamycin A with amphotericin B increased A. flavus killing, without significant cytotoxicity to human bronchial epithelial cells. We propose that validamycin A could potentially be used in vivo as an alternative treatment for A. flavus infections.

Silencing Br-C impairs larval development and chitin synthesis in Lymantria dispar larvae

In insects, 20-hydroxyecdysone (20E) mediates developmental transitions and regulates molting processes through activation of a series of transcription factors. Broad-Complex (Br-C), a vital gene in the 20E signalling pathway, plays crucial roles during insect growth processes. However, whether Br-C affects chitin synthesis in insects remains unclear. In the present study, the Br-C gene from Lymantria dispar, a notorious defoliator of forestry, was identified based on transcriptome data, and subjected to bioinformatic analysis. The regulatory functions of LdBr-C in chitin synthesis and metabolism in L. dispar larvae were analysed by RNA interference (RNAi). The full-length LdBr-C gene (1431 bp) encodes a 477 amino acid (aa) polypeptide containing a common BRcore region (391 aa) at the N-terminus and a C-terminal Zinc finger domain (56 aa) harbouring two characteristic C2H2 motifs (CXXC and HXXXXH). Phylogenetic analyses showed that LdBr-C shares highest homology and identity with Br-C isoform 7 (83.12%) of Helicoverpa armigera. Expression profiles indicate that LdBr-C was expressed throughout larval and pupal stages, and highly expressed in prepupal and pupal stages. Furthermore, LdBr-C expression was strongly induced by exogenous 20E, and suppressed dramatically after application of dsLdBr-C. Bioassay results showed that knockdown of LdBr-C caused larval developmental deformity, significant weight loss, and a mortality rate of 67.18%. Knockdown of LdBr-C significantly down-regulated transcription levels of eight critical genes (LdTre1, LdTre2, LdG6PI, LdUAP, LdCHS1, LdCHS2, LdTPS and LdCHT) related to chitin synthesis and metabolism, thereby lowering the chitin content in the midgut and epidermis. Our findings demonstrate that Br-C knockdown impairs larval development and chitin synthesis in L. dispar.

Fenoxycarb and methoxyfenozide (RH-2485) affected development and chitin synthesis through disturbing glycometabolism in Lymantria dispar larvae

Fenoxycarb as a juvenile hormone analogue and methoxyfenozide (RH-2485) as a 20-hydroxyecdysone (20E) agonist are two main insect growth regulators (IGRs) used for pest control, whose insecticidal mechanisms had been widely reported in past decades. However, there were few studies focused on their effects on the carbohydrate metabolism of insects. Here, we reported that two IGRs (fenoxycarb and RH-2485) significantly affected growth and development of L. dispar larvae and caused larval lethality. Furthermore, both contens of three sugars (glycogen, threhalose, glucose) in four tissues (fat body, midgut, hemolymph and epidermis) and trehalase activity in three tissues (fat body, midgut and hemolymph) of L. dispar larvae were markedly affected by these two IGRs. Moreover, we found that mRNA expression levels of LdTPS, LdTre1 and LdTre2 in L. dispar larvae were dramatically suppressed by two IGRs. Additionally, chitin content in both midgut and epidermis decreased significantly after L. dispar larvae treated with fenoxycarb or RH-2485. Summarily, these results indicated that these two IGRs disturbed glycometabolism in L. dispar larvae, resulting in impeding chitin synthesis, generating new epidermis failure, disrupting molting and larval lethality in the end.

Effect of glycogen synthase and glycogen phosphorylase knockdown on the expression of glycogen- and insulin-related genes in the rice brown planthopper Nilaparvata lugens

Nilaparvata lugens is a serious threat to rice growth. Glycogen metabolism is one of the important physiological processes of insects, which is mainly regulated by glycogen synthase (GS) and glycogen phosphorylase (GP). In the present study, trehalose content was significantly reduced at 72 h after NlGP and NlGS knockdown, whereas glucose content was significantly increased at both 48 h and 72 h after GS knockdown. RNAi combined with RNA-Seq was used to identify NlGP- and NlGS-related pathways and genes in N. lugens. A total of 593 genes were up-regulated and 5969 genes were down-regulated after NlGP and NlGS knockdown, respectively. Moreover, the NlGS-knockdown group was mapped to 10,967 pathways, whereas the NlGP-knockdown group was mapped to 7948 pathways, and the greatest differences between the groups were associated with carbohydrate, lipid, amino acid and energy metabolism. Meanwhile, 1800, 1217, and 1211 transcripts in the NlGP-knockdown group and 2511, 1666, and 1727 transcripts in the NlGS-knockdown group were involved in bioprocess, cellular ingredients and molecular function, respectively. Almost all these genes were down-regulated by either NlGP or NlGS knockdown, with significant down-regulation of the 6-trehalose phosphate synthase (TPS), trehalase (TRE), GS, GP, phosphoacetylglucosamine mutase (PGM, n = 2), Insulin receptors (InRs) and insulin-like peptides (Ilps) genes. These results have demonstrated that RNAi-mediated NlGP and NlGS knockdown could lead to content of trehalose and glucose out of balance, but have no obvious effect on glycogen content, and have suggested that GS plays more complex role in other metabolism pathway of N. lugens.

High-level expression of highly active and thermostable trehalase from Myceliophthora thermophila in Aspergillus niger by using the CRISPR/Cas9 tool and its application in ethanol fermentation

Trehalase catalyzes the hydrolysis of the non-reducing disaccharide trehalose. The highly active trehalase MthT from Myceliophthora thermophila was screened from the trehalase genes of six species of filamentous fungi. An ingenious multi-copy knock-in expression strategy mediated by the CRISPR/Cas9 tool and medium optimization were used to improve MthT production in Aspergillus niger, up to 1698.83 U/mL. The protein background was dramatically abated due to insertion. The recombinant MthT showed optimal activity at pH 5.5 and 60 °C, and exhibited prominent thermal stability between 50 and 60 °C under acid conditions (pH 4.5-6.5). The ethanol conversion rate (ethanol yield/total glucose) was significantly improved by addition of MthT (51.88%) compared with MthT absence (34.38%), using 30% starch saccharification liquid. The results of this study provided an effective strategy, established a convenient platform for heterologous expression in A. niger and showed a potential strategy to decrease production costs in industrial ethanol production.

Evaluation of the Expression and Function of the TRE2-like and TRE2 Genes in Ecdysis of Harmonia axyridis

Harmonia axyridis is an important predatory insect and widely used in biological control of agricultural and forestry pests. Trehalose is directly involved in the energy storage of the H. axyridis and in the oxidative function of various physiological activities thereby providing an energy source for its growth and development. The aim of this study was to explore the potential function of membrane-bound-like trehalase (TRE2-like) and membrane-bound trehalase (TRE2) genes in H. axyridis by RNAi. In addition, the activity of soluble and membrane-bound trehalase and the expression of genes related to trehalose and glycogen metabolism were determined in the larvae injected with dsTRE2-like or dsTRE2. The results showed that wing abnormality and mortality appeared in adults, as well as the activity of soluble trehalase and glycogen contents increased when interfering with TRE2-like gene. However, the activity of membrane-bound trehalase, trehalose and glucose contents in the larvae decreased. The expression of glycogen synthase (GS) and glycogen phosphorylase (GP) genes were decreased after RNAi in the ecdysis stage. The expression of chitin synthase gene A (CHSA), chitin synthase gene B (CHSB), and trehalose-6-phosphate synthase genes (TPS) were decreased significantly after RNAi, especially in the ecdysis stage. These results indicated that RNA interference is capable of knocking down gene expression of TRE2-like and TRE2, thereby disrupting trehalose metabolism which affects the chitin synthesis pathway in turn and also leads to developmental defects, such as wing deformities. This study could provide some theoretical guidance for the function of TRE2 gene in other insects.

Three novel trehalase genes from Harmonia axyridis (Coleoptera: Coccinellidae): cloning and regulation in response to rapid cold and re-warming

Trehalose is the main blood sugar in insects. To study the function of trehalase during exposure to low temperatures, three other novel cDNAs of trehalase were cloned from Harmonia axyridis by transcriptome sequencing and rapid amplification of cDNA ends. One of the cloned cDNAs encoded a soluble trehalase, the second trehalase cDNA encoded a transmembrane-like domain, and the third cDNA encoded a membrane-bound protein. Therefore, these cDNAs were, respectively, named HaTreh1-5, HaTreh2-like, and HaTreh2. HaTreh1-5, HaTreh2-like, and HaTreh2 cDNAs encoded proteins containing 586, 553, and 633 amino acids with predicted masses of approximately 69.47, 63.46, and 73.66 kDa, and pIs of 9.20, 5.52, and 6.31, respectively. All three novel trehalases contained signal motifs "PGGINKESYYLDSY", "QWDYPNAWPP", and a highly conserved glycine-rich (GGGGEY) region. The expression levels of HaTreh1-5 and HaTreh2 mRNAs were high during adult stages, whereas HaTreh2-like was expressed in low amounts in the fourth larval stage. The results showed that the activity of membrane-bound trehalases decreased from 25 to 10 °C and from 5 to - 5 °C during cooling. The results also revealed a decreasing trend in expression of the three HaTreh mRNAs during the cooling treatment, and an initial decrease followed by an increase during the process of re-warming.

TRE1 and CHS1 contribute to deltamethrin resistance in Culex pipiens pallens

Cuticular resistance, characterized by decreased epidermal penetration, has been reported on highly pyrethroid-resistant mosquitoes. In this study, we examined the role of genes in the chitin biosynthetic pathway in the context of deltamethrin-resistant (DR) Culex pipiens pallens. We found that expression of the trehalase (TRE1) gene and chitin synthase (CHS1) gene was upregulated 1.65- and 1.75-fold with quantitative reverse transcription polymerase chain reaction, respectively, in the DR strain as compared with the deltamethrin-susceptible (DS) strain. Examination of chitin content in DR and DS pupae showed an increased amount of chitin in DR pupae. To further establish the role of TRE1 and CHS1 in deltamethrin resistance, we injected mosquitoes with small interfering RNA (siRNA) for knockdown of TRE1 or CHS1 expression. The mortality rates of DR mosquitoes exposed to insecticides increased 17% and 26% after siTRE1 and siCHS1 injection, respectively. The siRNA treatment against TRE1 resulted in decreased expression of the downstream gene CHS1. Together, our findings support a role of TRE1 and CHS1 in the regulation of pyrethroid resistance.