Silencing of triazophos-induced Hexokinase-1-like reduces fecundity in Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

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.

3-Methylcatechol mediates anti-fecundity effect by inhibiting estrogen-related receptor-induced glycolytic gene expression in Myzus persicae

Aphids are a major problem in agriculture, horticulture, and forestry by feeding on leaves and stems, causing discoloration, leaf curling, yellowing, and stunted growth. Although urushiol, a phenolic compound containing a catechol structure, is known for its antioxidant and anticancer properties, using small molecules to control aphids via catechol-mediated mechanisms is poorly understood. In this study, we investigated the effects of 3-methylcatechol (3-MC) on Myzus persicae fecundity. Our results showed that treatment with 3-MC significantly reduced the intrinsic transcriptional activity of the aphid estrogen-related receptor (MpERR), which regulates the expression of glycolytic genes. Additionally, 3-MC treatment suppressed the promoter activity of MpERR-induced rate-limiting enzymes in glycolysis, such as phosphofructokinase and pyruvate kinase, by inhibiting MpERR binding. Finally, 3-MC also suppressed MpERR-induced glycolytic gene expression and reduced the number of offspring produced by viviparous female aphids. Overall, our findings suggest that 3-MC has the potential to be used as a new strategy for managing aphid populations by controlling their offspring production.

Afidopyropen suppresses silkworm growth and vitality by affecting carbohydrate metabolism and immune function

Afidopyropen has strong insecticidal toxicity to sucking pests by silencing the vanilloid-type transient receptor potential (TRPV) channels. However, the toxicity of afidopyropen to the Lepidoptera model insect silkworm remain unknown. In this study, the LC50 of afidopyropen to the silkworm at 72 h exposure was 256.82 mg/L. This indicates that afidopyropen is moderately toxic to the silkworm. Long-term exposure to concentrations of 100 mg/L, or less, of afidopyropen, significantly reduced silkworm growth, vitality, silk protein synthesis, and fecundity. A total of 220 differentially expressed genes (DEGs) were detected by transcriptome sequencing, among which 166 were downregulated and 54 were upregulated. Gene Ontology (GO) enrichment analysis showed that the DEGs were enriched in the immune system, immune response and carbohydrate metabolism. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that DEGs were primarily concentrated in carbohydrate metabolism and biosynthesis of neomycin, kanamycin and gentamicin. Genes related to carbohydrate metabolism and immune system pathways in silkworm were detected by quantitative real-time PCR. The results showed that the genes related to carbohydrate metabolism, silk protein synthesis, and immune response were significantly downregulated. These genes included BCL-6 corepressor-like protein 1 (BCORL1), hexokinase type 2 (HEXO2), phosphoserine aminotransferase 1 (PSAT1), relish (Rel), peptidoglycan recognition protein 2 (PGRP2) and 27 kda glycoprotein precursor (P27K). The data demonstrated the toxic effects of afidopyropen against the silkworm and its regulation of genes responsible for immune function and abscissa carbohydrate metabolism.

Molecular characterization of hexokinase (HK) in Haemaphysalis longicornis and evaluation of HK protein- and DNA-based vaccines against adult ticks

BACKGROUND

Haemaphysalis longicornis is an obligate hematophagous ectoparasite, which transmits various pathogens to humans, livestock and wild animals. Hexokinase (HK) is a key regulatory enzyme of the glycolytic pathway in the organisms. However, little is known about hexokinase and its functions in ticks.

RESULTS

The open reading frame of the H. longicornis HK (HlHK) gene was 1425 bp and encoded a protein of 474 amino acids, containing conserved domains for glucose, glucose 6-phosphate, and adenosine triphosphate. The expression of HlHK gene was detected at different developmental stages and in different tissues of unfed female ticks. Enzyme-linked immunosorbent assay revealed that both HK protein- and DNA-based vaccines increased the antibody levels of the immunized animals. A vaccination trail on rabbits against H. longicornis infestation indicated that the rHlHK protein and HlHK DNA vaccines reduced the number of attached female ticks by 9% and 12%, egg mass weight by 36% and 34%, and egg hatching rate by 41% and 17%, respectively. Overall, protein vaccination conferred 65.6% protection against adult female ticks, whereas the DNA vaccine conferred 51.8% protection.

CONCLUSION

This is the first report of the molecular characterization of the HK protein and sequencing of the HK gene from H. longicornis. Positive results from vaccination trials on rabbits of the recombinant HK protein and HK DNA suggest that these novel anti-tick vaccines potentially can be used as viable tick control tools for the management of the Asian longhorned tick. Additionally, inhibition of glucose metabolism may be a new strategy for tick control. © 2023 Society of Chemical Industry.

Transcriptome analysis of emamectin benzoate caused midgut damage by inducing oxidative stress, energy metabolism disorder and apoptosis in gypsy moth (Lymantria dispar)

BACKGROUND

Emamectin benzoate (EMB) is a semisynthetic bioinsecticide, which has been widely used in the control of forestry and agricultural pests. However, the mechanism of its toxic effects on the non-neural tissues has been rarely reported. Here, we explored the mechanism of the midgut damage induced by EMB in gypsy moth (Lymantria dispar) in order to better understand the toxicological mechanism of EMB.

RESULTS

Our results confirmed that EMB caused damage to the midgut of gypsy moth by inducing apoptosis. Transcriptome showed that 1469, 650 and 950 genes were significantly differentially expressed in the midgut of gypsy moth after 24, 48 and 72 h of EMB exposure, and oxidative stress, energy metabolism disorder and apoptosis may be related to the toxic effects of EMB. The indicators related to oxidative stress, energy metabolism and apoptosis were further examined. The results showed that EMB could cause oxidative stress by increasing ROS level and inhibiting antioxidant enzymes (P < 0.05), such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), which in turn causes mitochondria injury. Subsequently, energy metabolism was inhibited by downregulating the activities and mRNA level of energy metabolism enzymes. Furthermore, the mitochondrial apoptosis pathway was activated, triggering apoptosis, and eventually causing midgut injury in gypsy moth.

CONCLUSION

Our results indicated that EMB caused damage to midgut by inducing oxidative stress, energy metabolism disorder and apoptosis in gypsy moth. Our findings shed new light on the toxicological mechanism of EMB on non-neural tissues from oxidative stress, energy metabolism and apoptosis perspectives. © 2022 Society of Chemical Industry.

Knockdown of hexokinase in Diaphorina citri Kuwayama (Hemiptera: Liviidae) by RNAi inhibits chitin synthesis and leads to abnormal phenotypes

BACKGROUND

Silencing specific genes in pests using RNA interference (RNAi) technology is a promising new pest-control strategy. The Asian citrus psyllid, Diaphorina citri Kuwayama, is the most important citrus pest because it transmits Candidatus Liberibacter asiaticus, which causes huanglongbing. Chitin is essential for insect development, and enzymes in this pathway are attractive targets for pest control.

RESULTS

The hexokinase gene DcHK was characterized from D. citri to impair proper growth and chitin synthesis through RNAi. The transcription of DcHK was more highly developed in third-instar nymphs, adults and the Malpighian tube. The RNAi needed for D. citri is dose-dependent, with 600 ng μl^-1 dsDcHK sufficient to knockdown endogenous DcHK expression. The messenger RNA (mRNA) level was lowest at 36 h after dosing, and there were significant effects on the relative levels of mRNA in the chitin synthesis pathway (DcTre, DcG6PI, DcGNAT, DcGFAT, DcPGM, DcUAP and DcCHS), leading to mortality, reduced body weight and abnormal or lethal phenotypes.

CONCLUSION

RNAi can be triggered by orally delivered double-stranded RNA in D. citri. These results can provide support for HK genes as a new potential target for citrus psyllid control. © 2022 Society of Chemical Industry.

Disruption of the Serine/Threonine Kinase Akt Gene Affects Ovarian Development and Fecundity in the Cigarette Beetle, Lasioderma serricorne

Serine/threonine kinase Akt, an important component of the insulin signaling pathway, plays an essential role in many physiological processes. In this study, we identified and characterized an Akt gene (designated LsAkt) from the cigarette beetle, Lasioderma serricorne. LsAkt contains a 1614 bp open reading frame encoding a 537 amino acid protein that possesses a conserved pleckstrin homology domain and a serine/threonine kinase domain. The expression of LsAkt was high in pupal stages and peaked in day-4 female pupae. In adult tissues, LsAkt was highly expressed in the thorax, ovary, and midgut. The expression of LsAkt was induced by methoprene or bovine insulin in vivo, but significantly decreased by 20-hydroxyecdysone. RNA interference-mediated knockdown of LsAkt resulted in severely blocked ovarian development and reduced fecundity and hatchability. The vitellogenin (Vg) content and juvenile hormone (JH) titers of LsAkt-depletion beetles were decreased, and expressions of Vg and four JH signaling and biosynthetic genes were significantly decreased. Silencing of LsAkt reduced the amounts of glucose, glycogen, and trehalose in female adults and affected the expressions of seven key carbohydrate metabolic genes. Taken together, it is inferred that Akt implicates in L. serricorne reproduction by modification of Vg synthesis, juvenile hormone production and carbohydrate metabolism.

Hexokinase Is Required for Sex Pheromone Biosynthesis in Helicoverpa armigera

Acetyl-CoA, the precursor of sex pheromone biosynthesis in Helicoverpa armigera, is generated from glycolysis. As the first speed-limited enzyme in glycolysis, Hexokinase (HK) plays an important role in acetyl-CoA production. However, the function of HK in sex pheromone production remains unclear. This study employed H. armigera as material to explore the role of HK in sex pheromone production. Results demonstrated that the transcription profile of HaHK in female moth pheromone glands (PGs) was consistent with the release fluctuation of sex pheromone. Interference of HaHK prevented the increase of acetyl-CoA content induced by PBAN. Therefore, knockdown of HaHK in female PGs caused significant decreases in (Z)-11-hexadecenal (Z11-16:Ald) production, female capability to attract males, and mating rate. Furthermore, sugar feeding (5% sugar) increased the transcription and enzymatic activity of HK. Pheromone biosynthesis activating neuropeptide (PBAN) signal phospho-activated HaHK in PGs and Sf9 cells via protein kinase A (PKA), as shown by pharmacological inhibitor analysis. In general, our study confirmed that PBAN/cAMP/PKA signal activated HaHK, in turn promoted glycolysis to ensure the supply of acetyl-CoA, and finally facilitated sex pheromone biosynthesis and subsequent mating behavior.

Aphid estrogen-related receptor controls glycolytic gene expression and fecundity

Aphids, the major insect pests of agricultural crops, reproduce sexually and asexually depending upon environmental factors such as the photoperiod and temperature. Nuclear receptors, a unique family of ligand-dependent transcription factors, control insect development and growth including morphogenesis, molting, and metamorphosis. However, the structural features and biological functions of the aphid estrogen-related receptor (ERR) are largely unknown. Here, we cloned full-length cDNA encoding the ERR in the green peach aphid, Myzus persicae, (Sulzer) (Hemiptera: Aphididae) (MpERR) and demonstrated that the MpERR modulated glycolytic gene expression and aphid fecundity. The phylogenetic analysis revealed that the MpERR originated in a unique evolutionary lineage distinct from those of hemipteran insects. Moreover, the AF-2 domain of the MpERR conferred nuclear localization and transcriptional activity. The overexpression of the MpERR significantly upregulated the gene expression of rate-limiting enzymes involved in glycolysis such as phosphofructokinase and pyruvate kinase by directly binding to ERR-response elements in their promoters. Moreover, ERR-deficient viviparous female aphids showed decreased glycolytic gene expression and produced fewer offspring. These results suggest that the aphid ERR plays a pivotal role in glycolytic transcriptional control and fecundity.

Characterization, Knockdown and Parental Effect of Hexokinase Gene of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae) Revealed by RNA Interference

Hexokinase (HK) is a key enzyme in chitin biosynthesis in insects and plays an important role in development and energy regulation. It also performs a crucial role in the synthesis of Glucose-6-phosphate and its putative functions are studied via injection of dsRNA corresponding to the hexokinase gene from Cnaphalocrocis medinalis (CmHK). This study was designed to analyze the characteristics and expression patterns of HK-related genes in various tissues of C. medinalis at different developmental stages. The CmHK ORF is a 1359 bp in length, encoding a protein of 452 amino acids, with homology and cluster analysis showing that CmHK shares an 85.11% sequence similarity with hexokinase from Ostrinia furnacalis.CmHK was highly expressed in the ovary and in the fifth instar larvae. Injection of dsCmHK significantly suppressed mRNA expression (73.6%) 120 h post-dsRNA injection as compared to a control group. The results demonstrated an increased incidence of larval and pupal mortality of 80% and 78%, respectively, with significant variation in the sex ratio between males (68.33%) and females (35%), overt larval deformities, and a reduction in average weight gain observed 120 h post-dsRNA injection. In addition, dsCmHK-injected C. medinalis showed a significant reduction in ovulation per female and larval hatching rate, along with increased larval and pupal mortality and variation in male and female emergence over three generations (G1, G2, and G3). Taken together, the outcomes of the study provide a foundation to study gene function and a new dimension to control C. medinalis by transgenic RNAi technology.

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.

Triazophos-induced vertical transmission of rice stripe virus is associated with host vitellogenin in the small brown planthopper Laodelphax striatellus

BACKGROUND

Rice stripe virus (RSV) is one of the most serious rice diseases in East Asia. The small brown planthopper (SBPH), Laodelphax striatellus, is an economically important rice pest. SBPH transmits RSV horizontally and vertically, resulting in serious rice economic losses. Exposure to sublethal doses of insecticides can induce many physiological and cellular changes in insects. However, the mechanism underlying triazophos-induced RSV vertical transmission remains unclear. Here, we investigated the role of vitellogenin (Vg) in triazophos-induced RSV vertical transmission.

RESULTS

RSV vertical transmission rates were significantly induced by sublethal exposure to triazophos. The transcript abundance of viral RNA3 segment (RNA3) and capsid protein (CP) in the ovaries of SBPH were also significantly increased. Triazophos induced the expression level of Vg in L. striatellus (LsVg) and increased the contents of ovarian protein and fat body protein. Knockdown of Vg significantly reduced the expression levels of LsVg and Vg receptor (LsVgR), and decreased RSV accumulations in the ovaries. Double-stranded Vg (dsVg)-mediated down-regulation could be rescued by exposure to triazophos. Vertical transmission rate of the dsVg-injected group was significantly decreased compared with the dsGFP-injected group, and triazophos significantly rescued the RSV vertical transmission rate of the dsVg-injected group.

CONCLUSION

Our results indicate that triazophos-induced RSV vertical transmission is associated with Vg. This work will help us to further elucidate sublethal doses of insecticides-mediated effects and develop new strategies for pest control. © 2019 Society of Chemical Industry.

Progress and prospects of arthropod chitin pathways and structures as targets for pest management

Chitin is a structural component of the arthropod cuticular exoskeleton and the peritrophic matrix of the gut, which play crucial roles in growth and development. In the past few decades, our understanding of the composition, biosynthesis, assembly, degradation, and regulation of chitinous structures has increased. Many chemicals have been developed that target chitin biosynthesis (benzoyphenyl ureas, etoxazole), chitin degradation (allosamidin, psammaplin), and chitin regulation (benzoyl hydrazines), thus resulting in molting deformities and lethality. In addition, proteins that disrupt chitin structures, such as lectins, proteases, and chitinases have been utilized to halt feeding and induce mortality. Chitin-degrading enzymes, such as chitinases are also useful for improving the efficacy of bio-insecticides. Transgenic plants, baculoviruses, fungi, and bacteria have been engineered to express chitinases from a variety of organisms for control of arthropod pests. In addition, RNA interference targeting genes involved in chitin pathways and structures are now being investigated for the development of environmentally friendly pest management strategies. This review describes the chemicals and proteins used to target chitin structures and enzymes for arthropod pest management, as well as pest management strategies based upon these compounds, such as plant-incorporated-protectants and recombinant entomopathogens. Recent advances in RNA interference-based pest management, and how this technology can be used to target chitin pathways and structures are also discussed.

Male Selenoprotein F-Like (SPF-L) Influences Female Reproduction and Population Growth in Nilaparvata lugens (Hemiptera: Delphacidae)

Selenoproteins serve in anti-oxidant and cellular redox functions in almost all organisms. A recent study characterized a selenoprotein F-like (SPF-L) in the brown plant hopper’s (BPH), Nilaparvata lugens, male accessory glands (MAGs), raised the question of whether the SPF-L is associated with female fecundity. In this study, SPF-L mRNA was found to be enriched in the internal reproductive organ (IRO) of virgin males, also expressed relatively stably in virgin males and females, and dietary dsSPF-L-treatments led to reduced MAG protein and Arginine content. Knockdown of NlSPF-L in unmated males did not influence juvenile hormone (JH) III and ecdysteroid titers, however, dsSPF-L-treated mated males had increased JH III titer, and reduced ecdysteroid titer compared to controls. After mating with dsSPF-L-treated males, female partners had reduced fat body and ovary soluble proteins and JH III tier and vitellogenin (Vg) mRNA levels, but no alterations in ecdysteroid titer, body weight or longevity. The experimental females had prolonged pre-oviposition periods and they laid fewer eggs, which suffered reduced hatching rates and population growth index (PGI). Such mating also led to impaired IRO development in males and females, which was confirmed by immunofluorescence staining. We infer that SPF-L affects reproductive success of males and their partners.

Glucose Utilization in the Regulation of Chitin Synthesis in Brown Planthopper

Glucose-6-phosphatase (G6Pase) and hexokinase (HK) are two key enzymes in the glycolysis and gluconeogenesis pathways, which catalyze the synthesis and degradation of glucose in insects, respectively. G6Pase and HK play an important role in insect growth by regulating the metabolism of glucose, leading to the efficient metabolism of other macromolecules. However, it is unclear whether these genes could be investigated for pest control through their actions on chitin metabolism. We studied the potential functions of G6Pase and HK genes in the regulation of chitin metabolism pathways by RNAi technology. Interference with G6Pase expression did not affect trehalose and chitin metabolism pathways in brown planthopper, Nilaparvata lugens (Stål). However, knockdown of the HK gene resulted in a significant decrease of expression of genes associated with the trehalose metabolic pathway but had no significant effect on trehalase activity, trehalose content, or glucogen content. Additionally, HK knockdown resulting in downregulation of the genes involved in chitin metabolism in the brown planthopper. These insects also showed wing deformities and difficulty in molting to varying degrees. We suggest that the silencing of HK expression directly inhibited the decomposition of glucose, leading to impaired chitin synthesis.