A transferrin gene associated with development and 2-tridecanone tolerance in Helicoverpa armigera

A General Signal Pathway to Regulate Multiple Detoxification Genes Drives the Evolution of Helicoverpa armigera Adaptation to Xenobiotics

The study of insect adaptation to the defensive metabolites of host plants and various kinds of insecticides in order to acquire resistance is a hot topic in the pest-control field, but the mechanism is still unclear. In our study, we found that a general signal pathway exists in H. armigera which can regulate multiple P450s, GSTs and UGTs genes to help insects decrease their susceptibility to xenobiotics. Knockdown of HaNrf2 and HaAhR expression could significantly increase the toxicity of xenobiotics to H. armigera, and simultaneously decrease the gene expression of P450s, GSTs and UGTs which are related to the xenobiotic metabolism and synthesis of insect hormone pathways. Then, we used EMSA and dual luciferase assay to verify that a crosstalk exists between AhR and Nrf2 to regulate multiple P450s, GSTs and UGTs genes to mediate H. armigera susceptibility to plant allelochemicals and insecticides. The detoxification genes' expression network which can be regulated by Nrf2 and AhR is still unknown, and there were also no reports about the crosstalk between AhR and Nrf2 that exist in insects and can regulate multiple detoxification genes' expression. Our results provide a new general signaling pathway to reveal the adaptive mechanism of insects to xenobiotics and provides further insight into designing effective pest-management strategies to avoid the overuse of insecticides.

Silencing of multiple target genes via ingestion of dsRNA and PMRi affects development and survival in Helicoverpa armigera

RNA interference (RNAi) triggered by exogenous double-stranded RNA (dsRNA) is a powerful tool to knockdown genetic targets crucial for the growth and development of agriculturally important insect pests. Helicoverpa armigera is a pest feeding on more than 30 economically important crops worldwide and a major threat. Resistance to insecticides and Bt toxins has been gradually increasing in the field. RNAi-mediated knockdown of H. armigera genes by producing dsRNAs homologous to genetic targets in bacteria and plants has a high potential for insect management to decrease agricultural loss. The acetylcholinesterase (AChE), ecdysone receptor (EcR) and v-ATPase-A (vAA) genes were selected as genetic targets. Fragments comprising a coding sequence of < 500 bp were cloned into the L4440 vector for dsRNA production in bacteria and in a TRV-VIGS vector in antisense orientation for transient expression of dsRNA in Solanum tuberosum leaves. After ingesting bacterial-expressed dsRNA, the mRNA levels of the target genes were significantly reduced, leading to mortality and abnormal development in larva of H. armigera. Furthermore, the S. tuberosum plants transformed with TRV-VIGS expressing AChE exhibited higher mortality > 68% than the control plants 17%, recorded ten days post-feeding and significant resistance in transgenic (transient) plants was observed. Moreover, larval lethality and molting defects were observed in larva fed on potato plants expressing dsRNA specific to EcR. Analysis of transcript levels by quantitative RT–PCR revealed that larval mortality was attributable to the knockdown of genetic targets by RNAi. The results demonstrated that down-regulation of H. armigera genes involved in ATP hydrolysis, transcriptional stimulation of development genes and neural conduction has aptitude as a bioinsecticide to control H. armigera population sizes and therefore decreases crop loss.

Rice Defense against Brown Planthopper Partially by Suppressing the Expression of Transferrin Family Genes of Brown Planthopper

Transferrins are multifunctional proteins, but their role in the interaction of rice and brown planthopper (BPH) remains unclear. In this study, the full-length cDNA of transferrin genes NlTsf1, NlTsf2, and NlTsf3 was cloned. Reverse transcription quantitative polymerase chain reaction showed that the expressions of NlTsf1 and NlTsf3 were significantly suppressed in BPH reared on the resistant rice R1 by 68.0 and 86.7%, respectively, compared with that on the susceptible S9. The survival rate decreased to 3.3% for dsNlTsf3-treated nymphs, to 58.9% for dsNlTsf1, and to 56.7% for dsNlTsf2 on day 11. RNAi of NlTsf3 against females largely reduced the number of eggs by 99.4%, and it decreased by 48.6% for dsNlTsf1 but did not significantly decrease for dsNlTsf2. Collectively, NlTsf1, NlTsf2, and NlTsf3 are essential for the survival and fecundity of BPH and are differentially involved in the interaction between rice and BPH. Therefore, NlTsf1 and NlTsf3 may be used as targets to control BPH.

Differential Transcriptome Analysis Reveals Genes Related to Low- and High-Temperature Stress in the Fall Armyworm, Spodoptera frugiperda

The fall armyworm (FAW), Spodoptera frugiperda, is regarded as one of the world’s most harmful plant pests. This research examines the molecular response processes of FAW to low temperature (4°C) and high temperature (40°C) when gene expression is compared to controls (25°C). A total of 211,967 unigenes were collected, at least 14,338 of which were annotated with gene descriptions, gene ontology terms, and metabolic pathways. There were 50 Gene Ontology (GO) functional sub-groups and 21 EggNOG words as a result. Differentially expresses genes (DEGs) with log₂FC ≥ 2 were identified and compared at various temperatures. In comparison to the 25°C treated group, we discovered 199 and 1,248 individual DEGs co-regulated at 4 and 40°C, respectively. Comparing transcriptome profiles for differential gene expression revealed a number of DEGs, including cytochrome P450, odorant binding proteins (OBPs), and immune system genes previously implicated in cold and high temperature stresses. The enrichment pathways were identified using Kyoto Encyclopedia of Genes and Genomics (KEGG) analysis, and heatmaps of similar unigenes from both treatment groups (T4 and T40) were plotted. We used quantitative reverse transcription PCR (RT-qPCR) to confirm the RNA-seq data on 10 up- and down-regulated DEGs. These findings provide a foundation for future understanding of FAW adaptation mechanisms and the underlying basis underlying the response to low and high temperatures.

Diversity of insect antimicrobial peptides and proteins - A functional perspective: A review

The innate immune response of insects provides a robust line of defense against pathogenic microbes and eukaryotic parasites. It consists of two types of overlapping immune responses, named humoral and cellular, which share protective molecules and regulatory mechanisms that closely coordinate to prevent the spread and replication of pathogens within the compromised insect hemocoel. The major feature of the humoral part of the insect immune system involves the production and secretion of antimicrobial peptides from the fat body, which is considered analogous to adipose tissue and liver in vertebrates. Previous research has identified and characterized the nature of antimicrobial peptides that are directed against various targets during the different stages of infection. Here we review this information focusing mostly on the diversity and mode of action of these host defense components, and their critical contribution to maintaining host homeostasis. Extending this knowledge is paramount for understanding the evolution of innate immune function and the physiological balance required to provide sufficient protection to the host against external enemies while avoiding overactivation signaling events that would severely undermine physiological stability.

Knockdown of Helicoverpa armigera protease genes affects its growth and mortality via RNA interference

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), the cotton bollworm, is a destructive pest which is famous for its resistance to a variety of insecticides. RNA interference is a posttranscriptional gene silencing mechanism that has become a popular tool to control insect pests, triggered by double-stranded RNAs (dsRNAs). The effect of ingestion and injection delivery methods of dsRNA related to some protease genes including Trypsin (Ha-TRY39 and Ha-TRY96), Chymotrypsin (Ha-CHY), and Cathepsin L (Ha-CAT) on growth and development of H. armigera was investigated in this study. All protease genes encoded full ORFs and were expressed in all H. armigera larvae stages and tissues. In both injection and feeding bioassays, Ha-RNAi CHY's performance outperformed that of other protease genes. CHY enzyme activity in the midgut of larvae was significantly reduced after treatment with ds-HaCHY. Oral administration of ds-CHY also resulted in significant mortality of H. armigera larvae. However, because of the high RNase activity in the midgut lumen of lepidoptera, a large amount of dsRNA was needed to effectively kill instars of H. armigera. To reduce dsRNA degradation, bacterial expression and dsRNA formulation were used. After oral administration, it was toxic to H. armigera larvae. Before oral administration, bacterial cells were sonicated to increase dsRNA release. The RNA interference efficiency of sonicated bacteria was significantly increased, resulting in higher larval mortality when administered orally. All of these findings point to Ha-CHY as a new candidate for developing an effective dsRNA-based pesticide for H. armigera control.

Cellular Redox-Related Transcription Factor Nrf2 Mediation of HaTrf Response to Host Plant Allelochemical 2-Tridecanone in Helicoverpa armigera

Despite there being a number of excellent studies on detoxification enzyme-mediated interaction between insect and plant allelochemical, there are no reports on the pathway of the transferrin effect in insect response to host plant allelochemical. Our research indicates that Helicoverpa armigera transferrin (HaTrf) inhibited the apoptotic cell death treated by 2-tridecanone, a host plant allelochemical present in tomato species (Lycopersicon hirsutum f. glabratum), by cellular redox-related transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2). Nrf2 can defend organisms against the detrimental effects of oxidative stress and play pivotal roles in preventing host plant allelochemical-related toxicity. This study explains how HaTrf inhibited the apoptotic cell death during exposure to host plant allelochemical 2-tridecanone and provides a novel view on transferrin and its anti-apoptotic role in plant-insect interactions.

Suppression of Transferrin Expression Enhances the Susceptibility of Plutella xylostella to Isaria cicadae

Transferrins (Trfs) are multifunctional proteins with key functions in iron transport. In the present study, a Trf (PxTrf) from Plutella xylostella was identified and characterized. The PxTrf consisted of a 2046-bp open reading frame, which encoded a 681 amino acid protein with a molecular weight of 73.43 kDa and had an isoelectric point of 7.18. Only a single iron domain was predicted in the N-lobe of PxTrf. Although PxTrf was expressed ubiquitously, the highest levels of expression were observed in the fourth instar larvae. PxTrf transcript level was highest in fat bodies among various tissues. The PxTrf transcript levels increased significantly after the stimulation of pathogens. A decrease in PxTrf expression via RNA interference enhanced the susceptibility of P. xylostella to the Isaria cicadae fungus and inhibited hemocyte nodulation in response to the fungal challenge. In addition, a considerable increase in the pupation rate was observed in larvae treated with double-stranded PxTrf (dsPxTrf). Overall, according to the results, PxTrf may participate in P. xylostella immunity against fungal infection and insect development.

Comparative transcriptomic analysis of larval and adult Malpighian tubules from the cotton bollworm Helicoverpa armigera

Malpighian tubules (MTs) are usually considered the key excretory and osmoregulatory organs of insects. However, increasing evidence has suggested that MTs perform many more functions than just osmoregulation. Until now, the molecular and physiological functions of MTs in the cotton bollworm (Helicoverpa armigera), a very important agricultural pest, are largely unknown. In this study, the transcriptomes of H. armigera MTs from larvae, male adults and female adults were sequenced using RNA-Seq technology, and comparative analyses of transcriptomes between two life stages (larval and adult) and between adult sexes were conducted. We generated a total of 84 643 high-quality unigenes, and identified a large number of abundant transcripts putatively encoding proteins involved in diuresis, detoxification, immunity, carbohydrate transport and metabolism, development and reproduction. We found that the expression pattern of unigenes was relatively similar between female and male adult MTs, but different between larval and adult MTs. Our data suggest that insect MTs may take multiple physiological functions as versatile organs. The extensive alterations in gene expression in MTs occurred from larvae to adults reflect an ecological adaptation to different feeding habits. Sexual dimorphism in the cotton bollworm is somewhat indicated by the transcriptional difference of genes related to carbohydrate metabolism, detoxification, immunity and reproduction in the MTs of male and female adults.

Applying microarray-based technique to study and analyze silkworm (Bombyx mori) transcriptomic response to long-term high iron diet

To investigate the biological processes affected by long-term iron supplementation, newly hatched silkworms were exposed to high iron mulberry diet (10 and 100 ppm) and its effect on silkworm transcriptom was determined. The results showed that the silkworm was responsive to iron by increasing iron concentration and ferritin levels in the hemolymph and by regulating the expression of many other genes. A total of 523 and 326 differentially expressed genes were identified in 10 and 100 ppm Fe group compared to the control, respectively. Of these genes, 249 were shared between in both the 10 ppm and 100 ppm Fe group, including 152 up-regulated and 97 down-regulated genes. These shared genes included 19 known Fe regulated, 24 immune-related, 12 serine proteases and serine proteases homologs, 41 cuticular and cuticle genes. Ten genes (carboxypeptidases A, serine protease homologs 85, fibrohexamerin/P25, transferrin, sex-specific storage-protein 2, fungal protease inhibitor F, insect intestinal mucin, peptidoglycan recognition protein B, cuticle protein CPH45, unknown gene) were involved in the regulation of iron overload responses.

Role for Transferrin in Triggering Apoptosis in Helicoverpa armigera Cells Treated with 2-Tridecanone

2-Tridecanone, a plant allelochemical present in a large range of tomato species ( Lycopersicon hirsutum f. glabratum), can induce the expression of Helicoverpa armigera transferrin ( HaTrf), which is necessary for insect growth and development. To gain further insight into the mechanism of HaTrf in response to 2-tridecanone, we measured the iron and H₂O₂ levels in the hemolymph during exposure to 2-tridecanone and then explored the effect of transferrin downregulation in a H. armigera fat body cell line exposed to 2-tridecanone. We found that the reduction of HaTrf levels via RNA interference caused rapid apoptotic cell death during exposure to 2-tridecanone. There have been no reports about transferrin genes related to apoptosis induced by plant allelochemicals. Our results indicate that HaTrf mediates the inhibition of apoptotic cell death during exposure to 2-tridecanone and provides insight into the importance of transferrin in the interaction between plants and insects.

2-Tridecanone impacts surface-associated bacterial behaviours and hinders plant-bacteria interactions

Surface motility and biofilm formation are behaviours which enable bacteria to infect their hosts and are controlled by different chemical signals. In the plant symbiotic alpha-proteobacterium Sinorhizobium meliloti, the lack of long-chain fatty acyl-coenzyme A synthetase activity (FadD) leads to increased surface motility, defects in biofilm development and impaired root colonization. In this study, analyses of lipid extracts and volatiles revealed that a fadD mutant accumulates 2-tridecanone (2-TDC), a methylketone (MK) known as a natural insecticide. Application of pure 2-TDC to the wild-type strain phenocopies the free-living and symbiotic behaviours of the fadD mutant. Structural features of the MK determine its ability to promote S. meliloti surface translocation, which is mainly mediated by a flagella-independent motility. Transcriptomic analyses showed that 2-TDC induces differential expression of iron uptake, redox and stress-related genes. Interestingly, this MK also influences surface motility and impairs biofilm formation in plant and animal pathogenic bacteria. Moreover, 2-TDC not only hampers alfalfa nodulation but also the development of tomato bacterial speck disease. This work assigns a new role to 2-TDC as an infochemical that affects important bacterial traits and hampers plant-bacteria interactions by interfering with microbial colonization of plant tissues.

Transferrin Family Genes in the Brown Planthopper, Nilaparvata lugens (Hemiptera: Delphacidae) in Response to Three Insecticides

Transferrins are involved in iron metabolism, immunity, xenobiotics tolerance, and development in eukaryotic organisms including insects. However, little is known about the relationship between transferrins and insecticide toxicology and resistance. Three transferrin family genes, NlTsf1, NlTsf2, and NlTsf3, of the brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)a major insect pest of rice field in Asia, had been identified and characterized in this study. Quantitative polymerase chain reaction results demonstrated that NlTsf1 was significantly higher than the other two genes in different tissues. All of them were expressed at higher levels in abdomen and head than in antenna, leg, stylet, and thorax. Compared with the control, the expression of three N. lugens transferrin family genes decreased dramatically 24 h after treatment with buprofezin, pymetrozine and imidacloprid.

RNA interference-mediated knockdown of some genes involved in digestion and development of Helicoverpa armigera

Helicoverpa armigera is a significant agricultural pest and particularly notorious for its resistance to many types of common insecticides. RNA interference (RNAi) is a mechanism of post-transcriptional gene silencing and trigged by double-strand RNA (dsRNA), has become a widely used reverse genetics and potent tool for insect pest control. In this study, the effect of ingestion and injection delivery methods of dsRNA related two important enzyme genes, α-amylase (HaAMY48, Ha-AMY49) and juvenile hormone esterase (Ha-JHE), were examined on growth and development of H. armigera. After 24, 48, 72 and 96 h of feeding bioassay, significant down regulation was observed about; 56, 68, 78, 80.75% for HaAMY48, 60, 70, 86.5 and 96.75%, for Ha-AMY49 and 14, 27.5, 23 and 31.7% for Ha-JHE, respectively. The results for injection assay was 61.5, 71.5, 74 and 95.8% for Ha-AMY48; 70, 88, 91.5 and 97.7% for Ha-AMY49 and 22, 61, 75 and 74% for Ha-JHE after 24, 48 and 72 h of last injecting, respectively. Larvae that treated with dsRNA, fed or injected, lost more than half of their weight. 50% mortality in treated larvae was observed in the case injection bioassay with dsHa-JHE and 59% of larvae that fed of dsRNA-treated cubes survived. DsHa-AMY48 and 49 have significant mortality, but mixing of them is more effective in both bioassays. Injection bioassay has a potent inhibitory effect on α-amylase-specific activity about more than 87% in treated larvae with mix of dsHa-AMY48 and 49. Adult malformation percent was evaluated for feeding (28, 35.5 and 43% for Ha-AMY48, 49 and Ha-JHE, respectively) and injection bioassay (23, 42 and 29% for Ha-AMY48, 49 and Ha-JHE, respectively). All these finding suggest that Ha-AMY48, Ha-AMY49 and Ha-JHE can be new candidates to scheming effective dsRNAs pesticide for H. armigera control.

Optimization of recombinant bacteria expressing dsRNA to enhance insecticidal activity against a lepidopteran insect, Spodoptera exigua

Double-stranded RNA (dsRNA) has been applied to control insect pests due to its induction of RNA interference (RNAi) of a specific target gene expression. However, developing dsRNA-based insecticidal agent has been a great challenge especially against lepidopteran insect pests due to variations in RNAi efficiency. The objective of this study was to screen genes of chymotrypsins (SeCHYs) essential for the survival of the beet armyworm, Spodoptera exigua, to construct insecticidal dsRNA. In addition, an optimal oral delivery method was developed using recombinant bacteria. At least 7 SeCHY genes were predicted from S. exigua transcriptomes. Subsequent analyses indicated that SeCHY2 was widely expressed in different developmental stages and larval tissues by RT-PCR and its expression knockdown by RNAi caused high mortality along with immunosuppression. However, a large amount of dsRNA was required to efficiently kill late instars of S. exigua because of high RNase activity in their midgut lumen. To minimize dsRNA degradation, bacterial expression and formulation of dsRNA were performed in HT115 Escherichia coli using L4440 expression vector. dsRNA (300 bp) specific to SeCHY2 overexpressed in E. coli was toxic to S. exigua larvae after oral administration. To enhance dsRNA release from E. coli, bacterial cells were sonicated before oral administration. RNAi efficiency of sonicated bacteria was significantly increased, causing higher larval mortality at oral administration. Moreover, targeting young larvae possessing weak RNase activity in the midgut lumen significantly enhanced RNAi efficiency and subsequent insecticidal activity against S. exigua.

A P-glycoprotein gene serves as a component of the protective mechanisms against 2-tridecanone and abamectin in Helicoverpa armigera

P-glycoprotein (P-gp) exists in animals, fungi and bacteria and likely evolved as a defense mechanism against harmful substances. Here a cDNA (4054bp) encoding a putative P-glycoprotein gene from Helicoverpa armigera was cloned and named HaPgp1. This putative HaPgp1 sequence encoded a protein of 1253 amino acids with a molecular mass of approximately 137kDa. qPCR analyses demonstrated that the expression of HaPgp1 was significantly higher in 4th instar larvae when compared to other developmental stages. HaPgp1 transcripts were more abundant in the head and fat bodies than in other tissues. Compared with the control, the expression of HaPgp1 reach a peak at 12h after the treatment by 2-tridecanone in all tissues. However, the expression of HaPgp1 increased from 12h to 48h after treatment with abamectin in all tissues. Immunohistochemistry analyses also verified that 2-tridecanone and abamectin can induce the increase of HaPgp1 expression. RNAi of HaPgp1 significantly raised the mortality rate of larvae treated by 2-tridecanone and abamectin, as compared to control larvae fed with GFP dsRNA. These results illustrate the possible involvement of HaPgp1 as a component of the protective mechanisms to plant secondary chemicals such as 2-tridecanone and to certain classes of insecticides, like abamectin.

The Spermatophore in Glossina morsitans morsitans: Insights into Male Contributions to Reproduction

Male Seminal Fluid Proteins (SFPs) transferred during copulation modulate female reproductive physiology and behavior, impacting sperm storage/use, ovulation, oviposition, and remating receptivity. These capabilities make them ideal targets for developing novel methods of insect disease vector control. Little is known about the nature of SFPs in the viviparous tsetse flies (Diptera: Glossinidae), vectors of Human and Animal African trypanosomiasis. In tsetse, male ejaculate is assembled into a capsule-like spermatophore structure visible post-copulation in the female uterus. We applied high-throughput approaches to uncover the composition of the spermatophore in Glossina morsitans morsitans. We found that both male accessory glands and testes contribute to its formation. The male accessory glands produce a small number of abundant novel proteins with yet unknown functions, in addition to enzyme inhibitors and peptidase regulators. The testes contribute sperm in addition to a diverse array of less abundant proteins associated with binding, oxidoreductase/transferase activities, cytoskeletal and lipid/carbohydrate transporter functions. Proteins encoded by female-biased genes are also found in the spermatophore. About half of the proteins display sequence conservation relative to other Diptera, and low similarity to SFPs from other studied species, possibly reflecting both their fast evolutionary pace and the divergent nature of tsetse's viviparous biology.

Diet-delivered RNAi in Helicoverpa armigera--Progresses and challenges

Helicoverpa armigera (the cotton bollworm) is a significant agricultural pest endemic to Afro-Eurasia and Oceania. Gene suppression via RNA interference (RNAi) presents a potential avenue for management of the pest, which is highly resistant to traditional insecticide sprays. This article reviews current understanding on the fate of ingested double-stranded RNA in H. armigera. Existing in vivo studies on diet-delivered RNAi and their effects are summarized and followed by a discussion on the factors and hurdles affecting the efficacy of diet-delivered RNAi in H. armigera.