Methoprene-tolerant (Met) and Krüpple-homologue 1 (Kr-h1) are required for ovariole development and egg maturation in the brown plant hopper

Peroxisome biogenesis factor PEX14 is crucial for survival and fecundity of female brown planthopper, Nilaparvata lugens (Stål)

Peroxisomes are ubiquitous cellular organelles participating in a variety of critical metabolic reactions. PEX14 is an essential peroxin responsible for peroxisome biogenesis. In this study, we identified the human PEX14 homolog in the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae). N. lugens PEX14 (NlPEX14) showed significant topological similarity to its human counterpart. It is expressed throughout all developmental stages, with the highest expression observed in adult insects. Down-regulation of NlPEX14 through injection of NlPEX14-specific double-strand RNA impaired nymphal development. Moreover, females subjected to dsNlPEX14 treatment exhibited a significantly reduced lifespan. Additionally, we found abnormal ovarian development and a significant decrease in the number of eggs laid in NlPEX14-downregulated females. Further experiments support that the shortening of lifespan and the decrease in female fecundity can be attributed, at least partially, to the accumulation of fatty acids and reduced expression of vitellogenin. Together, our study reveals an indispensable function of NlPEX14 for insect reproduction and establishes a causal connection between the phenotypes and peroxisome biogenesis, shedding light on the importance of peroxisomes in female fecundity.

Effect of four chitinase genes on the female fecundity in Sogatella furcifera (Horváth)

BACKGROUND

The white-backed planthopper (WPH), Sogatella furcifera (Horváth), is a destructive rice pest with strong reproductive capacity. To gain insights into the roles of chitinases in the reproductive process of this insect species, this study represents the first-ever endeavor to conduct an in-depth exploration into the reproductive functions of four chitinase genes.

RESULTS

In this study, it was observed that four chitinase genes were expressed in female adults, with a relatively high expression level in the ovaries. SfCht2 and SfIDGF1 were highly expressed during later ovarian development. while SfENGase increased and then decreased with ovarian development. SfCht2, SfCht6-2 and SfENGase were highly expressed in fat body on the first and second days after eclosion, whereas SfIDGF1 highest on day 7. Compared with control group, Silencing four chitinase genes inhibited ovarian development and significantly shortened the oviposition period of S. furcifera, reducing egg-laying capacity but not affecting egg hatching. The detection demonstrated that the expression levels of SfVg, SfVgR and 70-90% juvenile hormone (JH) signaling pathway-related reproductive genes was significantly down-regulated. Moreover, SfCht6-2 and SfENGase significantly affected the expression levels of Target of Rapamycin (TOR) signaling pathway genes. SfENGase had the ability to impact nutrient signaling pathways and fatty acid metabolism, repressing vitellogenin synthesis and ultimately influencing ovarian development of S. furcifera.

CONCLUSIONS

Overall, this study provides insight into the function of chitinases in insect fecundity and is of great significance for enriching the cognition of insect chitinase function. They will become the suitable target genes for controlling the most destructive rice planthoppers. © 2023 Society of Chemical Industry.

Juvenile hormone receptor Methoprene tolerant: Functions and applications

During the past 15years, after confirming Methoprene tolerant (Met) as a juvenile hormone (JH) receptor, tremendous progress has been made in understanding the function of Met in supporting JH signal transduction. Met role in JH regulation of development, including metamorphosis, reproduction, diapause, cast differentiation, behavior, im`munity, sleep and epigenetic modifications, have been elucidated. Met's Heterodimeric partners involved in performing some of these functions were discovered. The availability of JH response elements (JHRE) and JH receptor allowed the development of screening assays in cell lines and yeast. These screening assays facilitated the identification of new chemicals that function as JH agonists and antagonists. These new chemicals and others that will likely be discovered in the near future by using JH receptor and JHRE will lead to highly effective species-specific environmentally friendly insecticides for controlling pests and disease vectors.

Methoprene-tolerant and Krüppel homolog 1 are actors of juvenile hormone-signaling controlling the development of male sexual behavior in the moth Agrotis ipsilon

In insects, juvenile hormone (JH) is critical for the orchestration of male reproductive maturation. For instance, in the male moth, Agrotis ipsilon, the behavioral response and the neuronal sensitivity within the primary olfactory centers, the antennal lobes (ALs), to the female-emitted sex pheromone increase with fertility during adulthood and the coordination between these events is governed by JH. However, the molecular basis of JH action in the development of sexual behavior remains largely unknown. Here, we show that the expression of the paralogous JH receptors, Methoprene-tolerant 1 and 2 (Met1, Met2) and of the JH-inducible transcription factor, Krüppel homolog 1 (Kr-h1) within ALs raised from the third day of adult life and this dynamic is correlated with increased behavioral responsiveness to sex pheromone. Met1-, Met2- and Kr-h1-depleted sexually mature males exhibited altered sex pheromone-guided orientation flight. Moreover, injection of JH-II into young males enhanced the behavioral response to sex pheromone with increased AL Met1, Met2 and Kr-h1 mRNA levels. By contrast, JH deficiency suppressed the behavioral response to sex pheromone coupled with reduced AL Met1, Met2 and Kr-h1 mRNA levels in allatectomized old males and these inhibitions were compensated by an injection of JH-II in operated males. Our results demonstrated that JH acts through Met-Kr-h1 signaling pathway operating in ALs, to promote the pheromone information processing and consequently the display of sexual behavior in synchronization with fertility to optimize male reproductive fitness. Thus, this study provides insights into the molecular mechanisms underlying the hormonal regulation of reproductive behavior in insects.

Burkholderia gut symbiont induces insect host fecundity by modulating Kr-h1 gene expression

Full-length cDNAs of the Broad-Complex (BR-C) from Riptortus pedestris were cloned. Moreover, Kr-h1 and BR-C expression levels in apo-symbiotic and symbiotic host insects were compared to verify whether they are modulated by Burkholderia gut symbionts. Interestingly, Kr-h1 expression level was significantly increased in symbiotic females. To determine how Kr-h1 affects fecundity in insects, the biosynthesis of two reproduction-associated proteins, hexamerin-α and vitellogenin, was investigated in R. pedestris females. Hexamerin-α and vitellogenin expression at the transcriptional and translational levels decreased in Kr-h1-suppressed symbiotic females, subsequently reduced egg production. These results suggest that Burkholderia gut symbiont modulates Kr-h1 expression to enhance ovarian development and egg production of R. pedestris by increasing the biosynthesis of the two proteins.

Involvement of Methoprene-tolerant and Krüppel homolog 1 in juvenile hormone-mediated vitellogenesis of female Liposcelis entomophila (End.) (Psocoptera: Liposcelididae)

Methoprene-tolerant (Met) as an intracellular receptor of juvenile hormone (JH) and the Krüppel-homolog 1 (Kr-h1) as a JH-inducible transcription factor had been proved to contribute to insect reproduction. Their functions vary in different insect orders, however, they are not clear in Psocoptera. In this study, LeMet and LeKr-h1 were identified and their roles in vitellogenesis and ovarian development were investigated in Liposcelis entomophila (Enderlein). Treatment with exogenous JH III significantly induced the expression of LeKr-h1, LeVg, and LeVgR. Furthermore, silencing LeMet and LeKr-h1 remarkably reduced the transcription of LeVg and LeVgR, disrupted the production of Vg in fat body and the uptake of Vg by oocytes, and ultimately led to a decline in fecundity. The results indicated that the JH signaling pathway was essential to the reproductive process of this species. Interestingly, knockdown of LeMet or LeKr-h1 also resulted in fluctuations in the expression of FoxO, indicating the complex regulatory interactions between different hormone factors. Besides, knockdown of both LeMet and LeKr-h1 significantly increased L. entomophila mortality. Our study provides initial insight into the roles of JH signaling in the female reproduction of psocids and provided evidence that RNAi-mediated knockdown of Met or Kr-h1 is a potential pest control strategy.

Functional Analysis of a Juvenile Hormone Inducible Transcription Factor, Krüppel homolog 1, in the Bean Bug, Riptortus pedestris

Juvenile hormone (JH) has two major functions in insects, i.e., suppression of metamorphosis in the larval or nymphal stage and promotion of reproduction in the adult stage. Krüppel homolog 1 (Kr-h1), a C2H2 zinc-finger type transcription factor, is reported to act downstream of the JH receptor complex. In the present study, the function of Kr-h1 was examined in adults and nymphs of Riptortus pedestris by RNA interference (RNAi). After injection of adults with dsRNA of Kr-h1, the expression level of Kr-h1 was significantly decreased in the abdomen. Kr-h1 dsRNA-injection resulted in a lower proportion of individuals with developed ovaries, but the difference was not statistically significant. The transcript levels of cyanoprotein-α and vitellogenin-1, which are JH-inducible genes encoding yolk proteins, were not affected in the abdomen by Kr-h1 knockdown. Kr-h1 dsRNA-injection was effective for suppression of Kr-h1 expression in nymphs. Some Kr-h1 dsRNA-injected fifth (final) instar nymphs had morphological defects in the wing bud. Moreover, they had several adult morphological features, including ocelli in the head, connexivum in the abdomen, coloring of the dorsal abdomen, and genitals. The nymphs possessing adult features did not emerge as adults during 1 month. These results demonstrated that Kr-h1 is necessary for maintaining nymphal characters in R. pedestris. The function of Kr-h1 in ovarian development remains unclear in R. pedestris.

Impact of JH Signaling on Reproductive Physiology of the Classical Insect Model, Rhodnius prolixus

In adult females of several insect species, juvenile hormones (JHs) act as gonadotrophic hormones, regulating egg production. JH binds to its nuclear receptor, Methoprene tolerant (Met), triggering its dimerization with the protein Taiman (Tai). The resulting active complex induces transcription of JH response genes, such as Krüppel homolog 1 (Kr-h1). In this study we report for the first time the participation of the isoform JH III skipped bisepoxide (JHSB₃) and its signaling pathway in the reproductive fitness of the classical insect model Rhodnius prolixus. The topical application of synthetic JHSB₃ increases transcript and protein expression of yolk protein precursors (YPPs), mainly by the fat body but also by the ovaries, the second source of YPPs. These results are also confirmed by ex vivo assays. In contrast, when the JH signaling cascade is impaired via RNA interference by downregulating RhoprMet and RhoprTai mRNA, egg production is inhibited. Although RhoprKr-h1 transcript expression is highly dependent on JHSB₃ signaling, it is not involved in egg production but rather in successful hatching. This research contributes missing pieces of JH action in the insect model in which JH was first postulated almost 100 years ago.

The Function of Nilaparvata lugens (Hemiptera: Delphacidae) E74 and Its Interaction With βFtz-F1

Drosophila E74 is an early gene located in the polytene chromosome 74EF puff position. E74 controls the production of late genes, indicating that it plays a crucial role in this cascade model. Nilaparvata lugens E74 is closely related to Diaphorina citri, Bemisia tabaci, and Laodelphax striatellus. After downregulating E74, molting, and nymphal mortality were increased, and ovarian development was delayed. Moreover, the expression of Vg was reduced at the transcriptional level, as measured by qRT-PCR, and the content of Vg protein was reduced, as detected by Western blotting. After downregulating E74, the expression of hormone-related genes, including Tai, βFtz-F1, Met, Kr-h1, UspA, UspB, E93, and Br, was changed. The expression of E74 was significantly decreased after downregulating hormone-related genes. When the expression of E74 and βFtz-F1 was downregulated together, nymph mortality and molting mortality were higher than those when E74 or βFtz-F1 was downregulated alone. Thus, E74 probably interacts with βFtz-F1 at the genetic level. In summary, this study showed that E74 plays a crucial role in the development, metamorphosis and reproduction of N. lugens, possibly via the interaction with βFtz-F1 at the genetic level. This study provides a basis for the development of new target-based pesticides and new methods for the effective control of N. lugens.

Inter-Alpha-Trypsin Inhibitor Heavy Chain 4 Plays an Important Role in the Development and Reproduction of Nilaparvata lugens

Simple Summary

The brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae), is a destructive insect pest of rice. It causes reductions in rice yield and great economic losses. In this study, we used RNAi to explore the function of the inter-alpha-trypsin inhibitor heavy chain 4 (ITIH4) gene in the development and reproduction of the brown planthopper. Our results revealed that ITIH4 influences the survival, ovarian development, egg production, and egg hatching of this insect, indicating that ITIH4 plays important roles in development and reproduction. Considering the importance of ITIH4 in the brown planthopper, it may be a potential target for pest management.

Abstract

The brown planthopper, Nilaparvata lugens, is a difficult-to-control insect pest affecting rice yields in Asia. As a structural component of the inter-alpha-trypsin inhibitor (ITI), the inter-alpha-trypsin inhibitor heavy chain (ITIH) has been reported to be involved in various inflammatory or malignant disorders, ovarian development, and ovulation. To reveal the function of ITIH4 in N. lugens, the gene encoding N. lugens ITIH4 (NlITIH4) was cloned and characterized. NlITIH4 contains a signal peptide, a vault protein inter-alpha-trypsin domain, and a von Willebrand factor type A domain. qPCR analysis showed that NlITIH4 was expressed at all developmental stages and in all tissues (fat body, ovary, and gut), with the highest expression in the fat body. Double stranded NlITIH4 (dsNlITIH4) injection clearly led to an RNAi-mediated inhibition of the expression of NlITIH4 and resulted in reduced survival, delayed ovarian development, and reduced egg production and egg hatching. These results indicate that NlITIH4 plays an important role in the development and reproduction of N. lugens.

Molecular Identification and Functional Characterization of Methoprene-Tolerant (Met) and Krüppel-Homolog 1 (Kr-h1) in Harmonia axyridis (Coleoptera: Coccinellidae)

Juvenile hormone (JH) plays a key role in regulating insect reproductive processes. Methoprene-tolerant (Met), as a putative JH receptor, transduces JH signals by activating the transcription factor krüppel homolog 1 (Kr-h1). To understand the effects of Met and Kr-h1 genes on female reproduction of natural enemy insects, the Met and Kr-h1 were identified and analyzed from Harmonia axyridis Pallas (HmMet and HmKr-h1). The HmMet protein belonged to the bHLH-PAS family with bHLH domain, PAS domains, and PAC domain. HmMet mRNA was detected in all developmental stages, and the highest expression was found in the ovaries of female adults. The HmKr-h1 protein had eight C2H2-type zinc finger domains. HmKr-h1 mRNA was highly expressed from day 7 to day 9 of female adults. The tissue expression showed that HmKr-h1 was highly expressed in its wing, leg, and fat body. Knockdown of HmMet and HmKr-h1 substantially reduced the transcription of HmVg1 and HmVg2, inhibited yolk protein deposition, and reduced fecundity using RNA interference. In addition, the preoviposition period was significantly prolonged after dsMet-injection, but there was no significant difference after dsKr-h1-silencing. However, the effect on hatchability results was the opposite. Therefore, we infer that both HmMet and HmKr-h1 are involved in female reproduction of H. axyridis, and their specific functions are different in certain physiological processes. In several continents, H. axyridis are not only beneficial insects, but also invasive pests. This report will provide basis for applying or controlling the H. axyridis.

Juvenile Hormone Synthesis Pathway Gene SfIPPI Regulates Sogatella furcifera Reproduction

Simple Summary

The juvenile hormone is essential for insect growth, development, and reproduction. Isopentenyl pyrophosphate isomerase is a key isomerase involved in the synthesis of the juvenile hormone. This study evaluates the effect of the targeted silencing of the SfIPPI gene on the reproduction of Sogatella furcifera (white-backed planthopper). We found that SfIPPI silencing significantly inhibits the ovarian development and egg production in female adults of S. furcifera and significantly inhibits the transcription of downstream genes in the juvenile hormone synthesis pathway. Our data provide insight into the function of juvenile hormone biosynthetic pathway genes in insect reproduction, which could be a potential target to control and prevent agricultural pests.

Abstract

The juvenile hormone (JH) is crucial for insect reproduction, and isopentenyl pyrophosphate isomerase (IPPI) is a key enzyme in the JH synthesis pathway. However, few studies have investigated how IPPI regulates insect reproduction. This study identifies and characterizes the IPPI gene (SfIPPI) from the important agricultural pest Sogatella furcifera. A phylogenetic analysis reveals a high homology of SfIPPI with the IPPI amino acid sequences of Laodelphax striatellus and Nilaparvata lugens (Stål). Furthermore, SfIPPI is expressed at various developmental stages and in various tissues of S. furcifera, and is significantly higher on the 5th day of adult emergence and in integument tissue, while lower levels are found on the 3rd day of adult emergence and in fat body and gut tissue. After silencing SfIPPI using RNA interference, the ovarian development is significantly inhibited and the fecundity is significantly reduced when compared with the control group. Additionally, SfIPPI silencing significantly decreases the expression levels of downstream JH signal transduction pathway genes (SfJHAMT, SfFAMeT, and SfKr-h1) and SfVg. Our findings are helpful in elucidating the molecular mechanism underlying the regulation of insect reproduction through genes in the JH synthesis pathway, and they provide a theoretical basis for the development of pest control treatments targeting SfIPPI.

Role of Groucho and Groucho1-like in Regulating Metamorphosis and Ovary Development in Nilaparvata lugens (Stål)

Juvenile hormone and ecdysone are key regulators in the metamorphosis and development. Grocho (Gro) is a highly conserved protein required for metamorphosis and development. Brown planthopper (Nilaparvata lugens) is a major pest affecting rice production in China and many Asian countries. Although the molecular function of Gro has been investigated in holometabolous insects such as Aedes aegypti and Drosophila melanogaster, their role in the hemimetabolous insect, brown planthopper, and the relationship between NlGro/NlGro1-L and JH/ecdysone signaling pathway, remained unknown. In this study, NlGroucho (NlGro) and NlGroucho1-like (NlGro1-L) were cloned. An analysis of the predicted protein sequence showed that NlGro has highly conserved Q domain and WD40 domain, and NlGro1-L has a highly conserved WD40 domain. The expression profiles of both genes were studied by quantitative real-time PCR (qRT-PCR). Their relative expressions were high in egg, head, wing, ovary, and testis. NlGro and NlGro1-L were found to interact genetically with juvenile hormone and ecdysone signaling by hormone treatment and RNAi of JH/ecdysone signaling-related genes. Moreover, when NlGro or NlGro1-L was down-regulated alone, the survival rate was decreased, the ovarian development was delayed, and the oviposition was also affected. All defects were aggravated when NlGro and NlGro1-L were down-regulated together. This study will help to develop new pesticides on the basis of the function of NlGro and NlGro1-L, and provide new possibilities for the control of Nilaparvata lugens.

20E and MAPK signal pathway involved in the effect of reproduction caused by cyantraniliprole in Bactrocera dorsalis Hendel (Diptera: Tephritidae)

BACKGROUND

It is a common phenomenon that insecticides affect insect reproduction and insect hormones. After cyantraniliprole treatment, the egg production and remating behavior of female Bactrocera dorsalis were affected, a phenomenon of 'hormesis' appeared, but the change at the molecular level was unknown. Therefore, we investigated the fertility, insect hormone titers and transcription levels and used RNAi to prove the function of genes, to explore the molecular mechanism of cyantraniliprole causing reproductive changes in female B. dorsalis.

RESULTS

LC₂₀ treatment promoted egg production, while LC₅₀ treatment inhibited it. Both high and low concentrations inhibited female ovaries' development and reduced the length of the ovarian tubes. Among insect hormones, only the titer of 20-hydroxyecdysone (20E) changed significantly. According to the KEGG pathway enrichment analysis of RNA-seq, there are significant differences in insect hormone synthesis and MAPK signal pathways between treatments. Furthermore, 20E biosynthetic genes, BdVgs and BdVgR were all down-regulated, and multiple MAPK signaling pathway genes were up-regulated. Based on qRT-PCR, the expression of BdCyp307A1, BdCyp302A1, BdMEKK4 and BdMAP2K6 within 1-11 days after treatment were consistent with the change of 20E titer. The BdVg1 and BdVg2 in LC₅₀ were still suppressed, while the LC₂₀ returned to normal in 9-11 days. RNAi indicated that BdMEKK4 and BdMAP2K6 participated in the transcriptional regulation of BdCyp307A1 and BdCyp302A1, then affected the levels of BdVgs.

CONCLUSION

Cyantraniliprole affected 20E through MAPK signal pathway, causing many genes to be down-regulated during the early period but up-regulated during the late period, ultimately affecting the reproduction of B. dorsalis. © 2021 Society of Chemical Industry.

Replication protein A is required for juvenile hormone-dependent vitellogenesis and oocyte maturation in locusts

Aside from inhibiting insect metamorphosis, juvenile hormone (JH) has a well-known role in stimulating various aspects of insect reproduction. Replication protein A (RPA), a heterotrimeric complex comprised of RPA1, RPA2 and RPA3 subunits plays an essential role in DNA replication and DNA repair. Here we report that RPAs are highly expressed in the fat body of adult female locust, Locusta migratoria. While RPA1 is upregulated by the JH receptor Methoprene-tolerant (Met), RPA2 and RPA3 expression appears to be primarily controlled by Forkhead box O transcription factor (FoxO). Knockdown of RPA1, RPA2 or RPA3 results in markedly reducd vitellogenin (Vg) expression in the fat body, accompanied by arrested ovarian growth and inhibited oocyte maturation. In addition, depletion of an RPA subunit leads to increased expression of other RPA subunits as well as a pro-apoptotic gene, Smac that is involved in DNA repair and apoptosis. The data indicate a crucial role of RPAs in JH-dependent vitellogenesis and oocyte maturation.

In silico identification and study of potential anti-mosquito juvenile hormone binding protein (MJHBP) compounds as candidates for dengue virus - Vector insecticides

Dengue has become a huge global health burden. It is currently recognized as the most rapidly spreading mosquito-borne viral disease. Yet, there are currently no licensed vaccines or specific therapeutics to manage the virus, thus, scaling up vector control approaches is important in controlling this viral spread. This study aimed to identify and study in silico, potential anti-mosquito compounds targeting Juvenile hormone (JH) mediated pathways via the Mosquito Juvenile Hormone Binding Protein (MJHBP). The study was implemented using series of computational methods. The query compounds included pyrethroids and those derived from ZINC and ANPDB databases using a simple pharmacophore model in Molecular Operating Environment (MOE). Molecular docking of selected compounds' library was implemented in MOE. The resultant high-score compounds were further validated by molecular dynamics simulation via Maestro 12.3 module and the respective Prime/Molecular Mechanics Generalized Born Surface Area (Prime/MM-GBSA) binding energies computed. The study identified compounds-pyrethroids, natural and synthetic - with high docking energy scores (ranging from 10.91-12.34 kcal/mol). On further analysis of the high-ranking (in terms of docking scores) compounds using MD simulation, the compounds - Ekeberin D4, Maesanin, Silafluofen and ZINC16919139- revealed very low binding energies (-122.99, -72.91 -104.50 and,-74.94 kcal/mol respectively), fairly stable complex and interesting interaction with JH-binding site amino acid residues on MJHBP. Further studies can explore these compounds in vitro/in vivo in the search for more efficient mosquito vector control.

Krüppel-homologue 1 Mediates Hormonally Regulated Dominance Rank in a Social Bee

Dominance hierarchies are ubiquitous in invertebrates and vertebrates, but little is known on how genes influence dominance rank. Our gaps in knowledge are specifically significant concerning female hierarchies, particularly in insects. To start filling these gaps, we studied the social bumble bee Bombus terrestris, in which social hierarchies among females are common and functionally significant. Dominance rank in this bee is influenced by multiple factors, including juvenile hormone (JH) that is a major gonadotropin in this species. We tested the hypothesis that the JH responsive transcription factor Krüppel homologue 1 (Kr-h1) mediates hormonal influences on dominance behavior. We first developed and validated a perfluorocarbon nanoparticles-based RNA interference protocol for knocking down Kr-h1 expression. We then used this procedure to show that Kr-h1 mediates the influence of JH, not only on oogenesis and wax production, but also on aggression and dominance rank. To the best of our knowledge, this is the first study causally linking a gene to dominance rank in social insects, and one of only a few such studies on insects or on female hierarchies. These findings are important for determining whether there are general molecular principles governing dominance rank across gender and taxa.

Involvement of Cis-Acting Elements in Molecular Regulation of JH-Mediated Vitellogenin Gene 2 of Female Periplaneta americana

Vitellogenins (Vgs) are yolk protein precursors that are regulated by juvenile hormone (JH) and/or 20-hydroxyecdysone (20E) in insects. JH acts as the principal gonadotropin that stimulates vitellogenesis in hemimetabolous insects. In this study, we cloned and characterized the Periplaneta americana Vitellogenin 2 (Vg2) promoter. Multiple sites for putative transcription factor binding were predicted for the 1,804 bp Vg2 promoter region, such as the Broad-Complex, ecdysone response element (EcRE), GATA, Hairy, JH response element (JHRE), and Methoprene (Met)-binding motif, among others. Luciferase reporter assay has identified that construct -177 bp is enough to support JH III induction but not 20E suppression. This 38 bp region (from -177 to -139 bp) contains two conserved response element half-sites separated by 2 nucleotides spacer (DR2) and is designated as Vg2RE (^-168GAGTCACGGAGTCGCCGCTG^-149). Mutation assay and luciferase assay data using mutated constructs verified the crucial role of G residues in Vg2RE for binding the isolated fat body nuclear protein. In Sf9 cells, a luciferase reporter placed under the control of a minimal promoter containing Vg2RE was induced by JH III in a dose- and time-dependent manner. Nuclear proteins isolated from previtellogenic female fat body cells bound to Vg2RE, and this binding was outcompeted by a 50-fold excess of cold Drosophila melanogaster DR4 and Galleria mellonella JH binding protein response elements (Chorion factor-I/Ultraspiracle). Affinity pull-down experiment with nuclear extracts of previtellogenic female fat body, using 31-bp probe Vg2RE as bait, yielded a 71 kDa candidate nuclear protein that may mediate the regulatory action of the JH III.

Juvenile hormone regulates the reproductive diapause through Methoprene-tolerant gene in Galeruca daurica

Juvenile hormone (JH) signalling plays an important role in regulation of reproductive diapause in insects. However, its underlying molecular mechanism has been unclear. Methoprene-tolerant (Met), as a universal JH receptor, is involved in JH action. To gain some insight into its function in the reproductive diapause of Galeruca daurica, a serious pest on the Inner Mongolia grasslands undergoing obligatory summer diapause at the adult stage, we cloned the complete open-reading frame (ORF) sequences of Met and other 7 JH signalling-related genes, including JH acid methyltransferase (JHAMT), JH esterase (JHE), JH epoxide hydrolase (JHEH), Krüppel homologue 1 (Kr-h1), vitellogenin (Vg), forkhead box O (FOXO) and fatty acid synthase 2 (FAS2), from this species. GdMet encoded a putative protein, which contained three domains typical of the bHLH-PAS family. Expression patterns of these eight genes were developmentally regulated during adult development. Topical application of JH analogue (JHA) methoprene into the 3-day-old and 5-day-old adults induced the expression of GdMet. Silencing GdMet by RNAi inhibited the expression of JHBP, JHE, Kr-h1 and Vg, whereas promoted the FAS2 expression, which enhanced lipid accumulation and fat body development, and finally induced the adults into diapause ahead. Combining with our previous results, we conclude that JH may regulate reproductive diapause through a conserved Met-dependent pathway in G. daurica.

Role of Endocrine System in the Regulation of Female Insect Reproduction

The proper synthesis and functioning of ecdysteroids and juvenile hormones (JHs) are very important for the regulation of vitellogenesis and oogenesis. However, their role and function contrast among different orders, and even in the same insect order. For example, the JH is the main hormone that regulates vitellogenesis in hemimetabolous insect orders, which include Orthoptera, Blattodea, and Hemiptera, while ecdysteroids regulate the vitellogenesis among the insect orders of Diptera, some Hymenoptera and Lepidoptera. These endocrine hormones also regulate each other. Even at some specific stage of insect life, they positively regulate each other, while at other stages of insect life, they negatively control each other. Such positive and negative interaction of 20-hydroxyecdysone (20E) and JH is also discussed in this review article to better understand the role of these hormones in regulating the reproduction. Therefore, the purpose of the present review is to deeply understand the complex interaction of endocrine hormones with each other and with the insulin signaling pathway. The role of microbiomes in the regulation of the insect endocrine system is also reviewed, as the endocrine hormones are significantly affected by the compounds produced by the microbiota.

Krüppel homolog 1 regulates photoperiodic reproductive plasticity in the cabbage beetle Colaphellus bowringi

Many insects exhibit reproductive plasticity where the photoperiod determines whether the insect becomes reproductively active or enters diapause. Adult reproductive diapause is a strategy that allows insects to survive harsh environmental conditions. A deficiency in juvenile hormone (JH) leads to reproductive diapause. However, little is known about the molecular mechanisms by which JH signaling regulates reproductive diapause. In this study, we used the cabbage beetle Colaphellus bowringi, a serious pest, to investigate the role of Krüppel homolog 1 (Kr-h1) in controlling photoperiodic plasticity of female reproduction. We focused on Kr-h1, since it acts as a key mediator of JH signaling. We show here that JH-Methoprene-tolerant signaling upregulated the expression of Kr-h1 in reproductively active C. bowringi females when reared under short day conditions. In the long day-treated diapausing females, Kr-h1 transcripts decreased dramatically. Interfering with Kr-h1 function repressed reproductive development by blocking vitellogenesis and ovarian growth. Further, Kr-h1 depletion induced other diapause-like traits, including elevated lipid accumulation and high expression of diapause-related genes. RNA-Seq showed that Kr-h1 played both activating and repressive roles, depending on whether downstream genes were acting in reproduction- or diapause pathways, respectively. Finally, we identified the DNA replication gene mini-chromosome maintenance 4 and two triacylglycerol lipase genes as critical downstream factors of Kr-h1 that are critical for reproductive plasticity in C. bowringi. These results reveal that Kr-h1 is a key component of the regulatory pathway that coordinates reproduction and diapause in insects in response to photoperiodic input.

The Draft Genome of Yellow Stem Borer, an Agriculturally Important Pest, Provides Molecular Insights into Its Biology, Development and Specificity Towards Rice for Infestation

Simple Summary

Yellow stem borer (YSB), is the most destructive and widely occurring pest that attacks rice throughout the growing season. Rice (Oryza sativa L.) is a major staple cereal worldwide, providing essential caloric requirements for more than half of the world’s population. Annual losses to rice borers are approximately 5–10%, but losses in individual fields may reach up to 50–60%. The use of traditional pest management strategies in controlling YSB is somewhat challenging due to its unique internal feeding habit. Genome sequence information of economically important crop pests is important for designing or developing pest-resistant rice varieties. In an approach to achieve this, we present our first-ever study on the draft genome sequence of YSB. The information provided from our current study might be useful in developing genome-based approaches for the management of pest species.

Abstract

Yellow stem borer (YSB), Scirpophaga incertulas (Walker) (Lepidoptera: Crambidae), a major monophagous insect pest of rice, causes significant yield losses. The rice–YSB interaction is very dynamic, making it difficult for management. The development of resistant lines has been unsuccessful as there are no effective resistant sources in the germplasm. Genome information is necessary for a better understanding of interaction with rice in terms of its recognition, response, and infestation mechanism. The draft genome of YSB is predicted to have 46,057 genes with an estimated size of 308 Mb, being correlated with the flow cytometry analysis. The existence of complex metabolic mechanisms and genes related to specific behavior was identified, being conditioned by a higher level of regulation. We deciphered the possible visual, olfactory, and gustatory mechanisms responsible for its evolution as a monophagous pest. Comparative genomic analysis revealed that YSB is unique in the way it has evolved. The obvious presence of high-immunity-related genes, well-developed RNAi machinery, and diverse effectors provides a means for developing genomic tools for its management. The identified 21,696 SSR markers can be utilized for diversity analysis of populations across the rice-growing regions. We present the first draft genome of YSB. The information emanated paves a way for biologists to design novel pest management strategies as well as for the industry to design new classes of safer and specific insecticide molecules.

Involvement of Methoprene-tolerant and Krüppel homolog 1 in juvenile hormone-signaling regulating the maturation of male accessory glands in the moth Agrotis ipsilon

Male accessory glands (MAGs) produce seminal fluid proteins that are essential for the fertility and also influence the reproductive physiology and behavior of mated females. In many insect species, and especially in the moth Agrotis ipsilon, juvenile hormone (JH) promotes the maturation of the MAGs but the underlying molecular mechanisms in this hormonal regulation are not yet well identified. Here, we examined the role of the JH receptor, Methoprene-tolerant (Met) and the JH-inducible transcription factor, Krüppel homolog 1 (Kr-h1) in transmitting the JH signal that upregulates the growth and synthetic activity of the MAGs in A. ipsilon. We cloned two full length cDNAs encoding Met1 and Met2 which are co-expressed with Kr-h1 in the MAGs where their expression levels increase with age in parallel with the length and protein content of the MAGs. RNAi-mediated knockdown of either Met1, Met2, or Kr-h1 resulted in reduced MAG length and protein amount. Moreover, injection of JH-II into newly emerged adult males induced the transcription of Met1, Met2 and Kr-h1 associated to an increase in the length and protein content of the MAGs. By contrast, JH deficiency decreased Met1, Met2 and Kr-h1 mRNA levels as well as the length and protein reserves of the MAGs of allatectomized old males and these declines were partly compensated by a combined injection of JH-II in operated males. Taken together, our results highlighted an involvement of the JH-Met-Kr-h1 signaling pathway in the development and secretory activity of the MAGs in A. ipsilon.

KIF2A regulates ovarian development via modulating cell cycle progression and vitollogenin levels

The kinesin superfamily of proteins (KIFs) are microtubule motor proteins that use the hydrolysis of ATP to power directional movement along microtubules. KIFs induce microtubule depolymerization to regulate the length and dynamics of microtubules in a variety of cell processes and structures, including the mitotic and meiotic spindles and centriole and interphase microtubules. KIF plays a significant role in the transport of organelles, protein complexes and mRNAs. The brown planthopper (Nilaparvata lugens) is a major insect pest in rice paddy fields. Ovarian development is regulated by multiple factors, including endocrine factors. The role of KIFs in brown planthopper ovarian development remains unknown. We found that downregulation of KIF2A significantly compromised the development and eclosion of the brown planthopper, delayed ovarian cell cycle progression, disrupted ovarian development, reduced the expression of MCM genes required for DNA replication and significantly reduced the number of nuclei in the follicles. We also found a significant reduction in Vg mRNA and protein levels. We conclude that downregulation of KIF2A disrupts the cell cycle progression of cells. Alternatively, the ovarian phenotype could be an indirect effect of a compromised trophic cord. In summary, KIF2A regulates ovarian development via modulating cell cycle progression and/or vitollogenin transportation.

20E-mediated regulation of BmKr-h1 by BmKRP promotes oocyte maturation

BACKGROUND

Krüppel homolog 1 (Kr-h1) is a critical transcription factor for juvenile hormone (JH) signaling, known to play a key role in regulating metamorphosis and adult reproduction in insects. Kr-h1 can also be induced by molting hormone 20-hydroxyecdysone (20E), however, the underlying mechanism of 20E-induced Kr-h1 expression remains unclear. In the present study, we investigated the molecular mechanism of Kr-h1 induction by 20E in the reproductive system of a model lepidopteran insect, Bombyx mori.

RESULTS

Developmental and tissue-specific expression analysis revealed that BmKr-h1 was highly expressed in ovaries during the late pupal and adult stages and the expression was induced by 20E. RNA interference (RNAi)-mediated depletion of BmKr-h1 in female pupae severely repressed the transcription of vitellogenin receptor (VgR), resulting in the reduction in vitellogenin (Vg) deposition in oocytes. BmKr-h1 specifically bound the Kr-h1 binding site (KBS) between - 2818 and - 2805 nt upstream of BmVgR and enhanced the transcription of BmVgR. A 20E cis-regulatory element (CRE) was identified in the promoter of BmKr-h1 and functionally verified using luciferase reporter assay, EMSA and DNA-ChIP. Using pull-down assays, we identified a novel transcription factor B. mori Kr-h1 regulatory protein (BmKRP) that specifically bound the BmKr-h1 CRE and activated its transcription. CRISPR/Cas9-mediated knockout of BmKRP in female pupae suppressed the transcription of BmKr-h1 and BmVgR, resulting in arrested oogenesis.

CONCLUSION

We identified BmKRP as a new transcription factor mediating 20E regulation of B. mori oogenesis. Our data suggests that induction of BmKRP by 20E regulates BmKr-h1 expression, which in turn induces BmVgR expression to facilitate Vg uptake and oogenesis.

Transcriptomic analysis reveals the regulation network of BmKrüppel homolog 1 in the oocyte development of Bombyx mori

Krüppel homolog 1 (Kr-h1), a zinc finger transcription factor, is involved in the metamorphosis and adult reproduction of insects. However, the role of Kr-h1 in reproduction of holometabolic insects remains to be elucidated. The regulation network of Kr-h1-associated genes in the reproduction in Bombyx mori was investigated in this study. The higher expression level of BmKr-h1 in the ovaries was detected during the late pupal stage and adults. RNA interference (RNAi)-mediated depletion of BmKr-h1 in the female at day 6 of pupae resulted in abnormal oocytes at 48 h post-double-stranded RNA treatment, which showed less yolk protein deposition and partially transparent chorion. RNA-seq and subsequent differentially expressed transcripts analysis showed that knockdown of BmKr-h1 caused a decrease in the expression of 2882 genes and an increase in the expression of 2565 genes in the oocytes at day 8 of pupae. Totally, 27 genes coding for transcription factors were down-regulated, while six genes coding for other transcription factors were up-regulated. BmKr-h1 bound to the Kr-h1 binding site of the transcription factors AP-1 (activating protein-1) and FOXG1 to increase their messenger RNA transcripts in the BmN cells, respectively. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses of that positively co-expressed with AP-1 and FOXG1 transcripts showed mainly enrichment in the metabolic-related pathways, the nutrient absorption and the yolk protein absorption processes. These data suggested that BmKr-h1 might directly regulate the metabolic-related pathways, the nutrient absorption and the yolk protein absorption processes or probably through AP-1 and /or FOXG1 to regulate oocyte development.

Regulatory Mechanisms of Vitellogenesis in Insects

Vitellogenesis is pre-requisite to insect egg production and embryonic development after oviposition. During insect vitellogenesis, the yolk protein precursor vitellogenin (Vg) is mainly synthesized in the fat body, transported by the hemolymph through the intercellular spaces (known as patency) in the follicular epithelium to reach the membrane of maturing oocytes, and sequestered into the maturing oocytes via receptor-mediated endocytosis. Insect vitellogenesis is governed by two critical hormones, the sesquiterpenoid juvenile hormone (JH) and the ecdysteriod 20-hydroxyecdysone (20E). JH acts as the principal gonadotropic hormone to stimulate vitellogenesis in basal hemimetabolous and most holometabolous insects. 20E is critical for vitellogenesis in some hymenopterans, lepidopterans and dipterans. Furthermore, microRNA (miRNA) and nutritional (amino acid/Target of Rapamycin and insulin) pathways interplay with JH and 20E signaling cascades to control insect vitellogenesis. Revealing the regulatory mechanisms underlying insect vitellogenesis is critical for understanding insect reproduction and helpful for developing new strategies of insect pest control. Here, we outline the recent research progress in the molecular action of gonadotropic JH and 20E along with the role of miRNA and nutritional sensor in regulating insect vitellogenesis. We highlight the advancements in the regulatory mechanisms of insect vitellogenesis by the coordination of hormone, miRNA and nutritional signaling pathways.

Effects of methyl farnesoate on Krüppel homolog 1 (Kr-h1) during vitellogenesis in the Chinese mitten crab (Eriocheir sinensis)

Methyl farnesoate (MF), a de-epoxidized form of juvenile hormone (JH) Ⅲ in insects, may regulate developmental processes such as reproduction and ovarian maturation in crustaceans. Krüppel homolog 1 (Kr-h1) is a target response gene for the methoprene-tolerant (Met) protein that is a component of the JH signaling pathway in insects. In the present study, Es-Kr-h1 was cloned from E. sinensis and characterized to ascertain whether JH/MF signaling in insects is conserved in crustaceans. The findings with molecular structure analysis indicated Es-Kr-h1 contains seven zinc finger motifs (Zn2-Zn8) commonly conserved in other crustaceans, but the Zn1 motif was not detected to be present. The PCR results indicated that relative abundance of Es-Kr-h1 mRNA transcript in the hepatopancreas was greatest in the Stage Ⅱ, followed by the Stage Ⅳ ovarian developmental categories. The relative abundance of Es-Kr-h1 mRNA transcript in vitro was greater after MF addition to the hepatopancreas, however, not the ovarian tissues. The results from in vivo and eyestalk ablation experiments indicated the relative abundance of Es-Kr-h1 mRNA transcript was greater after MF treatment and bilateral eyestalk removal in the hepatopancreas, however, not ovarian tissues. Notably, there were effects of MF on relative abundance of Es-Kr-h1 mRNA transcript pattern. The Es-Kr-h1 protein, therefore, may be involved in MF-mediated vitellogenesis resulting from the response to Es-Met in E. sinensis, and the JH/MF signaling pathway is potentially conserved in crustaceans.

Reproduction stage specific dysregulation of Daphnia magna metabolites as an early indicator of reproductive endocrine disruption

Rapid biomolecular observation in model indicator organisms has been considered as a potential predictor of water pollution from chronic and trace toxicants. This study evaluated the use of Daphnia magna metabolomic measurements as indicators for exposure to reproductive endocrine disruptors by using the model juvenile hormone analogue fenoxycarb. Because D. magna reproduction controls metabolic regulation, the reproduction stage was also carefully considered in metabolic observations and data analysis to examine differences. Comparisons of metabolite abundance regulation between 1 and 12 days of fenoxycarb exposure were performed to investigate the predictability of the sub-chronic (12 days) adverse impacts on reproduction and metabolic regulation based on acute (1 day) metabolic observations. ANOVA-simultaneous component analysis (ASCA) detected reversed patterns in direction of time-course metabolite abundance regulation with fenoxycarb exposure. For example, decreases in the abundances of leucine, asparagine, methionine, and isoleucine which then changed to increases were observed with time during fenoxycarb exposures. The reversed regulation pattern was observed at the last reproduction stage (stage 3), exclusively. Pearson correlation analysis showed that correlations of pairwise metabolites were disrupted with fenoxycarb exposure. Similar to ASCA, data normalization based on the reproduction stage improved the detectability of significant correlations. The disruption on ambient metabolite regulation patterns and pairwise metabolite correlations was consistently observed with both 1 and 12 days of fenoxycarb exposures for sets of select metabolites. The observed regulatory disruptions to these specific metabolites suggest altered oogenesis as the affected metabolites and the specific reproduction stage are related to successful oogenesis. This study demonstrates that D. magna metabolic dysregulation is a predictor of water contamination by endocrine disrupting compounds. The high predictability of sub-chronic (12 days) endocrine disruption was confirmed based on acute (1 day) metabolic observations. Furthermore, integration of the reproduction cycle information in D. magna metabolomics was validated by observing a reproduction stage specific dysregulation in metabolite abundance regulation, which was not observable from the broader data analysis. Consequently, this study confirms the potential for establishing a quantitative relationship between water quality and indicator species metabolic observations. Additionally, it was found that constraining variables relevant to toxicity mechanisms of interest, such as the reproduction stage, is a key consideration for extraction of ecologically meaningful information in environmental metabolomics.

Precocious Downregulation of Krüppel-Homolog 1 in the Migratory Locust, Locusta migratoria, Gives Rise to An Adultoid Phenotype with Accelerated Ovarian Development but Disturbed Mating and Oviposition

Krüppel-homolog 1 (Kr-h1) is a zinc finger transcription factor maintaining the status quo in immature insect stages and promoting reproduction in adult insects through the transduction of the Juvenile Hormone (JH) signal. Knockdown studies have shown that precocious silencing of Kr-h1 in the immature stages results in the premature development of adult features. However, the molecular characteristics and reproductive potential of these premature adult insect stages are still poorly understood. Here we report on an adult-like or 'adultoid' phenotype of the migratory locust, Locusta migratoria, obtained after a premature metamorphosis induced by the silencing of LmKr-h1 in the penultimate instar. The freshly molted adultoid shows precocious development of adult features, corresponding with increased transcript levels of the adult specifier gene LmE93. Furthermore, accelerated ovarian maturation and vitellogenesis were observed in female adultoids, coinciding with elevated expression of LmCYP15A1 in corpora allata (CA) and LmKr-h1 and vitellogenin genes (LmVg) in fat body, whereas LmE93 and Methoprene-tolerant (LmMet) transcript levels decreased in fat body. In adultoid ovaries, expression of the Halloween genes, Spook (LmSpo) and Phantom (LmPhm), was elevated as well. In addition, the processes of mating and oviposition were severely disturbed in these females. L. migratoria is a well-known, swarm-forming pest insect that can destroy crops and harvests in some of the world's poorest countries. As such, a better understanding of factors that are capable of significantly reducing the reproductive potential of this pest may be of crucial importance for the development of novel locust control strategies.

The Desaturase Gene Nlug-desatA2 Regulates the Performance of the Brown Planthopper Nilaparvata lugens and Its Relationship with Rice

Insect desaturases are known to play an important role in chemical communication between individuals. However, their roles in insect growth, development and fecundity, and in regulating interactions of insects with plants, remain largely unknown. In this study, we explored the functions of Nlug-desatA2, a desaturase gene of the brown planthopper (BPH), Nilaparvata lugens (Stål). The RNA interference-based knockdown of Nlug-desatA2 decreased the ratio of monounsaturated fatty acids to saturated fatty acids, and the level of fatty acids and triglycerides in BPH. Nlug-desatA2-knockdown also reduced the food intake, body mass and fecundity of female BPH adults, and led to abdomen atrophy and ovarian agenesis. Nlug-desatA2-knockdown suppressed the transcription of TOR (target of rapamycin), Lpp (Lipophorin) and AKHR (adipokinetic hormone receptor) in female adults. Moreover, the corrected survival rate of BPH with Nlug-desatA2-knockdown fed an artificial diet was higher than the survival rate of those fed on rice plants. Higher levels of salicylic acid in rice infested by Nlug-desatA2-knockdown female BPH adults than in rice infested by control BPH may be the reason. These findings demonstrate that Nlug-desatA2 has an essential role in lipid metabolism and is involved in the food intake, survival, development and fecundity of BPH. In addition, this gene is likely involved in regulating the responses of rice to BPH infestation.

Involvement of Two Paralogous Methoprene-Tolerant Genes in the Regulation of Vitellogenin and Vitellogenin Receptor Expression in the Rice Stem Borer, Chilo suppressalis

Besides the function of preventing metamorphosis in insects, the juvenile hormone (JH) plays a role in female reproduction; however, the underlying mechanism is largely unknown. The methoprene-tolerant (Met) protein belongs to a family of basic helix-loop-helix–Per-Arnt-Sim (bHLH-PAS) transcription factors and functions as the JH intracellular receptor. In this study, two full length cDNAs encoding Met (CsMet1 and CsMet2) were isolated from the rice stem borer, Chilo suppressalis. Structural analysis revealed that both CsMet1 and CsMet2 exhibited typical bHLH, PAS-A, PAS-B, and PAC (PAS C terminal motif) domains. Comparative analysis of transcript level using reverse transcription-quantitative PCR (RT-qPCR) revealed that CsMet1 was predominant in almost all examined developmental stages and tissues. Treatment with methoprene in vivo induces the transcription of both CsMet1 and CsMet2. Notably, injection of dsCsMet1 and dsCsMet2 suppressed the expression levels of vitellogenin (CsVg) and Vg receptor (CsVgR). These findings revealed the potential JH signaling mechanism regulating C. suppressalis reproduction, and provided evidence that RNAi-mediated knockdown of Met holds great potential as a control strategy of C. suppressalis.

Cloning and characterization of Methoprene-tolerant (Met) and Krüppel homolog 1 (Kr-h1) genes in the wheat blossom midge, Sitodiplosis mosellana

Juvenile hormone (JH), a growth regulator, inhibits ecdysteroid-induced metamorphosis and controls insect development and diapause. Methoprene-tolerant (Met) and Krüppel homolog 1 (Kr-h1) are two proteins involved in JH action. To gain some insight into their function in development of Sitodiplosis mosellana, an insect pest undergoing obligatory larval diapause at the mature 3rd instar stage, we cloned full-length complementary DNAs of Met and Kr-h1 from this species. SmMet encoded a putative protein, which contained three domains typical of the bHLH-PAS family and eight conserved amino acid residues important for JH binding. SmKr-h1 encoded a protein showing high sequence homology to its counterparts in other species, and contained all eight highly conserved Zn-finger motifs for DNA-binding. Expression patterns of SmMet and SmKr-h1 were developmentally regulated and JH III responsive as well. Their mRNA abundance increased as larvae entered early 3rd instar, pre-diapause and maintenance stages, and peaked during post-diapause quiescence, a pattern correlated with JH titers in this species. Different from reduced expression of SmMet, SmKr-h1 mRNA increased at mid-to-late period of post-diapause development. Topical application of JH III on diapausing larvae also induced the two genes in a dose-dependent manner. Expression of SmMet and SmKr-h1 clearly declined in the pre-pupal phase, and was significantly higher in female adults than male adults. These results suggest that JH-responsive SmMet and SmKr-h1 might play key roles in diapause induction and maintenance as well as in post-diapause quiescence and adult reproduction, whereas metamorphosis from larvae to pupae might be correlated with their reduced expression.

Knockdown of Methoprene-Tolerant Arrests Ovarian Development in the Sogatella furcifera (Hemiptera: Delphacidae)

Juvenile hormone (JH) is responsible for repressing larval metamorphosis and inducing vitellogenesis and egg production in insects. Methoprene-tolerant (Met) is known to be an intracellular receptor and transducer of JH. We examined the role of Met in ovarian development in the rice pest Sogatella furcifera (Horváth). We first cloned and sequenced S. furcifera Met (SfMet). The SfMet protein belongs to the basic helix-loop-helix/Per-Arnt-Sim (bHLH-PAS) family with a bHLH domain and two PAS domains (PAS-A and PAS-B). SfMet was expressed in all developmental stages and tissues but was most highly expressed in the ovaries of adult females. Furthermore, RNA interference (RNAi) mediated silencing of SfMet substantially reduced the expression of SfVg, decreased yolk protein deposition and blocked oocyte maturation and ovarian development. These results demonstrate that SfMet plays a key role in female reproduction in S. furcifera and suggest that targeting this gene could be an effective way of controlling this pest.

Molecular Characterization of Primary Juvenile Hormone Responders Methoprene-Tolerant (Met) and Krüppel Homolog 1 (Kr-h1) in Grapholita molesta (Lepidoptera: Tortricidae) with Clarification of Their Roles in Metamorphosis and Reproduction

Methoprene-tolerant (Met) is a putative JH intracellular receptor that transduces JH signal by activation of the inducible Krüppel homolog 1 (Kr-h1). We analyzed the gene sequences of Met and Kr-h1 and their patterns of expression in Grapholita molesta (Busck) immature and adult stages in order to better understand the roles of these primary JH responders in regulating the metamorphosis and reproduction of this global pest of fruit crops. The deduced amino acid sequences of both GmMet and GmKr-h1 were highly homologous to those of other Lepidoptera, especially the cotton bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae). Peak expression of GmMet occurred during the last 3 to 5 d of the final instar, followed by that of GmKr-h1, in the last 3 d of final instar. Similar patterns of GmMet and GmKr-h1 expression were detected across various tissue types in the fifth-instar larvae, with the highest expression observed in the head, followed by the epidermis, and the fat body. When expression of GmMet and GmKr-h1 was knocked down via dsRNA injection in the fifth instar, the results were increased larval mortality, abnormal pupation, delayed pupal duration, reduced adult emergence, extended preoviposition period, and reduced fecundity. We infer that both GmMet and GmKr-h1 participated in regulation of metamorphosis and reproduction in G. molesta, the former acting upstream of the latter, and could present biorational targets for novel pest control compounds.

Juvenile Hormone receptor Met is essential for ovarian maturation in the Desert Locust, Schistocerca gregaria

Juvenile hormones (JH) are key endocrine regulators produced by the corpora allata (CA) of insects. Together with ecdysteroids, as well as nutritional cues, JH coordinates different aspects of insect postembryonic development and reproduction. The function of the recently characterized JH receptor, Methoprene-tolerant (Met), appears to be conserved in different processes regulated by JH. However, its functional interactions with other hormonal signalling pathways seem highly dependent on the feeding habits and on the developmental and reproductive strategies employed by the insect species investigated. Here we report on the effects of RNA interference (RNAi) mediated SgMet knockdown during the first gonadotrophic cycle in female desert locusts (Schistocerca gregaria). This voracious, phytophagous pest species can form migrating swarms that devastate field crops and harvests in several of the world’s poorest countries. A better knowledge of the JH signalling pathway may contribute to the development of novel, more target-specific insecticides to combat this very harmful swarming pest. Using RNAi, we show that the JH receptor Met is essential for ovarian maturation, vitellogenesis and associated ecdysteroid biosynthesis in adult female S. gregaria. Interestingly, knockdown of SgMet also resulted in a significant decrease of insulin-related peptide (SgIRP) and increase of neuroparsin (SgNP) 3 and 4 transcript levels in the fat body, illustrating the existence of an intricate regulatory interplay between different hormonal factors. In addition, SgMet knockdown in females resulted in delayed display of copulation behaviour with virgin males, when compared with dsGFP injected control animals. Moreover, we observed an incapacity of adult dsSgMet injected female locusts to oviposit during the time of the experimental setup. As such, SgMet is an essential gene playing crucial roles in the endocrine communication necessary for successful reproduction of the desert locust.

The Direct Interaction between E93 and Kr-h1 Mediated Their Antagonistic Effect on Ovary Development of the Brown Planthopper

The juvenile hormone (JH) signalling and ecdysone signalling pathways are crucial endocrine signalling pathways that orchestrate the metamorphosis of insects. The metamorphic process, the morphological change from the immature to adult forms, is orchestrated by the dramatic reduction of JH and downstream transcription factors. The Krüppel-homologue 1 (Kr-h1), a downstream transcription factor of the JH signalling pathway, represses E93 expression with an anti-metamorphic effect. However, the biochemical interaction between Kr-h1 and E93 and how the interaction regulates ovary development, a sensitive readout for endocrine regulation, remain unknown. In brown planthopper, Nilaparvata lugens, we found that the downregulation of Kr-h1 partially recovered the deteriorating effect of E93 knock-down on metamorphosis. Dual knock down of E93 and Kr-h1 increased ovary development and the number of eggs laid when compared to the effects of the knock down of E93 alone, indicating that the knock down of Kr-h1 partially recovered the deteriorating effect of the E93 knock-down on ovary development. In summary, our results indicated that E93 and Kr-h1 have antagonistic effects on regulating metamorphosis and ovary development. We tested the biochemical interaction between these two proteins and found that these molecules interact directly. Kr-h1 V and E93 II undergo strong and specific interactions, indicating that the potential interacting domain may be located in these two regions. We inferred that the nuclear receptor interaction motif (NR-box) and helix-turn-helix DNA binding motifs of the pipsqueak family (RHF1) are candidate domains responsible for the protein–protein interaction between E93 and Kr-h1. Moreover, the HA-tagged E93 and FLAG-tagged Kr-h1 were co-localized in the nucleus, and the expression of E93 was increased when Kr-h1 was downregulated, supporting that these two proteins may interact antagonistically. JH and ecdysone signalling are critical for the control of ovary development and pest populations. Our result is important for understanding the interactions between E93 and related proteins, which makes it possible to identify potential targets and develop new pesticides for pest management.

Methoprene-Tolerant (Met) Is Indispensable for Larval Metamorphosis and Female Reproduction in the Cotton Bollworm Helicoverpa armigera

Juvenile hormone (JH) represses larval metamorphosis and induces adult reproduction in insects. Methoprene-tolerant (Met) is identified as an intranuclear receptor that mediates JH actions. In the present study, we characterized a Met from the severe agricultural pest, Helicoverpa armigera, namely HaMet. In the larval stage, HaMet is predominantly expressed in the epidermis and midgut, and is upregulated before each molting, whereas in adults HaMet is maximally expressed in the ovary, testis, and fat body. The immunofluorescence assay revealed that HaMet was distributed in the longitudinal and circular muscle layers of midgut in larvae, whereas in the ovary of female adults, HaMet was localized in the nucleus of the oolemma. Knockdown of HaMet in final-instar larvae shortened the time of pupation, induced abnormal pupation, and dampened pupation rate. In female adults, HaMet depletion severely suppressed the transcription of Vitellogenin (Vg) and Vitellogenin Receptor (VgR), disrupted the Vg accumulation in fat body and the yolk protein uptake in oocytes, and finally led to an impaired fecundity. Our findings therefore confirmed that HaMet acted as a nuclear receptor of JH and played an essential role in larval metamorphosis, vitellogenesis, and oocyte maturation.

Dissecting the role of Krüppel homolog 1 in the metamorphosis and female reproduction of the cotton bollworm, Helicoverpa armigera

In insects, metamorphosis and reproduction are controlled by juvenile hormone (JH) and 20-hydroxyecdysone (20E). Krüppel homolog 1 (Kr-h1), a transcription factor, is regarded as a JH-early inducible gene responsible for the repression of metamorphosis. However, the role of Kr-h1 in reproduction of holometabolic insects is relatively less understood. In this study, we studied the role of Kr-h1 in larvae-pupae transition and female reproduction in the major agricultural pest Helicoverpa armigera. Two HaKr-h1 isoforms (HaKr-h1α and HaKr-h1ß) were identified, with HaKr-h1α predominant in the cotton bollworm. In larvae, HaKr-h1 was predominately expressed in the epidermis and markedly up-regulated during the moult stage, whereas in adults HaKr-h1 was mainly expressed in females and the highest transcription was detected in the ovaries. Considering the function of hormones in larval metamorphosis, we examined the modulation of gene expression in response to hormones, which showed that HaKr-h1 was significantly induced by both JH analogue (JHA) and 20E. Knockdown of HaKr-h1 in fifth-instar larvae resulted in precocious metamorphosis from larvae to pupae. Moreover, a fluorescence immunoassay coupled with heterologous expression revealed that HaKr-h1 was localized in the nucleus of oocyte membrane. In female adults, depletion of HaKr-h1 severely repressed the transcription of vitellogenin, disrupted oocyte maturation and reduced the number of eggs laid, suggesting that HaKr-h1 is required for vitellogenesis and egg production in H. armigera. The present study provides insight into the roles of HaKr-h1 in JH-mediated reproduction and highlights HaKr-h1 as a target for suppression of lepidopteran pests.

Involvement of Met and Kr-h1 in JH-Mediated Reproduction of Female Bactrocera dorsalis (Hendel)

Juvenile hormone (JH) prevents metamorphosis during insect larval stages and promotes adult reproductive processes. Krüppel-homolog 1 (Kr-h1), a zinc finger transcription factor assumed to be induced by JH via the JH receptor methoprene-tolerant (Met), mediates the antimetamorphic effect of JH in insects, but its function in JH-mediated reproductive processes has not been fully explored. In this study, Met and Kr-h1 involved in the JH signaling pathway were first cloned and identified from the oriental fruit fly, Bactrocera dorsalis, an important pest infesting fruit and vegetables worldwide. Subsequent spatiotemporal expression analysis revealed that Met and Kr-h1 were both highly expressed in 7-day-old adults and fat body of female adults, respectively. Treatment with a JH analog (methoprene) significantly induced the expression of JH signaling and vitellogenin (Vg) genes and accelerated ovary development. RNA interference (RNAi) further revealed that either Met or Kr-h1 depletion at the adult stage of B. dorsalis impeded ovary development, with significantly lower egg production noted as well. In addition, rescue through methoprene application after RNAi stimulated the expression of JH signaling and Vg genes. Although there were still differences in ovary phenotype between rescued insects and the pre-RNAi control, ovary redevelopment with a larger surface area was observed, consistent with the spatiotemporal expression and phenotypes recorded in the original methoprene experiment. Our data reveal the involvement of Met and Kr-h1 in insect vitellogenesis and egg production, thus indicating the crucial role of the JH signaling pathway in insect reproduction.

Role of Broad-Complex (Br) and Krüppel homolog 1 (Kr-h1) in the Ovary Development of Nilaparvata lugens

Ovarian development plays an important role in the life history of insects and is crucial for control of the insect population. The metamorphosis of an insect is precisely regulated by the interaction of the juvenile hormone and ecdysone. To understand the role of NlBr and NlKr-h1 in ovary development, we used RNA interference (RNAi) to down-regulate the expression of Broad-Complex (Br) and Krüppel homolog 1 (Kr-h1), two important down-stream transcription factors of juvenile hormone and ecdysone signaling. We further investigated their effects on metamorphosis and ovary development. The results showed that both NlBr and NlKr-h1 are induced by ecdysone. The down-regulation of NlBr and NlKr-h1 alone or together by RNAi is more effective than the topical application of ecdysone on the number of ovarioles, suggesting the necessity of NlBr and NlKr-h1 in determining the number of ovarioles. The ovarian grade was significantly increased/decreased by the topical application of ecdysone and down-regulation of NlBr and NlKr-h1. The pre-oviposition period was also increased. When NlBr and NlKr-h1 were down-regulated together, the ovary grade was not significantly different compared to the control (dsGFP), indicating that the development of the ovary is under the control of both NlBr and NlKr-h1. The interaction between the NlBr and NlKr-h1 on the number of ovarioles and the development of the ovary indicates cross-talk between both juvenile hormone and ecdysone signaling at the transcription level in the brown planthopper. Both genes are nuclear transcription factors and may regulate signaling via down-stream genes. These results would help to both enhance the current understanding of the regulatory mechanism of the interaction between juvenile hormone and ecdysone signaling pathways during ovarian development and to design chemicals to control pests.

An isoform of Taiman that contains a PRD-repeat motif is indispensable for transducing the vitellogenic juvenile hormone signal in Locusta migratoria

Taiman (Tai) has been recently identified as the dimerizing partner of juvenile hormone (JH) receptor, Methoprene-tolerant (Met). However, the role of Tai isoforms in transducing vitellogenic signal of JH has not been determined. In this study, we show that the migratory locust Locusta migratoria has two Tai isoforms, which differ in an INDEL-1 domain with the PRD-repeat motif rich in histidine and proline at the C-terminus. Tai-A with the INDEL-1 is expressed at levels about 50-fold higher than Tai-B without the INDEL-1 in the fat body of vitellogenic adult females. Knockdown of Tai-A but not Tai-B results in a substantial reduction of vitellogenin expression in the fat body accompanied by the arrest of ovarian development and oocyte maturation, similar to that caused by depletion of both Tai isoforms. Either Tai-A or Tai-B combined with Met can induce target gene transcription in response to JH, but Tai-A appears to mediate a significantly higher transactivation. Our data suggest that the INDEL-1 domain plays a critical role in Tai function during reproduction as Tai-A appears be more active than Tai-B in transducing the vitellogenic JH signal in L. migratoria.

A Genome-Wide Identification and Analysis of the Basic Helix-Loop-Helix Transcription Factors in Brown Planthopper, Nilaparvata lugens

The basic helix-loop-helix (bHLH) transcription factors in insects play essential roles in multiple developmental processes including neurogenesis, sterol metabolism, circadian rhythms, organogenesis and formation of olfactory sensory neurons. The identification and function analysis of bHLH family members of the most destructive insect pest of rice, Nilaparvata lugens, may provide novel tools for pest management. Here, a genome-wide survey for bHLH sequences identified 60 bHLH sequences (NlbHLHs) encoded in the draft genome of N. lugens. Phylogenetic analysis of the bHLH domains successfully classified these genes into 40 bHLH families in group A (25), B (14), C (10), D (1), E (8) and F (2). The number of NlbHLHs with introns is higher than many other insect species, and the average intron length is shorter than those of Acyrthosiphon pisum. High number of ortholog families of NlbHLHs was found suggesting functional conversation for these proteins. Compared to other insect species studied, N. lugens has the highest number of bHLH members. Furthermore, gene duplication events of SREBP, Kn(col), Tap, Delilah, Sim, Ato and Crp were found in N. lugens. In addition, a putative full set of NlbHLH genes is defined and compared with another insect species. Thus, our classification of these NlbHLH members provides a platform for further investigations of bHLH protein functions in the regulation of N. lugens, and of insects in general.

JNK signaling mediates wing form polymorphism in brown planthoppers (Nilaparvata lugens)

Wing polyphenism is considered to be an adaptive trade-off between migration (long winged forms) and reproduction (short winged forms), determined by various environmental conditions. The c-Jun NH2-terminal kinase (JNK) is crucial for the regulation of the activity of a number of transcription factors, and is activated under stress and environmental fluctuations where it functions in maintaining cell viability and proliferation. We used RNA interference and a pharmacological inhibitor of JNK to test the role of JNK signaling in regulating the wing dimorphism of the brown planthopper, Nilaparvata lugens. Silencing NlJNK increased the proportion of short winged female adults, reminiscent of the effect of silencing inhibitory components of the insulin-signaling pathway, such as NlAkt. However, silencing of the JNK-activated transcription factors NlJun and NlFos did not change the wing form ratio significantly, indicating that NlJNK may not act through NlJun and NlFos in mediating this process. In summary, JNK signaling may play a role in determining wing polymorphism in N. lugens females.