BmSd gene regulates the silkworm wing size by affecting the Hippo pathway

Bombyx mori voltage-dependent anion-selective channel induces programmed cell death to defend against Bombyx mori nucleopolyhedrovirus infection

BACKGROUND

Voltage-dependent anion-selective channels (VDACs) serve as pore proteins within the mitochondrial membrane, aiding in the regulation of cell life and cell death. Although the occurrence of cell death is crucial for defense against virus infection, the function played by VDAC in Bombyx mori, in response to the influence of Bombyx mori nucleopolyhedrovirus (BmNPV), remains unclear.

RESULTS

BmVDAC was found to be relatively highly expressed both during embryonic development, and in the Malpighian tubule and midgut. Additionally, the expression levels of BmVDAC were found to be different among silkworm strains with varying levels of resistance to BmNPV, strongly suggesting a connection between BmVDAC and virus infection. To gain further insight into the function of BmVDAC in BmNPV, we employed RNA interference (RNAi) to silence and overexpress it by pIZT/V5-His-mCherry. The results revealed that BmVDAC is instrumental in developing the resistance of host cells to BmNPV infection in BmN cell-line cells, which was further validated as likely to be associated with initiating programmed cell death (PCD). Furthermore, we evaluated the function of BmVDAC in another insect, Spodoptera exigua. Knockdown of the BmVDAC homolog in S. exigua, SeVDAC, made the larvae more sensitive to BmNPV.

CONCLUSION

We have substantiated the pivotal role of BmVDAC in conferring resistance against BmNPV infection, primarily associated with the initiation of PCD. The findings of this study shine new light on the molecular mechanisms governing the silkworm's response to BmNPV infection, thereby supporting innovative approaches for pest biocontrol. © 2024 Society of Chemical Industry.

Studying the role of Bombyx mori molybdenum cofactor sulfurase in Bombyx mori nucleopolyhedrovirus infection

Molybdenum cofactor sulfurase (MoCoS) is a key gene involved in the uric acid metabolic pathway that activates xanthine dehydrogenase to synthesise uric acid. Uric acid is harmful to mammals but plays crucial roles in insects, one of which is the immune responses. However, the function of Bombyx mori MoCoS in response to BmNPV remains unclear. In this study, BmMoCoS was found to be relatively highly expressed in embryonic development, gonads and the Malpighian tubules. In addition, the expression levels of BmMoCoS were significantly upregulated in three silkworm strains with different levels of resistance after virus infection, suggesting a close link between them. Furthermore, RNAi and overexpression studies showed that BmMoCoS was involved in resistance to BmNPV infection, and its antivirus effects were found to be related to the regulation of uric acid metabolism, which was uncovered by inosine- and febuxostat-coupled RNAi and overexpression. Finally, the BmMoCoS-mediated uric acid pathway was preliminarily confirmed to be a potential target to protect silkworms from BmNPV infection. Overall, this study provides new evidence for elucidating the molecular mechanism of silkworms in response to BmNPV infection and new strategies for the prevention of viral infections in sericulture.

A Combinatorial Single-Molecule Real-Time and Illumina Sequencing Analysis of Postembryonic Gene Expression in the Asian Citrus Psyllid Diaphorina citri

Huanglongbing (HLB) is a systemic plant disease caused by 'Candidatus Liberibacter asiaticus (CLas)' and transmitted by Diaphorina citri. D. citri acquires the CLas bacteria in the nymph stage and transmits it in the adult stage, indicating that molting from the nymph to adult stages is crucial for HLB transmission. However, the available D. citri reference genomes are incomplete, and gene function studies have been limited to date. In the current research, PacBio single-molecule real-time (SMRT) and Illumina sequencing were performed to investigate the transcriptome of D. citri nymphs and adults. In total, 10,641 full-length, non-redundant transcripts (FLNRTs), 594 alternative splicing (AS) events, 4522 simple sequence repeats (SSRs), 1086 long-coding RNAs (lncRNAs), 281 transcription factors (TFs), and 4459 APA sites were identified. Furthermore, 3746 differentially expressed genes (DEGs) between nymphs and adults were identified, among which 30 DEGs involved in the Hippo signaling pathway were found. Reverse transcription-quantitative PCR (RT-qPCR) further validated the expression levels of 12 DEGs and showed a positive correlation with transcriptome data. Finally, the spatiotemporal expression pattern of genes involved in the Hippo signaling pathway exhibited high expression in the D. citri testis, ovary, and egg. Silencing of the D. citri transcriptional co-activator (DcYki) gene significantly increased D. citri mortality and decreased the cumulative molting. Our results provide useful information and a reliable data resource for gene function research of D. citri.

Wing expansion functional analysis of ion transport peptide gene in Sogatella furcifera (Horváth) (Hemiptera: Delphacidae)

Ion transport peptide (ITP), a superfamily of arthropod neuropeptides, serves a crucial role in regulating various physiological processes such as diuresis, ecdysis behavior, and wing expansion. However, the molecular characteristics, expression profile, and role of ITP in Sogatella furcifera are poorly understood. To elucidate the characteristics and biological function of ITP in S. furcifera, we employed reverse transcription-polymerase chain reaction (RT-PCR) and RNA interference (RNAi) methods. The identified SfITP gene encodes 117 amino acids. The expression of SfITP gradually increased followed the formation of 3-day-old of 5th instar nymph, peaking initially at 40 min after eclosion, and reaching another peak 24 h after eclosion, with particularly high expression levels in thorax and wing tissues. Notably, SfITP RNAi in 3rd instar nymphs of S. furcifera significantly inhibited the transcript levels of SfITP, resulting in 55% mortality and 78% wing deformity. These findings suggests that SfITP is involved in the regulation of wing expansion in S. furcifera, providing insights into the regulation of insect wing expansion and contributing to the molecular understanding of this process.

Characterization of two Bursicon genes and their association with wing development in the brown citrus aphid, Aphis citricidus

The tanning hormone, Bursicon, is a neuropeptide secreted by the insect nervous system that functions as a heterodimer composed of Burs-α and Burs-β subunits. It plays a critical role in the processes of cuticle tanning and wing expansion in insects. In this study, we successfully identified the AcBurs-α and AcBurs-β genes in Aphis citricidus. The open reading frames of AcBurs-α and AcBurs-β were 480 and 417 bp in length, respectively. Both AcBurs-α and AcBurs-β exhibited 11 conserved cysteine residues. AcBurs-α and AcBurs-β were expressed during all developmental stages of A. citricidus and showed high expression levels in the winged aphids. To investigate the potential role of AcBurs-α and AcBurs-β in wing development, we employed RNA interference (RNAi) techniques. With the efficient silencing of AcBurs-α (44.90%) and AcBurs-β (52.31%), malformed wings were induced in aphids. The proportions of malformed wings were 22.50%, 25.84%, and 38.34% in dsAcBurs-α-, dsAcBur-β-, and dsAcBurs-α + dsAcBur-β-treated groups, respectively. Moreover, feeding protein kinase A inhibitors (H-89) also increased the proportion of malformed wings to 30.00%. Feeding both double-stranded RNA and inhibitors (H-89) significantly downregulated the wing development-related genes nubbin, vestigial, notch and spalt major. Silence of vestigial through RNAi also led to malformed wings. Meanwhile, the exogenous application of 3 hormones that influence wing development did not affect the expression level of AcBursicon genes. These findings indicate that AcBursicon genes plays a crucial role in wing development in A. citricidus; therefore, it represents a potential molecular target for the control of this pest through RNAi-based approaches.

Bursicon regulates wing expansion via PKA in the oriental fruit fly, Bactrocera dorsalis

BACKGROUND

Bursicon is a heterodimeric neuropeptide that is involved in many physiological activities such as cuticle tanning, wing expansion, reproduction and immunity in insects. In this study, the role of bursicon in the wing expansion was investigated in Bactrocera dorsalis, an important invasive insect pest in agriculture.

RESULTS

The cDNA sequences and deduced amino acids of bursicon genes (named BdBurs-α and BdBurs-β) were determined, and two proteins typically contained 11 cysteine residues in conserved positions that were highly conserved in other insect species. The spatiotemporal expressions of bursicon genes showed that higher expression occurred at the pupal, early adult stage and ovaries, and lower expression at the late larval stage and in wing tissue (8-day-old pupae). Dysfunction of bursicon genes by dsRNA microinjection into 5-day-old pupae reduced PKA (a downstream component of the bursicon pathway) activity and resulted in malformed adult wings. PKA inhibitor injection into 5-day-old pupae also resulted in similar phenotypes. Hematoxylin & eosin staining of the adult wing showed that RNAi and PKA inhibitor treatment reduced the thickness of the wing cuticle, which wing cuticle thickness were ≈50% thinner than in the control. Furthermore, the expression of hedgehog (Bdhh) (one of 10 tested genes related to wing development) was significantly upregulated after RNAi and PKA inhibitor application.

CONCLUSION

The results indicate that bursicon plays a crucial role in the wing expansion of B. dorsalis, suggesting bursicon genes have potential to be the targets for B. dorsalis control. © 2023 Society of Chemical Industry.

Bmmp influences wing morphology by regulating anterior-posterior and proximal-distal axes development

Insect wings are subject to strong selective pressure, resulting in the evolution of remarkably diverse wing morphologies that largely determine flight capacity. However, the genetic basis and regulatory mechanisms underlying wing size and shape development are not well understood. The silkworm Bombyx mori micropterous (mp) mutant exhibits shortened wing length and enlarged vein spacings, albeit without changes in total wing area. Thus, the mp mutant comprises a valuable genetic resource for studying wing development. In this study, we used molecular mapping to identify the gene responsible for the mp phenotype and designated it Bmmp. Phenotype-causing mutations were identified as indels and single nucleotide polymorphisms in noncoding regions. These mutations resulted in decreased Bmmp messenger RNA levels and changes in transcript isoform composition. Bmmp null mutants were generated by clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated protein 9 and exhibited changed wing shape, similar to mp mutants, and significantly smaller total wing area. By examining the expression of genes critical to wing development in wildtype and Bmmp null mutants, we found that Bmmp exerts its function by coordinately modulating anterior-posterior and proximal-distal axes development. We also studied a Drosophila mp mutant and found that Bmmp is functionally conserved in Drosophila. The Drosophila mp mutant strain exhibits curly wings of reduced size and a complete loss of flight capacity. Our results increase our understanding of the mechanisms underpinning insect wing development and reveal potential targets for pest control.

Transcriptome-Wide Characterization of piRNAs during the Developmental Process of European Honey-Bee Larval Guts

piRNAs play pivotal roles in maintaining genome stability, regulating gene expression, and modulating development and immunity. However, there are few piRNA-associated studies on honey-bees, and the regulatory role of piRNAs in the development of bee guts is largely unknown. Here, the differential expression pattern of piRNAs during the developmental process of the European honey-bee (Apis mellifera) larval guts was analyzed, followed by investigation of the regulatory network and the potential function of differentially expressed piRNAs (DEpiRNAs) in regulating gut development. A total of 843 piRNAs were identified in the larval guts of A. mellifera; among these, 764 piRNAs were shared by 4- (Am4 group), 5- (Am5 group), and 6-day-old (Am6 group) larval guts, while 11, 67, and one, respectively, were unique. The first base of piRNAs in each group had a cytosine (C) bias. Additionally, 61 up-regulated and 17 down-regulated piRNAs were identified in the “Am4 vs. Am5” comparison group, further targeting 9, 983 genes, which were involved in 50 GO terms and 142 pathways, while two up-regulated and five down-regulated piRNAs were detected in the “Am5 vs. Am6” comparison group, further targeting 1, 936 genes, which were engaged in 41 functional terms and 101 pathways. piR-ame-742536 and piR-ame-856650 in the “Am4 vs. Am5” comparison group as well as piR-ame-592661 and piR-ame-31653 in the “Am5 vs. Am6” comparison group were found to link to the highest number of targets. Further analysis indicated that targets of DEpiRNAs in these two comparison groups putatively regulate seven development-associated signaling pathways, seven immune-associated pathways, and three energy metabolism pathways. Moreover, the expression trends of five randomly selected DEpiRNAs were verified based on stem-loop RT-PCR and RT-qPCR. These results were suggestive of the overall alteration of piRNAs during the larval developmental process and demonstrated that DEpiRNAs potentially modulate development-, immune-, and energy metabolism-associated pathways by regulating the expression of corresponding genes via target binding, further affecting the development of A. mellifera larval guts. Our data offer a novel insight into the development of bee larval guts and lay a basis for clarifying the underlying mechanisms.

Immune function analysis of LsSd, a transcription factor of the Hippo signaling pathway, in the cigarette beetle Lasioderma serricorne

The Scalloped (Sd) is a transcription factor that regulates organ size control in the Hippo-signaling pathway. Recent studies have showed that Hippo signaling also functions in the innate immune response. Although the Sd gene has been reported in many insects, their immune functions remain unexplored. In this study, the LsSd gene of Lasioderma serricorne, with a complete open reading frame that encodes a protein composed of 402 amino acids was identified. LsSd was predominantly expressed in early pupae. Tissue-specific analyses revealed that the highest concentrations of LsSd were detected in the midgut and brain. At 1–24 h after Escherichia coli infection, LsSd expression increased substantially. However, LsSd expression was downregulated 3–12 h after Staphylococcus aureus infection. RNA interference-mediated silencing of the LsSd transcript resulted in deformed, considerably smaller, and degenerated wings. Meanwhile, LsCycE, LsDiap1, and LsVg, which are involved in cell proliferation and wing development, were drastically reduced when LsSd was depleted. In a survival assay, the LsSd knockdown considerably decreased the susceptibility to S. aureus, a gram-positive bacterium. In addition, knockdown of LsSd remarkably downregulated the transcription of LsCact in response to S. aureus stimulation, while upregulating the expression of five immune-related genes. Our results provide conclusive proof for the important roles of LsSd in the immune response of L. serricorne.

Map-based cloning and functional analysis revealed ABCC2 is responsible for Cry1Ac toxin resistance in Bombyx mori

Bt toxins are parasporal crystals produced by Bacillus thuringiensis (Bt). They have specific killing activity against various insects and have been widely used to control agricultural pests. However, their widespread use has developed the resistance of many target insects. To maintain the sustainable use of Bt products, the resistance mechanism of insects to Bt toxins must be fully clarified. In this study, Bt-resistant and Bt-susceptible silkworm strains were used to construct genetic populations, and the genetic pattern of silkworm resistance to Cry1Ac toxin was determined. Sequence-tagged site molecular marker technology was used to finely map the resistance gene and to draw a molecular genetic linkage map, and the two closest markers were T1590 and T1581, indicating the resistance gene located in the 155 kb genetic region. After analyzing the sequence of the predicted gene in the genetic region, an ATP binding cassette transporter (ABCC2) was identified as the candidate gene. Molecular modeling and protein-protein docking result showed that a tyrosine insertion in the mutant ABCC2 might be responsible for the interaction between Cry1Ac and ABCC2. Moreover, CRISPR/Cas9-mediated genome editing technology was used to knockout ABCC2 gene. The homozygous mutant ABCC2 silkworm was resistant to Cry1Ac toxin, which indicated ABCC2 is the key gene that controls silkworm resistance to Cry1Ac toxin. The results have laid the foundation for elucidating the molecular resistance mechanism of silkworms to Cry1Ac toxin and could provide a theoretical basis for the biological control of lepidopteran pests.

CRISPR/Cas9 in lepidopteran insects: Progress, application and prospects

Clustered regularly spaced short palindrome repeats (CRISPR) structure family forms the acquired immune system in bacteria and archaea. Recent advances in CRISPR/Cas genome editing as derived from prokaryotes, confirmed the characteristics of robustness, high target specificity and programmability, and also revolutionized the insect sciences field. The successful application of CRISPR in a wide variety of lepidopteran insects, with a high genetic diversity, provided opportunities to explore gene functions, insect modification and pest control. In this review, we present a detailed overview on the recent progress of CRISPR in lepidopteran insects, and described the basic principles of the system and its application. Major interest is on wing development, pigmentation, mating, reproduction, sex determination, metamorphosis, resistance and silkworm breeding innovation. Finally, we outlined the limitations of CRISPR/Cas system and discussed its application prospects in lepidopteran insects.

CRISPR/Cas9-based knockout reveals that the clock gene timeless is indispensable for regulating circadian behavioral rhythms in Bombyx mori

Circadian rhythms, which are ubiquitous and adaptive, occur across all species, from microbes to humans, in which they organize and modify behavior and physiology. timeless (tim) is a canonical clock gene. The core composition of the Drosophila melanogaster endogenous circadian clock has been extensively investigated; however, in lepidopteran insects, including Bombyx mori, the mechanism is complicated and little is known regarding the participation of tim in the negative feedback loop responsible for behavioral activities. To arrive at a comprehensive understanding of the role of tim in the B. mori endogenous circadian clock, we exploited the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 gene editing system. We attempted to elucidate the functions of tim in the circadian clock of B. mori using Bmtim mutants. The knockouts affected two circadian behavioral activities: adult emergence and embryo hatching rhythms. Quantitative real-time polymerase chain reaction results confirmed that tim-knockouts induced relative reductions in the expression levels, and thereby the oscillation amplitudes, of Bmper and Bmclk messenger RNAs during both the photophase and scotophase. Additionally, the daily rhythmic expression of Bmdbt was upregulated in the photophase and downregulated in the scotophase in a tim-knockout. Our study reveals that tim is integral to the B. mori circadian clock and may be involved in regulating eclosion and hatching rhythms.

The hemolymph melanization response is related to defence against the AcMNPV infection in Bombyx mori

Melanization is mediated by the prophenoloxidase (proPO) activation cascade and plays an important role in the arthropods immune system. Previously, we found that the hemolymph of the p50 strain does not perform melanization after infection with Autographa californica multiple nucleopolyhedrovirus (AcMNPV). However, this mechanism is still unclear. In this study, the underlying mechanism of the inhibition of hemolymph melanization was investigated by analysing the AcMNPV-susceptible or -resistant silkworm strains after inoculation with AcMNPV. The results showed that the level of hemolymph melanization was higher in resistant strain C108 than in susceptible strain p50 at the late stage (72 to 120 h postinoculation). The PO activity decreased significantly at the late stage of infection (72 to 120 hpi), and the expression of BmPPO1 and BmPPO2 was downregulated in p50. However, the PO activity increased in the resistant strain C108, while the expression level of BmPPO1 and BmPPO2 displayed no significant changes. The expression of the BmPPAE gene was upregulated in two strains during viral infection. In addition, the hemolymph melanization can weaken the viral activity in vitro. Our results suggested that the silkworm hemolymph melanization response is related to defence against the AcMNPV infection.

De Novo Sequencing and High-Contiguity Genome Assembly of Moniezia expansa Reveals Its Specific Fatty Acid Metabolism and Reproductive Stem Cell Regulatory Network

Moniezia expansa (M. expansa) parasitizes the small intestine of sheep and causes inhibited growth and development or even death. Being globally distributed, it causes considerable economic losses to the animal husbandry industry. Here, using Illumina, PacBio and BioNano techniques, we obtain a high-quality genome assembly of M. expansa, which has a total length of 142 Mb, a scaffold N50 length of 7.27 Mb and 8,104 coding genes. M. expansa has a very high body fat content and a specific type of fatty acid metabolism. It cannot synthesize any lipids due to the loss of some key genes involved in fatty acid synthesis, and it may can metabolize most lipids via the relatively complete fatty acid β-oxidation pathway. The M. expansa genome encodes multiple lipid transporters and lipid binding proteins that enable the utilization of lipids in the host intestinal fluid. Although many of its systems are degraded (with the loss of homeobox genes), its reproductive system is well developed. PL10, AGO, Nanos and Pumilio compose a reproductive stem cell regulatory network. The results suggest that the high body lipid content of M. expansa provides an energy source supporting the high fecundity of this parasite. Our study provides insight into host interaction, adaptation, nutrient acquisition, strobilization, and reproduction in this parasite and this is also the first genome published in Anoplocephalidae.

Bmcas-1 plays an important role in response against BmNPV infection in vitro

Apoptosis, as one kind of innate immune system, is involved in host response against pathogens innovation. Caspases play a vital role in the execution stage of host cell apoptosis. It has been reported that Bmcaspase-1 (Bmcas-1) has a close relationship with Bombyx mori nucleopolyhedrovirus (BmNPV) infection for its differentially expressed patterns after viral infection. However, its underlying response mechanism is still unclear. The significant differential expression of Bmcas-1 in different tissues of differentially resistant strains revealed its vital role in BmNPV infection. To further validate its role in BmNPV infection, budded virus (BV)-eGFP was analyzed after knockdown and overexpression of Bmcas-1 by small interfering RNA and the pIZT-mCherry vector, respectively. The reproduction of BV-eGFP obviously increased at 72 h after knockdown of Bmcas-1, and decreased after overexpression in BmN cells. Moreover, the conserved functional domain of Cas-1 among different species and the closed evolutionary relationship of Cas-1 in Lepidoptera hinted that Bmcas-1 might be associated with apoptosis, and this was also validated by the apoptosis inducer, Silvestrol, and the inhibitor, Z-DEVD-FMK. Therefore, Bmcas-1 plays an essential antiviral role by activating apoptosis, and this result lays a fundament for clarifying the molecular mechanism of silkworm in response against BmNPV infection and breeding of resistant strains.

Identification of the in vitro antiviral effect of BmNedd2-like caspase in response to Bombyx mori nucleopolyhedrovirus infection

Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the most serious pathogens in sericulture, and the underlying antiviral mechanism in silkworm is still unclear. Bombyx mori Nedd2-like caspase (BmNc) has been identified as a candidate antiviral gene from previous transcriptome data, since it is differentially expressed in the midgut of differentially resistant silkworm strains following BmNPV infection. However, the molecular mechanism by which BmNc responds to BmNPV is unknown. In this study, the relationship between BmNc and BmNPV was confirmed by its significantly different expression in different tissues of differentially resistant strains after BmNPV infection. Moreover, the antiviral role of BmNc was confirmed by the significantly higher fluorescence signals of BV-eGFP after knockdown of BmNc in BmN cells, and a reduced signal after overexpression. This was further verified by the capsid gene vp39 expression, DNA copy number, and GP64 protein level in the RNAi and overexpression groups. Furthermore, the antiviral phenomenon of BmNc was found to be associated with apoptosis. In brief, BmNc showed a relatively high expression level in the metamorphosis stages, and the effect of BmNc on BmNPV infection following RNAi and overexpression was eliminated after treatment with the inducer, Silvestrol, and the inhibitor, Z-DEVD-FMK, respectively. Therefore, it is reasonable to conclude that BmNc is involved in anti-BmNPV infection via the mitochondrial apoptosis pathway. The results provide valuable information for elucidating the molecular mechanism of silkworm resistance to BmNPV infection.

The transcription factor of the Hippo signaling pathway, LmSd, regulates wing development in Locusta migratoria

Scalloped (Sd) is transcription factor that regulates cell proliferation and organ growth in the Hippo pathway. In the present research, LmSd was identified and characterized, and found to encode an N-terminal TEA domain and a C-terminal YBD domain. qRT-PCR showed that the LmSd transcription level was highest in the fifth-instar nymphs and very little was expressed in embryos. Tissue-specific analyses showed that LmSd was highly expressed in the wing. Immunohistochemistry indicated that LmSd was highly abundant in the head, prothorax, and legs during embryonic development. LmSd dsRNA injection resulted in significantly down-regulated transcription and protein expression levels compared with dsGFP injection. Gene silencing of LmSd resulted in deformed wings that were curved, wrinkled, and failed to fully expand. Approximately 40% of the nymphs had wing pads that were not able to close normally during molting from fifth-instar nymphs into adults. After silencing of LmSd, the transcription levels of cell division genes were suppressed and the expression levels of apoptosis genes were significantly up-regulated. Our results reveal that LmSd plays an important role in wing formation and development by controlling cell proliferation and inhibiting apoptosis.

The biological characters of Bmelav-like genes in the development of Bombyx mori

The ELAV/Hu family is a conserved multigene family of pan-neuronal RNA-binding protein involved in post-transcriptional regulation in metazoans. In Drosophila, three members of this family, ELAV, RBP9 and FNE, are involved in neuronal differentiation, gene expression regulation and so on. This family is less well characterized in Bombyx mori. Two orthologs BmELAV-like-1 (BmEL-1) and BmELAV-like-2 (BmEL-2) share 55%-71% and 47%-62% identity with that of in Drosophila and humans, respectively. Bmel-1 is ubiquitously expressed while Bmel-2 is expressed in the head and ovaries specifically. Proteins encoded by both genes are localized in nuclear and cytoplasm. The weight of body, cocoon, pupae and cocoon shell are differently affected in Bmel-1^- /-2^- mutants created using CRISPR/Cas9 technology. Mutations of both genes increase the expression of four silk protein genes, Fib-L, Fib-H, P25 and Ser-1. In addition, the oviposition ability of Bmel-2^- females is decreased. This study not only provides valuable insights into the functional roles of Bmelav-like genes in the growth, cocoon characters and regulation of silk protein genes expression, but also provides useful information for silkworm variety breeding.

Bmapaf-1 is Involved in the Response against BmNPV Infection by the Mitochondrial Apoptosis Pathway

Simple Summary

Apaf-1 is involved in the apoptosis pathway and Bmapaf-1 showed a significant response to BmNPV infection in our previous transcriptome data. In this study, the underlying mechanism of Bmapaf-1 in response to BmNPV infection was studied. To preliminarily determine the relationship of Bmapaf-1 with BmNPV, the expression pattern of Bmapaf-1 was analyzed in different tissues of differentially resistant silkworm strains following virus infection. To further define the role of Bmapaf-1 in BmNPV infection, the alteration of BmNPV infection in BmN cells and the expression patterns of Bmcas-Nc and Bmcas-1 were analyzed following knockdown and overexpression of Bmapaf-1 using siRNA and the pIZT/V5-His-mCherry insect vector, respectively. Furthermore, to analyze whether Bmapaf-1 is involved in BmNPV infection by apoptosis, the inducer NSC348884 and inhibitor Z-DEVD-FMK were used.

Abstract

Discovery of the anti-BmNPV (Bombyx mori nuclearpolyhedrovirus) silkworm strain suggests that some kind of antiviral molecular mechanism does exist but is still unclear. Apoptosis, as an innate part of the immune system, plays an important role in the response against pathogen infections and may be involved in the anti-BmNPV infection. Several candidate genes involved in the mitochondrial apoptosis pathway were identified from our previous study. Bombyx mori apoptosis protease-activating factor-1 (Bmapaf-1) was one of them, but the antiviral mechanism is still unclear. In this study, sequences of BmApaf-1 were characterized. It was found to contain a unique transposase_1 functional domain and share high CARD and NB-ARC domains with other species. Relatively high expression levels of Bmapaf-1 were found at key moments of embryonic development, metamorphosis, and reproductive development. Further, the significant difference in expression of Bmapaf-1 in different tissues following virus infection indicated its close relationship with BmNPV, which was further validated by RNAi and overexpression in BmN cells. Briefly, infection of budded virus with enhanced green fluorescent protein (BV-EGFP) was significantly inhibited at 72 h after overexpression of Bmapaf-1, which was confirmed after knockdown of Bmapaf-1 with siRNA. Moreover, the downstream genes of Bmapaf-1, including Bmnedd2-like caspase (BmNc) and Bmcaspase-1 (Bmcas-1), were upregulated after overexpression of Bmapaf-1 in BmN cells, which was consistent with the RNAi results. Furthermore, the phenomenon of Bmapaf-1 in response to BmNPV infection was determined to be related to apoptosis using the apoptosis inducer NSC348884 and inhibitor Z-DEVD-FMK. Therefore, Bmapaf-1 is involved in the response against BmNPV infection by the mitochondrial apoptosis pathway. This result provides valuable data for clarifying the anti-BmNPV mechanism of silkworms and breeding of resistant silkworm strains.

Characterization and analysis of full-length transcriptomes from two grasshoppers, Gomphocerus licenti and Mongolotettix japonicus

Acrididae are diverse in size, body shape, behavior, ecology and life history; widely distributed; easy to collect; and important to agriculture. They represent promising model candidates for functional genomics, but their extremely large genomes have hindered this research; establishing a reference transcriptome for a species is the primary means of obtaining genetic information. Here, two Acrididae species, Gomphocerus licenti and Mongolotettix japonicus, were selected for full-length (FL) PacBio transcriptome sequencing. For G. licenti and M. japonicus, respectively, 590,112 and 566,165 circular consensus sequences (CCS) were generated, which identified 458,131 and 428,979 full-length nonchimeric (FLNC) reads. After isoform-level clustering, next-generation sequencing (NGS) short sequences were used for error correction, and remove redundant sequences with CD-HIT, 17,970 and 16,766 unigenes were generated for G. licenti and M. japonicus. In addition, we obtained 17,495 and 16,373 coding sequences, 1,082 and 813 transcription factors, 11,840 and 10,814 simple sequence repeats, and 905 and 706 long noncoding RNAs by analyzing the transcriptomes of G. licenti and M. japonicus, respectively, and 15,803 and 14,846 unigenes were annotated in eight functional databases. This is the first study to sequence FL transcriptomes of G. licenti and M. japonicus, providing valuable genetic resources for further functional genomics research.