Characterization and expression profiling of serine protease inhibitors in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Strong resistance to β-cyfluthrin in a strain of the beetle Alphitobius diaperinus: a de novo transcriptome analysis

The lesser mealworm, Alphitobius diaperinus, is an invasive tenebrionid beetle and a vector of pathogens. Due to the emergence of insecticide resistance and consequent outbreaks that generate significant phytosanitary and energy costs for poultry farmers, it has become a major insect pest worldwide. To better understand the molecular mechanisms behind this resistance, we studied a strain of A. diaperinus from a poultry house in Brittany that was found to be highly resistant to the β-cyfluthrin. The strain survived β-cyfluthrin exposures corresponding to more than 100 times the recommended dose. We used a comparative de novo RNA-Seq approach to explore genes expression in resistant versus sensitive strains. Our de novo transcriptomic analyses showed that responses to β-cyfluthrin likely involved a whole set of resistance mechanisms. Genes related to detoxification, metabolic resistance, cuticular hydrocarbon biosynthesis and proteolysis were found to be constitutively overexpressed in the resistant compared to the sensitive strain. Follow-up enzymatic assays confirmed that the resistant strain exhibited high basal activities for detoxification enzymes such as cytochrome P450 monooxygenase and glutathione-S-transferase. The in-depth analysis of differentially expressed genes suggests the involvement of complex regulation of signaling pathways. Detailed knowledge of these resistance mechanisms is essential for the establishment of effective pest control.

A Genome-Wide Analysis of Serine Protease Inhibitors in Cydia pomonella Provides Insights into Their Evolution and Expression Pattern

Serine protease inhibitors (serpins) appear to be ubiquitous in almost all living organisms, with a conserved structure and varying functions. Serpins can modulate immune responses by negatively regulating serine protease activities strictly and precisely. The codling moth, Cydia pomonella (L.), a major invasive pest in China, can cause serious economic losses. However, knowledge of serpin genes in this insect remain largely unknown. In this study, we performed a systematic analysis of the serpin genes in C. pomonella, obtaining 26 serpins from the C. pomonella genome. Subsequently, their sequence features, evolutionary relationship, and expression pattern were characterized. Comparative analysis revealed the evolution of a number of serpin genes in Lepidoptera. Importantly, the evolutionary relationship and putative roles of serpin genes in C. pomonella were revealed. Additionally, selective pressure analysis found amino acid sites with strong evidence of positive selection. Interestingly, the serpin1 gene possessed at least six splicing isoforms with distinct reactive-center loops, and these isoforms were experimentally validated. Furthermore, we observed a subclade expansion of serpins, and these genes showed high expression in multiple tissues, suggesting their important roles in C. pomonella. Overall, this study will enrich our knowledge of the immunity of C. pomonella and help to elucidate the role of serpins in the immune response.

Identification and functional analysis of serine protease inhibitor gene family of Eocanthecona furcellata (Wolff)

The predatory natural enemy Eocanthecona furcellata plays a crucial role in agricultural ecosystems due to its effective pest control measures and defensive venom. Predator venom contains serine protease inhibitors (SPIs), which are the primary regulators of serine protease activity and play key roles in digestion, development, innate immunity, and other physiological regulatory processes. However, the regulation mechanism of SPIs in the salivary glands of predatory natural enemies is still unknown. In this study, we sequenced the transcriptome of E. furcellata salivary gland and identified 38 SPIs genes named EfSPI1∼EfSPI38. Through gene structure, multiple sequence alignment and phylogenetic tree analysis, real-time quantitative PCR (RT-PCR) expression profiles of different developmental stages and different tissues were analyzed. RNAi technology was used to explore the gene function of EFSPI20. The results showed that these 38 EfSPIs genes contained 8 SPI domains, which were serpin, TIL, Kunitz, Kazal, Antistasin, Pacifastin, WAP and A2M. The expression profile results showed that the expression of different types of EfSPIs genes was different at different developmental stages and different tissues. Most of the EfSPIs genes were highly expressed in the egg stage. The EfSPI20, EfSPI21, EfSPI22, and EfSPI24 genes of the Pacifastin subfamily and the EfSPI35 gene of the A2M subfamily were highly expressed in the nymphal and adult stages, which was consistent with the RT-qPCR verification results. These five genes are positively correlated with each other and have a synergistic effect on E. furcellata, and they were highly expressed in salivary glands. After interfering with the expression of the EfSPI20 gene, the survival rate and predatory amount of male and female adults were significantly decreased. Taken together, we speculated some EfSPIs may inhibit trypsin, chymotrypsin, and elastase, and some EfSPIs may be involved in autoimmune responses. EfSPI20 was essential for the predation and digestion of E. furcellata, and the functions of other EfSPIs were discussed. Our findings provide valuable insights into the diversity of EfSPIs in E. furcellata and the potential functions of regulating their predation, digestion and innate immunity, which may be of great significance for developing new pest control strategies.

SMRT Sequencing Technology Was Used to Construct the Batocera horsfieldi (Hope) Transcriptome and Reveal Its Features

Batocera horsfieldi (Hope) (Coleoptera: Cerambycidae) is an important forest pest in China that mainly infests timber and economic forests. This pest primarily causes plant tissue to necrotize, rot, and eventually die by feeding on the woody parts of tree trunks. To gain a deeper understanding of the genetic mechanism of B. horsfieldi, this study employed single-molecule real-time sequencing (SMRT) and Illumina RNA-seq technologies to conduct full-length transcriptome sequencing of the insect. Total RNA extracted from male and female adults was mixed and subjected to SMRT sequencing, generating a complete transcriptome. Transcriptome analysis, prediction of long non-coding RNA (lncRNA), coding sequences (CDs), analysis of simple sequence repeats (SSR), prediction of transcription factors, and functional annotation of transcripts were performed in this study. The collective 20,356,793 subreads (38.26 G, clean reads) were generated, including 432,091 circular consensus sequences and 395,851 full-length non-chimera reads. The full-length non-chimera reads (FLNC) were clustered and redundancies were removed, resulting in 39,912 consensus reads. SSR and ANGEL software v3.0 were used for predicting SSR and CDs. In addition, four tools were used for annotating 6058 lncRNAs, identifying 636 transcription factors. Furthermore, a total of 84,650 transcripts were functionally annotated in seven different databases. This is the first time that the full-length transcriptome of B. horsfieldi has been obtained using SMRT sequencing. This provides an important foundation for investigating the gene regulation underlying the interaction between B. horsfieldi and its host plants through gene editing in the future and provides a scientific basis for the prevention and control of B. horsfieldi.

The Chromosome-Level Genome Assembly of Bean Blossom Thrips (Megalurothrips usitatus) Reveals an Expansion of Protein Digestion-Related Genes in Adaption to High-Protein Host Plants

Megalurothrips usitatus (Bagnall) is a destructive pest of legumes, such as cowpea. The biology, population dynamics and control strategies of this pest have been well studied. However, the lack of a high-quality reference genome for M. usitatus has hindered the understanding of key biological questions, such as the mechanism of adaptation to feed preferentially on high-protein host plants and the resistance to proteinase inhibitors (PIs). In this study, we generated a high-resolution chromosome-level reference genome assembly (247.82 Mb, 16 chromosomes) of M. usitatus by combining Oxford Nanopore Technologies (ONT) and Hi-C sequencing. The genome assembly showed higher proportions of GC and repeat content compared to other Thripinae species. Genome annotation revealed 18,624 protein-coding genes, including 4613 paralogs that were preferentially located in TE-rich regions. GO and KEGG enrichment analyses of the paralogs revealed significant enrichment in digestion-related genes. Genome-wide identification uncovered 506 putative digestion-related enzymes; of those, proteases, especially their subgroup serine proteases (SPs), are significantly enriched in paralogs. We hypothesized that the diversity and expansion of the digestion-related genes, especially SPs, could be driven by mobile elements (TEs), which promote the adaptive evolution of M. usitatus to high-protein host plants with high serine protease inhibitors (SPIs). The current study provides a valuable genomic resource for understanding the genetic variation among different pest species adapting to different plant hosts.

The evolutionary process of invasion in the fall armyworm (Spodoptera frugiperda)

The fall armyworm (FAW; Spodoptera frugiperda) is one of the major agricultural pest insects. FAW is native to the Americas, and its invasion was first reported in West Africa in 2016. Then it quickly spread through Africa, Asia, and Oceania, becoming one of the main threats to corn production. We analyzed whole genome sequences of 177 FAW individuals from 12 locations on four continents to infer evolutionary processes of invasion. Principal component analysis from the TPI gene and whole genome sequences shows that invasive FAW populations originated from the corn strain. Ancestry coefficient and phylogenetic analyses from the nuclear genome indicate that invasive populations are derived from a single ancestry, distinct from native populations, while the mitochondrial phylogenetic tree supports the hypothesis of multiple introductions. Adaptive evolution specific to invasive populations was observed in detoxification, chemosensory, and digestion genes. We concluded that extant invasive FAW populations originated from the corn strain with potential contributions of adaptive evolution.

Genome-wide identification and immune response analysis of serine protease inhibitor genes in the blood clam Tegillarca granosa

Serine protease inhibitors (SPIs) are the main regulators of serine protease activities. In this study, we present a genome-wide identification of SPI genes in T. granosa（TgSPI genes）and their expression characteristics in respond to Vibrio stress. A total of 102 TgSPI genes belonging to eight families, including Serpin, TIL (trypsin inhibitor like cysteine rich domain), Kunitz, Kazal, I84, Pacifastin, WAP (whey acidic protein) and A2M (Alpha-2-macroglobulin) were identified, while no genes belonging to Bowman-Birk, amfpi and Antistasin families were identified. The Kazal family has the most TgSPI genes with 38, and 11 TgSPI genes belong to the mollusc-specific I84 family. The TgSPI genes were found to be randomly distributed on 17 chromosomes with 12 tandem duplicate gene pairs. Expression profiles showed that most TgSPI genes were mainly expressed in immune-related tissues such as hepatopancreas, gill and mantle. In the hepatopancreas, most of TgSPI genes were sensitive to Vibrio stress, 28 and 29 TgSPI genes were up-regulated and down-regulated, respectively. Some up-regulated genes with signal peptides, such as the TgSPIs of I84 family, may act as a mechanism to directly prevent Vibrio from invasion. Six Kazal-type TgSPIs (TgSPI29, 45, 49, 50, 51 and 52) were intracellular proteins and their expression was down-regulated in hemocytes after Vibrio stress. This may have boosted protease activity in hemocytes to the point that more hemoglobin derived peptides were produced and secreted into the hemolymph to exert their anti-Vibrio effects. These findings may provide valuable information for further clarifying the roles of SPIs in the immune defense and will benefit future exploration of the immune function of SPIs in molluscs.

Characterization and expression profiling of serine protease inhibitors in the yellow mealworm Tenebrio molitor

Serine protease inhibitors (SPIs) act in diverse biological processes in insects such as immunity, development, and digestion by preventing the unwanted proteolysis. So far, the repertoire of genes encoding SPIs has been identified from few insect species. In this study, 62 SPI genes were identified from the genome of the yellow mealworm, Tenebrio molitor. According to their modes of action, they were classified into three families, serpin (26), canonical SPI (31), and α-macroglobulins (A2M) (5). These SPIs feature eight domains including serpin, Kazal, TIL, Kunitz, WAP, Antistasin, pacifastin, and A2M. In total, 39 SPIs contain a single SPI domain, while the others encode at least two inhibitor units. Based on the amino acids in the cleaved reactive sites, the abilities of these SPIs to inhibit trypsin, chymotrypsin, or elastase-like enzymes are predicted. The expression profiling based on the RNA-seq data showed that these genes displayed stage-specific expression patterns during development, suggesting to us their significance in development. Some of the SPI genes were exclusively expressed in particular tissues such as hemocyte, fat body, gut, ovary, and testis, which may be involved in biological processes specific to the indicated tissues. These findings provide necessary information for further investigation of insect SPIs.

SMRT Sequencing Reveals Candidate Genes and Pathways With Medicinal Value in Cipangopaludina chinensis

Cipangopaludina chinensis is an economically important aquatic snail with high medicinal value. However, molecular biology research on C. chinensis is limited by the lack of a reference genome, so the analysis of its transcripts is an important step to study the regulatory genes of various substances in C. chinensis. Herein, we conducted the first full-length transcriptome analysis of C. chinensis using PacBio single-molecule real-time (SMRT) sequencing technology. We identified a total of 26,312 unigenes with an average length of 2,572 bp, of which the largest number of zf-c2h2 transcription factor families (120,18.24%) were found, and also observed that the majority of the 8,058 SSRs contained 4-7 repeat units, which provided data for subsequent work on snail genetics Subsequently, 91.86% (24,169) of the genes were successfully annotated to the four major databases, while the highest homology was observed with Pomacea canaliculata. Functional annotation revealed that the majority of transcripts were enriched in metabolism, signal transduction and Immune-related pathways, and several candidate genes involved in drug metabolism and immune response were identified (e.g., CYP1A1, CYP2J, CYP2U1, GST, ,PIK3, PDE3A, PRKAG). This study lays a foundation for future molecular biology research and provides a reference for studying genes associated with the medicinal value of C. chinensis.

A TIL-Type Serine Protease Inhibitor Involved in Humoral Immune Response of Asian Corn Borer Ostrinia furnaculis

To elucidate the application value of insect endogenous protease and its inhibitor genes in pest control, we analyzed in detail the transcriptome sequence of the Asian corn borer, Ostrinia furnacalis. We obtained 12 protease genes and 11 protease inhibitor genes, and comprehensively analyzed of their spatiotemporal expression by qRT-PCR. In which, a previous unstudied serine protease inhibitor gene attracted our attention. It belongs to the canonical serine proteinase inhibitor family, a trypsin inhibitor-like cysteine-rich domain (TIL)-type protease inhibitor, but its TIL domain lacks two cysteine residues, and it was named as ACB-TIL. Its expression level is relatively very low in the absence of pathogen stimulation, and can be up-regulated expression induced by Gram-negative bacteria (Escherichia coli), virus (BmNPV), and dsRNA (dsEGFP), but cannot be induced by fungus spores (Metarrhizium anisopliae). Prokaryotic expressed ACB-TIL protein can significantly inhibit the melanization in vitro. Injecting this protein into insect body can inhibit the production of antimicrobial peptides of attacin, lebocin and gloverin. Inhibition of ACB-TIL by RNAi can cause the responses of other immune-, protease- and inhibitor-related genes. ACB-TIL is primarily involved in Asian corn borer humoral immunity in responses to Gram-negative bacteria and viruses. This gene can be a potential target for pest control since this will mainly affect insect immune response.

Identification of ABCG transporter genes associated with chlorantraniliprole resistance in Plutella xylostella (L.)

BACKGROUND

Plutella xylostella (L.) is a serious worldwide pest that feeds on cruciferous plants and has evolved resistance to different classes of insecticides used for its control, including chlorantraniliprole. ATP-binding cassette (ABC) transporters, constituting the largest transport family in organisms, are involved in phase III of the detoxification process and may play important roles in insecticide resistance.

RESULTS

A total of 15 ABC transporter transcripts from subfamily G were identified in P. xylostella based on the latest DBM genome. Synergism studies showed that treatment with verapamil, a potent inhibitor of ABC transporters, significantly increased the toxicity of chlorantraniliprole against larvae of two chlorantraniliprole-resistant P. xylostella populations (NIL and BL). ABCG2, ABCG5, ABCG6, ABCG9, ABCG11, ABCG14 and ABCG15 were significantly overexpressed in NIL and BL compared with the susceptible population (SS), and ABCG1, ABCG6, ABCG8, ABCG9, ABCG14 and ABCG15 were significantly upregulated after treatment with the LC₅₀ of chlorantraniliprole in SS. Subsequently, ABCG6, ABCG9 and ABCG14, which were overexpressed in both NIL and BL and could be induced in SS, were chosen for functional study. RNAi-mediated knockdown of each of the three ABCGs significantly increased the sensitivity of larvae to chlorantraniliprole. These results confirmed that overexpression of ABCG6, ABCG9 and ABCG14 may contribute to chlorantraniliprole resistance in P. xylostella.

CONCLUSION

Overexpression of some genes in the ABCG subfamily is involved in P. xylostella resistance to chlorantraniliprole. These results may help to establish a foundation for further studies investigating the role played by ABC transporters in chlorantraniliprole resistance in P. xylostella or other insect pests. © 2021 Society of Chemical Industry.

SMRT sequencing of the full-length transcriptome of the Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

Background

Red palm weevil Rhynchophorus ferrugineus (Coleoptera: Curculionidae) is one of the most destructive insects for palm trees in the world. However, its genome resources are still in the blank stage, which limits the study of molecular and growth development analysis.

Methods

In this study, we used PacBio Iso-Seq and Illumina RNA-seq to first generate transcriptome from three developmental stages of R. ferrugineus (pupa, 7th larva, female and male) to increase our understanding of the life cycle and molecular characteristics of R. ferrugineus.

Results

A total of 63,801 nonredundant full-length transcripts were generated with an average length of 2,964 bp from three developmental stages, including the 7th instar larva, pupa, female adult and male adult. These transcripts showed a high annotation rate in seven public databases, with 54,999 (86.20%) successfully annotated. Meanwhile, 2,184 alternative splicing (AS) events, 2,084 transcription factors (TFs), 66,230 simple sequence repeats (SSR) and 9,618 Long noncoding RNAs (lncRNAs) were identified. In summary, our results provide a new source of full-length transcriptional data and information for the further study of gene expression and genetics in R. ferrugineus.

Immune responses to Bacillus thuringiensis in the midgut of the diamondback moth, Plutella xylostella

The diamondback moth, Plutella xylostella, is the first insect to develop resistance to Bacillus thuringiensis (Bt) in the field. To date, little is known about the molecular mechanism of the interaction between Bt and midgut immunity in P. xylostella. Here, we report immune responses in the P. xylostella midgut to Bt strain Bt8010 using a combined approach of transcriptomics and quantitative proteomics. Many genes in the Toll, IMD, JNK and JAK-STAT pathways and antimicrobial peptide genes were activated at 18 h post-infection. In the prophenoloxidase (PPO) cascade, four serpin genes were activated, and the PPO1 gene was suppressed by Bt8010. Inhibition of the two PPO proteins was observed at 18 h post-infection. Feeding Bt8010-infected larvae recombinant PPOs enhanced their survival. These results revealed that the Toll, IMD, JNK and JAK-STAT pathways were triggered and participated in the immune defence of the midgut against Bt8010, while the PPO cascade was inhibited and played an important role in this process.

Genomic and transcriptomic analyses of glutathione S-transferases in an endoparasitoid wasp, Pteromalus puparum

Pteromalus puparum is a gregarious pupal endoparasitoid with a wide host range. It deposits eggs into pierid and papilionid butterfly pupae. Glutathione S-transferases (GSTs) are a family of multifunctional detoxification enzymes that act in xenobiotic metabolism in insects. Insect genome projects have facilitated identification and characterization of GST family members. We identified 20 putative GSTs in the P. puparum genome, including 19 cytosolic and one microsomal. Phylogenetic analysis showed that P. puparum GSTs are clustered into Hymenoptera-specific branches. Transcriptomic data of embryos, larvae, female pupae, male pupae, female adults, male adults, venom glands, carcass, salivary glands, and ovaries revealed stage-, sex-, and tissue-specific expression patterns of GSTs in P. puparum. This is the most comprehensive study of genome-wide identification, characterization, and expression profiling of GST family in hymenopterans. Our results provide valuable information for understanding the metabolic adaptation of this wasp.

Comprehensive analysis of Cry1Ac protoxin activation mediated by midgut proteases in susceptible and resistant Plutella xylostella (L.)

Insecticidal Cry toxins produced by Bacillus thuringiensis (Bt) have been widely used to control agricultural pests in both foliage sprays and transgenic crops. Nevertheless, rapid evolution of insect resistance to Cry toxins requires elucidation of the molecular mechanisms involved in Cry resistance. Two proposed models have been described to explain the toxicity of Cry proteins, the classic model states that Cry protoxin is activated by midgut proteases resulting in activated toxin that binds to receptors and forms a pore in the midgut cells triggering larval death, and the newly proposed dual model of the mode of action of Bt Cry toxins states that protoxin and activated toxins may have different mechanisms of action since several resistant strains to activated Cry toxins are still susceptible to the same Cry-protoxin. Protoxin activation by midgut proteases is a key step in both models. Herein, we evaluated Cry1Ac protoxin activation in a susceptible Plutella xylostella (L.) strain (DBM1Ac-S) and in the near-isogenic strain (NIL-R) with high field-evolved Cry1Ac resistance. Previous work showed that Cry1Ac resistance in NIL-R correlates with reduced binding to midgut receptors due to enhanced MAPK signaling pathway and down regulation of ABCC2 receptor. However, reduced midgut trypsin levels and altered midgut protease gene transcription were also observed in the Cry1Ac-resistant field isolated strain that is parent of the NIL-R strain. Therefore, we analyzed the midgut protease activities in both DBM1Ac-S and NIL-R strains. Detection of enzymatic activities showed that caseinolytic protease, trypsin and chymotrypsin activities were not significantly different between the susceptible and resistant strains. Furthermore, treatment with different trypsin or chymotrypsin inhibitors, such as Nα-tosyl-l-lysine chloromethyl ketone (TLCK) or Np-tosyl-L-phenylalanine chloromethyl ketone (TPCK) did not affect the susceptibility to Cry1Ac protoxin of the DBM1Ac-S and NIL-R larvae. Bioassay results indicated that the NIL-R larvae showed similar resistant levels to both Cry1Ac protoxin and trypsin-activated toxin. Taken together, our results demonstrated that high-level field-evolved Cry1Ac resistance in the NIL-R strain is independent of Cry1Ac protoxin activation and the specific protoxin mechanism of action. This discovery will strengthen our comprehensive understanding of the complex mechanistic basis of Bt resistance in different insects.

Reduced Expression of a Novel Midgut Trypsin Gene Involved in Protoxin Activation Correlates with Cry1Ac Resistance in a Laboratory-Selected Strain of Plutella xylostella (L.)

Bacillus thuringiensis (Bt) produce diverse insecticidal proteins to kill insect pests. Nevertheless, evolution of resistance to Bt toxins hampers the sustainable use of this technology. Previously, we identified down-regulation of a trypsin-like serine protease gene PxTryp_SPc1 in the midgut transcriptome and RNA-Seq data of a laboratory-selected Cry1Ac-resistant Plutella xylostella strain, SZ-R. We show here that reduced PxTryp_SPc1 expression significantly reduced caseinolytic and trypsin protease activities affecting Cry1Ac protoxin activation, thereby conferring higher resistance to Cry1Ac protoxin than activated toxin in SZ-R strain. Herein, the full-length cDNA sequence of PxTryp_SPc1 gene was cloned, and we found that it was mainly expressed in midgut tissue in all larval instars. Subsequently, we confirmed that the PxTryp_SPc1 gene was significantly decreased in SZ-R larval midgut and was further reduced when selected with high dose of Cry1Ac protoxin. Moreover, down-regulation of the PxTryp_SPc1 gene was genetically linked to resistance to Cry1Ac in the SZ-R strain. Finally, RNAi-mediated silencing of PxTryp_SPc1 gene expression decreased larval susceptibility to Cry1Ac protoxin in the susceptible DBM1Ac-S strain, supporting that low expression of PxTryp_SPc1 gene is involved in Cry1Ac resistance in P. xylostella. These findings contribute to understanding the role of midgut proteases in the mechanisms underlying insect resistance to Bt toxins.

De novo transcriptome analysis and identification of genes associated with immunity, detoxification and energy metabolism from the fat body of the tephritid gall fly, Procecidochares utilis

The fat body, a multifunctional organ analogous to the liver and fat tissue of vertebrates, plays an important role in insect life cycles. The fat body is involved in protein storage, energy metabolism, elimination of xenobiotics, and production of immunity regulator-like proteins. However, the molecular mechanism of the fat body's physiological functions in the tephritid stem gall-forming fly, Procecidochares utilis, are still unknown. In this study, we performed transcriptome analysis of the fat body of P. utilis using Illumina sequencing technology. In total, 3.71 G of clean reads were obtained and assembled into 30,559 unigenes, with an average length of 539 bp. Among those unigenes, 21,439 (70.16%) were annotated based on sequence similarity to proteins in NCBI's non-redundant protein sequence database (Nr). Sequences were also compared to NCBI's non-redundant nucleotide sequence database (Nt), a manually curated and reviewed protein sequence database (SwissProt), and KEGG and gene ontology annotations were applied to better understand the functions of these unigenes. A comparative analysis was performed to identify unigenes related to detoxification, immunity and energy metabolism. Many unigenes involved in detoxification were identified, including 50 unigenes of putative cytochrome P450s (P450s), 18 of glutathione S-transferases (GSTs), 35 of carboxylesterases (CarEs) and 26 of ATP-binding cassette (ABC) transporters. Many unigenes related to immunity were identified, including 17 putative serpin genes, five peptidoglycan recognition proteins (PGRPs) and four lysozyme genes. In addition, unigenes potentially involved in energy metabolism, including 18 lipase genes, five fatty acid synthase (FAS) genes and six elongases of very long chain fatty acid (ELOVL) genes, were identified. This transcriptome improves our genetic understanding of P. utilis and the identification of a numerous transcripts in the fat body of P. utilis offer a series of valuable molecular resources for future studies on the functions of these genes.

Genome-Wide Identification of Destruxin A-Responsive Immunity-Related MicroRNAs in Diamondback Moth, Plutella xylostella

Plutella xylostella, a global key pest, is one of the major lepidopteran pests of cruciferous vegetables owing to its strong ability of resistance development to a wide range of insecticides. Destruxin A, a mycotoxin of the entomopathogenic fungus, Metarhizium anisopliae, has broad-spectrum insecticidal effects and has been used as an alternative control strategy to reduce harmful effects of insecticides. However, microRNA (miRNA)-regulated reactions against destruxin A have not been elucidated yet. Therefore, here, to identify immunity-related miRNAs, we constructed four small RNA libraries from destruxin A-injected larvae of P. xylostella at three different time courses (2, 4, and 6 h) with a control, and sequenced by Illumina. Our results showed that totally 187 known and 44 novel miRNAs were identified in four libraries by bioinformatic analysis. Interestingly, among differentially expressed known miRNAs, some conserved miRNAs, such as miR-263, miR-279, miR-306, miR-2a, and miR-308, predicted to be involved in regulating immunity-related genes, were also identified. Worthy to mention, miR-306 and miR-279 were also listed as common abundantly expressed miRNA in all treatments. The Kyoto Encyclopedia of Genes and Genomes pathway analysis also indicated that differentially expressed miRNAs were involved in several immunity-related signaling pathways, including toll signaling pathway, IMD signaling pathway, JAK-STAT signaling pathway, and cell adhesion molecules signaling pathway. To the best of our knowledge, this is the first comprehensive report of destruxin A-responsive immunity-related miRNAs in P. xylostella. Our findings will improve in understanding the role of destruxin A-responsive miRNAs in the host immune system and would be useful to develop biological control strategies for controlling P. xylostella.

Role of Antheraea pernyi serpin 12 in prophenoloxidase activation and immune responses

Serine protease inhibitors play a key role in the immune system of invertebrates by controlling proteolytic cascades. Besides its importance, the knowledge on immune functions of serpins in most of insects is fragmentary. In the present study, we identified serpin-12 from Antheraea pernyi encoding a predicted 402 amino acid residue protein (Apserpin-12). We expressed the recombinant protein in Escherichia coli and the purified protein was used for the synthesis of rabbit anti-Apserpin-12 polyclonal antibodies and functional studies. Quantitative real-time ploymerase chain reaction (qRT-PCR) analysis revealed that the knock-down of Apserpin-12 enhanced the prophenoloxidase (PPO) cascade stimulated by Micrococcus luteus in hemolymph, whereas addition of recombinant Apserpin-12 protein along with same elicitor led to down-regulate PPO activation. Following different microbial challenge (E. coli, Beauveria bassiana, M. Luteus, and nuclear polyhedrosis virus), the expression of Apserpin-12 mRNA was induced significantly. Furthermore, the Apserpin-12 double-stranded RNA administration elicited the expression of antimicrobial peptides, while the treatment with recombinant protein suppressed their expression. Tissue profile of Apserpin-12 indicated that it is expressed in all examined tissues, that is, hemolymph, malpighian tubules, midgut, silk gland, integument, and fat body with variation in their transcript levels. We concluded that Apserpin-12 may regulate PPO activation and inhibit the production of antimicrobial peptides in A. pernyi, suggesting important role in its immune system.

Identification and characterization of serine protease inhibitors in a parasitic wasp, Pteromalus puparum

Serine protease inhibitors (SPIs) regulate protease-mediated activities by inactivating their cognate proteinases, and are involved in multiple physiological processes. SPIs have been extensively studied in vertebrates and invertebrates; however, little SPI information is available in parasitoids. Herein, we identified 57 SPI genes in total through the genome of a parasitoid wasp, Pteromalus puparum. Gene structure analyses revealed that these SPIs contain 7 SPI domains. Depending on their mode of action, these SPIs can be categorized into serpins, canonical inhibitors and alpha-2-macroglobulins (A2Ms). For serpins and canonical inhibitors, we predicted their putative inhibitory activities to trypsin/chymotrypsin/elastase-like enzymes based on the amino acids in cleaved reactive sites. Sequence alignment and phylogenetic tree indicated that some serpins similar to known functional inhibitory serpins may participate in immune responses. Transcriptome analysis also showed some canonical SPI genes displayed distinct expression patterns in the venom gland and this was confirmed by quantitative real-time PCR (qPCR) analysis, suggesting their specific physiological functions as venom proteins in suppressing host immune responses. The study provides valuable information to clarify the functions of SPIs in digestion, development, reproduction and innate immunity.