Potential targets for controlling Bactrocera dorsalis using cuticle- and hormone-related genes revealed by a developmental transcriptome analysis

Comparative analyses of the transcriptome among three development stages of Zeugodacus tau larvae (Diptera: Tephritidae)

Studying differences in transcriptomes across various development stages of insects is necessary to uncover the physiological and molecular mechanism underlying development and metamorphosis. We here present the first transcriptome data generated under Illumina Hiseq platform concerning Zeugodacus tau (Walker) larvae from Nanchang, China. In total, 11,702 genes were identified from 9 transcriptome libraries of three development stages of Z. tau larvae. 7219 differentially expressed genes (DEGs) were screened out from the comparisons between each two development stages of Z. tau larvae, and their roles in development and metabolism were analyzed. Comparative analyses of transcriptome data showed that there are 5333 DEGs between 1-day and 7-day old larvae, consisting of 1609 up-regulated and 3724 down-regulated genes. Expressions of DEGs were more abundant in L7 than in L1 and L3, which might be associated with metamorphosis. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis suggested the enrichment of metabolic process. KOG annotation further confirmed that 20-hydroxyecdysone (20E) pathway related genes Cyp4ac1_1, Cyp4aa1, Cyp313a4_3 were critical for the biosynthesis, transport, and catabolism of secondary metabolites and lipid transport and metabolism. Expression patterns of 8 DEGs were verified using quantitative real-time PCR (RT-qPCR). This study elucidated the DEGs and their roles underlying three development stages of Z. tau larvae, which provided valuable information for further functional genomic research.

Comparative Transcriptome Analysis of Henosepilachna vigintioctomaculata Reveals Critical Pathways during Development

Henosepilachna vigintioctomaculata is distributed in several Asian countries. The larvae and adults often cause substantial economic losses to Solanaceae crops such as potato, tomato, eggplant, and Chinese boxthorn. Even though a chromosome-level genome has been documented, the expression profiles of genes involved in development are not determined. In this study, we constructed embryonic, larval, pupal, and adult transcriptomes, generated a comprehensive RNA-sequencing dataset including ~52 Gb of clean data, and identified 602,773,686 cleaned reads and 33,269 unigenes. A total of 18,192 unigenes were successfully annotated against NCBI nonredundant protein sequences, Swissprot, Eukaryotic Orthologous Groups, Gene Ontology (GO), or Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. There were 3580, 2040, 5160, 2496, 3008, and 3895 differentially expressed genes (DEGs) between adult/egg, egg/larval, larval/pupal, adult/pupal, egg/pupal, and adult/larval samples, respectively. GO and KEGG analyses of the DEGs highlighted several critical pathways associated with specific developing stages. This is the first comprehensive transcriptomic dataset encompassing all developmental stages in H. vigintioctomaculata. Our data may facilitate the exploitation of gene targets for pest control and can serve as a valuable gene resource for future molecular investigations.

Validamycin Inhibits the Synthesis and Metabolism of Trehalose and Chitin in the Oriental Fruit Fly, Bactrocera dorsalis (Hendel)

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a notorious invasive pest that has raised concerns worldwide. Validamycin has been demonstrated to be a very strong inhibitor against trehalase in a variety of organisms. However, whether validamycin can inhibit trehalase activity to suppress trehalose hydrolysis and affect any other relevant physiological pathways in B. dorsalis remains unknown. In this study, the effects of validamycin injection on the synthesis and metabolism of trehalose and chitin were evaluated. The results show that validamycin injection significantly affected trehalase activity and caused trehalose accumulation. In addition, the downstream pathways of trehalose hydrolysis, including the synthesis and metabolism of chitin, were also remarkably affected as the expressions of the key genes in these pathways were significantly regulated and the chitin contents were changed accordingly. Intriguingly, the upstream trehalose synthesis was also affected by validamycin injection due to the variations in the expression levels of key genes, especially BdTPPC1. Moreover, BdTPPC1 was predicted to have a binding affinity to validamycin, and the subsequent in vitro recombinant enzyme activity assay verified the inhibitory effect of validamycin on BdTPPC1 activity for the first time. These findings collectively indicate that validamycin can be considered as a promising potential insecticide for the management of B. dorsalis.

Genome-wide analysis of long noncoding RNAs and their association in regulating the metamorphosis of the Sarcophaga peregrina (Diptera: Sarcophagidae)

BACKGROUND

The flesh fly, Sarcophaga peregrina (Diptera: Sarcophagidae), is an important hygiene pest, that causes myiasis in humans and other mammals, typically livestock, and as a vector for various parasitic agents, including bacteria, viruses, and parasites. The role of long non-coding RNAs (lncRNAs) in regulating gene expression during metamorphosis of the flesh fly has not been well established.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we performed genome-wide identification and characterization of lncRNAs from the early pupal stage (1-days pupae), mid-term pupal stage (5-days pupae), and late pupal stage (9-days pupae) of S. peregrina by RNA-seq, and a total of 6921 lncRNAs transcripts were identified. RT-qPCR and enrichment analyses revealed the differentially expressed lncRNAs (DE lncRNAs) that might be associated with insect metamorphosis development. Furthermore, functional analysis revealed that the DE lncRNA (SP_lnc5000) could potentially be involved in regulating the metamorphosis of S. peregrina. RNA interference of SP_lnc5000 caused reduced expression of metamorphosis-related genes in 20-hydroxyecdysone (20E) signaling (Br-c, Ftz-F1), cuticle tanning pathway (TH, DOPA), and chitin related pathway (Cht5). Injection of dsSP_lnc5000 in 3rd instar larvae of S. peregrina resulted in deformed pupae, stagnation of pupal-adult metamorphosis, and a decrease in development time of pupal, pupariation rates and eclosion rates. Hematoxylin-eosin staining (H&E), scanning electron microscope (SEM) observation and cuticle hydrocarbons (CHCs) analysis indicated that SP_lnc5000 had crucial roles in the metamorphosis developmental by modulating pupal cuticular development.

CONCLUSIONS/SIGNIFICANCE

We established that the lncRNA SP_lnc5000 potentially regulates the metamorphosis of S. peregrina by putatively affecting the structure and composition of the pupal cuticle. This study enhances our understanding of lncRNAs as regulators of metamorphosis in S. peregrina, and provide valuable insights into the identification of potential targets for vector control and the development of effective strategies for controlling the spread of myiasis and parasitic diseases.

BdcSP10 is a prophenoloxidase-activating protease in Bactrocera dorsalis

Insects rely on a powerful and efficient innate immune system against microbial invaders. One of the most important immune processes is the melanization reaction, in which eumelanin is synthesized and deposited on the physically injured site or the surface of invading pathogens. The melanization reaction is mediated by prophenoloxidase (PPO), which is synthesized as an inactive zymogen and requires proteolytic activation through a clip serine protease cascade. This cascade has been characterized in several Lepidoptera insect species, but it is less understood in most Diptera insects. Here, with the means of reverse genetics and biochemistry, we characterized the function of a clip serine protease BdcSP10 from the oriental fruit fly Bactrocera dorsalis (Hendel), a significant agriculture pest to a broad variety of fruit and vegetable crops. BdcSP10 knockdown inhibited the melanization reaction and rendered adult flies more vulnerable to pathogenic infections. In addition, purified and activated BdcSP10 proteases promoted the melanization reaction in larval hemolymph and directly cleaved and activated purified PPO1 and PPO2 in vitro. Taken together, we identified BdcSP10 as a PPO-activating protease and validated its important role in the defense against microbial infection in B. dorsalis. This work broadens the understanding of the activation mechanism of the melanization reaction in Diptera insects.

miR-309a is a regulator of ovarian development in the oriental fruit fly Bactrocera dorsalis

Fecundity is arguably one of the most important life history traits, as it is closely tied to fitness. Most arthropods are recognized for their extreme reproductive capacity. For example, a single female of the oriental fruit fly Bactrocera dorsalis, a highly invasive species that is one of the most destructive agricultural pests worldwide, can lay more than 3000 eggs during its life span. The ovary is crucial for insect reproduction and its development requires further investigation at the molecular level. We report here that miR-309a is a regulator of ovarian development in B. dorsalis. Our bioinformatics and molecular studies have revealed that miR-309a binds the transcription factor pannier (GATA-binding factor A/pnr), and this activates yolk vitellogenin 2 (Vg 2) and vitellogenin receptor (VgR) advancing ovarian development. We further show that miR-309a is under the control of juvenile hormone (JH) and independent from 20-hydroxyecdysone. Thus, we identified a JH-controlled miR-309a/pnr axis that regulates Vg2 and VgR to control the ovarian development. This study has further enhanced our understanding of molecular mechanisms governing ovarian development and insect reproduction. It provides a background for identifying targets for controlling important Dipteran pests.

The ovary is a very critical organ for insect reproduction. Especially, many insect pests are famous for their large reproductive capacity. Therefore, understanding the molecular mechanisms involved in ovarian development could significantly contribute in the development of new insect pest control strategies. In this study, we report that miR-309a regulates the development of the ovary in an important dipteran pest, B. dorsalis, through a transcriptional factor, pannier (GATA-binding factor A/pnr), which in turn directly mediates the expression of yolk vitellogenin 2 (Vg 2) and vitellogenin receptor (VgR). Moreover, miR-309a is under the upstream control of juvenile hormone (JH). Here, in Dipterans, a novel JH-miR-309a-pnr-Vg-related genes regulatory pathway was found in ovarian development. This finding advances our understanding of a mechanism regulating insect ovarian development and provides new insights for potential targets to control dipteran pests through the reproductive strategy.

Fatty acid synthases and desaturases are essential for the biosynthesis of α-linolenic acid and metamorphosis in a major mulberry pest, Glyphodes pyloalis walker (Lepidoptera: Pyralidae)

BACKGROUND

α-linolenic acid is an essential unsaturated fatty acid in organisms. However, there is a large gap between α-linolenic acid accumulation and its synthesis mechanism in insects. Fatty acid synthases (FASs) and desaturases (Desats) are vital enzymes required for the synthesis of unsaturated fatty acids.

RESULTS

The pupae of Glyphodes pyloalis (Lepidoptera: Pyralidae), which is a destructive pest of mulberry trees, contain the highest level of α-linolenic acid compared to other life-history stages. To further explore the synthesis mechanism of α-linolenic acid in G. pyloalis pupae, we constructed a pupal transcriptome dataset and identified 106 genes related to fatty acid metabolism from it. Among these, two fatty acid synthases (GpylFAS) and five desaturases (GpylDesat) were identified. A qRT-PCR validation revealed that GpylFAS1 and GpylDesat1, 2, 3, 5 were expressed highest at pupal stages. Furthermore, the content of α-linolenic acid decreased significantly after silencing GpylFAS1 and GpylDesat5, respectively. Besides, knocking down GpylFAS1 or GpylDesat5 resulted in more malformed pupae and adults, as well as lower emergence rates. Meanwhile, silencing GpylFAS1 or GpylDesat5 affected the expressions of the other GpylFASs and GpylDesats.

CONCLUSION

The present results illustrate the pivotal function of FASs and Desats in α-linolenic acid biosynthesis and metamorphosis in insects. Our research also broadens the sources of unsaturated fatty acids, especially for α-linolenic acid from insects, and provides novel insights for the management of mulberry insect pests from the perspective of utilization rather than control. © 2022 Society of Chemical Industry.

Temporal Expression Profiles Reveal Potential Targets during Postembryonic Development of Forensically Important Sarcophaga peregrina (Diptera: Sarcophagidae)

Sarcophaga peregrina (Robineau-Desvoidy, 1830) is a species of medical and forensic importance. In order to investigate the molecular mechanism during postembryonic development and identify specific genes that may serve as potential targets, transcriptome analysis was used to investigate its gene expression dynamics from the larval to pupal stages, based on our previous de novo-assembled genome of S. peregrina. Totals of 2457, 3656, 3764, and 2554 differentially expressed genes were identified. The specific genes encoding the structural constituent of cuticle were significantly differentially expressed, suggesting that degradation and synthesis of cuticle-related proteins might actively occur during metamorphosis. Molting (20-hydroxyecdysone, 20E) and juvenile (JH) hormone pathways were significantly enriched, and gene expression levels changed in a dynamic pattern during the developmental stages. In addition, the genes in the oxidative phosphorylation pathway were significantly expressed at a high level during the larval stage, and down-regulated from the wandering to pupal stages. Weighted gene co-expression correlation network analysis (WGCNA) further demonstrated the potential regulation mechanism of tyrosine metabolism in the process of puparium tanning. Moreover, 10 consistently up-regulated genes were further validated by qRT-PCR. The utility of the models was then examined in a blind study, indicating the ability to predict larval development. The developmental, stage-specific gene profiles suggest novel molecular markers for age prediction of forensically important flies.

Integrative Analysis of lncRNA-mRNA Co-expression Provides Novel Insights Into the Regulation of Developmental Transitions in Female Varroa destructor

Varroa destructor is a major pathogenic driver of the Western honeybee colony losses globally. Understanding the developmental regulation of V. destructor is critical to develop effective control measures. Development is a complex biological process regulated by numerous genes and long non-coding RNAs (lncRNAs); however, the underlying regulation of lncRNAs in the development of V. destructor remains unknown. In this study, we analyzed the RNA sequencing (RNA-Seq) data derived from the four stages of female V. destructor in the reproductive phase (i.e., egg, protonymph, deutonymph, and adult). The identified differentially expressed mRNAs and lncRNAs exhibited a stage-specific pattern during developmental transitions. Further functional enrichment established that fat digestion and absorption, ATP-binding cassette (ABC) transporters, mitogen-activated protein kinase (MAPK) signaling pathway, and ubiquitin-proteasome pathway play key roles in the maturation of female V. destructor. Moreover, the lncRNAs and mRNAs of some pivotal genes were significantly upregulated at the deutonymph stage, such as cuticle protein 65/6.4/63/38 and mucin 5AC, suggesting that deutonymph is the key stage of metamorphosis development and pathogen resistance acquisition for female V. destructor. Our study provides novel insights into a foundational understanding of V. destructor biology.

Expression profiles of tyrosine metabolic pathway genes and functional analysis of DOPA decarboxylase in puparium tanning of Bactrocera dorsalis (Hendel)

BACKGROUND

Tanning is an important physiological process with critical roles in cuticle pigmentation and sclerotization. Previous studies have shown that insect cuticle tanning is closely associated with the tyrosine metabolism pathway, which consists of a series of enzymes.

RESULTS

In this study, 24 tyrosine metabolism pathway genes were identified in the oriental fruit fly Bactrocera dorsalis (Hendel) genome. Gene expression profiles throughout 15 developmental stages of B. dorsalis were established based on our previous RNA sequencing data, and we found that 13 enzyme genes could be involved in the process of pupariation. Accordingly, a tyrosine-mediated tanning pathway during the pupariation of B. dorsalis was predicted and a critical enzyme, 3,4-dihydroxyphenylalanine (DOPA) decarboxylase (DDC), was used to explore its possible roles in formation of the puparium. First, a real-time quantitative polymerase chain reaction confirmed that BdDDC had an epidermis-specific expression pattern, and was highly expressed during larval metamorphosis in B. dorsalis. Subsequent disruption of BdDDC by feeding 5-day-old larvae with DDC inhibitor (l-α-methyl-DOPA) could lead to: (i) a significant decrease in BdDDC enzyme activity and dopamine concentration; (ii) defects in puparium pigmentation; (iii) impairment of the morphology and less thickness of the puparium; and (iv) lower pupal weight and obstacles to eclosion.

CONCLUSION

This study provided a potential tyrosine metabolic pathway that was responsible for insect tanning during pupariation, and the BdDDC enzyme has been shown to have crucial roles in larval-pupal tanning of B. dorsalis. © 2021 Society of Chemical Industry.

Transcriptome Analysis of Hormone-and Cuticle-Related Genes in the Development Process of Deutonymph in Tetranychus urticae

Tetranychus urticae is an important agricultural pest that feeds on more than 1100 plant species. To investigate gene expression network in development process of deutonymph, a comprehensive transcriptome analysis of different developmental time points of deutonymph in T. urticae was performed. Comparing with expression profile of 7 h, 309, 876, 2736, and 3432 differential expression genes were detected at time points 14 h, 21 h, 28 h, and 35 h, respectively. The expression dynamic analysis indicated that genes in hormone- (ecdysteroid and juvenile hormone) and cuticle- (chitin and cuticle proteins) related pathways were indispensable for development process in deutonymph. Among hormone related pathway genes, the ecdysteroid biosynthesis pathway genes were highly expressed at the growth period of development process, which is opposite to the expression patterns of juvenile hormone biosynthesis pathway genes. For cuticle related pathway genes, 13 chitinase genes were identified in the genome of T. urticae, and 8 chitinase genes were highly expressed in different time points of developmental process in the deutonymph of T. urticae. Additionally, 59 cuticle protein genes were identified from genome, and most of the cuticle protein genes were expressed in the molting period of developmental process in deutonymph. This study reveals critical genes involved in the development process of deutonymph and also provides comprehensive development transcriptome information for finding more molecular targets to control this pest.

Phytosanitary risk associated with illegal importation of pest-infested commodities to the South African agricultural sector

We evaluated the phytosanitary risk associated with illegal importation of pest-infested plant commodities into South Africa. Samples were collected from different South African ports of entry over 8 years (2011 to 2019) and data were analysed descriptively using Statistical Software Package. Pests were frequently detected on commodity species such as Citrus (18.31%), Zea mays (13.22%), Phaseolus vulgaris (12.88%), Musa spp. (9.15%) and Fragaria ananassa (5.08%). The highest number of pests intercepted occurred on fresh fruits (44.06%), followed by grains (26.44%) and vegetables (14.23%). The most intercepted organisms were Callosobruchus rhodesianus (7.79%), Dysmicoccus brevipes (7.11%), Callosobruchus maculates (6.10%) and Phyllosticta citricarpa (4.74%). The majority of intercepted organisms were non-quarantine organisms (70.50%), followed by pests of unknown status (17.28%), quarantine pests (10.84%) and potential quarantine pests (1.35%). Phyllosticta citricarpa, Bactrocera dorsalis, Spodoptera frugiperda and Prostephanus truncatus were the only quarantine pests intercepted in terms of South African regulatory status. The interception was mainly from southern African countries, particularly Mozambique, Zimbabwe and Eswatini. The findings present the level of phytosanitary risk associated with illegal importation and/or non-compliance in regard to plants and plant commodities from different countries through South African ports of entry. Crop production, biodiversity, food security, existing export markets, and access to new export markets could be threatened as importing countries may impose stringent phytosanitary measures to limit the chances of introduction and establishment of quarantine pests into their territories.

Genome-Wide Characterization and Identification of Long Non-Coding RNAs during the Molting Process of a Spider Mite, Panonychus citri

Molting is essential for arthropods to grow. As one of the important arthropod pests in agriculture, key spider mite species (Tetranychus and Panonychus) can normally molt three times from the larva to adult stage within a week. This physiological strategy results in the short lifecycle of spider mites and difficulties in their control in the field. Long non-coding RNAs (lncRNAs) regulate transcriptional editing, cellular function, and biological processes. Thus, analysis of the lncRNAs in the spider mite molting process may provide new insights into their roles in the molting mechanism. For this purpose, we used high-throughput RNA-seq to examine the expression dynamics of lncRNAs and mRNAs in the molting process of different development stages in Panonychus citri. We identified 9199 lncRNAs from 18 transcriptomes. Analysis of the lncRNAs suggested that they were shorter and had fewer exons and transcripts than mRNAs. Among these, 356 lncRNAs were differentially expressed during three molting processes: late larva to early protonymph, late protonymph to early deutonymph, and late deutonymph to early adult. A time series profile analysis of differentially expressed lncRNAs showed that 77 lncRNAs were clustered into two dynamic expression profiles (Pattern a and Pattern c), implying that lncRNAs were involved in the molting process of spider mites. Furthermore, the lncRNA-mRNA co-expression networks showed that several differentially expressed hub lncRNAs were predicted to be functionally associated with typical molting-related proteins, such as cuticle protein and chitin biosynthesis. These data reveal the potential regulatory function of lncRNAs in the molting process and provide datasets for further analysis of lncRNAs and mRNAs in spider mites.

RNA-seq analysis of gene expression changes in cuticles during the larval-pupal metamorphosis of Plutella xylostella

The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) is a holometabolous insect that its cuticles must undergo the significant changes during the larval-pupal metamorphosis development. To elucidate these changes at molecular levels, RNA-seq analysis of cuticles from LLS (later fourth instar larval stage), PPS (prepupal stage) and PS (pupal stage) were performed in P. xylostella. In this paper, a total of 17,710 transcripts were obtained in the larval-pupal transition of P. xylostella, and out of which 2293 (881 up-regulated and 1412 down-regulated) and 2989 transcripts (2062 up-regulated and 927 down-regulated) were identified to be differentially expressed between LLS and PPS, as well as PPS and PS, respectively. The further GO and KEGG analysis of differentially expressed genes (DEGs) revealed that the 'structural constituent of cuticle', 'chitin metabolic process', 'chitin binding', 'tyrosine metabolism' and 'insect hormone biosynthesis' pathways were significantly enriched, indicating these pathways might be involved in the process of larval pupation in P. xylostella. Then, we found some genes that encoded cuticular proteins, chitinolytic enzymes, chitin synthesis enzymes, and cuticle tanning proteins changed their expression levels remarkably, indicating these genes might play important roles in the restruction (degradation and biosynthesis) of insect cuticles during the larval metamorphosis. Additionally, the significant changes in the mRNA levels of 20-hydroxyecdysone (20E) and juvenile hormone (JH) related genes suggested their crucial roles in regulating cuticle remodeling during the larval metamorphosis of P. xylostella. In conclusion, the present study provide us the comprehensive gene expression profiles to explore the molecular mechanisms of cuticle metamorphosis in P. xylostella, which laid a molecular basis to study roles of specific pathways and genes in insect development.

Identification and profiling of Bactrocera dorsalis microRNAs and their potential roles in regulating the developmental transitions of egg hatching, molting, pupation and adult eclosion

MicroRNAs (miRNAs) are endogenous small noncoding RNAs (18-25 nt) that are involved in many physiological processes including development, cancer, immunity, apoptosis and host-microbe interactions through post-transcriptional regulation of gene expression. In this study, we measured the profile of small RNAs over the developmental transitions of the oriental fruit fly Bactrocera dorsalis from egg hatching, molting, and pupation to adult eclosion. We identified 250 miRNAs, including 83 known and 167 novel miRNAs, and 47 isomiRNAs. In addition, we identified the miRNAs differentially expressed over the developmental transitions. Interestingly, the miR-309 cluster, the miR-2 cluster/family and the let-7 cluster were among these differentially expressed miRNAs, suggesting a role in the regulation of egg hatching, molting and pupation/adult eclosion, respectively. Moreover, a detailed analysis of the temporal expression patterns of 14 highly expressed miRNAs in the pupal stage revealed three types of expression profiles. Furthermore, injection of a miR-100 mimic in the 3rd instar larvae resulted in a significant decrease in pupation and adult eclosion rates, whereas injection of a miR-317 antagomir resulted in a significant decrease in the pupation rate and a decrease in the pupation time, indicating that miR-100 and miR-317 are involved in the process of pupation. Finally, injection of a miR-100/miR-285 mimic or antagomir in pupae resulted in a significant decrease in the eclosion rate and a significant increase in the prevalence of a partial eclosion phenotype, implying the involvement of miR-100 and miR-285 in the process of adult eclosion. This study identified critical miRNAs involved in the transitions of this important holometabolic model and pest insect B. dorsalis from egg hatching to adult eclosion, thus providing a useful resource for exploring the regulatory role of miRNAs during insect post-embryonic development.