Identification of two clip domain serine proteases involved in the pea aphid's defense against bacterial and fungal infection

Immune Gene Repertoire of Soft Scale Insects (Hemiptera: Coccidae)

Insects possess an effective immune system, which has been extensively characterized in several model species, revealing a plethora of conserved genes involved in recognition, signaling, and responses to pathogens and parasites. However, some taxonomic groups, characterized by peculiar trophic niches, such as plant-sap feeders, which are often important pests of crops and forestry ecosystems, have been largely overlooked regarding their immune gene repertoire. Here we annotated the immune genes of soft scale insects (Hemiptera: Coccidae) for which omics data are publicly available. By using immune genes of aphids and Drosophila to query the genome of Ericerus pela, as well as the transcriptomes of Ceroplastes cirripediformis and Coccus sp., we highlight the lack of peptidoglycan recognition proteins, galectins, thaumatins, and antimicrobial peptides in Coccidae. This work contributes to expanding our knowledge about the evolutionary trajectories of immune genes and offers a list of promising candidates for developing new control strategies based on the suppression of pests' immunity through RNAi technologies.

Research progress of aphid immunity system: Potential effective target for green pest management

Due to the absence of acquired immunity, insects primarily rely on their innate immune system to resist pathogenic microorganisms and parasitoids in natural habitats. This innate immune system can be classified into cellular immunity and humoral immunity. Cellular immunity is mediated by hemocytes, which perform phagocytosis, aggregation, and encapsulation to fight against invaders, whereas the humoral immunity primarily activates the immune signaling pathways and induces the generation of immune effectors. Existing studies have revealed that the hemipteran aphids lack some crucial immune genes compared to other insect species, indicating the different immune mechanisms in aphids. The current review summarizes the adverse impacts of pathogenic microorganisms and parasitoids on aphids, introduces the cellular and humoral immune systems in insects, and analyzes the differences between aphids and other insect species. Furthermore, our review also discussed the existing prospects and challenges in aphid immunity research, and proposed the potential application of immune genes in green pest management.

Differential gene expression between viruliferous and non-viruliferous Schizaphis graminum (Rondani)

An experiment was performed to measure the effect of Cereal Yellow-Dwarf Virus (CYDV), strain CYDV-RPV, on gene expression in its insect vector, greenbug aphid (Schizaphis graminum (Rondani)). RNA was sampled in three replicates from four treatments (biotypes B and H with or without carried CYDV), at 0, 1, 2, 3, 5, 10, 15 and 20 days from the introduction of carrier and virus-free greenbugs to uninfected wheat cv. 'Newton'. Illumina paired-end sequencing produced 1,840,820,000,000 raw reads that yielded 1,089,950,000 clean reads, which were aligned to two greenbug, Trinity transcriptome assemblies with bowtie2. Read counts to contigs were analyzed with principal components and with DESeq2 after removing contaminating contigs of wheat or microbial origin. Likelihood ratio tests with one transcriptome showed that CYDV influenced gene expression about seven-fold less than time or biotype, which were approximately equal. With the other transcriptome, virus, time, and biotype were about equally important. Pairwise comparisons of virus to no virus for each timepoint yielded estimates of fold-change that comprised expression profiles for each contig when ordered by timepoint. Hierarchical clustering separated expression profiles into 20 groups of contigs that were significantly differentially expressed for at least one timepoint. Contigs were also sorted by timepoint of maximally differential expression between virus and no virus. All contigs that were significantly differentially expressed at FDR = 0.05 were annotated by blast searches against NCBI nr and nt databases. Interesting examples of up-regulation with virus included a lysosomal-trafficking regulator, peptidylprolylisomerase, RNA helicase, and two secreted effector proteins. However, carried virus did not consistently change aphid gene expression overall. Instead there was complex interaction of time, biotype, host response, and virus.

Characterization and Functional Analysis of Toll Receptor Genes during Antibacterial Immunity in the Green Peach Aphid Myzus persicae (Sulzer)

The insect Toll receptor is one of the key members of the Toll signaling pathway, which plays an indispensable role in insect resistance to pathogen infection. Herein, we cloned and characterized five Toll receptor genes from Myzus persicae (Sulzer), which were found to be highly expressed in the first-instar nymphs and adults (both wingless and winged) at different developmental stages. Expressions of MpToll genes were highest in the head, followed by the epidermis. High transcription levels were also found in embryos. Expressions of these genes showed different degrees of positive responses to infection by Escherichia coli and Staphylococcus aureus. The expression of MpToll6-1 and MpToll7 significantly increased after infection with E. coli, whereas the expression of MpToll, MpToll6, MpToll6-1, and MpTollo continuously increased after infection with S. aureus. RNA interference-mediated suppressed expression of these genes resulted in a significant increase in the mortality of M. persicae after infection with the two bacterial species compared with that in the control group. These results suggest that MpToll genes play vital roles in the defense response of M. persicae against bacteria.

Mating Stimulates the Immune Response and Sperm Storage-Related Genes Expression in Spermathecae of Bumblebee (Bombus terrestris) Queen

Bumblebee queens have remarkable spermathecae that store sperm for year-round reproduction. The spermathecal gland is regarded as a secretory organ that could benefit sperm storage. Queen mating provokes substantial physiological, behavioral, and gene expression changes. Here, the transcriptomes of spermathecae were compared between virgins and mated queens of the bumblebee, Bombus terrestris L., at 24 h post mating. Differentially expressed genes were further validated by real time quantitative PCR and immunofluorescence assay. In total, the expression of 11, 069 and 10, 862 genes were identified in virgins and mated queens, respectively. We identified that 176 differentially expressed genes between virgin and mated queen spermathecae: 110 (62.5%) genes were upregulated, and 66 (37.5%) genes were downregulated in mated queens. Most of the differentially expressed genes validated by RT-qPCR were concentrated on immune response [i.e., leucine-rich repeat-containing protein 70 (35.8-fold), phenoloxidase 2 (41.9-fold), and defensin (4.9-fold)] and sperm storage [i.e., chymotrypsin inhibitor (6.2-fold), trehalose transporter Tret1 (1.7-, 1.9-, 2.4-, and 2.4-fold), and heterogeneous nuclear ribonucleoprotein A3 (1.2-, and 2.6-fold)] functions in the spermathecae of mated queens. Procollagen-lysine, 2-oxoglutarate 5-dioxygenase 1 (PLOD1) was hypothesized to promote the mating behavior according to RT-qPCR and immunofluorescence assay. The expression levels of most upregulated immune genes were decreased significantly at 3 days post mating. In conclusion, the external sperm transfer into spermathecae led to the significantly upregulated immune response genes in bumblebees. These gene expression differences in queen spermathecae contribute to understanding the bumblebee post mating regulatory network.

Melanization induced by Heliothis virescens ascovirus 3h promotes viral replication

Melanization is an important innate immune defense mechanism of insects, which can kill invading pathogens. Most pathogens, for their survival and reproduction, inhibit the melanization of the host. Interestingly, our results suggested that after infection with Heliothis virescens ascovirus 3h (HvAV-3h), the speed of melanization in infected Spodoptera exigua larval hemolymph was accelerated and that the phenoloxidase (PO) activity of hemolymph in larvae infected with HvAV-3h increased significantly (1.20-fold at 96 hpi, 1.52-fold at 120 hpi, 1.23-fold at 144 hpi, 1.12-fold at 168 hpi). The transcription level of the gene encoding S. exigua prophenoloxidase-1 (SePPO-1 gene) was upregulated dramatically in the fat body during the middle stage of infection. In addition, when melanization was inhibited or promoted, the replication of HvAV-3h was inhibited or promoted, respectively. In conclusion, infection with HvAV-3h can markedly induce melanization in the middle stage of infection, and melanization is helpful for HvAV-3h viral replication.

PCE3 Plays a Role in the Reproduction of Male Nilaparvata lugens

Simple Summary

The brown planthopper (BPH), Nilaparvata lugens, is one of the most harmful rice crop pest insects. The use of RNAi is a feasible strategy for controlling this pest. In this study, we evaluated the importance of PCE3 in the development and reproduction of male BPH. We found that PCE3 could regulate the development of the male internal genitalia and reduce the oviposition level of the females that mated with males treated with dsRNA targeting the N. lugens PCE3 gene, causing eggs not to hatch. Our findings indicate that PCE3 is an important gene in regulating male fecundity and a promising target for controlling BPH.

Abstract

Nilaparvata lugens proclotting enzymes (NlPCEs) belong to the clip domain serine protease (clip-SP) family, which is a characteristic protease family in arthropods. NlPCE3 was previously reported to regulate egg production and development in female N. lugens, but its role in male N. lugens is unclear. In the present study, qPCR analysis showed that NlPCE3 was expressed in three different tissues (gut, testis and fat body). RNAi revealed that dsNlPCE3 injection made the male vas deferens thinner and reduced the oviposition level of the females that mated with dsNlPCE3-treated males, causing eggs not to hatch. Furthermore, immunofluorescence staining showed that NlPCE3 was widely expressed in the male internal genitalia. However, after dsNlPCE3 injection, expression of NlPCE3 was diffuse in the male internal genitalia, whose peripheral cells seemed degraded. Overall, these results indicate that NlPCE3 is important for reproduction in male N. lugens.