A lipase-like gene from Heliothis virescens ascovirus (HvAV-3e) is essential for virus replication and cell cleavage

Larval-Transcriptome Dynamics of Ectropis grisescens Reveals Differences in Virulence Mechanism between Two EcobNPV Strains

The biological insecticide, Ectropis obliqua nucleopolyhedrovirus (EcobNPV), has been applied to control the major tea-pest Ectropis grisescens. Previously, the virus strain EcobNPV-QF4 showed higher a mortality rate (58.2% vs. 88.2%) and shorter median lethal-time (13.9 d vs. 15.4 d) on E. grisescens than the strain EcobNPV-QV. However, the mechanism of the difference in virulence between the two strains remains unclear. Using the leaf-disc method, we detected the virulence of the two strains on 3^rd-instar larvae, and found that median lethal-dose (LD₅₀) of EcobNPV-QF4 is 55-fold higher than that of EcobNPV-QV (4.35 × 10⁸ vs. 7.89 × 10⁶). Furthermore, fourteen larva transcriptomes of E. grisescens were subsequently sequenced at seven time-points after ingestion of the two virus strains, yielding 410.72 Gb of raw reads. Differential gene-expression analysis shows that 595, 87, 27, 108, 0, 12, and 290 genes were up-regulated in EcobNPV-QF4 at 0, 2, 6, 12, 24, 36 h and 48 h post ingestion (hpi), while 744, 68, 152, 8, 1, 0, 225 were down-regulated. KEGG enrichment showed that when the virus first invades (eats the leaf-discs), EcobNPV-QF4 mainly affects pathways such as ribosome (p-value = 2.47 × 10^-29), and at 48 hpi EcobNPV-QF4, causes dramatic changes in the amino-acid-synthesis pathway and ribosome pathway (p-value = 6.94 × 10^-13) in E. grisescens. Among these, thirteen key genes related to immunity were screened. The present study provides the first ever comprehensive analysis of transcriptional changes in E. grisescens after ingestion of the two strains of EcobNPV.

Early in vivo transcriptome of Trichoplusia ni ascovirus core genes

Ascoviruses are large double-stranded DNA insect viruses that destroy the nucleus and transform each cell into 20 or more viral vesicles for replication. In the present study we used RNA-sequencing to compare the expression of Trichoplusia ni ascovirus 6a1 (TnAV-6a1) core genes during the first week of infection, with emphasis on the first 48 h, comparing transcript levels in major somatic tissues (epidermis, tracheal matrix and fat body), the sites infected initially, with those of the haemolymph, where viral vesicles circulate and most replication occurs. By 48 h post-infection (p.i.), only 26 genes were expressed in somatic tissues at ≥5 log2 reads per kilobase per million, whereas in the haemolymph 48 genes were expressed at a similar level by the same time. Early and high expression of TnAV caspase-2-like gene occurred in all tissues, implying it is required for replication, but that it is probably not associated with apoptosis induction, which occurs in infections of Spodoptera frugiperda ascovirus 1 a (SfAV-1a), the ascovirus type species. Other highly expressed viral genes at 48 h p.i. in viral vesicles included a dynein-like beta chain and lipid-modifying enzymes, suggesting their importance to vesicle formation and growth as well as virion synthesis. Finally, as occurs in SfAV expression, we found bicistronic and tricistronic mRNA messages produced by TnAV.

Comprehensive identification of protein orthologs in the family Ascoviridae facilitates an understanding of phylogenomics, protein conservation, and phosphorylation

Analysis of orthology is important for understanding protein conservation, function, and phylogenomics. In this study, we performed a comprehensive analysis of gene orthology in the family Ascoviridae based on identification of 366 protein homologue groups and phylogenetic analysis of 34 non-single-copy proteins. Our findings revealed 90 newly annotated proteins, five newly identified core proteins for the family Ascoviridae, and 14 core proteins for the genus Ascovirus. A phylogenomic tree of 11 Ascoviridae members was constructed based on a concatenation of 35 of the 45 ortholog groups. In combination with phosphoproteomic results and conservation estimations, 30 conserved phosphorylation sites on 17 phosphoproteins were identified from a total of 176 phosphosites on 57 phosphoproteins from Heliothis virescens ascovirus 3h (HvAV-3h), providing potential research targets for investigating the role of these protein in the regulation of viral infection. This study will facilitate genome annotation and comparison of further Ascoviridae members as well as functional genomic investigations.

3H-31, A Non-structural Protein of Heliothis virescens ascovirus 3h, Inhibits the Host Larval Cathepsin and Chitinase Activities

3h-31 of Heliothis virescens ascovirus 3h (HvAV-3h) is a highly conserved gene of ascoviruses. As an early gene of HvAV-3h, 3h-31 codes for a non-structural protein (3H-31) of HvAV-3h. In the study, 3h-31 was initially transcribed and expressed at 3 h post-infection (hpi) in the infected Spodoptera exigua fat body cells (SeFB). 3h-31 was further inserted into the bacmid of Autographa californica nucleopolyhedrovirus (AcMNPV) to generate an infectious baculovirus (AcMNPV-31). In vivo experiments showed that budded virus production and viral DNA replication decreased with the expression of 3H-31, and lucent tubular structures were found around the virogenic stroma in the AcMNPV-31-infected SeFB cells. In vivo, both LD₅₀ and LD₉₀ values of AcMNPV-31 were significantly higher than those of the wild-type AcMNPV (AcMNPV-wt) in third instar S. exigua larvae. An interesting finding was that the liquefaction of the larvae killed by the infection of AcMNPV-31 was delayed. Chitinase and cathepsin activities of AcMNPV-31-infected larvae were significantly lower than those of AcMNPV-wt-infected larvae. The possible regulatory function of the chitinase and cathepsin for 3H-31 was further confirmed by RNAi, which showed that larval cathepsin activity was significantly upregulated, but chitinase activity was not significantly changed due to the RNAi of 3h-31. Based on the obtained results, we assumed that the function of 3H-31 was associated with the inhibition of host larval chitinase and cathepsin activities, so as to restrain the hosts in their larval stages.

A Novel Digestive Proteinase Lipase Member H-A in Bombyx mori Contributes to Digestive Juice Antiviral Activity Against B. mori Nucleopolyhedrovirus

Previous studies have revealed that some proteins in Bombyx mori larvae digestive juice show antiviral activity. Here, based on the label-free proteomics data, BmLipase member H-A (BmLHA) was identified as being involved in the response to BmNPV infection in B. mori larvae digestive juice. In the present study, a gene encoding the BmLHA protein in B. mori was characterized. The protein has an open reading fragment of 999 bp, encoding a predicted 332 amino acid residue-protein with a molecular weight of approximately 35.9 kDa. The phylogenetic analysis revealed that BmLHA shares a close genetic distance with Papilio xuthus Lipase member H-A. BmLHA was highly expressed in the middle part of the B. mori gut, and the expression level increased with instar rising in larvae. There was higher expression of BmLHA in A35 than in P50 strains, and it was upregulated in both A35 and P50 strains, following BmNPV infection. The expression level of VP39 decreased significantly in appropriate recombinant-BmLHA-treated groups compared with the PBS-treated group in B. mori larvae and BmN cells. Meanwhile, overexpression of BmLHA significantly reduced the infectivity of BmNPV in BmN cells. These results indicated that BmLHA did not have digestive function but had anti-BmNPV activity. Taken together, our work provides valuable data for the clarification of the molecular characterization BmLHA and supplements research on proteins of anti-BmNPV activity in B. mori.

Amsacta moorei entomopoxvirus encodes a functional esterase (amv133) with protease activity

OBJECTIVES

Lipolytic genes have been investigated in several viral genomes, and some of them show enzyme activity which can be used for various functions including the production of DNA replication metabolites, rescue from endosomes, and membrane fusion. Amsacta moorei entomopoxvirus (AMEV) replicates in nearly the entire insect body, especially in the adipose tissue. One of the open reading frames (ORFs) in the AMEV genome, amv133, encodes a putative lipase enzyme. In this study, we therefore investigate the enzyme activity of amv133.

METHODS

amv133 was aligned with known lipase genes and their homologs in entomopoxviruses. Expressed proteins were partially purified and assayed for lipase, esterase and protease.

RESULTS

We found that amv133 contains all the domains required for a functional lipase enzyme and that it shows a significant similarity with homologs in other entomopoxviruses. Since there is a similarity of the catalytic triad between lipases and serine proteases, we also investigated the protease activity of amv133. Lipase, esterase and protease assays showed that amv133 encodes a functional esterase enzyme with protease activity.

CONCLUSION

The current data show that amv133 is a conserved gene in all entomopoxvirus genomes sequenced so far and might contribute greatly to degrading the lipids or proteins and hence improve the virus infection.

The salivary secretome of the tsetse fly Glossina pallidipes (Diptera: Glossinidae) infected by salivary gland hypertrophy virus

BACKGROUND

The competence of the tsetse fly Glossina pallidipes (Diptera; Glossinidae) to acquire salivary gland hypertrophy virus (SGHV), to support virus replication and successfully transmit the virus depends on complex interactions between Glossina and SGHV macromolecules. Critical requisites to SGHV transmission are its replication and secretion of mature virions into the fly's salivary gland (SG) lumen. However, secretion of host proteins is of equal importance for successful transmission and requires cataloging of G. pallidipes secretome proteins from hypertrophied and non-hypertrophied SGs.

METHODOLOGY/PRINCIPAL FINDINGS

After electrophoretic profiling and in-gel trypsin digestion, saliva proteins were analyzed by nano-LC-MS/MS. MaxQuant/Andromeda search of the MS data against the non-redundant (nr) GenBank database and a G. morsitans morsitans SG EST database, yielded a total of 521 hits, 31 of which were SGHV-encoded. On a false discovery rate limit of 1% and detection threshold of least 2 unique peptides per protein, the analysis resulted in 292 Glossina and 25 SGHV MS-supported proteins. When annotated by the Blast2GO suite, at least one gene ontology (GO) term could be assigned to 89.9% (285/317) of the detected proteins. Five (∼1.8%) Glossina and three (∼12%) SGHV proteins remained without a predicted function after blast searches against the nr database. Sixty-five of the 292 detected Glossina proteins contained an N-terminal signal/secretion peptide sequence. Eight of the SGHV proteins were predicted to be non-structural (NS), and fourteen are known structural (VP) proteins.

CONCLUSIONS/SIGNIFICANCE

SGHV alters the protein expression pattern in Glossina. The G. pallidipes SG secretome encompasses a spectrum of proteins that may be required during the SGHV infection cycle. These detected proteins have putative interactions with at least 21 of the 25 SGHV-encoded proteins. Our findings opens venues for developing novel SGHV mitigation strategies to block SGHV infections in tsetse production facilities such as using SGHV-specific antibodies and phage display-selected gut epithelia-binding peptides.