Deep sequencing-based transcriptome analysis of Plutella xylostella larvae parasitized by Diadegma semiclausum

Abstract

BackgroundParasitoid insects manipulate their hosts' physiology by injecting various factors into their host upon parasitization. Transcriptomic approaches provide a powerful approach to study insect host-parasitoid interactions at the molecular level. In order to investigate the effects of parasitization by an ichneumonid wasp (Diadegma semiclausum) on the host (Plutella xylostella), the larval transcriptome profile was analyzed using a short-read deep sequencing method (Illumina). Symbiotic polydnaviruses (PDVs) associated with ichneumonid parasitoids, known as ichnoviruses, play significant roles in host immune suppression and developmental regulation. In the current study, D. semiclausum ichnovirus (DsIV) genes expressed in P. xylostella were identified and their sequences compared with other reported PDVs. Five of these genes encode proteins of unknown identity, that have not previously been reported.ResultsDe novo assembly of cDNA sequence data generated 172,660 contigs between 100 and 10000 bp in length; with 35% of > 200 bp in length. Parasitization had significant impacts on expression levels of 928 identified insect host transcripts. Gene ontology data illustrated that the majority of the differentially expressed genes are involved in binding, catalytic activity, and metabolic and cellular processes. In addition, the results show that transcription levels of antimicrobial peptides, such as gloverin, cecropin E and lysozyme, were up-regulated after parasitism. Expression of ichnovirus genes were detected in parasitized larvae with 19 unique sequences identified from five PDV gene families including vankyrin, viral innexin, repeat elements, a cysteine-rich motif, and polar residue rich protein. Vankyrin 1 and repeat element 1 genes showed the highest transcription levels among the DsIV genes.ConclusionThis study provides detailed information on differential expression of P. xylostella larval genes following parasitization, DsIV genes expressed in the host and also improves our current understanding of this host-parasitoid interaction.

Conserved microRNA miR-8 blocks activation of the Toll pathway by upregulating Serpin 27 transcripts

“…44,47,49 In our previous RNA-seq transcriptomebased study we reported that AMPs such as gloverin, moricin, lysozyme II, and cecropin were upregulated after parasitization in P. xylostella larvae. 24 Among those antimicrobial peptides, gloverin had the highest transcription levels, which suggests that following parasitoid attack by suppression of miR-8 and its target Serpin 27 gloverin gene expression is activated.…”

“…[21][22][23] Several studies have shown that parasitic wasps have significant effects on host metabolism and development through interruption of host gene transcription, immune pathways, nutrition, and endocrine systems, and even regulate miRNA levels. 18,[24][25][26][27][28][29] Therefore, endoparasitoid wasps provide ideal biological tools to study the basic mechanisms underlying insect immune responses due to their profound impact on the host immune system.…”

“…The P. xylostella transcriptome database 24 was screened for an miR-8 potential target using the BLAST algorithm. A candidate target gene, Px-Serpin 27, which is a serine protease inhibitor, was identified and subsequently confirmed with the RNAHybrid software.…”

Functional Annotation of Cotesia congregata Bracovirus: Identification of Viral Genes Expressed in Parasitized Host Immune Tissues

“…To date, only two other high-throughput transcriptomic approaches have been conducted on similar host-parasitoid systems involving DsIV and CchBV; in each case, the expressions of only 19 viral genes from 5 and 6 gene families, respectively, were detected (30,31). Even if the reference genomes are not available for these viruses, the expression of a larger number of genes might have been expected, considering the number of genes predicted in related viruses (19,23).…”

“…In addition, deep sequencing approaches at the transcriptome level concerned the expression of the Diadegma semiclausum ichnovirus (DsIV) in Plutella xylostella larvae and the expression of Cotesia chilonis bracovirus (CchBV) in the Chilo suppressalis host. In these de novo transcriptomic approaches applied to new model species, the relative contributions of IV and BV gene expression could not be evaluated because the genomes of these PDVs have not yet been sequenced (30,31).…”