Abstract
BackgroundThe Asian corn borer (Ostrinia furnacalis (Guenée)) is one of the most serious corn pests in Asia. Control of this pest with entomopathogenic fungus Beauveria bassiana has been proposed. However, the molecular mechanisms involved in the interactions between O. furnacalis and B. bassiana are unclear, especially under the conditions that the genomic information of O. furnacalis is currently unavailable. So we sequenced and characterized the transcriptome of O. furnacalis larvae infected by B. bassiana with special emphasis on immunity-related genes.Methodology/Principal FindingsIllumina Hiseq2000 was used to sequence 4.64 and 4.72 Gb of the transcriptome from water-injected and B. bassiana-injected O. furnacalis larvae, respectively. De novo assembly generated 62,382 unigenes with mean length of 729 nt. All unigenes were searched against Nt, Nr, Swiss-Prot, COG, and KEGG databases for annotations using BLASTN or BLASTX algorithm with an E-value cut-off of 10−5. A total of 35,700 (57.2%) unigenes were annotated to at least one database. Pairwise comparisons resulted in 13,890 differentially expressed genes, with 5,843 up-regulated and 8,047 down-regulated. Based on sequence similarity to homologs known to participate in immune responses, we totally identified 190 potential immunity-related unigenes. They encode 45 pattern recognition proteins, 33 modulation proteins involved in the prophenoloxidase activation cascade, 46 signal transduction molecules, and 66 immune responsive effectors, respectively. The obtained transcriptome contains putative orthologs for nearly all components of the Toll, Imd, and JAK/STAT pathways. We randomly selected 24 immunity-related unigenes and investigated their expression profiles using quantitative RT-PCR assay. The results revealed variant expression patterns in response to the infection of B. bassiana.Conclusions/SignificanceThis study provides the comprehensive sequence resource and expression profiles of the immunity-related genes of O. furnacalis. The obtained data gives an insight into better understanding the molecular mechanisms of innate immune processes in O. furnacalis larvae against B. bassiana.
Highlights
Innate immunity is an ancient and universal host defense mechanism found in both vertebrates and invertebrates
Sequencing and Unigene Assembly Parasitization of corn borer by B. bassiana provides a good system to study the interactions between insect hosts and entomopathogenic fungi, but the lack of genomic data of corn borer retards the relative progresses
In O. furnacalis transcriptom, we totally identified at least 45 pattern recognition proteins (PRPs) transcripts including 10 peptidoglycan recognition protein (PGRP), 4 bGRPs, 14 C-type lectin (CTL), 9 scavenger receptors (SCRs), 2 hemocytins, 1 hemolin, 2 galectins, 1 dscam, 1 draper and 1 eater (Table 2)
Summary
Innate immunity is an ancient and universal host defense mechanism found in both vertebrates and invertebrates. Insects lack adaptive immunity and mainly rely on innate immunity for defense against the invasion of pathogens or parasites [1,2]. The innate immune reactions in insects can be divided into three steps: (1) recognition of pathogen-associated molecular patterns; (2) signal modulation and transduction; (3) production or replenishment of immune-related molecules including effectors (for review see [22,23]). Immune effectors including AMPs are induced in specific tissues, such as fat body (liver analogue) and hemocytes (insect blood cells). These effector molecules combat the invasive microorganisms in the hemolymph (insect blood), and play direct roles in insect innate immunity. We sequenced and characterized the transcriptome of O. furnacalis larvae infected by B. bassiana with special emphasis on immunity-related genes
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