Abstract
BackgroundPathogens can infect their hosts through different routes. For studying the consequences for host resistance, we here used the entomopathogen Bacillus thuringiensis and the red flour beetle Tribolium castaneum for oral and systemic (i. e. pricking the cuticle) experimental infection. In order to characterize the molecular mechanisms underpinning the two different infection routes, the transcriptomes of beetles of two different T. castaneum populations – one recently collected population (Cro1) and a commonly used laboratory strain (SB) – were analyzed using a next generation RNA sequencing approach.ResultsThe genetically more diverse population Cro1 showed a significantly larger number of differentially expressed genes. While both populations exhibited similar reactions to pricking, their expression patterns in response to oral infection differed remarkably. In particular, the Cro1 population showed a strong response of cuticular proteins and developmental genes, which might indicate an adaptive developmental flexibility that was lost in the SB population presumably as a result of inbreeding. The immune response of SB was primarily based on antimicrobial peptides, while Cro1 relied on responses mediated by phenoloxidase and reactive oxygen species, which may explain the higher resistance of this strain against oral infection.ConclusionsOur data demonstrate that immunological and physiological processes underpinning the two different routes of infection are clearly distinct, and that host populations particularly differ in responses to oral infection. Furthermore, gene expression upon pricking infection entailed a strong signal of wounding, highlighting the importance of pricking controls in future infection studies.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-445) contains supplementary material, which is available to authorized users.
Highlights
Pathogens can infect their hosts through different routes
Single-nucleotide resolution transcriptome of T. castaneum by RNA-seq RNA-seq experiments were performed for two different T. castaneum populations, San Bernardino (SB) and Croatia 1 (Cro1), both at 6 h and 18 h after infection with B. thuringiensis
Our study shows that different routes of infection lead to strongly divergent gene expression profiles in the host, and that it is important to include the aspect of infection routes into studies of host-pathogen interactions
Summary
Pathogens can infect their hosts through different routes. For studying the consequences for host resistance, we here used the entomopathogen Bacillus thuringiensis and the red flour beetle Tribolium castaneum for oral and systemic (i. e. pricking the cuticle) experimental infection. For studying the consequences for host resistance, we here used the entomopathogen Bacillus thuringiensis and the red flour beetle Tribolium castaneum for oral and systemic Pathogens that can infect through alternative routes are interesting systems with which to test the evolutionary for the routes of infection It is currently unclear whether such route-specificity is a general phenomenon or restricted to this particular host-pathogen system. We studied infection routespecificity in the red flour beetle Tribolium castaneum upon oral and pricking infection with the entomopathogen Bacillus thuringiensis [4,5]. We compared gene expression between pricking and oral infection, using an Illumina generation sequencing approach (RNA-seq). For our comparative RNA-seq based study, a sterile wounding treatment was included to distinguish between effects of wounding alone and bacterial infection
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