title: Infection routes matter in population-specific responses of the red flour beetle to the entomopathogen Bacillus thuringiensis.
abstract: BACKGROUND
  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. 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  Our 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.
authors.affiliation: Institute for Evolution and Biodiversity, University of Münster, Hüfferstr, 1, 48149 Münster, Germany. sbehrens@uni-muenster.de.
authors.forename: Sarah
authors.initials: S
authors.lastname: Behrens
authors.forename: Robert
authors.initials: R
authors.lastname: Peuß
authors.forename: Barbara
authors.initials: B
authors.lastname: Milutinović
authors.forename: Hendrik
authors.initials: H
authors.lastname: Eggert
authors.forename: Daniela
authors.initials: D
authors.lastname: Esser
authors.forename: Philip
authors.initials: P
authors.lastname: Rosenstiel
authors.forename: Hinrich
authors.initials: H
authors.lastname: Schulenburg
authors.forename: Erich
authors.initials: E
authors.lastname: Bornberg-Bauer
authors.forename: Joachim
authors.initials: J
authors.lastname: Kurtz
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000472:pathogenicity*; D016000:Cluster Analysis; D001517:Coleoptera / Q000235:genetics* / Q000276:immunology / Q000378:metabolism / Q000382:microbiology*; D019295:Computational Biology; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D054884:Host-Pathogen Interactions / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction; D013997:Time Factors; D059467:Transcriptome