Behrens S, Peuß R, Milutinovic B, Eggert H, Esser D, Rosenstiel P, Schulenburg HS, Bornberg-Bauer E, Kurtz J
Infection routes matter in population-specific responses of the red flour beetle to the entomopathogen Bacillus thuringiensis
BMC Genomics 15: 445, 2014

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Abstract

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. A differential expression analysis reveals that
the genetically more diverse population Cro1 shows a significantly larger number of
differentially expressed genes. While both populations showed 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. Furthermore, gene
expression upon pricking infection entailed a strong signal of wounding, highlighting
the importance of pricking controls in future infection studies. 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.