Abstract

Social insects have evolved acute mechanisms for sensing and mitigating the spread of microbial pathogens within their communities that include complex behaviors such as grooming and sanitation. Chemical sensing involves detection and transport of olfactory and other chemicals that are mediated by at least two distinct classes of small molecular weight soluble proteins known as chemosensory- and odorant binding proteins (CSPs and OBPs, respectively) that exist as protein families in all insects. However, to date, a systematic examination of the expression of these genes involved in olfactory and other pathways to microbial infection has yet to be reported. The red imported fire ant, Solenopsis invicta, is one of the most successful invasive organisms on our planet. Here, we examined the temporal gene expression profiles of a suite of S. invicta CSPs (SiCSPs1-22) and OBPs (SiOBPs1-16) in response to infection by the broad host range fungal insect pathogen, Beauveria bassiana. Our data show that within 24 h post-infection, i.e., before the fungus has penetrated the host cuticle, the expression of SiCSPs and SiOBPs is altered (mainly increased compared to uninfected controls), followed by suppression of SiCSP and select SiOBP expression 48 h post-infection and mixed responses at 72 h post-infection. A smaller group of SiBOPs, however, appeared to respond to fungal infection, with expression of SiOBP15 consistently higher during fungal infection over the time course examined. These data indicate dynamic gene expression responses of CSPs and OBPs to fungal infection that provide clues to mechanisms that might mediate detection of microbial pathogens, triggering grooming, and nest sanitation.

Highlights

  • Chemosensory and odorant binding proteins (CSPs and OBPs, respectively), represent two evolutionarily distinct protein families, that share several features (Pelosi et al, 2006, 2014; Kulmuni and Havukainen, 2013)

  • Members of the CSP and OBP families are recognized as functioning in a wide range of physiological processes beyond olfaction (Pelosi et al, 2018)

  • Subsets of CSPs and OBPs have been found to function as reservoirs for the storage and release of semiochemicals from pheromone glands (JacquinJoly et al, 2001; Briand et al, 2002; Iovinella et al, 2013)

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Summary

Introduction

Chemosensory and odorant binding proteins (CSPs and OBPs, respectively), represent two evolutionarily distinct protein families, that share several features (Pelosi et al, 2006, 2014; Kulmuni and Havukainen, 2013). CSPs and OBPs are small molecular weight (typically 10–18 kDa) soluble proteins capable of binding a wide range of ligands including hydrophobic and volatile compounds such as pheromones, organic and fatty acids, and other semiochemicals and environmental odors (Calvello et al, 2005; Dani et al, 2011; Pelosi et al, 2011). Members of the CSP and OBP families are recognized as functioning in a wide range of physiological processes beyond olfaction (Pelosi et al, 2018). To date, changes in the expression of insect CSPs and OBPs to infection by a microbial (fungal) pathogen have not been directly examined

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