Abstract
BackgroundWolbachia are vertically transmitted bacteria known to be the most widespread endosymbiont in arthropods. They induce various alterations of the reproduction of their host, including feminization of genetic males in isopod crustaceans. In the pill bug Armadillidium vulgare, the presence of Wolbachia is also associated with detrimental effects on host fertility and lifespan. Deleterious effects have been demonstrated on hemocyte density, phenoloxidase activity, and natural hemolymph septicemia, suggesting that infected individuals could have defective immune capacities. Since nothing is known about the molecular mechanisms involved in Wolbachia-A. vulgare interactions and its secondary immunocompetence modulation, we developed a transcriptomics strategy and compared A. vulgare gene expression between Wolbachia-infected animals (i.e., “symbiotic” animals) and uninfected ones (i.e., “asymbiotic” animals) as well as between animals challenged or not challenged by a pathogenic bacteria.ResultsSince very little genetic data is available on A. vulgare, we produced several EST libraries and generated a total of 28 606 ESTs. Analyses of these ESTs revealed that immune processes were over-represented in most experimental conditions (responses to a symbiont and to a pathogen). Considering canonical crustacean immune pathways, these genes encode antimicrobial peptides or are involved in pathogen recognition, detoxification, and autophagy. By RT-qPCR, we demonstrated a general trend towards gene under-expression in symbiotic whole animals and ovaries whereas the same gene set tends to be over-expressed in symbiotic immune tissues.ConclusionThis study allowed us to generate the first reference transcriptome ever obtained in the Isopoda group and to identify genes involved in the major known crustacean immune pathways encompassing cellular and humoral responses. Expression of immune-related genes revealed a modulation of host immunity when females are infected by Wolbachia, including in ovaries, the crucial tissue for the Wolbachia route of transmission.
Highlights
Wolbachia are vertically transmitted bacteria known to be the most widespread endosymbiont in arthropods
First reference transcriptome in isopods Expressed Sequence Tag (EST) were generated from seven high quality cDNA libraries, including four Suppression Subtractive Hybridization (SSH) libraries, two non-normalized libraries and one normalized library
The different EST libraries generated in this study constitute the first reference transcriptome ever obtained in the Isopoda group [51]
Summary
Wolbachia are vertically transmitted bacteria known to be the most widespread endosymbiont in arthropods. Deleterious effects have been demonstrated on immunocompetence of infected females [10,11] These females have a lower hemocyte density, a decrease in PO activity, and a more severe hemolymph septicemia that could result in a reduced life span in A. vulgare [10,11]. This latter effect could impact host fitness including lower or higher resistance to intruders as it has been shown in many insect species [12]. Host immune genes are up-regulated in Ae. aegypti [17] and Anopheles gambiae [18] when infected by wMelPop
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