Associations between eukaryotes and microorganisms are frequently observed in nature. They are highly diverse and range along a continuum between parasitism and mutualism. Although numerous symbiotic associations have been well described at the phenotypic level, the mechanisms involved in the maintenance of the association and their evolutionary consequences are rarely studied. However, the presence of a permanent resident can have direct consequences on the host developmental program and immune system, and dramatically change the outcome of a secondary infection by a pathogen. As the oxidative environment is known to play pleiotropic roles in development and immunity, I propose to determine to what extent its control plays a role in the stability of symbiotic associations and in the evolution of both partners.
To address these issues, I plan to work on various symbiotic associations, differing in the characteristics of the symbiotic relationship. I will focus on two monospecific interactions between invertebrates and bacteria (Squid/Vibrio, Insect/Wolbachia), natural but easily examined systems for defining the biochemical/genetic events that underlie long-term infection by non-pathogenic bacteria. In each model system, I will first characterize the molecular mechanisms involved in the control of the oxidative environment, then determine how the oxidative environment varies in response to symbiosis, and finally assess to what extent its regulation affects the stability of the symbiosis. In particular, I propose to determine if: 1) the symbiont manipulates the host oxidative environment to favour its maintenance, 2) the host evolves to tolerate the presence of the symbiont, and 3) changes of the oxidative environment only constitute a by-product of the symbiotic association. Finally, the comparative analysis will allow me to determine potential shared mechanisms that play a key role in the maintenance of symbiotic associations.
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