En savoir plus

Abstract:

Interspecific associations are widespread in nature and occur at different levels of organism complexity, ranging from bacteria and protists associations to heteroclite species combinations involving plants and animals. In insects, most species thriving on nutritionally poor and unbalanced habitats house integrated intracellular bacteria (endosymbionts) that are transmitted vertically for million years and supplement the host diet with several metabolic products.

However, maintaining the beneficial nature of this long-term relationship constrains both the host and the symbiont to adaptive changes in their interactions. For instance, comparative genomics have shown that endosymbionts experience drastic genomic deletions and gene mutations, some of which impact bacterial virulence and their ability to be tolerated by the host. In Sitophilus-Sodalis association, we recently have demonstrated that genomic shrinkage occurs rapidly at early stages of symbiogenesis (Oakeson et al., 2014). An extensive IS element expansion was unraveled in the bacterial genome, which appears to have mediated numerous genome rearrangements, deletions, and duplications that might be beneficial to the association.

On the host side, the immune system is permanently struggling to keep beneficial symbionts while activating defense effectors to prevent pathogenic infections. We showed that cereal weevils have selected a “compartmentalization” strategy that consists to seclude endosymbionts within the bacteriome organ and to protect them from the host systemic immune response (Anselme et al., 2008; Masson et al., 2015). The bacteriome organ expresses selected immune effectors, including the Coleoptericin A antimicrobial peptide, which targets endosymbionts, inhibits their cell division, and prevents their externalization from the bacteriome (Login et al., 2011). Recently, we showed that endosymbiont load is under the control of a fine-tuned integration of symbiont costs and benefits, according to host developmental and physiological requirements. Weevil endosymbionts intensively multiply in young adults to support a massive need for tyrosine and phenylalanine required during insect cuticle tanning and hardening. Once the cuticle is achieved, endosymbionts are rapidly recycled through apoptosis and autophagy in a tissue-dependent manner that preserves female germline-associated endosymbionts and thus their transmission to next generations (Vigneron et al., 2014).

This talk will focus on evolutionary processes occurring during early stages of endosymbiont integration and on the host immune mechanisms involved in endosymbiont maintenance, control, and regulation.

References:

Anselme C. et al. 2008. Identification of the weevil immune genes and their expression in the bacteriome tissue. BMC Biology, 6: 43

Login F. et al. 2011. Antimicrobial peptides keep insect endosymbionts under control. Science 362-5

Oakeson K.F. et al. 2014. Genome Degeneration and Adaptation in a Nascent Stage of Symbiosis. Genome Biology & Evolution 6: 76

Vigneron A. et al. 2014. Insects recycle endsoymbionts when the benefit is over. Current Biology 24: 2267

Masson F. Systemic infection generates a local-like immune response of the bacteriome organ in insect symbiosis. Journal of Innate Immunity 2015 Jan 23. [Epub ahead of print]

Consulter la page de son laboratoire >>>