Soutenance de l'Habilitation à Diriger des Recherches en sciences : Anna Rachel ZAIDMAN

Insect immune regulations, in pathogenesis and mutualism

Maître de conférences : Anna Rachel ZAIDMAN

Laboratoire INSA :  BF2I

Rapporteurs :

• Mme Destoumieux-Garzón Delphine
• M. Imler Jean-Luc
• M. Rolff Jens

Jury :    

• Mme Destoumieux-Garzón Delphine
• M. Imler Jean-Luc
• M. Leulier François
• Mme Popowycz Florence
• M. Rolff Jens
• Mme Valiente Moro Claire

Immune regulations are essential in all animals as they maintain a balance between defence activation against pathogenic microorganisms, and immune homeostasis in the presence of commensal or mutualistic bacteria. This immune homeostasis preserves the beneficial bacteria and limit the damage of a chronic activation on the host itself. My research focusses on the study of immune regulations and host-bacteria interactions in insects, with a functional genomic approach.
I first studied immune regulations using the Drosophila melanogaster genetic model. During my PhD I described the function of an enzyme belonging to the conserved family of the PeptidoGlycan Recognition Protein (PGRP) in the modulation of humoral immunity. PGRP-LB restricts the induction of local and systemic immune responses to severe infections, and avoids chronical activation in presence of gut commensals. During my post-doc, I focussed on the regulation of another side of immunity, the cellular responses, and showed that these responses are synchronized with the insect development through a hormonal signal. This signal increases their efficiency at a critical moment of the insect’s life, the metamorphosis of the larva into an adult.
Many insects do not only interact with pathogenic or gut commensal bacteria, but also with heritable mutualistic symbiotic bacteria. Indeed, it is estimated that 20% of insects, including many strongly impacting human health or agricultural activities, have established long-term relationships with nutritional intracellular bacteria (endosymbionts). Nutritional endosymbioses are considered as a driving force of insect adaptive success: endosymbionts provide their hosts with nutrients lacking in their diet, allowing insects to thrive on unbalanced habitats. The symbiotic bacteria are transmitted vertically over host generations. They are housed in specialized host cells, the bacteriocytes, which isolate endosymbionts from the systemic immune system, and constitute the endosymbiont-insect interface for nutrient biosynthesis and exchange. Since 2013, I switched to a model that allows me to address the importance of immune regulations in the context of endosymbiosis: the association between the cereal weevil Sitophilus sp. and the bacteria Sodalis pierantonius. I present in this HDR three research axes developed together with PhD students and colleagues of the Symbiosis and Immune Signalling group, in the “Biologie Fonctionnelle, Insectes et Interactions” lab.
In a first research axis, we demonstrated that in cereal weevils, one of the canonical insect immune signalling pathway, the Imd/Relish pathway, is not only involved in the defence against pathogenic infections, but also functions in the control of endosymbiotic bacteria. We further showed that this pathway regulates the expression of a key regulator, the enzyme PGRP-LB, which expression in the bacteriocytes is important to maintain the host immune homeostasis in an endosymbiotic context. In a second research axis, we deciphered the mechanisms involved in symbiosis integration with the host development during the insect metamorphosis, and demonstrated an active role of endosymbionts in this process. In a third research axis, we address the integration of endosymbiotic bacteria at a cellular scale, to identify the cell ultrastructures that ensure the nutrients exchanges between the bacteria and host. My current project is to understand the functioning of the very efficient « metabolic factories » formed by the bacteria and bacteriocytes, at a cellular and genetic level.