Abstract
The field of microbial symbiosis has achieved astonishing advances during the past two decades demonstrating its universality and significance in multicellular life and evolution. For example, it has been estimated that microbes in the human body collectively make up to 100 trillion cells. The majority resides in the gut and has a profound influence on human nutrition and physiology. Accordingly, disequilibrium of the gut microbiome has been shown to be often associated with immune-related diseases. /nInsects, such as Drosophila, are developing models to decipher microbial interactions. Insights can also be expected from the study of insects thriving on nutritionally poor habitats that have evolved long-term mutualistic relationships with one or a few endosymbiotic bacteria. These bacteria are vertically transmitted and are housed within specific host cells, the bacteriocytes that are thought to isolate endosymbionts and protect them against a systemic host immune response. However, whilst physiological and evolutionary features of these insect associations have been investigated in detail over the past decades, current knowledge of specific host factors leading to endosymbiont tolerance, localization, transmission and control by the host remains limited. It is suggested that components of host immunity are in a constant struggle between managing beneficial symbionts while turning on host defenses to prevent pathogenic infections. /nHere, we will investigate insect immune and metabolic regulations potentially involved in endosymbiont maintenance and control, as well as explore the effects of endosymbionts on insect immune performance. Our focus will be on the comparison of two agronomic pest insects that have different and independent evolutionary and symbiotic histories. The cereal weevil Sitophilus oryzae, a holometabolous insect, exhibits an evolutionary recent symbiosis with strictly one primary endosymbiont, while the pea aphid Acyrthosiphon pisum, a hemimetabolous insect, lives a relatively old association with one primary and several secondary endosymbionts. These insects are expected to become emerging models in functional genomics thanks to the recent initiatives in genome and transcriptome sequencing and to the development of new genetic, and cellular experimental tools. We will use a multidisciplinary approach to understand the links between humoral immune responses, hemocyte and bacteriocyte immune function and specificity, and metabolism, so as to decipher the role of these different players in endosymbiosis homeostasis. We expect from this project to open new insights into insect symbiosis establishment and maintenance and to identify potential gene targets useful for the development of new strategies for pest insects control and management.
France