Molecular basis of the relationship between microbiota and the plant’s immune system

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This project will identify principles of microbiota recognition by the plant’s immune system and evaluate a role for immunity in hosting a microbiota.Critical to many aspects of eukaryotic health are the intimate associations hosts form with the micro-organisms of their biotic environment. Plants are able to tolerate and even promote associations with commensal or beneficial microbes while retaining the ability to defend microbial pathogens. Hosting a microbiota represents a long-term microbial load that can provoke lasting immune stimulation.Plant immunity is triggered upon sensing of pathogens. Like animal Toll-like receptors (TLRs), plant immune receptors recognize bacterial molecular patterns that are present across bacterial families. Induction of plant immunity is characterized by acute, transient and moderate, sustained defences. How bacterial communities are sensed by the plant immune system and how perception leads to association with microbiota but immunity against pathogen colonization is an incomplete understood process.Using state-of-the-art proteomics methods such as metaproteomics and parallel reaction monitoring (PRM), we will define at a community and family level the bacterial molecular patterns, and the types and abundancies present in a hosted microbiota. Bacterial EF-Tu and flagellin are molecular patterns abundantly found in the phyllosphere microbiota and are recognized by the EFR and FLS2 receptors of the plant’s immune system, eventually inducing defenses to control bacterial infection. We will reveal the EF-Tu and flagellin eliciting complement that is perceived by the host upon colonization with synthetic bacterial communities and aim at identifying potential novel molecular patterns found in microbiota. We will also test plants upon induction of pattern-triggered immunity, at the level of the microbiota eliciting complement, and plants deficient in immunity for their ability to achieve microbial homeostasis and community composition. By infecting with a bacterial pathogen, we will evaluate whether induction of plant immunity by the microbiota is critical for the establishment of successful defence.At its completion, this project will define principles how immune perception occurs in the long-term association with bacterial communities, and lead to new insight into immunity mechanisms leading to microbial homeostasis. This will pave the way for an improved understanding of a fundamental question in plant-microbiome interactions.