Origin and evolution of intracellular symbioses in plants

ongoing

Mutualism between plants and microorganisms has been essential for the evolution of terrestrial ecosystems for millions of years. It has been proposed that even the colonization of lands by plants was facilitated by a mutualistic symbiosis formed with arbuscular mycorrhizal fungi. This symbiosis, by far the most widespread in land plants, results in the accommodation of the symbiotic fungus inside the plant cells. Following this initial symbiosis, multiple other intracellular symbioses have evolved in plants as diverse as orchids, Ericaceae such as cranberry, legumes or the Jungermanniales, a group of bryophytes. These symbioses provide numerous benefits, improving plant nutrient acquisition and fitness. Despite their absolute importance in terrestrial ecosystems, the molecular mechanisms underlying the origin and subsequent evolution of intracellular symbioses in plants remain poorly understood. In a first objective, we will use CRISPR/Cas9 in the bryophyte Marchantia paleacea to test the conservation across land plants of symbiotic mechanisms known in angiosperms. Then, we will decipher how these mechanisms evolved by comparing land plants with their closest algal relatives. In a second objective, we will conduct transcriptomics coupled with genetic manipulations of most known intracellular symbioses in plants. This will allow determining how the ability to host intracellularly microbial symbionts recruited in the environment evolved repeatedly in land plants and how functional specificity evolved in these different symbioses. Lastly, we will investigate why the evolution of intracellular symbioses is constrained to a unique genetic pathway. Through this project, combining phylogenomics, biochemistry, transcriptomics and genetic validations in six plant lineages covering more than 500 million years of evolution, we will provide a comprehensive understanding of the molecular mechanisms underlying the evolution of intracellular mutualistic symbioses in plants.