The tremendous role of microbiome in plant health and productivity is increasingly recognized, and has led to international initiatives to further explore and exploit the capabilities of Earth’s microbial ecosystems. One of the most significant environmental services that microbes play to plants is biological nitrogen fixation i. e. the capacity to convert atmospheric nitrogen in a reduced form utilizable by plants. During evolution thousands of species in a few angiosperm lineages have evolved a mutualistic symbiosis with nitrogen-fixing bacteria so that they directly benefit from fixed nitrogen and do not depend on nitrogen fertilizers for growth, contrary to most cultivated plants.
A major challenge of this century is to increase crop production while reducing the environmental impact of agriculture by reducing the use of fertilizers. This may take several paths, such as promoting pre-existing or new associative or endophytic nitrogen-fixing relationships with cereals, the engineering of the legume symbiosis into cereals or of cereals expressing nitrogenase. Achieving this goal requires better understanding of how the natural associations are established and have evolved, as well as developing innovative tools for optimizing current associations and engineering new symbioses.
The overall objective of the REPLAY project is to i) provide a better understanding of adaptive mechanisms leading to bacterial symbiosis with legumes, and ii) develop a conceptual and practical framework for the design of new nitrogen-fixing plant symbionts. REPLAY will use the biological material and findings generated during the experimental evolution of a plant pathogen, Ralstonia solanacearum, into a legume symbiont to address the following new and important questions: (i) have different evolutionary paths shaped the experimental evolution of symbiotic Ralstonia in different lineages? (ii) how can mutualism based on nitrogen fixation evolve from a parasitic interaction? (iii) how does lab-evolution compare to natural evolution of rhizobia? (iv) could plasmid mutagenesis cassettes be exploited to manipulate the evolvability of plant-associated bacteria in a biotech perspective?
REPLAY is a collaborative research project bringing together three partners with complementary and established expertise in plant microbiology, bacterial evolutionary genomics and bioinformatics. The scientific program is designed in four independent scientific tasks, each addressing one of the above questions. The project is unique worldwide in the field of plant-microbe interactions as it tentatively replays the evolution of a new rhizobial genus and tackles the emergence and evolution of a complex biotic interaction. In addition it will explore pathogenesis-symbiosis relationships and how a pant pathogen can rewire into a legume symbiont. The project is timely regarding the challenging goals of microbiome engineering for microbe-assisted crop production and developing nitrogen-fixing associations with cereals that would revolutionize world agriculture. The REPLAY project has received “Agreement” of the Competitive cluster Agri Sud Ouest Innovation.