Context and objectives This research project on plant-plant interactions is part of the current context of pesticide reduction and the development of innovative solutions for a more environmentally friendly agriculture. New knowledge on the natural mechanisms that allow plants to adapt to their environment is essential in this context. The objective of this project is to identify the genes involved in plant-plant interactions due to the release in the rhizosphere of specialized metabolites, known as allelopathy. The identification of the genes involved in these interactions will allow, for example, the selection of varieties that repress the development of weeds or genotypes adapted to plant associations. Like animals, plants are able to communicate with each other’s by producing and releasing chemical compounds. The release of these chemical compounds, that can be beneficial (cooperation) or harmful (competition), can occur in the air (volatile compounds) or in the soil. Despite the importance of allelopathy in shaping plant communities or in the success of invasive plants, the molecular mechanisms involved in these interactions are still poorly understood. This project aims to elucidate plant-plant communication within the rhizosphere, by identifying novel allelochemicals and novel mechanisms of action, together with the genes involved in the biosynthesis and the perception of these molecules. With the selection of genotypes with strong potential in weed suppression or with a good aptitude for association with other genotypes/species, this project will contribute to the current challenge of the agroecological transition of agriculture. Identification of genes involved in allelopathy Plant-plant interactions involve a complex combination of competition for nutrients, light, water that can hide the allelopathic processes occurring in the soil. In a Plant2pro project (ALLELO), we have developed methods (based on Plant Soil Feedback effect) to estimate the allelopathic phenotype of Arabidopsis accessions using the phenotyping platform of IJPB (Phenoscope). We have combined the phenotyping of allelopathy for the large collections of sequenced Arabidopsis accessions with genetic approaches (Genome-Wide Association Study (GWAS)) to identify genomic regions and candidate genes associated with allelopathy. The Genome Wide Association (GWA) mapping based on data generated by next generation sequencing technologies and the development of new analytical methods (collaboration O. Loudet (IJPB), F. Roux (LIPM)) make it possible not only to determine the genetic architecture of a quantitative trait (allelopathic effect, response to allelopathic effect) but also to finely map genomic regions (Single Nucleotide Polymorphisms (SNPs)) associated with phenotypic variation. In well-chosen populations of A. thaliana accessions, the mean linkage desequilibrium (r² = 0.5) can be very short (~18 bp) and extends up to the gene level (20). We are currently using heterogeneous inbred family (HIF) and mutants to validate genomic regions and candidate genes of particular interest (involved in glucosinolates biosynthesis or coumarine metabolism).