P-446 - Spatial interplay between tryptophan-derived specialized metabolites, physical barriers and the Arabidopsis thaliana root microbiome

Plants are constantly confronted with complex environmental conditions. To survive in such a dynamic environment, they have evolved diverse physical and biochemical defense strategies, which are precisely balanced between the different -sometimes contrasting- demands they meet. When it comes to plant-microbe interactions, both resolute defense responses as well as  beneficial interactions are essential for plant health. While numerous studies investigate these associations, the majority either analyses whole roots of relatively young plants or focuses on developmentally young tissues like the root tip. Thus, it remains overlooked that with progressing age, an increasing proportion of the root system undergoes secondary growth. This radial expansion is achieved via the emergence of an exceptionally fortified tissue – the periderm. However, its role in resistance to microbial infection is almost entirely unknown. Here, we address this by using Arabidopsis thaliana mutants with disrupted periderm formation, grown under complex soil conditions. In summary, our spatially-resolved multi-omics approach reveals a tight association between a functional periderm and the spatially distinct activation of biochemical defences and their impact on fungal colonization and infection. This provides a model suitable to probe spatial aspects of root development and barrier deployment in the context of plant-microbe interactions and defenses under more natural, agriculturally-relevant conditions.