We will block you: The Interplaying role of chemical and physical barriers in roots

Lecture with Professor, Dr. Tonni Grube Andersen, Max Planck Institute for Plant Breeding Research.

Abstract

Roots represent long-lived interfaces with complex soil microbial communities, yet how mature root barrier tissues regulate host–microbe interactions remain poorly understood. During secondary growth, the periderm replaces outer root tissues and becomes the dominant interface between plants and soil. In this work, we show that the periderm functions as a microbiome control interface that links barrier integrity to chemical defence, fungal colonization, community assembly, and plant performance in soil. Transcriptome profiling revealed that disruption of periderm formation triggers a wound-like transcriptional program enriched for tryptophan-derived defence metabolism confined to mature periderm-containing root tissues. Spatial metabolite profiling demonstrated pronounced chemical zonation along the root axis, with tryptophan-derived metabolites enriched in mature root regions and redistributed upon barrier impairment. These metabolites restricted fungal colonization in mono-association experiments and influenced fungal community composition in natural soil. Plants lacking either periderm integrity or tryptophan-derived defence metabolism exhibited moderate growth reductions, whereas simultaneous disruption of both defence layers resulted in a pronounced fitness penalty. Together, our findings establish a causal chain linking periderm integrity to the deployment of spatial defence, fungal community assembly, and plant performance. Taken together, we propose that the periderm acts as a dynamic interface that integrates barrier function, chemical immunity, and microbiome assembly in mature roots.