Plant Roots Employ Cell-Layer-specific Programs to Respond to Pathogenic and Beneficial Microbes

Plant roots are built of concentric cell layers that are thought to respond to microbial infections by employing specific, genetically defined programs. Yet, the functional impact of this radial organization remains elusive, particularly due to the lack of genome-wide techniques for monitoring expression at a cell-layer resolution. Here, cell-type-specific expression of tagged ribosomes enabled the isolation of ribosome-bound mRNA to obtain cell-layer translatomes (TRAP-seq, translating ribosome affinity purification and RNA sequencing). After inoculation with the vascular pathogen Verticillium longisporum, pathogenic oomycete Phytophthora parasitica, or mutualistic endophyte Serendipita indica, root cell-layer responses reflected the fundamentally different colonization strategies of these microbes. Notably, V. longisporum specifically suppressed the endodermal barrier, which restricts fungal progression, allowing microbial access to the root central cylinder. Moreover, localized biosynthesis of antimicrobial compounds and ethylene differed in response to pathogens and mutualists. These examples highlight the power of this resource to gain insights into root-microbe interactions and to develop strategies in crop improvement.