4. Dr. Elisa Korenblum

The first step in plant-microbe interactions is usually chemical-based, e.g. plant roots and rhizosphere microbes exchange various chemical signals, nutrients, and metabolites. The metabolites exuded by the roots shape the composition of the root microbiota; that is, plant roots select specific soil microbial populations and can govern microbial activity for their benefit. The focus of my research is to decode these chemical dialogues to understand the complex interactions belowground between plants and microbes. Interestingly, the plant microbiome may also trigger, on the host side, a sequence of events from signal perception to metabolic changes locally (at the colonization site) or at distal parts of the plant. By conducting a series of split-root experiments in tomato plants, where half of the root system of each plant was treated with a soil microbiome, and the other half was grown in sterile conditions, we analyzed the systemic changes in the host metabolome and transcriptome controlled by a local root microbiome colonization. We found that the root microbiome induces systemic metabolic responses and changes tomato root exudation via root-to-root signaling. We termed this process “SIREM” for “Systemic Induced Root Exudation of Metabolites”. SIREM is chemically diverse and microbiome specific. For instance, in tomato plants, systemic exudation of specific acylsugars is associated with local colonization of bacteria affiliated with the Bacillales. We also discovered that glycosylated azelaic acid is microbiome induced and might act as a mobile signal in SIREM. SIREM is a microbiome-reprogrammed systemic root exudation that governs carbon sink in the rhizosphere. SIREM and the entire metabolic circular economy in the rhizosphere present a so far underexplored chemical diversity that may regulate soil conditioning and plant-soil feedbacks in natural and agricultural systems.