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Title: “Getting to the root of plant disease resistance in tomato”

Host: Jamie Van Norman

Abstract: Plant roots constantly defend themselves against soilborne pathogens, and root diseases are a severe limiting factor in crop production throughout the world. Although roots are often critical to whole plant resistance, root defense responses are not well understood. Our long-term goal is to decipher the mechanisms of root-mediated resistance to the soilborne pathogens that cause a large class of root diseases known as vascular wilts. Ralstonia solancearum, the causal agent of bacterial wilt, is one of the most globally destructive soilborne bacteria. Using the tomato – R. solanacearum pathosystem as a model, we are exploring the role of root architecture, root anatomy, and the root microbiome in resistance. Light and scanning electron microscopy revealed that bacteria are differentially distributed in tomato root cell types of resistant and susceptible varieties, and that resistant plants delay colonization of the root vasculature. A time-course of tomato whole root global expression profiling after R. solanacearum infection demonstrated that roots of resistant plants activate defense responses faster than their susceptible counterparts and alter auxin pathways after infection. Subsequent mutational analysis in tomato revealed the critical nature of auxin in bacterial wilt disease. Preliminary results from 16S amplicon sequencing reveal quantitative differences in the root microbiome between resistant and susceptible plants. Our data suggest that root-mediated resistance to R. solanacearum in tomato is due to differences in root transcriptional events, hormone signaling, and in the microbiome.