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SPECIAL SESSION: Genomics and Phenomics to Characterize Host Resistance

Genomics and Phenomics Approaches to Understanding Root-mediated Resistance to Ralstonia solanacearum in Tomato
Anjali Iyer-Pascuzzi - Purdue University. Denise Caldwell- Purdue University, Tri Tran- Purdue University, Katherine Rivera-Zuluaga- Purdue University, Rachel Hiles- Purdue University

Plant roots constantly defend themselves against soilborne pathogens. 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 bacteria and fungi that cause a large class of root diseases known as vascular wilts. Ralstonia solancearum (Rs), the causal agent of bacterial wilt disease, causes upwards of 90% disease loss during epidemics. Using the tomato – Rs pathosystem as a model, we are exploring the interplay between root development and disease in root-mediated 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 root global gene expression profiling after Rs infection demonstrated that roots of resistant plants alter auxin pathways after infection. Mutational analyses with tomato mutants with altered auxin pathways revealed the critical nature of auxin in bacterial wilt disease. We have optimized the tomato hairy root system to examine Rs type III effectors in tomato root infection and find effector localization to the nucleus, cytoskeleton, and plasma membrane of tomato roots. Our data suggest that root-mediated resistance operates at multiple scales – from subcellular to cellular and whole organ levels.