Getting to the Root of Bacterial Wilt Resistance in Tomato

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 bacteria and fungi 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, and causes upwards of 90% disease loss during epidemics. Using the tomato – R. solanacearum pathosystem as a model, we are exploring the role of root architecture, root anatomy, and root cell-type specific transcriptional programs 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. Consistent with this, a time-course of tomato whole root expression profiling after R. solanacearum infection demonstrated that roots of resistant plants activate defense responses faster than their susceptible counterparts. We find that R. solanacearum infection differentially alters the root architecture of resistant and susceptible plants. Changes in the whole root transcriptomic programs after infection identified root development genes that likely function in these root architecture changes. Our data suggest that root-mediated resistance to R. solanacearum in tomato is due to a combination of root developmental and transcriptomic changes.