The goal of this project is to investigate the molecular basis for the virulence of Melampsora larici-populina towards Populus species. Genome-wide, high-throughput screens will be used to identify pathogen effectors that suppress host immunity, host factors that are targets of pathogen effectors, as well as the components of poplar nutrient homeostasis that are hijacked by the pathogen to establish disease. This information will shed new light on the mechanism of rust-poplar interactions, and will enable the construction of transgenic poplars as a resource for the research community to accelerate the evaluation of disease models.