Evolution of a pathogen resistance pathway in the tomato genus

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In this project, we will investigate the selective forces that have shaped the evolution of five genes involved in resistance to a bacterial pathogen of tomato, Pseudomonas syringae pv. tomato. One of these genes, Pto, has been identified as the receptor for the pathogen ligand. Another gene, Prf, ist closely linked to Pto and is required for activating the resistance response once the pathogen has been detected. The other three genes encode proteins which physically interact with Pto and contribute to plant disease resistance. Our study will focus on DNA sequence variation in a natural population of the self-incompatible species, Lycopersicon peruvianum. Since these genes are involved in the same pathway, we will evaluate how position in pathway influences the selective constraints acting on these genes. Using linkage disequilibrium analysis, we will also determine if Pto and Prf show correlated evolution, as may be expercted due to their physical linkage and/or functional interaction.