Comparative Analyses of Resistance Gene Evolution

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We will utilize a comparative genomics approach to understand the evolutionary forces and genetic events that have determined the outcome of the interactions between a major group of bacterial pathogens and diverse crop species. A broad range of genetic mechanisms has been shown to influence the evolution of disease resistance in plants. It is becoming apparent that different mechanisms may have been important at different stages and influence different parts of the resistance protein and that resistance genes may exhibit different rates of evolution. These different rates of evolution may be indicative of different characteristics of the pathogen ligands detected and suggest different efficacies in disease control strategies.We will characterize related series of bacterial proteins involved in pathogenicity, the plant targets they interact with, and the plant resistance genes that detect these genes. This will be done by: 1) identifying the majority of the so-called "Type III effector" genes in four strains of strains and species of the bacterial pathogen Pseudomonas; 2) determining the genetic variation in the plants ability to detect these effector proteins by analysis of diverse germplasm of lettuce, tomato, and Arabidopsis as well as a less detailed analysis of at least five other crop species; 3) isolating a subset of the plant targets of these effectors from Arabidopsis and the crop species; 4) characterizing the rates and evolution of known and novel resistance genes as well as the genes encoding the target proteins and to correlate the rates of evolution with the prevalence and fitness contribution of the ligands detected. This will provide a related series of these three interacting determinants of resistance and a matrix of the interactions between them. This will also provide insights into the basis of non-resistance and the potential durability of resistance genes.Understanding the molecular determinants of disease resistance has practical as well as fundamental importance. Lettuce and tomato are two of the top ten most valuable crops in the US and disease resistance is one of the most agriculturally important traits targeted in crop improvement programs. Understanding the molecular basis of specificity in plant-pathogen interactions and the events resulting in resistance will provide new possibilities for developing more durable disease resistance in pants and decrease the use of chemical protectants.