Dissertation Research: Mechanisms Maintaining Variation for Disease Resistance at Rpm1 in Arabidopsis thaliana

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Kreitman 9800957 Plant species generally exhibit variation for resistance to disease. This striking observation implies that a balance of opposing forces acts to maintain variation for disease resistance. Since the cost imposed by disease would drive populations toward increased resistance, a trade-off should oppose increased resistance to account for the observed variation. In the model plant species Arabidopsis thaliana, a balance of opposing forces maintains molecular variation at disease resistance gene Rpm1. The proposed research will investigate the origin and determinants of variation for disease resistance within populations. High through-put methods will allow genotyping of hundreds of A. thaliana individuals from local populations in Indiana and Michigan. Analyses will measure associations between Rpm1 and nearby genetic markers. Little association would support a balance within populations, while greater association would support a balance due to migration among populations where different forces dominate. Arabidopsis disease resistance has come under intense study recently, and the ecological and evolutionary work proposed here will complement molecular genetic work on this system. Plant disease resistance must be understood to facilitate the management of disease in crops, for assessing planting strategies and predicting the impact of disease in natural plant populations and weeds. Furthermore, plant disease resistance can be compared with the animal immunity for a more general understanding of the pressures pathogens place on host species. This project continues in the vein of Kreitman's work on the fruit fly Drosophila, at the interface between population genetic theory and empirical data. Arabidopsis Rpm1 is a strong example of balancing selection maintaining molecular variation. Continuing study of Rpm1 will help elucidate the patterns and processes shaping genetic variation and change. Finally, the proposed work continues to develop Arabidopsis as an important new model organism for population genetics. Arguably, no other model organism affords as much potential for interplay with ecology and genetics, both well-established fields in Arabidopsis biology.