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The population genetics and functional analysis of the Pto disease resistance gene in Lycopersicon spp. and the RPP13 gene in Arabidopsis thaliana

Posted on:2003-02-04Degree:Ph.DType:Thesis
University:University of California, DavisCandidate:Rose, Laura EllenFull Text:PDF
GTID:2460390011486806Subject:Agriculture
Abstract/Summary:
Historically host-pathogen interactions have served as a rich source of evolutionary and ecological theory. The study of the genetic basis of the interactions between host and pathogen lies at the heart of many important issues in evolutionary theory. In this thesis, I explore the evolutionary genetic evidence for coevolution by studying the naturally occurring variation in resistance responses and sequence variation at resistance gene (R-gene) loci in species of Lycopersicon and Arabidopsis. The levels of sequence polymorphism and divergence at the Pto locus in Lycopersicon and the RPP13 locus in Arabidopsis are compared to the levels of variation at non-R gene loci in these same species; in both cases, the rate of amino acid evolution is shown to be higher at the R-genes. Inoculations and plant transformations are used to establish correlations between the naturally occurring amino acid sequence variation and pathogen recognition. The maintenance of functionally differentiated alleles in species of Lycopersicon and Arabidopsis is consistent with balancing selection operating to maintain allelic diversity at these loci.; Phylogenetic analyses are used to determine the age and rate of diversification of the Pto gene family. These analyses indicate that the origin of the Pto gene coincided approximately with the diversification of the genus Solanum. The specific amino acid changes along the branch subtending the clade of Pto orthologs are inferred to determine which changes may have been correlated with the acquisition of pathogen recognition. The functional effects of these changes are discussed in the context of what is known about the Pto protein in particular and protein kinases in general.
Keywords/Search Tags:Gene, Pto, Arabidopsis, Lycopersicon, Resistance
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