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Download 1 Sequence evolution of the disease resistance genes Rcr3 and
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Sequence evolution of the disease resistance genes Rcr3 and Rin4 in wild tomato (Lycopersicon peruvianum) Diploma Thesis by Anja Hörger Summary The objective of my diploma thesis was to reveal evolutionary forces, which are working on the two disease resistance genes Rcr3 and Rin4 in the wild tomato species Lycopersicon peruvianum. Both genes are involved in different disease resistance pathways. Knowledge of evolutionary mechanisms shaping these two genes will contribute to the understanding of the evolution of disease resistance pathways in plants. To reveal the evolutionary history of Rcr3 and Rin4 I amplified and sequenced both genes and analyzed them with population genetic methods. As basic material I used ten individuals of the L. peruvianum accession LA2744 and one individual of the species Solanum lycopersicoides as outgroup. Rcr3 revealed itself as putative paralogue within an old gene family, which occurs in several Lycopersicon species. There is also evidence that Rcr3 was duplicated within the genome of L. peruvianum again. The Rcr3 interacting guard molecule Cf-2 is part of a gene family as well. Therefore, duplication events of both interaction partners could be the consequence of specific coadaption of these two genes. The Rcr3 gene shows evidence of purifying selection. There is little nucleotide diversity within the gene and expectations under neutrality were not met in almost all kinds of neutrality tests I performed. These observations support the assumption that Rcr3 is tightly integrated in its disease resistance network and therefore has to be highly conserved. Additionally, the specific interaction between Rcr3 and Cf-2 should contribute to purifying selection as well. For the Rin4 gene I reported a very low level of nucleotide diversity as well. Tests of neutrality could not be rejected significantly, but all results tended to show a 1 limitation of the variation due to purifying selection. These findings are very likely for the Rin4 gene as well. The Rin4 protein is involved in an extremely complex signaling system of herbal disease resistance. It is known to interact with at least seven - probably even more - different resistance-mediating factors. All these interactions are realized in different ways. To keep all these ways of interaction stable, a high level of conservation within the Rin4 gene is required. 2