Recombination and genome evolution in Plasmodium falciparum

Plasmodium falciparum is the etiological agent of the most virulent form of human malaria. This parasite is known to be highly adaptable to the human host, evading the immune system through antigenic diversity and quickly developing drug resistance. This dissertation examines the influence of role of recombination in the rapid evolution of the P. falciparum genome. The first chapter is a broad overview of the micro- and macroevolutionary history of human malaria parasites, with a particular emphasis on its application to medical genetics, and presents the context for all subsequent chapters. The second chapter discusses the impact of recombination on the evolution of a pair of host-cell invasion proteins, the Plasmodium falciparum Reticulocyte Binding Protein homolog 2 gene paralogs. Using genetic and phylogenetic methods, it is revealed that these genes likely evolved by concerted evolution, homogenizing 90% of the genes. The significance of this is in both the frequency of recombination (as gene conversion) and the breakpoint location, at a low-complexity region. Chapter three examines a rapidly evolving gene family, the Plasmodium falciparum Acyl-CoA Synthetases. Though a stable family of four enzyme genes in most eukaryotes, it can contain twelve or thirteen genes in P. falciparum. Molecular biology and phylogenetic studies show the significant impact of recombination in this gene family, producing multiple species- and population-specific gene duplications and gene conversions. The fourth and fifth chapters examine the evolution of low-complexity regions in the P. falciparum genome, and their role as recombination breakpoints.For previously unknown reasons, these regions are unusually frequent in proteins of the P. falciparum genome. Though early concepts of their evolution emphasized their adaptive significance, this research supports evidence of only neutral evolution in all but a small subset of low-complexity regions. Regions in this small subset, however, are found to be associated with increased recombination in genes for surface antigens and host-cell invasion proteins. The final, concluding, chapter places the results from the preceding chapters in a broader context. Additional data is presented which elucidates the roles of recombination and gene family evolution in the rapid adaptive changes in the P. falciparum genome.