How does ploidy level impact repetitive DNA? Insights from di-, tetra- and hexaploid populations of Orobanche gracilis

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Repetitive sequences, such as ribosomal rRNA genes, satellite DNA, and dispersed mobile genetic elements, play an essential role in plant genome evolution. This is due to their effects on genome size (they are main contributors to genome size increases), gene evolution, gene regulation, and gene expression. Despite this essential role, we know little about the individual contributions of different repetitive DNA types to plant genome evolution. We will apply 454 pyrosequencing to characterize repetitive DNA in a group of nonphotosynthetic flowering plants that show contrasting genome dynamics. Previous work on the holoparasitic Orobanche and Phelipanche has shown that they differ in ploidy levels, range of nuclear genome sizes, and retroelement diversity. We will test the hypothesis that this is mainly due to their repetitive DNA fractions by comparing four species of Orobanche and three of Phelipanche that exemplify these differences. Specifically, we will identify the kinds of repetitive DNA responsible for genome differentiation in (i) species groups of different ages, (ii) species with narrow vs. wide host ranges, (iii) perennial vs. annual species, and (iv) diploid vs. a polyploid species. Next-generation sequencing technology has already proven successful to address these types of questions. The primary novelty of this project is the broad comparative context, which will allow assessing evolutionary trends. That all members of Orobanche and related genera are holoparasites and that some have been shown to harbor horizontally transferred genes furthermore may allow assessing the role of retrotransposons in HGT.