adapTEd · The role of adaptive evolution in the success of transposable elements

All eukaryotic genomes contain transposable elements (TEs), sequences that duplicate themselves semi-autonomously. Although TEs can have beneficial effects, the vast majority of TE insertions are thought to be either neutral or deleterious. TEs can be harmful because they disrupt important sequences, such as regulatory elements and protein-coding sequences, attract epigenetic markers that can alter expression, and lead to duplication, deletion and rearrangement of DNA through ectopic recombination. Hosts therefore have mechanisms to repress the transposition of TEs, repression that TEs are under selection to avoid. To accomplish this, it is expected that TEs should be undergoing adaptive evolution. In this project we propose to test (i) whether TEs are undergoing adaptive evolution at the primary sequence level, (ii) whether TEs assimilate host gene fragments as a means to escape host silencing, and (iii) whether either strategy leads to an increase in TE success. We will investigate these questions in plants using examples of the two broad classes of TEs: the Sireviruses (class I LTR retrotransposon), and Mutator (class II DNA transposon). We will consider the evolution of these two families in maize and Arabidopsis thaliana, species that have very different genome sizes and numbers of TEs. To the best of our knowledge, the project represents the first attempt to elucidate the correlation between TE evolution and TE success, and only the second attempt to analyze patterns of adaptive evolution in either plant or animal TEs. Based in a highly successful research group in a worldwide recognized institute, and among a network of collaborators across Europe and USA, it will allow the applicant to obtain a strong background in population genetics theory, molecular evolution, and the implementation of state of the art statistical analysis and mathematical modeling.