Transposons and genome evolution

Transposable elements and repeats in genomes have for a long-time been regarded as ‘junk’, and as a danger to genome stability. However, recent results suggest that transposable elements play important roles as facilitators of (adaptive) genome evolution.

Transposable elements (also known as transposons) are highly repetitive and thus abundant DNA sequences that can alter their position within a genome. Many eukaryotic genomes contain a large proportion of transposable elements. For example, around 50% of the human genome is considered to be of repetitive nature. Due to their mobile nature, transposable elements can cause genomic alterations such as chromosomal breaks or gene knock-outs, and thus have been considered a threat to genome stability, and a cause of many diseases.

Transposable elements are also abundant in many plant pathogens. For example, repeats and transposable elements account for ~74% of the genome of the late blight pathogen Phytophthora infestans. Notably, transposable elements and other repeats are enriched in distinct genomic regions that also contain so-called effector genes that code for proteins with crucial roles in the interaction between pathogens and their hosts. These regions are highly variable, displaying frequent sequence polymorphisms. Transposable elements have therefore been hypothesized to play important roles in genomic variability. However, the exact roles of transposable elements in the genome evolution of plant pathogens remain largely unknown. We study the evolution of repeat-rich compartments in different filamentous pathogens. By using long-read sequencing technologies and comparative genomics, we have recently demonstrated how transposable elements contribute to evolution of variable genomic regions in the vascular wilt pathogen Verticillium dahliae. Variable genomic regions evolved independently in different pathogens, and thus we aim to determine if similar molecular mechanisms operate in different species. Moreover, we study the activity and evolutionary dynamics of transposable elements to shed light on their adaptive roles in short and long evolutionary time scales.