P-277 - Evolution in action: ongoing chromosomal rearrangements drive Verticillium dahliae adaptation and host colonization

Verticillium dahliae is a pathogenic fungus that infects hundreds of plant species. Its two-speed genome, characterized by the compartmentalization of core and plastic genomic regions, drives fungal evolution. Adaptive genomic regions (AGRs) represent the plastic component of V. dahliae's genome, enriched in virulence genes, transposable elements, and heterochromatin, and often associated with large chromosomal rearrangements. While these rearrangements are hypothesized to facilitate V. dahliae genome evolution, it remained unclear whether they are the product of ancient events that surface because of selection events or continue to arise due to novel rearrangement events.

To address this, we investigated whether chromosomal rearrangements actively form in V. dahliae. In an experimental evolution approach, we performed repeated inoculations of a poorly adapted V. dahliae strain on Arabidopsis while re-isolating the fungus from the first symptomatic plants after each inoculation round. Notably, we obtained one evolved strain that exhibited an inter-chromosomal rearrangement, allowing enhanced plant colonization, not only on Arabidopsis but also on tomato. We are currently trying to understand how the chromosomal rearrangement enhanced the ability of the evolved strain to colonize plants. However, importantly, our findings demonstrate that chromosomal rearrangements continue to occur in extant strains and play a crucial role in V. dahliae genome evolution.