Pathogenicity chromosomes as Trojan horses: the costs of mobile DNA in pathogen evolution

Pathogenic Fusarium oxysporum (Fo) strains are host-specific and cluster genes involved in infection together with transposons on separate, dispensable pathogenicity chromosomes. Horizontal transfer of a pathogenicity chromosome can transform a non-pathogenic strain into a pathogenic one, yet for this soil fungus pathogenicity is the exception rather than the rule. This suggests that the costs of obtaining a pathogenicity chromosome counterbalance the positive effects of being able to infect a new host. One example of such a cost is the fact that transposons that reside on a pathogenicity chromosome may colonize and disrupt the rest of the genome.

We investigate the level and timescale of genome colonization by transposons from a transferred chromosome by reconstructing transferred chromosomes and subsequent transposon insertion events within several distinct Fo clonal lines. Moreover, we apply experimental evolution using strains that obtained pathogenicity chromosomes in the lab, to study genome dynamics directly after horizontal transfer, in vitro and in planta. Together these two approaches will give insight into the dynamics of genome organization and the likelihood of emergence of new diseases through horizontal chromosome transfer.