| Non-sexual or ?horizontal? gene transfer has played a decisive role in evolution of bacteria, notably in their ability to interact with the environment and to cause disease in plants and animals. Recent breakthrough discoveries have demonstrated that this also holds for fungi, leading to a new view on fungal evolution and in particular on fungal pathogenicity towards plants. It has now become clear that entire chromosomes consisting of millions of DNA base pairs can travel from one individual fungal strain to another without need for a sexual cycle. In my group we have demonstrated this experimentally: a chromosome containing virulence genes was transferred from a pathogenic strain to a previously harmless strain. The latter thereby acquired pathogenicity towards tomato plants. Currently, despite its obviously large impact on evolution of pathogenicity in fungi and on the emergence of novel diseases, virtually nothing is known about the mechanism of horizontal chromosome transfer. From a cell biological perspective, the occurrence of this process raises a number of exciting questions, like: 1) how do particular chromosomes survive the incompatibility reactions common in fusions between different fungal strains? 2) do chromosomes exit and/or enter a nucleus? 3) only few chromosomes appear amenable for transfer ? which unique features are responsible for that? This project aims to answer these questions and analyse the impact of chromosome transfer on the evolution of host-specific pathogenicity, using the plant-pathogenic fungus Fusarium oxysporum as a model. A threefold approach is proposed. First, a genomics approach will be used to reconstruct evolution of pathogenicity chromosomes with different host-specificities. Second, a genetic approach will identify genes required for chromosome transfer and determine ?transferability? of individual chromosomes. Third, in a cytological approach actual transfer events will be visualized with fluorescence microscopy and the unique features of transferable chromosomes will be determined on the chromatin level. |
