Group Leader Max Planck Institute for Biology Tübingen, Baden-Wurttemberg, Germany
Plant pathogens evolve rapidly to adapt to their host plants, new environments, or to compete for environmental niches. Genome structure and maintenance are crucial for ensuring such rapid adaptation while maintaining house-keeping functions. Plant pathogen genomes are often structured heterogeneously, harboring highly dynamic compartments and compartments of relative stability. Rapidly evolving, virulence-related genes are often encoded in dynamic regions, that are rich in transposable elements. An extreme case of such genomic structural compartmentalization are supernumerary mini-chromosomes (mChr), that show presence-absence and extensive structural variation within a species, thereby contributing to their overall genetic diversity. However, their role in adaptive evolution is still poorly understood. We identified highly diverse mChrs in the wheat and rice infecting blast fungus, Magnaporthe (syn. Pyricularia) oryzae, including a mChr that is rare in the rice-infecting but prevalent in wild grass-infecting lineages. Combining experimental and population genomics methods, we show that this mChr was recurrently horizontally transferred between wild pathogen populations and rice infecting isolates, suggesting that wild pathogen populations can act as genetic reservoir for gene flow between host-adapted lineages. Here, I will discuss recent progress we made towards understanding mChr biology and their contribution to gene flow and adaptive evolution in the blast fungus.
