Host jump enabling factors in a fungal/grass pathosystem

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Smut fungi are biotrophic pathogens which infect mainly grasses, among them important cereal crop plants like barley, wheat, corn, sorghum, sugarcane and forage grasses. The so far 1200 smut fungi species identified show relatively strict host specificity and can infect in sum up to 4000 different plant species. The host range of a pathogen is likely a product of the acquisition of novel or adapted virulence factors (like small secreted proteins, so called effectors) or/and loss of avirulence factors (avr-Genes). On the host side the lack of restricting molecules like for example specific R-genes that would lead to strict defense responses or quantitative traits that in sum would lead to resistance can limit the host range of the pathogen. We identified interspecific mate pairs between Ustilago bromivora and different other grass-infecting but not Brachypodium infecting smuts which are able to cause infection symptoms and full completion of their lifecycle as hybrids on the model grass Brachypodium distachyon..This finding is the basis to dissect exemplary the molecular basis of host jump enabling factors by the employment of a genetic backcross approach assisted with comparative genomic approaches. Host jump events caused severe damage in the past and will also be in the future a constant threat to crops. Beside their economic importance an understanding of the molecular basis will have also impact on our view on evolutionary aspects of the ~1200 smuts and maybe beyond.