How a fungal pathogen evolved host specialization by chromosomal rearrangements
Our paper on host specialization by chromosomal rearrangements in a fungal pathogen of wheat just came out in The ISME Journal and is now available online:
Despite the use of fungicides and resistant crop varieties, fungi cause major economic losses in agriculture. One major concern is the ability of plant pathogens to circumvent crop resistance and adapt to exploit the host. In plant-pathogen interactions, the specific recognition of a pathogen effector by a host resistance protein can trigger plant defences and prevent invasion by the pathogen. Mutations or deletions in pathogen effector genes are thought to enable pathogens to escape host recognition. However, we know very little about the loci and the mechanisms enabling virulence evolution in pathogen populations. A better understanding of these mechanisms is essential for the control of fungal diseases.
We identified multiple loci in the pathogen genome associated with virulence on each cultivar. However, the loci identified for the two different cultivars hardly overlapped showing that the pathogen evolved distinct loci to exploit genetically different wheat. The strongest association in the pathogen genome was linked to the deletion of a gene. This gene encoded a small secreted protein that was highly expressed during the appearance of the first disease symptoms. The deletion of the gene was associated to a gain in virulence on one cultivar only. This is likely due to the fact that this cultivar has the ability to detect this specific protein and activate defences. The pathogen gene seems to be very young, because we found no evidence in any of the most closely related species. We also found that the deletion of the gene happened thanks to the action of a large block of repetitive DNA containing selfish genomic elements (transposable elements). Hence, the pathogen likely benefited from the action of selfish elements to become more virulent on wheat. In summary, our study demonstrates that chromosomal rearrangements can play a major role in host specialization in fungal pathogens.