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Researchers at the University of Amsterdam (UvA) have discovered that pathogenic chromosomes in the fungus known as Fusarium oxysporum are capable of moving from one fungus to another. Their finding, which will be published in the current edition of 'Nature'.

Researchers at the University of Amsterdam (UvA) have discovered that pathogenic chromosomes in the fungus known as Fusarium oxysporum are capable of moving from one fungus to another. Their finding, which will be published in the current edition of Nature (Volume 464, Number 7287), solves the riddle of how new pathogenic strains of fungi arise in nature and in agriculture and horticulture.

The UvA team, led my Dr Martijn Rep, is investigating small proteins secreted by the Fusarium oxysporum fungus during colonisation of the xylem vessels of tomato plants. Fusarium oxysporum has four extra chromosomes, which makes it different from related fungi in the Fusarium genus.

It turns out that the small proteins contribute to the pathogenic capacity, or ‘pathogenicity', of the fungus. Research conducted in collaboration with Dr Li-Jun Ma of the Broad Institute in Cambridge (USA) showed that the genes for these proteins are located on one of those extra chromosomes. This additional ‘pathogenicity chromosome' is only found in individual fungi (‘strains') that can make tomato plants sick, and not in the many other strains that are harmless or have other host plants.

Chromosome relocation

The researchers wondered if the pathogenicity chromosome was perhaps moving from one fungal strain to another via an unknown mechanism. A subsequent experiment by UvA PhD candidate Lotje van der Does made clear that this is precisely what happens when two strains are growing side-by-side on the same matrix.

The finding has enabled the researchers to explain how new pathogenic strains of certain fungi arise in nature and in agriculture and horticulture and, additionally, to reveal the immense genetic flexibility and adaptability of fungi. The mechanism driving such chromosomal relocations remains a mystery, however. Solving that mystery is the next step in Rep's research, who has been awarded a Vici grant from the Netherlands Organisation for Scientific Research (NWO) to pinpoint this mechanism and to map the evolution of pathogenicity chromosomes in Fusarium oxysporum.