Mycotoxin protects against nematodes, study finds

Most terrestrial plants enter into biocoenosis with fungi. Both sides benefit: the fungus, which surrounds the small roots of the host plant with a thick felt, supplies the plant with trace elements and water. The plant, in turn, supplies the fungus with sugars and other metabolites which it is unable to produce itself.

ETH researchers from the research group of microbiology professor Markus Aebi have discovered a protein in the cells of one such ectomycorrhizal fungus which offers an additional advantage to the fungus-plant duo. It protects the fungus and possibly its roots, too, against nematodes as it is toxic to the parasites.

"This toxin is probably part of this fungus' defence system against predators," says Markus Künzler, senior assistant in Aebi's group. If the nematodes feed on the fungal cells, they ingest the toxic protein. The nematode's intestinal cells are destroyed by a mechanism which has still to be elucidated.

The mushroom mainly forms the protein in its pileus, i.e. the part of the fruiting body visible above ground and in the dense fungal net around the tips of the roots. The fact that the toxin is close to the root tips could be an indication that the toxin not only protects the fungus but also the plant roots against predators. Many nematodes that live in the soil feed not only on fungal tissue but also on plant cells.

In their study, which has just been published in the journal PNAS, the researchers demonstrate that the defence protein docks on to a specific target in the nematode : a modified sugar found on the surfaces of the worm's intestinal cells but also on those of molluscs like snails. However, there doesn't seem to be any such surface structure on the cells of vertebrates.