Genome Modifications Turn Fungal Plant Pathogen into Beneficial Organism

Plants take advantage of unknown molecular mechanisms to determine what benefits or harms them. They also allow microorganisms to access their roots in exchange for essential nutrients in the soil. The soil fungus Colletotrichum tofieldiae and the model plant Arabidopsis have this relationship, where the plant accepts the fungus as a phosphate supplier when it has no access to the mineral itself, but rejects the fungus when it can get phosphate supplies on its own. In the process, the plant's immune system plays a key role.

Stéphane Hacquard, Paul Schulze-Lefert and Richard O'Connell of the Max Planck Institute for Plant Breeding Research in Cologne are looking at the changes that ensure C. tofieldiae no longer has to contend with the full brunt of the plant's immune system under certain conditions. They found that just a few changes in the genome are sufficient to turn a pathogen into a partner.

The scientists compared the genomes of several strains of the beneficial species C. tofieldiae from various continents with the genomes of its harmful cousin C. incanum. They also investigated which genes the two fungi switch on when they gain access to a root. They found that the beneficial and pathogenic fungi have similar genomes, and the change from pathogen to beneficial lodger is based on relatively few genetic changes. Of the 13,000 genes, 11,300 are identical. During the eight million years since the two species diverged, the beneficial fungus gained 1,009 genes and lost 198.

The research team also discovered that the beneficial fungus either does not read the genes it has inherited through its pathogenic phylogeny or reads them very late. "We conclude that the symbiotic relationship is due to the fact that the genes originally responsible for the pathogenesis of the fungus remain switched off and do not come into play," Hacquard says.

For more details, read the news release at the Max Planck Institute for Plant Breeding Research website.