Coniferous forests in Europe and North America have suffered several hundred million dollars in damages annually from the fungal pathogen Heterobasidion annosum. Aside from the economic losses, scientists are concerned by the white rot fungus that not only breaks down the wood for nutrients, but also releases the carbon dioxide trapped in the wood, changing the forests from carbon sinks to carbon sources.
After infecting the trees, Heterobasidion species gain nourishment by switching between two different pathways: acting as parasites on their hosts or obtaining nutrients from the decaying wood (saprotrophy). Learning more about how the fungi switch between these two pathways was one of the incentives for researchers at the DOE JGI and collaborators around the world to sequence and analyze the genome of the North American fungal pathogen H. irregulare.
In a study published in the June 2012 issue of New Phytology, the 33.6 million-base genome was shown to be “almost as well equipped as [previous DOE JGI projects] S. commune and C. cinerea with regard to the gene families involved specifically in plant cell wall degradation.” However the analysis also revealed that the fungus isn’t maximizing its use of wood-degrading enzymes when acting as a pathogen since it also has to deal with plant defenses and other factors.
“We conclude that there is a trade-off between maximal nutritional gain and access to a different ecological niche which must be balanced by the fungus,” the team wrote in their conclusion.