Dig beneath a plant and you’ll probably find an army of fungi.
Living amid plant roots, most of these mycorrhizal fungi get plant sugars in exchange for providing minerals harvested from soil. Long before the fungi engaged in trade with their plant hosts, though, their fungal ancestors primarily were decomposers, breaking down wood from dead trees. So how did this mutually beneficial relationship with live plants evolve?
Scientists analyzed 49 fungal genomes to find out. They discovered a toolkit of symbiosis genes that evolved independently in different fungi a few times within the last 200 million years. The researchers, from the U.S. Department of Energy’s Joint Genome Institute, the French National Institute for Agricultural Research, and Clark University in Worcester, Mass., report the results February 23 in Nature Genetics.
These fungi still have a few genes for enzymes that break down plant cell walls, as well as ones for proteins linked to the symbiotic lifestyle. Some of these genes — as many as 38 percent — are unique to a single species, suggesting novel genes emerge fairly frequently in symbiosis.