Symbiotic nitrogen fixation in the reproductive structures of a basidiomycete fungus

Nitrogen (N) fixation is a driving force for the formation of symbiotic associations between N2-fixing bacteria and eukaryotes.1 Limited examples of these associations are known in fungi, and none with the sexual structures of species outside of lichens.2-6  The basidiomycete, Guyanagaster necrorhizus, is a sequestrate fungus endemic to the Guiana Shield.7 Much like the root rot-causing species in its sister genera, Armillaria and Desarmillaria, G. necrorhizus sporocarps fruit from the roots of decaying trees (Figures 1A, 1B and 1C),8 and genome sequencing is consistent with observations that G. necrorhizus is a white-rotting decomposer. This species also represents the first documented instance of an arthropod-dispersed sequestrate fungus. Numerous species of distantly related wood-feeding termites, which scavenge for N-rich food, feed on mature G. necrorhizus gleba, the interior spore-bearing tissue. During feeding, mature spores adhere to termites for subsequent dispersal.9 Using che...