This genome was sequenced as a part of the large-scale multi-genome JGI CSP Saprotrophic Agaricomycotina Project (SAP), which focuses on the diversity and evolution of decay mechanisms, organismal phylogenetic relationships, and developmental evolution. A large collaborative effort led by PI of this project, David Hibbett (Clark University) aims for master publication(s) of the SAP data analysis. Researchers who wish to publish analyses using data from unpublished SAP genomes are respectfully required to contact the PI and JGI to avoid potential conflicts on data use and coordinate other publications with the SAP master paper(s).
Fibulorhizoctonia sp. CBS 109695 is a member of the Atheliales, a small (probably less than 100 species) clade of Agaricomycetes that is closely related to the Boletales, Amylocorticiales and Agaricales (collectively, the Agaricomycetidae). Most Atheliales produce simple, "corticioid" fruiting bodies, which are often little more than a loose aggregation of fungal filaments on the surface of the substrate. However, what the Atheliales lack in morphological diversity, they more than make up for in ecological diversity. The group contains saprotrophs, plant pathogens, algal parasites, and ectomycorrhizal symbionts. Fibulorhizoctonia sp. is the second species of Atheliales to have its genome sequenced; the first, Piloderma crocea, is ectomycorrhizal. In contrast, Fibulorhizoctonia sp. is a presumed saprotroph that enters into a unique symbiosis with certain termites. In this association, Fibulorhizoctonia sp. produces sclerotia (spherical structures composed of fungal hyphae) that mimic termite eggs. Termite workers manipulate the fungal sclerotia just as if they were eggs, moving them from place to place within the colony and piling them in heaps alongside termite eggs. The biology of the Fibulorhizoctonia symbiosis has been studied by Matsuura and colleagues1,2 who have nick-named Fibulorhizoctonia the "cuckoo fungus" after another egg mimic. Fibulorhizoctonia appears to benefit from the association, which provides favorable growth conditions in an environment with few competitors, but the benefit to the termites, if any, is not known. Fibulorhizoctonia has a number of apparent adaptations that facilitate egg-mimicry. First, the sclerotia have a regular diameter that matches that of termite eggs (other Atheliales produce sclerotia as well, but they are more variable in size), and their surface texture is similar to that of termite eggs. Second, the Fibulorhizoctonia sclerotia produce the enzyme b-glucosidase, which appears to act as a pheromone necessary for inducing egg-tending behavior by the termite hosts. Diversity and evolution of decay related enzymes, such as b-glucosidase, is the central focus of the Saprotrophic Agaricomycotina Project. By comparing the genome of Fibulorhizoctonia sp. to Piloderma crocea and other Agaricomycetidae, it may be possible to understand the biochemical adaptations that enable these fungi to switch between substrates and from saprotrophic to symbiotic lifestyles.
- Matsuura, K. Termite-egg mimicry by a sclerotium-forming fungus. Proc Biol Sci 273, 1203-1209, doi:10.1098/rspb.2005.3434 (2006).
- Matsuura, K., Yashiro, T., Shimizu, K., Tatsumi, S. & Tamura, T. Cuckoo fungus mimics termite eggs by producing the cellulose-digesting enzyme beta-glucosidase. Curr Biol 19, 30-36, doi:10.1016/j.cub.2008.11.030 (2009).