Truffle Ecology: Genetic Diversity, Soil Interactions and Functioning

Truffles are fungi producing hypogeous fruiting bodies belonging to at least 13 phylogenetically distant orders. The most studied are "true truffles" belonging to genus Tuber, which is the most important economically group. Truffle fruiting bodies are colonized by bacteria, yeasts, guest filamentous fungi and viruses that, all together, constitute the truffle microbiota. Research on the role of this community has demonstrated that bacteria contribute to truffle aroma. From the ecological point of view, truffle aroma attracts mycophagous animals, which in turn disperse and diffuse truffle spores in the soil, and mediates interactions with microorganisms and plant roots. Truffles have a heterothallic organization whereby for truffle reproduction it is necessary that strains of opposite mating type meet. Regarding truffle development, the truffle ascocarps use carbon coming from the host plant and not from dead host tissues or soil organic matter as believed so far. In addition to form ectomycorrhizas with a wide diversity of host plants, some truffle species are able to form also arbutoid and orchid mycorrhizas. Knowledge of truffles diversity, traditionally relied on the survey and molecular identification of fruiting bodies, moved over the years towards the survey of mycorrhizas and, recently, on the distribution in soil of the mycelium, with the determination of genets and mating types. The possibility of studying (micro)organisms directly in the field (metagenomics or environmental genomics) and the introduction of high-throughput sequencing techniques (454 pyrosequencing) have given a strong impulse to the study of the microbial communities interacting with truffles and their habitat.