The Périgord black truffle (Tuber melanosporum Vittad.) and the Piedmont white truffle dominate today’s truffle market^1,2. The hypogeous fruiting body of T. melanosporum is a gastronomic delicacy produced by an ectomycorrhizal symbiont³ endemic to calcareous soils in southern Europe. The worldwide demand for this truffle has fuelled intense efforts at cultivation. Identification of processes that condition and trigger fruit body and symbiosis formation, ultimately leading to efficient crop production, will be facilitated by a thorough analysis of truffle genomic traits. In the ectomycorrhizal Laccaria bicolor, the expansion of gene families may have acted as a ‘symbiosis toolbox’⁴. This feature may however reflect evolution of this particular taxon and not a general trait shared by all ectomycorrhizal species⁵. To get a better understanding of the biology and evolution of the ectomycorrhizal symbiosis, we report here the sequence of the haploid genome of T. melanosporum, which at ∼ 125 megabases is the largest and most complex fungal genome sequenced so far. This expansion results from a proliferation of transposable elements accounting for ∼ 58% of the genome. In contrast, this genome only contains ∼ 7,500 protein-coding genes with very rare multigene families. It lacks large sets of carbohydrate cleaving enzymes, but a few of them involved in degradation of plant cell walls are induced in symbiotic tissues. The latter feature and the upregulation of genes encoding for lipases and multicopper oxidases suggest that T. melanosporum degrades its host cell walls during colonization. Symbiosis induces an increased expression of carbohydrate and amino acid transporters in both L. bicolor and T. melanosporum, but the comparison of genomic traits in the two ectomycorrhizal fungi showed that genetic predispositions for symbiosis—‘the symbiosis toolbox’—evolved along different ways in ascomycetes and basidiomycetes.

Summary: Truffles (Tuber spp.) are symbiotic fungi that develop underground in association with plant roots. Food connoisseurs describe their scent as sensual, seductive and unique. These mysterious fungi, however, do not produce their aroma for the mere pleasure of humans. Truffle volatiles act as odorant cues for mammals and insects which are thus able to locate the precious fungi underground and spread their spores. They also freely diffuse in the soil and mediate interactions with microorganisms and plant roots, potentially regulating a complex molecular dialogue among soil fauna and flora. The aim of this review is to synthesize 30 yr of research on truffle volatiles, spanning fields of study from chemical ecology to aroma biosynthesis. Specific aspects of truffle volatile ecology and biology will be discussed, including which species have been studied so far and for what purpose, what ecological role has been demonstrated or speculated to exist for specific truffle volatiles, which volatiles are common or unique to certain species and what their biosynthetic route might be. Future challenges in truffle aroma research will also be addressed, focusing on how high‐throughput post‐genomic technologies may advance our understanding of truffle aroma biosynthesis and chemical ecology.

Truffles are hypogeous fungi which live in symbiosis with plant host roots in order to accomplish their life cycle. Some species, such as Tuber magna

Tuberaceae is one of the most diverse lineages of symbiotic truffle-forming fungi. To understand the molecular underpinning of the ectomycorrhizal truffle lifestyle, we compared the genomes of Piedmont white truffle ( Tuber magnatum ), Périgord black truffle ( Tuber melanosporum ), Burgundy truffle ( Tuber aestivum ), pig truffle ( Choiromyces venosus ) and desert truffle ( Terfezia boudieri ) to saprotrophic Pezizomycetes. Reconstructed gene duplication/loss histories along a time-calibrated phylogeny of Ascomycetes revealed that Tuberaceae-specific traits may be related to a higher gene diversification rate. Genomic features in Tuber species appear to be very similar, with high transposon content, few genes coding lignocellulose-degrading enzymes, a substantial set of lineage-specific fruiting-body-upregulated genes and high expression of genes involved in volatile organic compound metabolism. Developmental and metabolic pathways expressed in ectomycorrhizae and fruiting bodies of T. magnatum and T. melanosporum are unexpectedly very similar, owing to the fact that they diverged ~100 Ma. Volatile organic compounds from pungent truffle odours are not the products of Tuber -specific gene innovations, but rely on the differential expression of an existing gene repertoire. These genomic resources will help to address fundamental questions in the evolution of the truffle lifestyle and the ecology of fungi that have been praised as food delicacies for centuries.

Frommeëlla (Phragmidiaceae, Pucciniales, Basidiomycota), which currently includes two species and is typified by F. tormentillae, causes rust on members of tribe Potentilleae (Rosaceae). The genus has been distinguished from Phragmidium on the basis of having only one germ pore per teliospore cell rather than two or three and by aecial characters. Phylogenetic analyses of both currently accepted Frommeëlla spp. with nLSU rDNA data suggest that Frommeëlla was derived from within a clade representing Phragmidium. Thus Frommeëlla should be considered to be a later generic synonym of Phragmidium. Analyses also indicate that Frommeëlla tormentillae on Potentilla species includes two taxa recognized herein as Phragmidium potentillae-canadensis and P. tormentillae. Frommeëlla mexicana on Potentilla spp. formerly classified in Duchesnea, is distinct from but sister to the other two species. Based on data regarding type specimens that were presented in a study by McCain and Hennen, the new combination Phragmidium mexicanum is proposed as the correct name for this species. Necessary studies of original material were made, and Phragmidium potentillae-canadensis is lectotpyified and epitypified. Although considered and expanded here, further examination of species boundaries and host ranges of the fungi formerly classified in Frommeëlla is warranted.

The aims of the work were to elucidate the distribution of the ectomycorrhizal fungus Tuber magnatum Pico during its symbiotic stage, and to identify the root-associated fungi in a natural truffle-ground located in North Italy. Ectomycorrhizal root tips were harvested in the truffle ground, sorted in morphotypes and analyzed by ITS. Morphological and molecular analyses revealed that (i) T. magnatum mycorrhizae were rare and independent on the fruitbody productions and (ii) the dominant fungal species belonged to Thelephoraceae, followed by Tuberaceae and Sebacinaceae.