In 2010, the team of microbiologists at INRA-Nancy teamed up with Genoscope (France’s national center of sequencing) and with Italian counterparts to successfully sequence the genome of the Périgord black truffle. It took eight years to complete this substantial study, published in Nature Ecology and Evolution. By sequencing the genomes of other renowned truffles such as the Alba white truffle, summer truffle and desert truffle), the international consortium succeeded in identifying the genes responsible for the development of symbiosis and fruiting bodies, which are remarkably well-preserved in all of the sequenced truffles. The study and comparison of these genomes has improved scientists’ understanding of the biology and ecology of different kinds of truffles. These genomic resources have revealed certain aspects of these mysterious fungi, such as their modes of reproduction and methods of synthesizing the complex, distinctive aromatic cocktails.
A truffle species’ flavour is composed of nearly 50 aromatic molecules
A truffle’s odour is composed of a complex cocktail of volatile organic compounds. The release of these compounds is a biological function closely linked to reproduction which has ensured the perpetuation of truffle species for nearly 150 million years. Truffles produce their fruiting bodies underground, out of sight and protected from drought. However their pungent odour attracts boars and rodents which unearth and eat them, thus dispersing their spores around the truffle-field. Deconstructing aromas has naturally taken centre stage in research on truffles. A typical aroma in a species of truffle is made up of nearly 50 different molecules. Genes coding for enzymes involved in aroma biosynthesis were particularly active in the different truffles studied, allowing the production of very specific aromatic molecules, including several sulphur compounds. The compounds from pungent truffle odours – humus and musk in the Périgord black truffle, and camembert and garlic in the famous Alba white truffle – rely on the differential gene activity in mature fruiting bodies. More surprising, researchers discovered that the bacteria and yeasts abundant on the truffle’s surface as well as in the centre of the fruiting bodies could modify the composition of the released aromatic cocktail. As is the case with cheeses, bacteria and fungi appear to work in tandem to produce the complex aromas that seduce food lovers.
Researchers in the consortium are now using these genomic resources to explore symbiotic interaction between truffles and trees, as well as the formation of fruiting bodies. Resources are also used to develop new tools aimed at better understanding truffle-field ecology, such as the CulturTruf project.
In the Périgord region of France or Alba in Italy, truffles have become rare and therefore expensive: the Périgord black truffle (Tuber melanosporum) sells for approximately 1,000 euros / kilo on the retail market, while the Alba white truffle (Tuber magnatum) sells for over 3,000 euros / kilo. At these prices, the symbiosis between fungi and tree produces an effect most appreciated by Michelin star chefs and connoisseurs. Mastering all of the biological and ecological parameters that make effective symbiosis and regular, abundant fruiting bodies possible in nature remains unattainable. For this reason, truffle growers and scientists are working together to optimise truffle growing.
Claude Murat, Thibaut Payen, […]Francis M. Martin. Pezizomycetes genomes reveal the molecular basis of ectomycorrhizal truffle lifestyle. Nature Ecology & Evolution, 2018, 2: 19656-1965.