Genomes of Famous Truffles Reveal Secret of their Perfumes

An international consortium led by Francis Martin and his colleagues at the French National Institute for Agricultural Research (INRA), Genoscope, and University of Torino, and including researchers at the U.S. Department of Energy (DOE) Joint Genome Institute (JGI), sought insights into the ectomycorrhizal (ECM) lifestyle of truffle-forming species. The team conducted a comparative analysis of eight Pezizomycete fungi, including four species prized as delicacies.

While truffles signify dining extravagance, they play an important role in soil ecosystem services. Truffles are the fruiting bodies of the ECM fungal symbionts residing on host plant roots. JGI de novo sequenced the genomes of two truffle-forming fungi: the Pig truffle (Choiromyces venosus) and the Desert truffle (Terfezia boudieri), as well as of two other Pezizomycetes not forming truffles: Ascobolus immersus and Morchella importuna. These four genomes as well as the genome of the Piedmont white truffle (Tuber magnatum) were annotated through the JGI's pipeline. The genome of the Burgundy Truffle (T. aestivum) was sequenced by Genoscope.

This work builds on earlier studies involving the first ECM fungal genome (Laccaria bicolor, sequenced a decade ago by the JGI), and the first truffle genome (T. melanosporum) sequenced by Genoscope. The team learned from the L. bicolor and T. melanosporum genome that the ECM symbiosis evolved by the massive loss of genes involved in plant cell wall degradation (CAZymes) and de novo innovation of communication proteins, such as the mycorrhiza-induced small secreted proteins controlling the host plant immunity.

The team also found that about 50 molecules constitute the typical fragrance of each of the different species of truffles. The genes involved in the synthesis of these fragrances are active in the various truffles studied, allowing the production of very particular aromatic molecules, including many sulfur compounds. The composition of the characteristic fragrance of each of the truffles is the result of the differential activity of the genes in mature fructifications.

For more details, read the news releases from INRA (French) and JGI.