Symbiosis a driver of truffle diversity

November 14, 2018, Lawrence Berkeley National Laboratory
The Périgord black truffle (Tuber melanosporum) was the first truffle to have its genome sequenced. Its genome was used in a comparative analysis of truffle-forming fungal species reported in Nature Ecology & Evolution from an international team including JGI researchers. Credit: Francis Martin

While the sight of black or white truffle being shaved over on pasta is generally considered a sign of dining extravagance, they play an important role in soil ecosystem services. Truffles are the fruiting bodies of the ectomycorrhizal (ECM) fungal symbionts residing on host plant roots. In many Ascomycota and Basidiomycota lineages, truffle-forming species have evolved independently in nearly every major group. This suggests that symbiosis drives evolution of truffle diversity and selects for specific traits.

A team 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), a DOE Office of Science User Facility, sought insights into the ECM lifestyle of truffle-forming species. As reported in Nature Ecology & Evolution, the team conducted a comparative analysis of eight Pezizomycete fungi, including four species prized as delicacies.

A Decade of ECM Symbiosis Studies

The underground networks that link ECM fungi and their host plant roots shape these ecosystems, impacting the plant's health and tolerance to stressors such as drought or disease, as well as the global carbon cycle. Studies have suggested that ectomycorrhizal fungi may slow soil carbon cycling down by limiting nitrogen. The fungi absorb mineral nutrients from the soil and exchange them for sugars that plants produce through photosynthesis.

Through the JGI's Community Science Program, 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.

The work builds on earlier fungal symbiosis 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, which is part of this analysis. "We have learned from the Laccaria bicolor and Tuber melanosporum 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," said study senior author and longtime JGI collaborator Martin. In a 2015 study with the JGI, Martin and his colleagues then showed that ECM species evolved from saprotrophs that feed on decaying organic matter, and that these evolutionary patterns are present in many Basidiomycota groups.

"Here," Martin added, "we showed that the loss of genes involved in lignocellulose/plant cell wall degradation (CAZymes) and a higher evolution rate of symbiosis-related orphan genes have shaped the genomes of pezizomycetes truffles, one of the oldest/basal clade of ectomycorrhizal Ascomycota. This means that similar evolutionary mechanisms have independently driven symbiosis in Ascomycota and Basidiomycota. We also showed that developmental and metabolic pathways expressed in ectomycorrhizal roots and fruiting bodies of the white (T. magnatum) and black (T. melanosporum) truffles are unexpectedly very similar, owing to the fact that they diverged ~100 million years ago."

Scenting Next Steps

Detecting and disseminating these underground delicacies depends on trained animals scenting the distinctive odors of truffles. Martin and his team suggest the volatile organic compounds that produce these scents may also be altered by the microbial communities flourishing into truffles .

'In addition to the small secreted proteins critical for fungal interactions with their plant hosts these small molecules encoded in the genomes by clusters of secondary metabolite genes offer another channel of communications between fungi and the environment,' adds Igor Grigoriev, the JGI Fungal Program head and concludes: "Thus, the sequenced genomes open doors for exploration of multi-dimensional fungal plant interactions'

Explore further: Scientists sniff out Thailand's first truffle species

More information: Claude Murat et al, Pezizomycetes genomes reveal the molecular basis of ectomycorrhizal truffle lifestyle, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0710-4

Related Stories

Sniffing out real truffles

May 30, 2018

At a cost of thousands of dollars per pound, truffles are an expensive food. The fungi are prized for their distinctive aroma, and many foods claim truffles or their aromas as ingredients. But some of these foods may actually ...

Gap closed in the genetic map of kingdom fungi

September 20, 2013

An international research team headed by PD Dr Minou Nowrousian from the Ruhr-Universität Bochum (RUB) has sequenced the genome of the ascomycete Pyronema confluens, thus closing a gap in the genetic map of fungi. For the ...

New species of truffle found in Finland

May 16, 2013

A species of truffle that is considered to be rare has been found for the first time in Finland. Previously it has been thought to exist only in the Pacific Northwest region of the United States. The truffle was found in ...

Recommended for you

Double the stress slows down evolution

December 6, 2018

Like other organisms, bacteria constantly have to fight to survive in hostile living conditions. Together with colleagues in Finland, researchers at the Max Planck Institute for Evolutionary Biology in Plön have discovered ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.