Truffles are some of the most delicious (and expensive) foods you can eat. Now, researchers have analyzed their genomes to understand the molecular underpinnings of what makes them so special.

Black truffle (Tuber melanosporum).

With about 1.5 million species, fungi represent one of the most diverse branches of life. However, despite their diversity and usefulness, we know surprisingly little about how they interact in natural and synthetic communities. To bridge this gap, a team of researchers has started a large-scale project, called 1000 Fungal Genomes Project. This project will help us better understand how mushrooms really work, and how we can harvest their benefits for agricultural, industrial, and even climate management purposes. Essentially, the project wants to map the genomes of 1,000 important mushroom species, over the course of five years.

Now, a large team led by Francis Martin hassequenced the genomes of the prized Piedmont white truffle and the Burgundy, desert and pig truffles — four of the most prized species.

A mushroom is not a mushroom

What we typically call “mushroom” is only the above-ground fruiting body of a complex organism that lies mostly underground. Like most mushrooms, truffles are fruiting bodies filled with spores, each spore being capable of sending out a branching filament (hypha) that can develop into a group and form its own mycelium (the vegetative part of a fungus consisting of many branching filaments). So in a way, it doesn’t make sense to say that a fungus is a truffle, but rather that it has or forms a truffle.

Truffles rely on animals to eat the fruiting body and spread the spores around — but like a few other mushrooms, they made the mistake of being too delicious to humans. They are highly appreciated for their exquisite flavor and have been cherished since ancient times, although domestication has largely remained impossible.

Martin and colleagues were looking at how truffles first came to be, and found that truffle-forming species evolved independently more than a hundred times in history. They appear in most groups group of fleshy fungi and remarkably, share numerous genetic similarities with each other, even between unrelated species.

For instance, the Piedmont white truffle, the Burgundy, desert and pig truffles all share similarities with another species, called the Périgord black truffle, as well as non-truffle-forming fungi — despite the fact that they branched out over a hundred million years ago.

They also found that truffles have more genes that produce smelly, pungent, volatile organic compounds, which are likely responsible for generating their distinct aroma that attracts animals and makes them so appreciated by humans.

From a genomic point of view, the analyzed truffle-forming species appear quite similar overall, and although the functions of some genes still remains to be uncovered, the study will go a long way towards helping us understand the lifestyle and morphological functions of these  remarkable organisms.

The study has been published in Nature. https://doi.org/10.1038/s41559-018-0710-4

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