Live by the truffle code

Molecular biologists have explored the brave new worlds of the human genome, various animal models, a plethora of pathogenic organisms, crops and plants. Even the platypus saw his nucleic secrets revealed to the world. European researchers have now added one more genome organism to the databases; fruity, aromatic and expensive, princes of the fungi and diamonds of the kitchen: the black truffle.

For centuries, gourmands considered the truffle a delicacy, searching among oak roots where the symbiotic fungi hid. At first, they used truffle hogs, boars attracted by the truffle's aroma, until trufficulture was developed in the 19^th century. The last ice age nearly wiped out truffles completely, except for two species: Tuber magnatum, the white truffle in one in a warm pocket of northern Italy and, in the region of Piedmont, southern France, Tuber melanosporum, the Black truffle. Today, you might pay close to 500$ for one black truffle.

The market for truffles justifies the research effort by European agricultural agencies: wines, cheeses, crops, the cultures of food want to optimize and preserve their natural treasures. The genome of the black truffle will not help only contribute to its culture, but also to curb smuggling and counterfeiting and has a genuine fundamental biological value. It is only the second genome from a symbiotic fungi uncovered. Its comparison with the previously sequenced Laccaria bicolor genome demonstrated many genetic mechanisms behind symbiosis. First rule of the symbiotic fungi: Travel light. The truffle's genome contains very little similar gene pairs for a genome of its size (125 Mb), starting from a Pezizomycotina ancestor with a compact genome, the organism evolved by loosing little genes, but gaining highly specialized ones. This brings us to the second rule of symbiotic fungi: Milk them dry. Many of the genes the truffle developed encode membrane transporters. The diamonds of the kitchen knows how to cannibalize their host for everything they got. To preserve their ecological edge, the truffle got their third rule: Shuffle the cards. Their gene is highly heterogeneously distributed between areas of transposable elements. These flexible areas facilitated genetic rearrangements of the truffle’s ancestor genome during the last Ice Age, separating then from other ascomycetes, but allowing some populations to survive.

Of course, the genome of the black truffle revealed an array of enzymes involved in sulphides biosynthesis, giving the visually unappetizing mushroom its status of delicacy. One of the most important of these, 2,4-dithiapentane caused uproar in the gastronomic circles in February 2008. In a much-publicized article in the New York Times, chef Daniel Patterson revealed that truffle oil was not made by infusing truffles in olive oil like most cook assumed, but by spiking the oil with pure 2,4-dithiapentane. Many shunned this “artificial” condiment. After all, if 2,4-dithiapentane comes is extracted from a truffle, it is NOT a chemical… right?

Further reading :

Martin F et al. (2010) Périgord black truffle genome uncovers evolutionary origins and mechanisms of symbiosis. Nature. 464(7291):1033-8.