Do black truffles avoid sexual harassment by linking mating type and vegetative incompatibility?

Abstract

Do black truffles avoid sexual harassment by linking mating type and vegetative incompatibility?The black Perigord truffle (Tuber melanosporum) is recognized worldwide as an icon of European gastronomy. Its edible fruitbody is a hypogeous fleshy structure producing meiospores (Fig. 1). This ascomycete fungus is ectomycorrhizal, that is, symbiotically associates with tree roots. The demand for this highly appreciated delicacy and the decrease of its production over the twentieth century (Savignac et al., 2012) have fuelled intense efforts at its cultivation, and at sequencing its genome (Martin et al., 2010). In this issue of New Phytologist, Murat et al. (pp. 176-187) analyze T. melanosporum population genetics in two truffle plantations. They reveal genotypes extending over a few meters, displaying a strong genetic structure at fine scale, with a pattern of isolation-bydistance within the plantation, and a striking spatial segregation of genotypes according to their mating type.

Certainties and uncertainties about the life cycle of the Périgord black truffle (Tuber melanosporum Vittad.)

“…Anastomoses have never been observed between hyphae of different T. melanosporum strains grown under controlled conditions, but have frequently been observed between hyphae of the same strain (Iotti et al 2012). Selosse et al (2013) made the hypothesis that vegetative incompatibility could explain the exclusion of one mating type by the other from the same host plant.…”

Black Truffle, a Hermaphrodite with Forced Unisexual Behaviour

“…The underlying mechanism is not yet fully understood, but a role for vegetative incompatibility has been suggested [6,10]. Vegetative incompatibility is a common mechanism in fungi [11], where genetically close individuals reciprocally cooperate, mainly by hyphal fusion and resource sharing.…”

“…On the other hand, this appears at odds with the statement that fathers should be spatially close to mothers and that there is no another, yet unidentified, niche close to mothers. It has been proposed that germinating spores of the opposite mating type, although not able to settle permanently, may act as fathers [7,9,10]; yet other niches in the soil remain to be explored, including short saprotrophic survival: indeed, both mating type alleles TIMI 1467 1-4…”

Black truffle cultivation: a global reality

“…In the field intraspecific competition causes a spatial separation between mating types that can affect fruiting potential (Rubini et al, 2011b). Selosse et al (2013) hypothesised that the mating-type genes could also be controlling vegetative incompatibility, but Iotti et al (2012) did not find genes related to mating-type heterokaryon incompatibility in T. melanosporum.…”

“…The cultivation of T. melanosporum is not completely domesticated, as the uncertainties around the mating process remain (Selosse et al, 2013). Basic research on truffles has been constricted by the difficulties to observe their development: the symbiotic phase is microscopic and the growth of the mycelium in pure culture is slow, whereas the sporocarp grows underground and over a period of several months.…”