Sex in Cheese: Evidence for Sexuality in the Fungus Penicillium roqueforti

Abstract

Although most eukaryotes reproduce sexually at some moment of their life cycle, as much as a fifth of fungal species were thought to reproduce exclusively asexually. Nevertheless, recent studies have revealed the occurrence of sex in some of these supposedly asexual species. For industrially relevant fungi, for which inoculums are produced by clonal-subcultures since decades, the potentiality for sex is of great interest for strain improvement strategies. Here, we investigated the sexual capability of the fungus Penicillium roqueforti, used as starter for blue cheese production. We present indirect evidence suggesting that recombination could be occurring in this species. The screening of a large sample of strains isolated from diverse substrates throughout the world revealed the existence of individuals of both mating types, even in the very same cheese. The MAT genes, involved in fungal sexual compatibility, appeared to evolve under purifying selection, suggesting that they are still functional. The examination of the recently sequenced genome of the FM 164 cheese strain enabled the identification of the most important genes known to be involved in meiosis, which were found to be highly conserved. Linkage disequilibria were not significant among three of the six marker pairs and 11 out of the 16 possible allelic combinations were found in the dataset. Finally, the detection of signatures of repeat induced point mutations (RIP) in repeated sequences and transposable elements reinforces the conclusion that P. roqueforti underwent more or less recent sex events. In this species of high industrial importance, the induction of a sexual cycle would open the possibility of generating new genotypes that would be extremely useful to diversify cheese products.

Unequal Recombination and Evolution of the Mating-Type (MAT) Loci in the Pathogenic FungusGrosmannia clavigeraand Relatives

“…Evidence of purifying selection on the MAT genes at the inter-specific level indicated that sexual reproduction is important in nature or occurs regularly (López-Villavicencio et al 2010). Our data showed that these fungi previously deemed asexual have the potential to reproduce sexually, as was demonstrated for other asexual fungi such as Penicillium , Aspergillus , and Fusarium (Butler 2007; Ropars et al 2012). This ability potentially increases genetic variability and can enhance fitness of fungal pathogens in new, ecological niches (Coppin et al 1997).…”

Induction of sexual reproduction and genetic diversity in the cheese fungus Penicillium roqueforti

“…), and indirect evidence of sexual reproduction has recently been reported for P. roqueforti (Ropars et al. ). Mating type genes (MAT genes), which are involved in gamete recognition and mating in fungi, and other genes involved in meiosis, have been detected in the P. roqueforti genome and appear to be subject to strong purifying selection, suggesting that they are still used and functional.…”

“…Penicillium roqueforti, like other industrial filamentous fungi and an estimated one-fifth of fungal species, was thought to lack a sexual cycle. However, evidence for the occurrence of sexual reproduction has been obtained for many of the supposed 'asexual' species (Burt et al 1996;Pringle et al 2005;Rydholm et al 2006), and indirect evidence of sexual reproduction has recently been reported for P. roqueforti (Ropars et al 2012). Mating type genes (MAT genes), which are involved in gamete recognition and mating in fungi, and other genes involved in meiosis, have been detected in the P. roqueforti genome and appear to be subject to strong purifying selection, suggesting that they are still used and functional.…”

The genomics of microbial domestication in the fermented food environment

“…These approaches have recently been applied to yeast to map quantitative trait loci (QTL) responsible for industrially important traits such as sulfite resistance [90], aromatic compound production [91], flocculation [92], and thermotolerance [93]. Future work on other domesticated microbes would first have to focus on establishing conditions to induce sexual reproduction in cryptically sexual food-related eukaryotic microbes [94], as has been initiated in Aspergillus oryzae [95,96] and Penicillium roqueforti [97,98]. This would enable QTL analysis, and is promising for breeding strains with combinations of desirable traits.…”