During the 1960s a ‘sexual revolution’ occurred in many Western human societies. In a similar fashion, mycologists now find themselves caught up in a fungal sexual revolution as previously accepted norms for fungal sex are being overturned. In particular need of reappraisal is the view that a significant number of fungal species are restricted solely to asexual reproduction. Fungi are unusual amongst eukaryotic organisms in that at least 20% of all species lack a known sexual state and instead appear to rely solely on asexual methods of reproduction. This is very surprising because a sexual phase in the life cycle, even if only intermittent, has several evolutionary advantages over purely asexual reproduction. In the specific case of fungi, sexual reproduction also confers the ability to produce dormant survival structures and a transient ‘capacitor’ diploid state that might allow selection of evolutionarily favourable sets of genes in a fitness ‘selection arena’.
However, recent experimental and genomic discoveries are now challenging the supposed asexual status of mitosporic fungi. Instead it is becoming apparent that many species have a previously unidentified ‘cryptic’ or ‘covert’ sexual state and are ‘holding back the truth’ about their sexuality. This review focuses on lessons being learnt from investigations involving Aspergillus and Penicillium species that are helping pave the way to fungal sexual realisation.
A fungal sexual revolution: Aspergillus and Penicillium show the way. Curr Opin Microbiol. Oct 25 2011
Fungi have some of the most diverse sex lives in nature, ranging from self-fertility to obligate outcrossing systems with several thousand different sexes, although at least 20% of fungal species have no known sexual stage. However, recent evidence suggests that many supposed ‘asexual’ species do indeed have the potential to undergo sexual reproduction. Using experimental and genomic findings from Aspergillus and Penicillium species as examples, it is argued that evidence such as the presence and expression of apparently functional sex-related genes, the distribution of mating-type genes, detection of recombination from population genetic analyses, and the discovery of extant sexual cycles reveal an on-going revolution in the understanding of fungal asexuality.