Mating and sexual interactions in fungal mycelia

摘要

Sexual reproduction is a major factor aiding adaptability and fitness in organisms throughout the natural world, and the fungi are no exception in exploiting its potential. Fungal mycelia in natural environments, unless they are self-fertile, are faced with the problem of finding a compatible partner. Their major senses are chemical, i.e. taste and smell, so we can imagine each mycelium, in for example the soil, exuding its own specific repertoire of chemicals, to announce its presence to potential mates. These chemicals have to be at least reasonably specific to fungal species, and completely specific to mating type within that species, so that attempts at mating stand a good chance of being successful. Thus poten-tially there are probably as many different chemicals as there are species. Such specific chemicals can be termed 'hormones' used in the context as defined by Raper (1952) for fungi 'substances produced by the affected plant or by others of the same species . . . performing indispensable regulatory roles in the sexual process'. An alternative term, increasingly used as a synonym in the fungal literature, is 'pheromone' for a chemical acting at a distance (cf., insect sex attractants). The very small number of such compounds that have been identified to date fall into two classes: isoprenoids (derived from mevalonic acid) among the 'lower fungi' (a very diverse phylogenetic group), and hydrophobic peptides, mostly iso-prenylated, among Ascomycetes and Basidiomycetes. Reviews of various aspects of these fungal hormones/pheromones include those of Raper (1952), Machlis (1972), Gooday (1974), Van den Ende (1984) Gooday & Adams (1993), Gooday (1994) and Duntze, Betz & Nientiedt (1994). As well as these very specific effectors, there are numerous reports throughout the fungi of apparently less-specific sex factors, which include growth substances regulating development by their overall concentration, and morphogens regulating localized differentiation by providing posi-