The Mating Systems of Fungi

Abstract

Isolations of Mycocalia denudata and M. diiriaeana were grown in plate culture and their mating systems studied. The former species is heteromictic and shows both bipolar diaphoromixis and facultative homo-heteromixis, the latter species is almost certainly homomictic. None of these mating systems have been found before in Nidulariales. It is suggested that the abundance, morphological variation and ecological tolerance of these species may be related to their kinds of mating system. Facultative homo-heteromixis in M. denudata results in spores being produced in a single peridiolum which are either homocaryotic or heterocaryotic in respect of mating-type factors. The condition is due to a dominant gene Pd which determines a precocious division of the four nuclei, formed by a normal meiosis, in each basidium. The eight nuclei so formed appear to migrate at random, in respect of the mating-type factors they carry, into the basidiospores which are each ultimately binucleate. This mechanism is not yet known in other Basidiomycetes.Isolations of M. denudata fell into two groups (I and II) between which there was complete sterility but no other constant distinguishing features could be observed between them. The occurrence of such groups is thought to be of significance in fungi and at present it seems best to regard them as comparable to sibling species. Four mating-type factors were identified amongst the six isolations of group I, seven amongst the sixteen isolations of group II. Estimates of the total numbers of mating-type factors in group I and group II are seven to eight and twelve to thirteen respectively. Thus, like other Nidulariales, M. denudata appears to have only a relatively small number of mating-type factors and the relation of this to inbreeding and dispersal mechanisms is discussed.

Secondarily homothallic Hymenomycetes: several examples of bipolarity are reinterpreted as being tetrapolar

“…The principal difference between them is that for all spores of a four-spored species to receive two haploid nuclei, a postmeiotic mitotic division must produce eight nuclei in the basidium. Eight-nucleate basidia have been reported by Burnett and Boulter (1963) and Lamoure (1960, p. 82). Two-spored species have two sterigmata on each basidium, and two of the four meiotic nuclei migrate into each basidiospore (Skolko 1944).…”

Spore behaviors reveal a category of mating-competent infertile heterokaryons in the offspring of the medicinal fungus Agaricus subrufescens

“…Such positive mating reactions between homokaryons and heterokaryons (the Buller phenomenon) are not rare in Basidiomycota (Buller 1931;Quintanilha 1937;Raper et al 1972;Callac et al 2006). Considering that all these heterokaryons should theoretically mate with all tester homokaryons regardless their mating type alleles (Fig.…”

“…The first point indicates that postmeiotic mitosis must occur in basidia as in Mycocalia denudata in which eight postmeiotic nuclei migrate into four spores (Burnett and Boulter 1963). Postmeiotic mitosis also occurs in A. bisporus but in the spores or during the migration of the nuclei through the sterigmata and rarely in the basidia (Kamzolkina et al 2006); consequently, only four postmeiotic nuclei migrate into the two to four spores of each basidium.…”

Genetics of secondarily homothallic basidiomycetes

“…For mating-type, direct observations have shown that strains heteroallelic for mating-type predominate in random spore isolates: Agaricus bisporus, (Sinden, 1937;Kligman, 1943;Raper et a!., 1972); Aleurodiscus canadensis, (Skolko, 1944); Coprinus sassii, (Lange, 1952); Clitocybe iituus, (Kuhner, 1953); Mycocalia denudata, (Burnett and Boulter, 1963). That strains heteroallelic for mating-type predominate in species with two mating-type factors such as Coprinus sassii suggests that second division segregation occurs infrequently and that the mating-type loci are located close to their respective centromeres.…”

“…In those species such as Mycocalia denudata (Burnett and Boulter, 1963) and Omphalia flavida (Sequeira, 1954) which have four-spored basidia the formation of binucleate spores is a consequence of a post-meiotic mitosis in the basidium, and different ratios are expected. Eight nuclei are available for migration into four spores and the random migration of nuclei segregating for a gene A-a would give a 16: 12 (4:3) ratio.…”