Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

Abstract

In Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3-5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described.

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

“…1a are binucleate. However, in A. subrufescens, it is still unknown if the two identical daughter nuclei remain in the mature spores as in A. bisporus (Kamzolkina et al 2006) or if one of the two nuclei passes in the basidium making the spores uninucleate at maturity. In each of the three other basidia illustrated in the model, postmeiotic mitoses occur in the basidia and the eight postmeiotic nuclei are randomly paired in the four spores.…”

“…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. The basidium spore number is determined by a major locus BSN linked to MAT (Imbernon et al 1996).…”

“…For this species, Challen and Elliott (1989) proposed a random bisporic model with a category of heterokaryotic spores called Bsister nuclei^progeny because they receive nuclei arising from the same second meiotic division and bearing the same mating type alleles. In A. bisporus, such sister nuclei heterokaryons are infrequent (Summerbell et al 1989); the spatial position of the spindles of the second meiotic divisions (Evans 1959) and/or their asynchrony (Kamzolkina et al 2006) could explain the preferential migration in the same spore of two non-sister nuclei, each one per second meiotic divisions. In A. subrufescens, Thongklang et al (2014) reported the following three primary categories of single spore isolates that are represented in the theoretical tetrasporic random model of Fig.…”

The phylogenetic position ofHaasiella(Basidiomycota, Agaricomycetes) and the relationships betweenH. venustissimaandH. splendidissima

“…A similar situation was demonstrated for Agaricus bisporus ( J.E. Lange) Imbach, where three different types of life cycles are present in cross-fertile populations (Kamzolkina et al 2006).…”

“…(Lamoure 1968(Lamoure , 1969, Coprinus s.l. (Lange 1952), Agaricus (Volkova et al 2003, Kamzolkina et al 2006, Favolaschia (Vizzini et al 2009) and Hygrocybe (Boertmann 2010).…”