Basidiosporogenesis, meiosis, and post-meiotic mitosis in the ectomycorrhizal fungus Pisolithus microcarpus

Abstract

Pisolithus microcarpus (Cooke and Massee) G. Cunn. is a model organism for the studies on the ecology, physiology, and genetics of the ectomycorrhizal associations. However, little is known about the basidiosporogenesis in this species and, in particular, the nuclear behavior after karyogamy. In this work, the events involved in basidiosporogenesis and meiosis in P. microcarpus were analyzed using fluorescence and scanning electron microscopy. The basidia are formed inside peridioles by the differentiation of the cells along the whole hyphae. Basidial cells measure 12-18 microm in length and 6-7 microm in diameter. P. microcarpus produces eight basidiospores per basidium imbibed in a gelatinous matrix in the basidiocarp. The basidiospores are globose, equinate, with blunt spines, and measure 6-8 microm. Karyogamy can take place inside basidia as well as in undifferentiated hyphal cells followed by nuclear migration to a newly developed basidium where meiosis takes place. After the formation of the meiotic tetrad, one round of post-meiotic mitosis occurs, resulting in the production of eight nuclei per basidium. The newly-formed nuclei migrate into the basidiospores asynchronously, resulting in the production of eight uninucleate spores. This corresponds to pattern A of post-meiotic mitosis. This work is the first report on meiosis and post-meiotic mitosis during basidiosporogenesis in P. microcarpus and contributes to clarify some aspects of the biology and genetics of this ectomycorrhizal species.

Function of Cryptococcus neoformans KAR7 ( SEC66 ) in Karyogamy during Unisexual and Opposite-Sex Mating

“…C. neoformans forms holobasidia (single-celled basidia), unlike the closely aligned species Cryptococcus heveanensis, where phragmobasidia (basidia divided into four cells by septa) are formed (41). We also found that karyogamy could occur in the subapical area of hyphae of the basidium as well as more apically within the basidium proper, as seen in Pisolithus microcarpus (9) (Fig. 3; see Fig.…”

Biological Characteristics of Teleomorph and Optimized In Vitro Fruiting Conditions of the Hoelen Medicinal Mushroom, Wolfiporia extensa (Higher Basidiomycetes)

“…Binucleate basidiospores could possibly originate from the aberrant migration of 2 haploid nuclei to a single basidiospore or, alternatively, from the absence of nuclear disjunction at the end of postmeiotic mitosis in basidiospores. 24 Fluorescence microscopy was used to analyze hymenium to reveal the pattern of nuclear behavior in W. extensa; however, it failed because the honeycomb-like structure on the surface of fruiting bodies (location of hymenia) of W. extensa is small, and it was difficult to clearly observe the pattern of nuclear behavior. In addition, whether the 2 nuclei were genetically different or not needs to be confirmed by further experiments.…”

The transcriptional landscape of basidiosporogenesis in mature Pisolithus microcarpus basidiocarp

“…The fungus produces a complex basidiocarp which serves as a structure within which the peridium (or “nest”) contains small capsules known as peridioles (or “eggs”) in various developmental stages. Enclosed in these peridioles are immature basidiospores and an upper layer of free basidiospores ready for dispersion upon rupture of the basidiocarps cellular cortical layer known as the pellis [ 11 , 12 ] (Fig. 1a, b ).…”

“…Finally, free spores are the mature spores that collect at the upper portion of the basidiocarp from fully ruptured peridioles (Fig. 1g ) [ 11 ].

Fig.

…”

“…Furthermore, the constitution of lipid reserves and fatty acid distribution during P. microcarpus basidiosporogenesis is also known and the evidence that these contents are important for basidiosporogenesis, as well as their distribution throughout the development of the fungal basidiocarp [ 14 ]. Despite progress that has been made thus far towards understanding basidiosporogenesis and the distribution of reserve compounds in P. microcarpus basidiospores, relatively little is known about the main factors involved in this crucial activation stage of the fungal life cycle [ 11 , 12 , 14 ].…”