Sex in the Rest: Mysterious Mating in the Chytridiomycota and Zygomycota
This chapter discusses mating biology of basal fungi with emphasis on chytridiomycetes and zygomycetes. The chytrids and zygomycetes are ecologically diverse. Many of them are parasites, on hosts such as plants, algae, invertebrates, or other fungi. These nutritional requirements have precluded their isolation into axenic culture. Both chytrids and zygomycetes are capable of causing diseases in humans and other animals. A number of zygomycete fungi cause human diseases that are particularly difficult to treat with current antifungal agents. Most of the knowledge of sex in basal fungi comes from studies of behaviors of axenic cultures or careful observations made using light microscopy on natural substrates for the fungi. Chytridiomycetes have long been recognized to be divisible into several major groups based on life cycles and sexual mechanisms. Blastocladiales are exceptional among Fungi by having a life cycle with alternation of generations in which a diploid sporophyte can undergo extensive vegetative growth including asexual reproduction. The Zygomycota comprise nine orders, eight of which include species that undergo homothallic or heterothallic sex. Among the Zygomycota, the Mucorales are the best studied: it is generally inferred that similar patterns of mating occur in the other zygomycetes, although this may not be the case. Microsporidia are obligate intracellular parasites of animals (often insects) and humans, characterized by the absence or remnants of mitochondria and the presence of a specialized structure, the polar tube, with which they infect cells.
