The progress made in the molecular characterization of the mating types in several filamentous ascomycetes has allowed us to better understand their role in sexual development and has brought to light interesting biological problems. The mating types of Neurospora crassa, Podospora anserina, and Cochliobolus heterostrophus consist of unrelated and unique sequences containing one or several genes with multiple functions, related to sexuality or not, such as vegetative incompatibility in N. crassa. The presence of putative DNA binding domains in the proteins encoded by the mating-type (mat) genes suggests that they may be transcriptional factors. The mat genes play a role in cell-cell recognition at fertilization, probably by activating the genes responsible for the hormonal signal whose occurrence was previously demonstrated by physiological experiments. They also control recognition between nuclei at a later stage, when reproductive nuclei of each mating type which have divided in the common cytoplasm pair within the ascogenous hyphae. How self is distinguished from nonself at the nuclear level is not known. The finding that homothallic species, able to mate in the absence of a partner, contain both mating types in the same haploid genome has raised more issues than it has resolved. The instability of the mating type, in particular in Sclerotinia trifolorium and Botrytinia fuckeliana, is also unexplained. This diversity of mating systems, still more apparent if the yeasts and the basidiomycetes are taken into account, clearly shows that no single species can serve as a universal mating-type model.

Mating types and sexual development in filamentous ascomycetes.

The advantage of sex has been among the most debated issues in biology. Surprisingly, the question of why sexual reproduction generally requires the combination of distinct gamete classes, such as small and large gametes, or gametes with different mating types, has been much less investigated. Why do systems with alternative gamete classes (i.e. systems with either anisogamy or mating types or both) appear even though they restrict the probability of finding a compatible mating partner? Why does the number of gamete classes vary from zero to thousands, with most often only two classes? We review here the hypotheses proposed to explain the origin, maintenance, number, and loss of gamete classes. We argue that fungi represent highly suitable models to help resolve issues related to the evolution of distinct gamete classes, because the number of mating types vary from zero to thousands across taxa, anisogamy is present or not, and because there are frequent transitions between these conditions. We review the nature and number of gamete classes in fungi, and we attempt to draw inferences from these data on the evolutionary forces responsible for their appearance, loss or maintenance, and number.

http://max2.ese.u-psud.fr/publications/Billiard_2010_brv_153.pdf

Having sex, yes, but with whom? Inferences from fungi on the evolution of anisogamy and mating types.

Genetic control of the sexual cycle in Neurospora

This chapter provides an up-to-date review of complex cellular transition steps in Pezizomycotina, from the differentiation of reproductive cells to the development of the fructification. Initiation of sexual reproduction in the sordariomycete Arachniotus albicans, as it is for several ascomycetes, is clearly not dependent on a particular pH range. In many fungi, light is one of the prominent physical factors controlling sexual reproduction, either by stimulating or inhibiting the formation of reproductive structures. Although most Pezizomycotina can be classified as self-compatible or self-incompatible, some species present peculiar mating characteristics. There are several studies showing that pheromone and pheromone receptors are essential for the fusion of the trichogyne with the male cell in self-incompatible filamentous ascomycetes. Recent data have begun to shed light on the various molecular processes occurring during sexual reproduction in filamentous Ascomycetes. In addition to the well-known variety of body plan exhibited by Pezizomycotina fruiting bodies, sequencing has uncovered a large set of mating-type structures, all based on a common pattern. Indeed, it is now well established that MAT1-1-1 and MAT1-1-2 genes control fertilization by using pheromone/receptor genes in self-incompatible Pezizomycotina, but little is known about their roles after fertilization. The few indications that come from Podospora anserina, N. crassa, and C. heterostrophus indicate that they control the formation of biparental ascogenous hyphae and meiosis.

Mating systems and sexual morphogenesis in Ascomycetes

Summary: Analysis of 213 field isolates of Botrytis cinerea and 240 ascospore isolates of its sexual form Botryotinia fuckeliana indicated that sexual compatibility of this fungus is controlled by a single mating type gene with two alleles. Most isolates were heterothallic, that is, they were self-sterile and able to produce ascospore progeny when crossed with reference strains carrying the mating type gene MAT1-1 or MAT1-2. About 16% of the field isolates and 6% of the ascospore progeny were homothallic, that is, self fertile and compatible with both MAT1-1 and MAT1-2 strains. Both mating types are widespread in nature. The close association of MAT1-1 and MAT1-2 field isolates on various hosts in several regions of Italy shows that sexual reproduction and meiotic recombination might be an important source of genetic variation in this pathogenic fungus.

/pdf/sexual-behaviour-and-mating-system-of-botryotinia-fuckeliana-ecvqh8rwcu.pdf

J. Y. Uhm

Papers

Heterothallism and Mating Type Mutation inSclerotinia trifoliorum