Morphogenetic Control Elements

The only major morphogenetic control elements known in fungi are the mating type factors, which regulate pheromone production and pheromone receptors involved in mating, ranging from recognition between sexually competent cells in yeast to governing growth of clamp connections, internuclear recognition and regulation of the distance between the two nuclei in Basidiomycota (Casselton, 2002). However, not all fungi possess mating type factors, and, indeed, even in species that have a well-developed mating type system apparently normal fruit bodies can be formed by haploid cultures, and fruit body formation can usually be separated from other parts of the sexual pathway by mutation (see Chapter 5 in Moore, 1998a).

Generally, vegetative compatibility genes define the individuals of fungal populations, while mating type factors are usually interpreted as favouring the outbreeding of a fungal population (Chiu and Moore, 1999). Consequently, mating type genes contribute to management of the genetics of the population as well as to the sexual development of the individual. Sexual reproduction generates genetic variation, offers an escape from DNA parasites and provides a means to repair DNA damage (Bernstein et al., 1985).

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