Demonstrating the Concepts of Mutagenesis and Genetic Screening Using the Fungal System Coprinus cinereus

 

Marilee A. Ramesh & Nicole Randall

Tested Studies in Laboratory Teaching, 2008, Volume 29

Abstract

Coprinus cinereus, basidiomycete fungus, is an excellent model system to use for the studies of meiosis because the process is naturally synchronous. C. cinereus can grow as a monokaryon or a dikaryon. As a monokaryon, it can reproduce asexually through the production of asexual spores called oidia. Two compatible haploid strains can mate (fuse) to form a dikaryon. Under the appropriate conditions triggered by a light/dark cycle, the dikaryon can be induced to form a fruiting body or mushroom. Within the cap of this mushroom, meiosis occurs to produce haploid spores. These spores will germinate to form the next generation of haploid individuals. Mating is controlled by two mating type genes, A and B. In order to mate, two haploid strains must have different alleles at both loci. Mutations in both of these genes gave rise to a strain that is self-compatible or can mate with itself. This strain, AmutBmut (Swamy et al., 1984), is utilized in screens for mutations that affect the processes of mushroom formation and meiosis. In this laboratory exercise, we will harvest the asexual spores (oidia) from cultures of the AmutBmut strain. The oidia will be mutagenized using UV radiation. Surviving mutants will be capable of selfmating, eliminating the need for backcrossing the mutation into a compatible strain. These mutants will be screened for the ability to undergo meiosis and produce spores. Potential meiotic mutants will produce white mushrooms (no spores) compared to those survivors that produce black mushrooms (spores), indicating the capacity to undergo meiosis. This exercise demonstrates the process of creating random mutants and the necessity of a specific genetic screen to identify only those mutants with meiotic defects.

Keywords:  meiosis, fungi, mutagenesis, Coprinus

University of Kentucky (2007)