A simple and rapid technique for obtaining a high proportion of hybrid cleistothecia in Aspergillus nidulans

Selection arena in Aspergillus nidulans

The selection arena hypothesis states that overproduction of zygotes--a widespread phenomenon in animals and plants--can be explained as a mechanism of progeny choice. As a similar mechanism, the ascomycetous fungus Aspergillus nidulans may overproduce dikaryotic fruit initials, hereafter called dikaryons. Then, progeny choice might involve selection on which of these dikaryons will thrive to produce thousands of zygotes. These zygotes each produce eight sexual spores which together fill up one fruiting body. In this study, we test the selection arena hypothesis in this homothallic fungus that produces both sexual and asexual spores. We analyzed two mitochondrial and 15 auxotrophic mutations for consequences on sexual and asexual reproduction. We found that many of these mutations confer sexual self-sterility as a pleiotropic effect under conditions of normal asexual spore production. This confirms an important prediction of the selection arena, namely that dikaryons carrying a (slightly) deleterious mutation are not able to proliferate and produce sexual spores. The selection arena ensures that reproductive energy is invested mainly in dikaryons and thus sexual spores of good genetic quality.

An intragenic map of the brlA locus of Aspergillus nidulans

We have constructed an intragenic map for the Aspergillus nidulans brlA gene, mutants in which are distinguishable by visual criteria only. Most of the leaky phenotype mutants map near the right (3') end. The gene shows distinct recombinational polarity consistent with recombination initiation at the promoter (centromere-proximal) end of the gene. brlA12 and brlA20 mutants gave abnormal DNA restriction patterns consistent with the III; VIII and VI; VIII translocations, respectively, determined by haploidization.