B-Mating-type genes influence survival of nuclei separated from heterokaryons of Schizophyllum

Abstract

Separation of single haploid nuclei from dikaryons of Schizophyllum commune, via protoplast formation and regeneration, has revealed significant asymmetric ratios of the two component nuclear types despite the strict 1:1 ratio that prevails in these highly structured heterokaryons. Skewed ratios of one type of nucleus to the other were previously shown to be characteristic of hemicompatible heterokaryons in which the A-mating-type alleles were identical but the B-mating-type alleles were different. This study has determined a genetic basis for this phenomenon by demonstrating that alleles of the B-mating-type genes influence nuclear survival. Specificity of alleles at bothBα andBβ loci has been shown to correlate with percentage survival of the component nuclear types recovered from both kinds of heterokaryons, suggesting differential effects of these series of multiple alleles on nuclear function in monokaryons isolated from heterokaryons. The alleles can be put in an hierarchical order with respect to this function. Mutation to loss or impairment ofB function results in a shift in hierarchical order relative to the progenitor allele. Evidence is given for an effect on nuclear division as a basis for the differential recovery of nuclei carrying different B-gene alleles. A scheme with some analogy to the system for establishing mitotic synchrony in cells of opposite mating type in Saccharomyces cerevisae is suggested as a possible basis for the observed effects of the B-mating-type genes in basidiomycetes.