Mutants with decreased differentiation to plasmodia in Physarum polycephalum

Summary Mutant (APT) amoebae that display reduced ability to form plasmodia asexually were isolated by the use of an enrichment procedure. The results of reconstruction experiments show that the procedure enriches only for mutants blocked early in the pathway from amoeba to plasmodium. Mutants were isolated from four parents, two of which produce plasmodia asexually because they carry the allele mth of the mating type locus, and two because they carry gad (greater asexual differentiation) mutations. The APT mutants varied widely in the frequency of residual plasmodium formation, which occurred, in some cases, by reversion. The mutants, called apt (amoeba to plasmodium transition), were recessive in diploids and linked to the mating type (mt) locus. Mutants derived from the gad parents, unlike the parents themselves, crossed readily with heterothallic amoebae. Progeny analysis from such crosses indicates that both gad mutations are linked to mt. The mutants derived from one of the mth parents fell into two groups on the basis of their ability to cross with the mutants derived from the mt2 gad-8 parent. The result suggests that the mth-derived mutants represent two or more complementation groups. Mutants derived from the mt2 gad-8 parent cross with mt2 amoebae and hence display an altered mating specificity.