NEW MUTATIONS THAT SUPPRESS MATING-TYPE VEGETATIVE INCOMPATIBILITY INNEUROSPORA-CRASSA

The mating-type locus in the ascomycete Neurospora crassa functions as a vegetative-incompatibility locus during asexual growth such that A + a heterokaryons and A/a partial diploids are inhibited in their grow th. In this study, we sought mutations that suppress mating-type assoc iated vegetative incompatibility by using A/a partial diploids. Mutant s were selected as spontaneous escapes from inhibited growth. Suppress ors were identified by selecting escapes that retained the capacity to mate with both A and a strains. The escaped partial diploids were the n outcrossed to remove the duplication. Seven suppressors were identif ied that segregated as single, recessive mutations. All seven of the s uppressors were shown to be allelic to a previously obtained suppresso r, tol, by segregation analyses and heterokaryon tests. This result in dicates that all seven mutations are new alleles of tol and suggests t hat tol is a key regulatory locus in the expression of mating-type ass ociated vegetative incompatibility in N. crassa.