Behavior of Neurospora sitophila mating-type alleles in heterozygous duplications after introgression into Neurospora crassa

Abstract

In Neurospora sitophila , strains of opposite mating type can form stable A + a heterokaryons ( Mishra, 1971, Genetics 67: 55–59 ). In Neurospora crassa , however, both A + a heterokaryons and heterozygous A/a duplications (partial diploids) usually exhibit a strong vegetative incompatibility reaction that prevents normal growth. N. sitophila mating-type alleles were introgressed into N. crassa by recurrent backcrosses to determine whether the mating-type genes were in fact different in the two species. In the N. crassa genetic background, the alleles originating from N. sitophila ( A S and a S ) were indistinguishable from those of N. crassa ( A C and a C ), using as a criterion their incompatibility behavior in heterozygous duplications obtained from crosses involving a duplication-producing chromosome rearrangement, In ( IL → IR ) H4250 . Vegetative incompatibility is equally strong for A S / a S , A C / a C , A S / a C , and A C / a S . The vegetative incompatibility in N. crassa is completely alleviated by an unlinked suppressor gene tol (tolerant), both for A S / a S and for A C / a C . Mating-type genes of the two species thus appear to be functionally identical.