Molecular and functional analyses of incompatibility genes at het-6 in a population of Neurospora crassa

Two closely linked genes, un-24 and het-6, associated with the het-6 hetero karyon incompatibility functional haplotype were examined in 40 Neurospora crassa strains from a Louisiana sugarcane field. Partial diploid analyses w ere used to determine that half of the strains were functionally Oak Ridge (OR) and half were non-OR and indistinguishable from the standard Panama (P A) form. PCR-based markers were developed to identify polymorphisms within both un-24 and het-6, Two common forms of each gene occur based on these mo lecular markers. Rare forms of both un-24 and het-6 were identified as vari ants of the non-OR form by a DNA transformation assay. The heterokaryon inc ompatibility function of haplotypes, based on partial diploid analyses, was perfectly correlated with the PCR-based markers at both loci. This correla tion indicates that the two loci are in severe linkage disequilibrium in th is population sample and may act as an incompatibility gene complex. Southe rn hybridizations using OR- and PA-derived cloned probes from the region th at spans un-24 and het-6 showed that the apparent absence of recombination in this similar to 25-kbp region is associated with low levels of overall s equence identity between the PA and OR forms. (C) 2000 Academic Press.