title: Neurospora tetraspermacrosses heterozygous for hybrid translocation strains produce rare eight-spored asci-bearing heterokaryotic ascospores.
abstract: During ascogenesis in Neurospora, the ascospores are partitioned at the eight-nucleus stage that follows meiosis and a post-meiotic mitosis, and the ascospores that form in eight-spored asci are usually homokaryotic. We had previously created novel TNt strains by introgressing four Neurospora crassa insertional translocations (EB4, IBj5, UK14-1, and B362i) into N. tetrasperma. We now show that crosses of all the TNt strains with single-mating-type derivatives of the standard N. tetrasperma pseudohomothallic strain 85 (viz. TNta x 85A or TNtA x 85a) can produce rare eight-spored asci that contain heterokaryotic ascospores, or ascospores with other unexpected genotypes. Our results suggest that these rare asci result from the interposition of additional mitoses between the post-meiotic mitosis and the partitioning of nuclei into ascospores, leading to the formation of supernumerary nuclei that then generate the heterokaryotic ascospores. The rare asci probably represent a background level of ascus dysgenesis wherein the partitioning of ascospores becomes uncoupled from the post-meiotic mitosis. Ordinarily, the severest effect of such dysgenesis, the production of mating-type heterokaryons, would be suppressed by the N. crassa tol (tolerant) gene, thus explaining why such dysgenesis remained undetected thus far.
authors.affiliation: Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500 001, India, kas@cdfd.org.in.
authors.forename: Durgadas P
authors.initials: DP
authors.lastname: Kasbekar
authors.forename: Selvam
authors.initials: S
authors.lastname: Rekha
mesh_terms: D002467:Cell Nucleus / Q000235:genetics*; D003433:Crosses, Genetic; D005838:Genotype; D006579:Heterozygote; D008540:Meiosis / Q000235:genetics*; D008938:Mitosis; D009491:Neurospora / Q000235:genetics* / Q000254:growth & development; D013172:Spores, Fungal / Q000235:genetics* / Q000254:growth & development