Contemporary Quests of Classical Neurospora Genetics: Do Fungi Contain Nucleus-Limited Genes

Dr.Durgadas P. Kasbekar
Centre for DNA Fingerprinting & Diagnostics, India
Tuesday, March 11, 2014 - 4:00pm
Marley 230

Contemporary Quests of Classical Neurospora Genetics: Do fungi contain nucleus-limited genes? Does Genome Sequence Polymorphism Suppress Meiotic Silencing? Durgadas P. Kasbekar, Centre for DNA Fingerprinting & Dignostics, Hyderabad 500001, India ( We are introgressing translocation chromosomes from the heterothallic fungus Neurospora crassa into the related pseudohomothallic species N. tetrasperma . Our idea is to produce self-fertile heterokaryotic [(T) + (N)] strains whose self-cross should generate [(T) + (N)] and [(Dp) + (Df)] progeny. If any [(Dp) + (Df)] is self-sterile, it would provide the first evidence for the existence of “nucleus-limited” genes, i.e., where the wild-type allele (WT) fails to complement a null allele ) in a [(WT) + ()] heterokaryon. Such genes have not yet been found, but they are predicted by extrapolating from the phenotype of the sconc mutant of N. crassa (Butler and Metzenberg 1972 J Bacteriol. 109:140-51), or the MatIS process in Aspergillus nidulans (Czaja et al. 2013 Genetics 193:1149-1162). Additionally, we are investigating why four wild-isolated N. crassa strains show suppression of meiotic silencing of the bml and mei-3 genes in crosses with the OR-derived testers ::Bmlr and ::mei-3. The four stains typified the “Sad type” strains. Crosses of the testers with 68 other wild strains showed suppression of silencing in mei-3, but not in bml, and typified the intermediate “Esm type”. Only eight wild strains, the “OR” type, behaved like the standard laboratory strains of the OR background, and showed silencing in crosses with both the testers. Bichpuri-1 a (B) and Spurger A (S) are two Sad type strains. A B x S cross followed by 10 generations of sibling crosses was used to create isogenic mat A and mat a strains in the B/S background. If a new mei-3- like tester were to be made heterozygousin a cross in this background, and the cross were to show meiotic silencing, it would support our hypothesis that the Sad or Esm phenotype arises from heterozygosity for sequence polymorphism in the cross of the wild strains with the OR-derived testers. It is conceivable that sequence polymorphisms reduce pairing and silence meiotic silencing genes in wild x tester crosses.