Isolation and partial characterization of a dominant mutant defective in the production of viable ascospores in Neurospora crassa.

Abstract

A dominant mutant Asc (KH2A83), defective in ascospore formation, was obtained as a spontaneous mutation by the application of allelic complementation between inl (37401) and inl (83201(t)). The heterozygous cross of this mutant with wild type as protoperithecial parent produced 10-40% of white abortive ascospores, and that with wild type as conidial parent formed 60-90% of white abortive ascospores. The homozygous cross of Asc (KH2A83) produced 90-95% of ascospore abortion. The mutation was mapped between his-1 and al-3 at a distance of 0.8% to al-3 on LG VR. The UV sensitivity of Asc(KH2A83) was 2.8-4.0-fold higher than that of wild type, but that of Mei-2, mapped near al-3, was 2.3-fold. Whereas, unlike Mei-2, Asc(KH2A83) did not show sensitivity to methyl methanesulfonate and to histidine. Conidia of Asc(KH2A83) showed about 1% of viability in sorbose agar minimal medium, but those of Mei-2 did not show such character. Markers near Asc (KH2A83) including al-3 and inl represented low recombination recovery rates (2.6-28.9%) indicating reduced viability of ascospores which includedAsc (KH2A83). The aneuploid formation in a heterozygous cross with Asc(KH2A83) as a protoperithecial parent was estimated to be 0.9%.