Mitochondrial inheritance in ustilago violacea

The anther smut fungus U stilago violacea has been developed as an important model organIsm for genetic, morphological and physiological studies. Valuable information on the nuclear genetics on U stilago violacea has been obtained in the last 20-25 years. However, in this organism almost nothing is known about mitochondria which make up an important aspect of the fungal genetic system. One fundamental aspect, mitochondrial inheritance, was addressed by this investigation. Mitochondrial DNA (mtDNA) of U. violacea was purified and restriction fragments cloned. MtDNA restriction fragment length polymorphisms (RFLPs) were identified among different isolates and were used as genetic markers for studying mitochondrial inheritance in crosses between polymorphic isolates. Matings of the yeast-like haploid cells of opposite mating types resulted in dikaryons containing mitochondria from both parents. The dikaryons were induced to form hyphae and then allowed to revert to haploid growth, resulting 1ll a colony that is bisectored for the two nuclear types. Both nuclear-type progeny of each cross were examined for parental mitochondrial type: Either mitochondrial type was observed 1ll the progeny. Thus, mitochondrial inheritance is biparental in this organism. The recovery of both mitochondrial types in the progeny was non-random. In progeny with the nuclear genotype of the al mating type parent mitochondria from both parents were inherited equally well. However, 1ll progeny with the a2 mating type, mitochondria were inherited almost exclusively (94%) from the a2 parent.

The genetics of glucosamine in yeast : cytoplasmic determinants conferring resistance

Two cytoplasmic, glucosamine resistant mutants of Saccharomyces cerevisiae, GR6 and GR10, were examined to determine whether or not the lesions involved were located on mitochondrial DNA. Detailed investigation of crosses of GR6 and GR10 or their derivatives to strains bearing known mitochondrial markers demonstrated that: 1. the frequency of glucos~~ine resistance in diploids was independent of factors influencing mitochondrial marker output. 2. upon tetrad analysis a variety of tetrad ratios was observed for glucosamine resistance whereas mitochondrial markers segregated 4:0 or 0:4 (resistant:sensitive). 3. glucosamine resistance and mitochondrial markers segregated differentially with time. 4. glucosamine resistance persisted following treatment of a GRIO derivative with ethidium bromide at concentrations high enough to eliminate all mitochondrial DNA. 5. haploid spore clones displayed two degrees of glucosamine resistance, weak and strong, while growth due to mitochondrial mutations was generally thick and confluent. 6. a number of glucosamine resistant diploids and haploids, which also possessed a mithchondrial resistance mutation, were unable to grow on medium containing both glucosamine and the particular drug involved. 3 These observations 1~ 6 provided strong evidence that the cytoplasmic glucosamine resistant mutations present in GR6 and GRiO were not situated on mitochondrial DNA. Comparison of the glucosamine resistance mutations to some other known cytoplasmic determinants revealed that: 7. glucosamine resistance and the expression of the killer phenotype were separate phenomena. 8. unlike yeast carrying resistance conferring episomes GR6 and GR10 were not resistant to venturicidin or oligomycin and the GR factor exhibited genetic behaviour different from that of the episomal determinants. These results 7--+8 suggested that glucosamine resistance was not associated with the killer determinant nor with alleged yeast episomes. It is therefore proposed that a yeast plasmid(s), previously undescribed, is responsible for glucosamine resistance. The evidence to date is compatible with the hypothesis that GR6 and GR10 carry allelic mutations of the same plasmid which is tentatively designated (GGM).