Mitochondrial inheritance in ustilago violacea
Wilch, Gerhard A. A.
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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.