MITOCHONDRIAL VARIANTS OFNEUROSPORA INTERMEDIAFROM NATURE

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Abstract
From a sample of 122 natural isolates of N. intermedia collected recently from around the world, 5 variants had erratic stop-start growth patterns reminiscent of the phenotype of stopper laboratory extranuclear mutants of N. crassa. Like laboratory isolated mutants, the natural stopper variants were sterile as protoperithecial parents and transmitted the variant growth phenotypes very inefficiently, if at all, as male parents. Heterokaryon tests could not be made because of strain incompatibilities. Four of the variants have mitochondrial cytochrome aa3 and b deficiencies. These 4 variants are all defective in mitochondrial ribosome assembly and have abnormal ratios of large to small subunits. Restriction enzyme analyses revealed some similarity of N. intermedia to N. crassa mt[mitochondrial]DNA. One normal and 4 variant strains had additional DNA in comparison to a standard normal strain. Cumulatively, the results indicate that the genetic alterations which cause stopper phenotypes of these natural isolates of N. intermedia are of mitochondrial rather than nuclear origin.