Genetics of Neurospora

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PERKINS 9728675 Neurospora is being used to investigate genetic problems that are not as readily approached with yeast or other organisms: (1) In a study of internuclear cis-trans position effects, progeny that are heterokaryotic for deficiencies of defined chromosome segments will be obtained from crosses heterozygous for translocations. These will be examined for impaired complementation between haploid nuclei, with the object of identifying segments and genes that specify nucleus-limited or nucleus-associated functions. The study is made possible by the existence of many well characterized chromosome rearrangements and the ability to obtain ascospores that are heterokaryotic for different products of the same meiosis. (2) The structure and content of a complex chromosome region that is responsible for meiotic drive will be examined using different Spore killer haplotypes in N. crassa and in the heterokaryotic species N. tetrasperma. New variants responsible for resistance to killing will be sought and characterized. The study is feasible because presence of a drive element is signaled visually by asci containing four black and four white ascospores. (3) Strains from natural populations will be examined for genetic polymorphisms at two molecularly sequenced vegetative incompatibility (het) loci, which govern the ability of nuclei to coexist in the same cytoplasm in a heterokaryon. This study of self-nonself recognition is made possible by the availability of insertional translocations that can be used to generate partial-diploid progeny heterozygous for each of the individual het genes. The filamentous fungus Neurospora serves as a modal for economically important fungi and for fungal plant and animal pathogens. It also continues to provide basic information on processes common to many higher organisms. Neurospora strains with cells that contain nuclei of two different genetic types, one with a deficient chromosome segment and the other with the corresponding active segement, will be used to identify genes whose functions are nucleus-limited or nucleus-localized. By using a series of defined segmental deficiencies, the experiments should reveal whether genes with completely or partially impaired internuclear complementation are widely distributed in the chromosomes. This noninvasive approach should provide new insights into cell organization. Make-up of the chromosomal Spore-killer complex is being examined. The direct effects of this selfish chromosomal DNA element are displayed visually in Neurospora in the pigmented ascospores of sexual hybrids. Genetic resolution of the complex should aid in understanding the evolutionary history and significance of similar meiotic drive elements in higher organisms. Neurospora is ideal for detecting vegetative incompatibility genes that are able to distinguish "self" from "nonself", thus controlling the ability of genetically different fungal cells to fuse and form a stable multinucleate heterokaryon. The frequency and nature of differences at two such gene loci are being examined in an extensive survey of Neurospora cultures from nature. The study is expected to increase understanding of the molecular basis of vegetative incompatibility and the significance of incompatibility for the organism.