Neurospora crassa will be used to investigate gene silencing, development, and cell biology during the sexual phase of the life cycle. Studies will continue on the silencing of genes in DNA segments that are unpaired in meiosis, using new green fluorescent protein (GFP)-tagged genes to affirm the generality of silencing and to determine its time of onset and duration. GFP will be used to follow the movement of tagged gene products away from the nucleus of origin following reactivation of genes in giant ascospores where all meiotic products are present in a common cytoplasm. Suppressors of silencing will be used to explore a possible relationship between meiotic silencing and the inactivation of sensitive ascospores by Spore-killer meiotic-drive elements. Parallel studies will investigate meiotic silencing in N. tetrasperma, a pseudohomothallic species in which ascus development is reprogrammed to produce four self-fertile heterokaryotic products. Other N. tetrasperma studies will examine strains from nature for the presence of cryptic Spore killer meiotic drive elements and deleterious recessive mutations. Crossing over in N. tetrasperma is abolished over most of the mating-type chromosome, possibly due to recently discovered structural differences between the chromosomes of opposite mating type. Genetically exchanging mating-type chromosomes between N. crassa and N. tetrasperma, via introgression, will examine the origin of differences in chromosome structure and assess their role in the evolution of the 4-spored condition in N. tetrasperma.
The laboratory continues to draw on its long experience using the filamentous fungus Neurospora to explore fundamental problems of theoretical and practical interest. The research is expected to advance knowledge of gene-silencing mechanisms (important in development and defense), to further the understanding of genetic systems that are based on heterokaryons (two genetically different nuclei in the same cell), and to enhance the value of Neurospora as a reference model organism with which to compare other filamentous fungi, including plant and animal pathogens, commercially important species, and innumerable ecologically important forms.
