Molecular dissection of the spore killer elements in Neurospora

Abstract

The role of selfish genetic elements in shaping the evolution of genomes (and subsequently species) has been a great subject of scientific interest for much of the last century. These selfish elements act at both the genetic and cellular level to insure that they are propagated within the genome, species, or both. Meiotic drive elements, which increase in number by destroying allelic counterparts, have been implicated in the extinctions of whole species and in the evolution of RNAi-mediated genome defense mechanisms. In fungi, several meiotic drive systems are known but not well understood. In the experiments described below, we attempt to characterize and differentiate the Spore killer (Sk) meiotic drive systems of the genus Neurospora as well as examine the defensive mechanisms that have arisen to prevent the spread of these and other selfish genetic elements. The Neurospora Spore killer meiotic drive elements are believed to resemble other classic drive systems in their composition of two loci, a killer locus that creates drive for itself and a resistance locus that protects the killer from self-killing. The majority of my research herein has been a combined effort with Dr. Thomas Hammond on the mapping and characterization of the resistance locus in the Spore killer systems. We began by utilizing the recently created Neurospora gene knockout library to create a series of 3-point testcrosses to map the location of a natural resistance gene in an r(Sk-2) strain. Testcross analysis narrowed the gene candidate field to just six genes. Next, knockout mutants were created for the remaining genes. Crosses of these mutants to Sk revealed that only one of the genes, NCU09151, confers resistance to Sk-2 . We therefore identify NCU09151 as resistant to Spore killer 2 [rsk[superscript r(Sk-2)]]. Next, we showed that when rsk[superscript r(Sk-2)] is inserted into a sensitive strain, resistance to Sk-2 is granted to that strain, further solidifying the notion that NCU09151 is the resistant gene in the r(Sk-2) strains. Bas