Distribution and evolutionary significance of mitochondrial plasmids in Neurospora spp

A mitochondrial plasmid line in the fungal genus Neurospora is geographically widely distributed and occurs in isolates of at least two species. On the basis of characterization with restriction endonucleases, it is apparent that plasmids from isolates of Neurospora tetrasperma are more closely related to one another than to an evolutionarily homologous plasmid from Neurospora intermedia; N. tetrasperma plasmids from Surinam and Hawaii differed from one another only slightly by our analysis, whereas the plasmid from N. intermedia (Fiji) exhibited substantial restriction site divergence from all N. tetrasperma plasmids. We believe these observations strengthen the presumption that four-spored isolates of Neurospora spp. represent a natural taxonomic grouping (N. tetrasperma). The plasmids from N. tetrasperma and N. intermedia (Fiji), although clearly related to each other as shown by hybridization studies, exhibited no detectable homology with either of two additional plasmid lines from isolates of Neurospora spp. Nor did they exhibit homology with the mitochondrial genome. Despite this lack of homology among three distinct plasmid lines, all the plasmids may possess a common mode of replication.