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UBC Theses and Dissertations

Investigation of kalilo-like plasmids in Neurospora and Gelasinospora He, Cynthia Yingxin


Mitochondrial DNA plasmids sharing great sequence homology with the senescenceinducing kalilo plasmid have been identified in natural isolates of Neurospora crassa, Neurospora intermedia, Neurospora tetrasperma, Neurospora discreta and a Neurospora-related genus Gelasinospora. Restriction enzyme analysis and sequence analysis have revealed that these plasmids are closely related by descent from a common ancestral plasmid. The phylogenetic tree constructed on the basis of the terminal inverted repeat sequences of the kalilo-like plasmids correlates well with the established taxonomy of their host fungi. The attempt to transfer kalilo-like plasmids to standard lab strains of N. crassa has had limited success. Only a few transferrants were obtained and they all proved to be unstable. Therefore, the comparison of plasmid function can not yet be made at the plasmid level with identical mitochondrial DNA and nuclear DNA background. However, the comparison of plasmid TIR sequences reveals some interesting features which may be relevant to the plasmid function. The failure of plasmid transfer indicates that horizontal transfer must be a rare event, though it may be evolutionarily significant as to contribute to the current distribution pattern of kalilo-related plasmids.

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