MITOCHONDRIAL RNA EDITING OF CYTOCHROME-C-OXIDASE SUBUNIT-II (COXII) IN THE PRIMITIVE VASCULAR PLANT PSILOTUM-NUDUM

A 634-nucleotide tract, including primers, was amplified via the polym erase chain reaction within a mitochondrial coxII gene of the primitiv e vascular plant Psilotum nudum and sequenced. Alignment with homologo us coxII gene sequences from diverse plant species having known RNA ed iting sites which restore amino acid sequence consensus was used to in fer eight sites of C-to-U transitions in Psilotum. In every case, the predicted editing event would confer the selective advantage of conser ving the amino acid residue at a site where amino acid sequence diverg ence has not been observed in other plant species. The plant mitochond rial editing machinery is shown for the first time to extend to one of the deepest branches of vascular plant phylogeny.