Characterization of the mitochondrial nad7 gene in Physcomitrella patens: Similarity with angiosperm nad7 genes

The nad7 gene, encoding the subunit 7 of NADH dehydrogenase complex I, is located in the mitochondrial genome in some species of green algae and seed plants, while it is nuclear-encoded in fungi and animals. In a liverwort, the presence of a mitochondrial nad7 pseudogene, and a nuclear nad7 gene has been reported. We have isolated the mitochondrial nad7 gene of the moss Physcomitrella patens. This gene is transcribed as a monocistronic mRNA and contains two group II introns that correspond to the first two of the four introns in the nad7 genes in angiosperms. Results of phylogenetic analysis supported monophyly of the nad7 genes of mosses and tracheophytes. Available data suggest that the nuclear transfer of the nad7 gene occurred only in the liverwort lineage, which diverged extensively from the mosses and tracheophytes with respect to the nad7 gene.