We sequenced four circular, mitochondrial subgenomes from the potato cyst nematode Globodera pallida. These subgenomes contained overlapping subsets of the 37 genes normally found in animal mitochondrial genomes, a feature not previously reported for any other animal species. A previous search for full length genomes within this nematode failed to find any. Analysis of the sequence data indicate that three of these subgenomic mitochondrial circles are mosaics, comprising long, multigenic fragments derived from fragments of the other circles. This pattern is consistent with the operation of intermitochondrial recombination, a process generally considered absent in animal mitochondria. Many of the duplicated genes contain deleterious mutations (primarily point indels that disrupt the reading frame), but sequencing of multiple copies of these genes indicates that there is variation at polythymidine tracts. Comparison of the genomic sequences with cDNA is consistent with the operation of insertion/deletion editing of mitochondrial transcripts.

We then sequenced five mitochondrial genomes from the close relative, Globodera rostochiensis, and found that these were similarly subgenomes, each containing only a subset of the 37 genes normally found on animal mitochondrial genomes. Variation at polythymidine tracts was also evident, and comparison of genomic sequences with an EST database of this nematode similarly was consistent with the operation of insertion/deletion editing.

We are currently investigating the mitochondrial structure of the heteroderid nematodes, in order to more accurately determine the evolutionary origin of these novel mitochondrial structures.