Assembly of the Didymium Iridis Mitochondrial Genome by Genome Walking

Organelle inheritance and RNA editing has been studied in Didymium iridis even though the genome has not been completely sequenced. Four segments, comprising 66 kb, have been sequenced in the past. Several approaches have been taken to complete the sequence including restriction mapping and southern hybridization, as well as screening clone banks by PCR with the sequence of contig ends. In this study, genome walking was used to uncover sequences connecting the four segments. Using genome walking, approximately 4,113 bp of new sequence was identified. With the new sequence and the characterization of two previously sequenced D. iridis mt regions (3009 bp and 5,257 bp), 21 new ORFs and 12 putative genes were found. Although the new sequence data connected the four sequenced segments, a single circular genomic map could not be resolved. Instead, the data suggest that intragenomic recombination has occurred. Further studies will be required to understand the complete structure of the genome