Multiple insertions and deletions determine the size differences between the mitochondrial DNAs of the EAN and NAN races of Ophiostoma novo-ulmi

Abstract

Restriction endonuclease fragment maps of the mitochondrial DNAs (mtDNAs) of two isolates of the North American (NAN) race and two isolates of the Eurasian (EAN) race of the Dutch elm disease pathogen, Ophiostoma novo-ulmi , were constructed and compared. Over half of the restriction maps of all four isolates were indistinguishable. Furthermore, the relative map positions of the fragments that hybridized with cloned fragments of Podospora anserina mtDNA containing genes of known function were the same in all the isolates. These results indicate a close relationship between the NAN and EAN mtDNAs. The mtDNAs of the two NAN isolates W2 tol1 (55·7 kb) and PG402 (56·7 kb), differed by only a single 1·0 kb insertion. However, the sizes of the mtDNAs of the two EAN isolates, H2023 (63·6 kb) and H277 (65·6 kb), were significantly greater than those of the two NAN isolates, due to the presence of additional insertions at a variety of locations in the mtDNA genome. Compared to the NAN PG402 mtDNA, the EAN H2023 and H277 mtDNAs contained four and five additional insertions, respectively, only two of which were in common. Unique restriction sites due to very small insertions/deletions or point mutations were also found in H2023 mtDNA. The implications of these results with regard to the evolution of O. novo-ulmi and its NAN and EAN races are discussed.