Plasmid RNA polymerase-like mitochondrial sequences inAgaricus bitorquis

A linear mitochondrial plasmid, pEM, found in certain isolates of the basidiomyceteAgaricus bitorquis potentially encodes virus-like DNA and RNA polymerases. Mitochondrial DNA fromAgaricus bisporus that hybridizes to an internal region of pEM contains a fragmented and potentially non-functional version of the carboxy terminal end of the plasmid RNA polymerase. In this study, we present the sequence of the corresponding region of mitochondrial DNA fromA. bitorquis. This sequence contained the same region of the plasmid RNA polymerase gene as was reported for the mitochondrial DNA ofA. bisporus, and the level of similarity between theA. bisporus andA. bitorquis mitochondrial sequences was much higher than the level of similarity between either mitochondrial sequence and the plasmid. We propose that this plasmid RNA polymerase-like sequence was present in theAgaricus mitochondrial genome before the divergence ofA. bisporus andA. bitorquis, and thus is unlikely to be a recent derivative of the plasmid pEM.