Widespread Distribution of Low-Copy-Number Variants of Mitochondrial Plasmid pEM in the GenusAgaricus

Molecular evolution of a mitochondrial polB gene, encoding a family B DNA polymerase, towards the elimination from Agrocybe mitochondrial genomes

“…In the latter species, giant linear molecules composed of mtDNA and specific sequences of the mitochondrial plasmid pAL-2-1 have been described (Hermanns et al 1995). In basidiomycetes, cryptic linear mitochondrial plasmids, encoding a family B DNA polymerase and a RNA polymerase, have been reported in numerous species such as F. velutipes (Nakai et al 2000) and nine studied Agaricus species (Robison and Horgen 1999), with the exception of Agaricus bisporus. However, in A. bisporus, a large but disrupted sequence possessing extensive homology to the plasmid pEM RNA polymerase gene described in the closely related species A. bitorquis, has been reported.…”

“…So far, we have not been able to detect such a linear plasmid in Agrocybe mitochondria by agarose gel electrophoresis of purified mtDNA (data not shown). However, in certain Agaricus species, certain linear plasmids can only be detected by PCR with primers derived from the closely related A. bitorquis plasmid pEM (Robison and Horgen 1999).…”

The Agrocybe aegerita mitochondrial genome contains two inverted repeats of the nad4 gene arisen by duplication on both sides of a linear plasmid integration site

“…Moreover, Robison and Horgen (1999) showed by PCR a widespread distribution of lowcopy-number plasmids related to the A. bitorquis pEM plasmid in eight species belonging to the Agaricus genus. The A. bisporus species was an exception.…”

The mitochondrial genome of the phytopathogenic basidiomycete Moniliophthora perniciosa is 109kb in size and contains a stable integrated plasmid

“…Conversely, in Podospora anserina strain AL2 and in the slime mould Physarum polycephalum, which are species that normally senesce, insertion of the plasmids into the mtDNA has been correlated with an increased life-span (Hermanns et al 1994;Maas et al 2007;Nakagawa et al 1998). Among Basidiomycota, invertron-like DNA plasmids have been completely sequenced in Agaricus bitorquis (Robison & Horgen 1999), Flammulina velutipes (Nakai et al 2000), and Pleurotus ostreatus (Kim et al 2000), but no specific function has been associated with their presence in these hosts.…”