Mm. Robison et Pa. Horgen, Widespread distribution of low-copy-number variants of mitochondrial plasmid pEM in the genus Agaricus, FUNGAL G B, 26(1), 1999, pp. 62-70
The incidence of the linear mitochondrial plasmid pEM in Agaricus spp. was
believed to be rare, based on visualization by gel electrophoresis and Sout
hern hybridization. However, we report in this study PCR amplification of p
EM-like sequences from all but one species of Agaricus examined. Regions am
plified included (1) the pEM RNA polymerase gene and (2) adjoining carboxy-
termini of the DNA and RNA polymerase genes. Sequence data from the RNA pol
ymerase-like products support a plasmid, rather than mitochondrial, origin
for these sequences. Sequence variation was low, and most differences were
silent or conservative at the amino acid level. Stop codons were found in t
wo of seven sequence types suggesting that functional constraints are low.
A parsimony-derived phylogeny for these sequences did not match expected ph
ylogenies for the host species. Recent acquisition of the plasmid is presen
ted as the most likely hypothesis explaining these observations. (C) 1999 A
cademic Press.