PLASMID LOSS IN AGARICUS-BITORQUIS WITHOUT ALTERATIONS IN HOMOLOGOUS MITOCHONDRIAL SEQUENCES

An isolate of the basidiomycete Agaricus bitorquis, a common edible la wn mushroom, contains two linear mitochondrial plasmids. With the inte nt of creating a plasmidless (or ''cured'') version of this isolate fo r future studies on a plasmid-homologous mitochondrial sequence, mycel ium was grown in the presence of 50 mu g/ml ethidium bromide. Regenera tes were recovered that had lost only the larger plasmid or both plasm ids. No obvious effects on mycelial or mushroom phenotype, associated with plasmid loss, were observed. Restriction fragment length polymorp hism analysis of mitochondrial DNAs from 23 regenerates indicated that no apparent deletions or rearrangements of the mitochondrial DNA, par ticularly the plasmid-homologous mitochondrial sequence, occurred as a result of plasmid loss or ethidium bromide treatment. (C) 1994 Academ ic Press, Inc.