RECOMBINATION OF MITOCHONDRIAL DNAS FOLLOWING TRANSMISSION OF MITOCHONDRIA AMONG INCOMPATIBLE STRAINS OF BLACK ASPERGILLI

Successful intra- and interspecific mitochondrial transfers were perfo rmed by polyethylene glycol (PEG)-induced protoplast fusion among inco mpatible strains belonging to the Aspergillus niger species aggregate. The mitochondrial DNAs (mtDNAs) of the strains examined were of three main types based on their restriction fragment length polymorphism (R FLP) profiles. mtDNA types 1 and 2 correspond to A. niger and A. tubin gensis species, respectively, while type 3 is represented by some Braz ilian wild-type isolates (possibly a distinct species or subspecies). mtDNA types 1 and 2 could be further divided into several subgroups (1 a-1e and 2a-2f). All these strains, representing different RFLP groups or subgroups, were fully incompatible with respect to nuclear complem entation. The transfer experiments were carried out under selection pr essure, using a mitochondrial oligomycin-resistant mutant of mtDNA typ e 1a as donor. Following fusion mitochondrial oligomycin-resistant pro genies were recovered in the presence of oligomycin by selecting for t he nuclear phenotypes of the oligomycin-sensitive recipient strains. A ll attempted transfers were successful, and resulted in different vari eties of resistant recombinant mitochondrial progenies at various freq uencies. Within the group of strains of mtDNA type 1, the transfer of oligomycin-resistant mitochondria resulted in the appearance of a sing le recombinant type of RFLP profile in each case. The recombination ev ents were more complex when the transfer of oligomycin resistance occu rred between strains representing different species (mtDNA groups 1a-- >2 and 1a-->3). A great variety of recombinant mtDNA RFLP profiles app eared. Explanation for this phenomenon are discussed on the basis of p reliminary physical mapping data.