THE MOLECULAR-BASIS FOR THE NATURAL-RESISTANCE OF THE CYTOCHROME BC(1) COMPLEX FROM STROBILURIN-PRODUCING BASIDIOMYCETES TO CENTER Q(P) INHIBITORS

Mitochondria from the strobilurin A producing basidiomycetes Strobilur us tenacellus and Mycena galopoda exhibit natural resistance to (E)-be ta-methoxyacrylate inhibitors of the ubiquinol oxidation center (cente r Q(P)) of the cytochrome be, complex. Isolated cytochrome be, complex from S. tenacellus was found to be highly similar to that of Saccharo myces cerevisiae with respect to subunit composition, as well as spect ral characteristics and midpoint potentials of the heme centers. To un derstand the molecular basis of natural resistance? we determined the exon/intron organization and deduced the sequences of cytochromes b fr om S. tenacellus, M. galopoda and a third basidiomycete, Mycena viridi marginata, which produces no strobilurin A. Comparative sequence analy sis of two regions of cytochrome b known to contribute to the formatio n of center Q(P) suggested that the generally lower sensitivity of all three basidiomycetes was due to the replacement of a small amino acid residue in position 127 by isoleucine. For M. galopoda replacement of Gly143 by alanine and Gly153 by serine, for S. tenacellus replacement of a small residue in position 254 by glutamine and Asn261 by asparta te was found to be the likely causes for resistance to (E)-beta-methox yacrylates. The latter exchange is also found in Schizosaccharomyces p ombe, which we found also to be naturally resistant to (E)-beta-methox yacrylates.