REMI-INDUCED MUTANTS OF MYCOSPHAERELLA-ZEAE-MAYDIS LACKING THE POLYKETIDE PM-TOXIN ARE DEFICIENT IN PATHOGENESIS TO CORN

The polyketide PM-toxin, produced by Mycosphaerella zeae-maydis, is sp ecifically active against corn containing Texas male sterile (T) cytop lasm, as is the fungus itself. To determine if PM-toxin is required fo r disease development, Tox(-) mutants were generated using the restric tion enzyme-mediated integration (REMI) strategy, which is designed to tag the mutations it creates. As a mutagenic procedure, REMI was high ly efficient, yielding five stable PM-toxin-deficient mutants among 50 4 transformants recovered. All Tox(-) mutants lost the ability to caus e disease on T-cytoplasm corn, establishing a role for PM-toxin in pat hogenesis. Examination of genomic DNAs from the Tox(-) mutants reveale d one that carried the transformation vector at multiple insertion sit es and two that had no apparent ORFs at single vector insertion sites; three sustained deletions. (C) 1998 Academic Press Limited.