REMI-induced mutants of lacking the polyketide PM-toxin are deficient in pathogenesis to corn

The polyketide PM-toxin, produced byMycosphaerella zeae-maydis, is specifically active against corn containing Texas male sterile (T) cytoplasm, as is the fungus itself. To determine if PM-toxin is required for disease development,Tox−mutants were generated using the restriction enzyme-mediated integration (REMI) strategy, which is designed to tag the mutations it creates. As a mutagenic procedure, REMI was highly efficient, yielding five stable PM-toxin-deficient mutants among 504 transformants recovered. AllTox−mutants lost the ability to cause disease on T-cytoplasm corn, establishing a role for PM-toxin in pathogenesis. Examination of genomic DNAs from theTox−mutants revealed one that carried the transformation vector at multiple insertion sites and two that had no apparent ORFs at single vector insertion sites; three sustained deletions.