Function and chromosomal location of the Cochliobolus heterostrophus TOX1 locus

Conventional genetic analyses have firmly established that the difference in virulence between race T and O of the corn pathogen Cochliobolus heterostrophus is determined by a single genetic locus called Tox1, which also controls production of T-toxin, a polyketide specifically toxic to corn with Texas male sterile (T) cytoplasm. More recently, molecular genetic analyses have revealed that Tox1 is not a single gene but rather at least two genetic loci situated on two different chromosomes. DNA at both of these loci is required for the biosynthesis of T-toxin and for the high virulence of race T to corn carrying T-cytoplasm. One of the loci encodes a polyketide synthase that is necessary for the assembly of the T-toxin molecule. Key words: polyketide, restriction enzyme mediated integration (REMI), host-specific toxin, corn, fungus, virulence.