FUNCTION AND CHROMOSOMAL LOCATION OF THE COCHLIOBOLUS-HETEROSTROPHUS TOX1 LOCUS

Conventional genetic analyses have firmly established that the differe nce in virulence between race T and O of the corn pathogen Cochliobolu s heterostrophus is determined by a single genetic locus called Tox1, which also controls production of T-toxin, a polyketide specifically t oxic to corn with Texas male sterile (T) cytoplasm. More recently, mol ecular genetic analyses have revealed that Tox1 is not a single gene b ut rather at least two genetic loci situated on two different chromoso mes. DNA at both of these loci is required for the biosynthesis of T-t oxin 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.