IDENTIFICATION OF PEPTIDE SYNTHETASE-ENCODING GENES FROM FILAMENTOUS FUNGI PRODUCING HOST-SELECTIVE PHYTOTOXINS OR ANALOGS

Race 1 of Cochliobolus carbonum (Cc) makes a cyclic tetrapeptide, HC-t oxin, that is necessary for its virulence on certain genotypes of maiz e. The synthesis of HC-toxin is catalyzed by a 570-kDa multifunctional enzyme, HC-toxin synthetase (HTS). The gene encoding HTS (HTS1) is ab sent from other races of Cc and from other species of Cochliobolus. Fo ur other unrelated filamentous fungi make cyclic peptides closely rela ted to HC-toxin, raising the possibility that the corresponding cyclic peptide synthetase (CPS)-encoding genes have moved between these fung i by horizontal gene transfer. Degenerate PCR primers were designed ba sed on several highly conserved amino acid (aa) motifs common to known CPS domains and used to amplify genomic sequences from different fung i. PCR products representing CPS genes from Diheterospora chlantydospo ria, which makes the HC-toxin analog chlamydocin, Cylindrocladium macr osporum, which makes the analog Cyl-2, and C. victoriae, which makes t he unrelated cyclic pentapeptide victorin, were cloned and analysed. T heir sequences are more closely related to HTS1 than to other cloned C PS, but the percent aa identity is not consistent with very recent hor izontal movement of these genes.