Cloning and characterization of a cyclic peptide synthetase gene from Alternaria alternata apple pathotype whose product is involved in AM-toxin synthesis and pathogenicity

Alternaria alternata apple pathotype causes Alternaria blotch of susceptibl e apple cultivars through the production of a cyclic peptide host-specific toxin, AM-toxin. PCR (polymerase chain reaction), with primers designed to conserved domains of peptide synthetase genes, amplified several products f rom A. alternata apple pathotype that showed high similarity to other funga l peptide synthetases and were specific to the apple pathotype, Screening o f a Lambda Zap genomic library with these PCR-generated probes identified o verlapping clones containing a complete cyclic peptide synthetase gene of 1 3.1 kb in length with no introns, Disruption of this gene, designated AM-to xin synthetase (AMT), by transformation of wild-type A. alternata apple pat hotype with disruption vectors resulted in toxin-minus mutants, which were also unable to cause disease symptoms on susceptible apple cultivars, AM-to xin synthetase is therefore a primary determinant of virulence and specific ity in the A, alternata apple pathotype/apple interaction.