Disparate Independent Genetic Events Disrupt the Secondary Metabolism GeneperAin Certain Symbiotic Epichloë Species
ABSTRACTPeramine is an insect-feeding deterrent produced byEpichloëspecies in symbiotic association with C3grasses. TheperAgene responsible for peramine synthesis encodes a two-module nonribosomal peptide synthetase. Alleles ofperAare found in mostEpichloëspecies; however, peramine is not produced by manyperA-containingEpichloëisolates. The genetic basis of these peramine-negative chemotypes is often unknown. Using PCR and DNA sequencing, we analyzed theperAgenes from 72Epichloëisolates and identified causative mutations ofperAnull alleles. We found nonfunctionalperA-ΔR* alleles, which contain a transposon-associated deletion of theperAregion encoding the C-terminal reductase domain, are widespread within theEpichloëgenus and represent a prevalent mutation found in nonhybrid species. Disparate phylogenies of adjacent A2 and T2 domains indicated that the deletion of the reductase domain (R*) likely occurred once and early in the evolution of the genus, and subsequently there have been several recombinations between those domains. A number of novel point, deletion, and insertion mutations responsible for abolishing peramine production in full-lengthperAalleles were also identified. The regions encoding the first and second adenylation domains (A1 and A2, respectively) were common sites for such mutations. Using this information, a method was developed to predict peramine chemotypes by combining PCR product size polymorphism analysis with sequencing of theperAadenylation domains.