Inheritance of Pisatin Demethylase in the Fusaria

Abstract

Upon recognition of the pathogen, plants initiate defense responses that can include the production of antimicrobial compounds such as phytoalexins. Nectria haematococca mating population VI (MPVI) is a filamentous ascomycete that contains a cluster of genes known as the pea pathogenicity (PEP) cluster in which the pisatin demethylase (PDA) gene resides. PDA is responsible for the detoxification of the phytoalexin, pisatin, produced by the pea plant (Pisum sativum). Thus, PDA allows the fungus to colonize and become a pea pathogen. It has been proposed that the evolutionary origin of PDA and the PEP cluster is explained by a horizontal gene transfer (HGT) event. The observations supporting this hypothesis include the location of the PEP cluster on a conditionally dispensable (CD) chromosome, the phylogenetically discontinuous distribution of the cluster among closely related species, and bias in GC content and codon usage. This study used a three-pronged approach to test the hypothesis that PDA and the PEP cluster were inherited via HGT. Percent identities of conserved genes, along with GC content analysis and phylogenetics support vertical inheritance.