Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2001
Publication Date: N/A
Interpretive Summary: Fungi are the microbes most likely to cause plant disease. However, little is known about their biochemical and genetic requirements for pathogenicity. In this paper we discovered three genes involved in determining pathogenicity to pea in the root rot fungus, Nectria haematoccoa. The group of genes, clustered on a relatively small portion of a chromosome in the fungus, has similarity to "pathogenicity islands" found in bacterial pathogens of animals. Knowledge of the arrangement of genes suggest that they may be transferred as a unit to different strains of the same species or even to other fungal species. This work may help predict how fungi with new host specificity arise relatively quickly in evolutionary time. By understanding how pathpgenic strains arise we may be better able to predict their occurrence and to combat their ability to cause plant disease epidemics.
Technical Abstract: Three genes that contribute to the ability of the fungus Nectria haematococca to cause disease on pea palnts have been identified. These pea pathogenicity or "PEP" genes are within 25 kilobase pairs of each other and located on a supernumerary chromosome. Altogether, the PEP gene cluster contains six transcriptional units that are ecpresses during infection of pea tissue. The biochemical function of only one of the gene is known with certainty. This gene, PDA1, encodes a specific cytochrome P450 that confers resistance to pisatin, and antibiotic produced by pea plants. The three new PEP genes, in addition to PDA1, can independently increase the ability of the fungus to cause lesions on pea when added to an isolate lacking the supernumerary chromosomes. Based on predicted amino acid sequences, funcaitons for two of these three genes are hypothesized. The deduced amino sequence of another transcribed portion of the PEP cluster, as well as foour other open reading frames in the cluster, have a high degree of similarity to known fungal transposases. Several of the features of the PEP cluster - a cluster of pathogenicity genes, the presence of transposable elements and suggestions of exogenous origin are shared by pathogenicity islands in pathogenic bacteria of plants and animals.