|Shim, Won bo|
Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/2/2002
Publication Date: 10/1/2002
Citation: Shim, W., Dunkle, L.D. 2002. Identification of genes expressed during cercosporin biosynthesis in cercospora zeae-maydis. Physiological and Molecular Plant Pathology. 61:237-248. Interpretive Summary: The fungus Cercospora zeae-maydis causes gray leaf spot, the most prevalent and economically threatening disease of corn throughout the world. The pathogen produces a phytotoxin known as cercosporin, which is thought to be important for disease development. However, the metabolic pathway and enzymes involved in cercosporin synthesis are not known. From an analysis of genes that were uniquely expressed when the pathogen was producing cercosporin, we selected seven genes for further characterization. According to identities with genes already characterized, these fungal genes were determined to code for enzymes that function in fatty acid metabolism and secondary metabolism. Further characterization of these and other genes is in progress to help us understand their role in cercosporin biosynthesis and in gray leaf spot of corn. In addition to providing fundamental details about the molecular basis of plant disease, such information will be important to corn breeders, geneticists, and pathologists in devising novel disease management strategies through application of molecular and genetic technologies.
Technical Abstract: Gray leaf spot, caused by the fungus Cercospora zeae-maydis, is the most destructive foliar disease of maize in the United States. However, little is known about the biochemical and molecular events of pathogenesis. C. zeae-maydis produces cercosporin, a phytotoxin shown to be a virulence factor in diseases caused by other Cercospora species. To identify genes involved in cercosporin biosynthesis and ultimately determine the role of cercosporin in disease development, we constructed a cDNA subtraction library of C. zeae-maydis by suppression subtractive hybridization. Poly (A)+ RNA isolated from cultures grown in cercosporin-suppressing medium was subtracted from poly (A)+ RNA isolated from cultures grown in cercosporin-inducing medium, resulting in transcripts that are specific to the cercosporin-producing culture. Analyses of 768 sequences in this cDNA subtraction library revealed 197 cDNAs with high similarity to genes in the GenBank and Saccharomyces Genome Database, and these genes were grouped into nine categories based on predicted functions of the encoded proteins. Northern analysis of seven selected clones with predicted functions in fatty acid metabolism (fatty acid synthase, oleate delta-12 desaturase, and linoleate diol synthase) and secondary metabolism (cytochrome P450 oxidoreductase, cytochrome P450 monooxygenase, phenol oxidase, and coproporphyrinogen oxidase) indicated that those genes were expressed in cercosporin-inducing conditions. Analysis of expression kinetics confirmed that those genes are expressed concomitantly with cercosporin accumulation.