Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2009
Publication Date: 11/15/2009
Citation: Wicklow, D.T., Jordan, A.M., Gloer, J.B. 2009. Antifungal Metabolites (Monorden, Monocillins I, II, III) from Colletotrichum graminicola (Ces.) G.W. Wils. NRRL 47511, a Systemic Vascular Pathogen of Maize. Mycological Research. 113(12):1433-1442. Interpretive Summary: Colletotricum graminicola is a fungal pathogen that causes anthracnose stalk rot and leaf blight of corn and can result in substantial annual losses to the U.S. corn crop. Cultural tests showed that that this fungus is antagonistic to several other stalk and kernel rotting pathogens of corn. Chemical studies revealed that the metabolites accounting for this activity were known antibiotics monorden (also known as radicicol) and monocillin I. This is the first report of natural products from C. graminicola, as well as the production of monorden and monocillins by a pathogen of cereals. Monorden was detected in maize stalk residues inoculated with C. graminicola and could contribute to pathogen survival through the exclusion of other fungal colonists. Monorden and monocillin I were recently shown to bind and inhibit a plant protein that is essential to an effective defense against pathogen invasion. It is hypothesized that monorden and monocillins support C. graminicola infection by targeting and disrupting corn defenses. The corn industry will benefit from knowledge of the means by which this major fungal pathogen of cereals has targeted a basic plant defense response while also excluding fungal competitors.
Technical Abstract: Colletotricum graminicola is a systemic vascular pathogen that causes anthracnose stalk rot and leaf blight of maize. In the course of an effort to explore the potential presence and roles of C. graminicola metabolites in maize, ethyl acetate extracts of solid substrate fermentations of several C. graminicola isolates from Michigan and Illinois were found to be active against Aspergillus flavus and Fusarium verticillioides, both mycotoxin-producing seed-infecting fungal pathogens. Chemical investigations of the extract of one such isolate (NRRL 47511) led to the isolation of known metabolites monorden and monocillins I-III as major components. Monorden and monocillin I displayed in vitro activity against the stalk- and ear-rot pathogen Stenocarpella maydis while only the most abundant metabolite (monorden) showed activity against foliar pathogens Alternaria alternata, Bipolaris zeicola, and Curvularia lunata. Using LC-HRESITOFMS, monorden was detected in steam-sterilized maize stalks and stalk residues inoculated with C. graminicola but not in the necrotic stalk tissues of wound-inoculated plants grown in an environmental chamber. Monorden (also known as radicicol) and monocillin I can bind and inhibit plant Hsp90, a chaperone of R-proteins. It is hypothesized that monorden and monocillins could support the C. graminicola disease cycle by disrupting maize plant defenses and by excluding other fungi from necrotic tissues and crop residues. This is the first report of natural products from C. graminicola, as well as the production of monorden and monocillins by a pathogen of cereals.