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Title: In vitro interactions between Fusarium verticillioides and Ustilago maydis through real-time PCR and metabolic profiling

item RODRIGUEZ ESTRADA, ALMA - University Of Minnesota
item HEGEMAN, ADRIAN - University Of Minnesota
item Kistler, Harold
item MAY, GEORGIANNA - University Of Minnesota

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2011
Publication Date: 9/15/2011
Citation: Rodriguez Estrada, A.E., Hegeman, A., Kistler, H.C., May, G. 2011. In vitro interactions between Fusarium verticillioides and Ustilago maydis through real-time PCR and metabolic profiling. Fungal Genetics and Biology. 48:874-885.

Interpretive Summary: Fungi interact with plants in many ways in the natural environment. They may actively decompose dead and dying plants, cause plant diseases or harmlessly colonize plant leaves, stem and roots. In this study we find that two fungi that actively colonize corn leaves and that are capable of causing disease are antagonistic when grown together on a petri plate. One fungus in fact can completely inhibit the growth of the other in artificial culture and cause changes in the concentration of small metabolites which ultimately influence the growth of the corn plant. This study thus establishes that complex interactions between microbes may ultimately determine the outcome of plant infection and plant health. This information will be helpful to plant improvement specialists who are working to develop plants resistant to these fungi or for developing novel strategies for disease control.

Technical Abstract: The goal of this research was to determine mechanisms of interaction between endophytic strains of Fusarium verticillioides and the pathogen, Ustilago maydis. Endophytic strains of the fungus F. verticillioides are commonly found in association with maize (Zea mays) and when co-inoculated with U. maydis, often lead to decreased disease severity caused by the pathogen. Here, we developed methods (liquid chromatography–mass spectrometry) to evaluate changes in relative concentration of metabolites produced during in vitro interactions between the endophyte and pathogen. Fungi were grown on two different media, in single and in confronted cultures. We used real-time PCR (qPCR) assays to measure relative changes in fungal biomass, that occurred in confronted cultures compared to single cultures. The results showed that most secondary metabolites are constitutively produced by each species. Metabolite profiles are complex for U. maydis (twenty chromatographic peaks detected) while relatively fewer compounds were detected for F. verticillioides (six chromatographic peaks). In confronted cultures, metabolite ratio (metabolite concentration/biomass) generally increases for U. maydis metabolites while no significant changes were observed for most F. verticillioides metabolites. The results show that F. verticillioides is a strong antagonist of U. maydis as its presence leads to large reductions in U. maydis biomass.We infer that few U. maydis metabolites likely serve antibiotic functions against F. verticillioides. The methods described here are sufficiently sensitive to detect small changes in biomass and metabolite concentration associated with differing genotypes of the interacting species.