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Title: Interactions between Fusarium verticillioides, Ustilago maydis, and Zea mays: an endophyte, a pathogen, and their shared plant host

item RODRIGUEZ ESTRADA, ALMA - University Of Minnesota
item JONKERS, WILFRIED - University Of Minnesota
item Kistler, Harold
item MAY, GEORGIANA - University Of Minnesota

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2012
Publication Date: 5/12/2012
Citation: Rodriguez Estrada, A.E., Jonkers, W., Kistler, H.C., May, G. 2012. Interactions between Fusarium verticillioides, Ustilago maydis, and Zea mays: an endophyte, a pathogen, and their shared plant host. Fungal Genetics and Biology. 49:578-587.

Interpretive Summary: In the natural environment, plants interact with fungi in many ways. They may harmlessly colonize plant stems, leaves or roots, cause plant diseases or actively decompose dead and dying plants. This manuscript shows that two fungi that infect corn leaves actively interact with each other in the plant. One fungus colonizes corn leaves without harmful effect and can inhibit the growth of the other, pathogenic fungus thereby reducing disease symptoms. This fungal interaction in corn also causes changes in gene expression and in the concentration of small metabolites which may ultimately influence the growth of the corn plant. This study thus establishes that complex interactions between these fungi 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: Highly diverse communities of microbial symbionts occupy eukaryotic organisms, including plants. While many well-studied symbionts may be characterized as either parasites or as mutualists, the prevalent but cryptic endophytic fungi are less easily qualified because they do not cause observable symptoms of their presence within their host. Here, we investigate the interactions of an endophytic fungus, Fusarium verticillioides with a pathogen, Ustilago maydis, as they occur within maize (Zea mays). We used experimental inoculations to evaluate metabolic mechanisms by which these three organisms might interact. We assessed the impacts of fungal-fungal interactions on endophyte and pathogen growth within the plant, and on plant growth. We find that F. verticillioides modulates the growth of U. maydis and thus, decreases the pathogen's aggressiveness toward the plant. With co-inoculation of the endophyte with the pathogen, plant growth is similar to that which would be gained without the pathogen present. However, the endophyte may also break down plant compounds that limit U. maydis growth, and obtains a growth benefit from the presence of the pathogen. Thus, an endophyte such as F. verticillioides may function as both a defensive mutualist and a parasite, and express nutritional modes that depend on ecological context.