Mutualistic fungal endophytes infect many grass species and often confer benefits to the hosts such as reduced herbivory by insects and animals. The physiological interactions between the endophytes and their hosts have not been well characterized. Fungal-secreted proteins are likely to be important components of the interaction. In the interaction between Poa ampla and the endophyte Neotyphodium sp., a fungal ␤-1,6-glucanase is secreted into the apoplast, and activity of the enzyme is detectable in endophyte-infected plants. Sequence analysis indicates the ␤-1,6-glucanase is homologous to enzymes secreted by the mycoparasitic fungi Trichoderma harzianum and Trichoderma virens. DNA gel-blot analysis indicated the ␤-1,6-glucanase was encoded by a single gene. As a secreted protein, the ␤-1,6-glucanase may have a nutritional role for the fungus. In culture, ␤-1,6-glucanase activity was induced in the presence of ␤-1,6-glucans. From RNA gel blots, similar ␤-1,6-glucanases were expressed in tall fescue (Festuca arundinacea Schreb.) and Chewings fescue (Festuca rubra L. subsp. fallax [Thuill] Nyman) infected with the endophyte species Neotyphodium coenophialum and Epichloë festucae, respectively.Fungal endophytes of the genus Neotyphodium (formerly Acremonium; Glenn et al., 1996) infect many grass species, some of which are important turf and forage grasses. The fungi colonize the intercellular spaces of the aerial plant parts but do not invade the plant cells. The endophyte-grass associations are generally considered to be mutualistic symbioses (Clay, 1988). In many associations, the production of alkaloids by the fungus results in reduced herbivory by insects and animals, thus benefiting the host (Breen, 1994;Bush et al., 1997). The fungi benefit from the access to nutrients provided by the plants.Within the past 20 years, considerable knowledge has been gained on the synthesis and effects of alkaloids, the genetics and taxonomic relationships of endophytes, and the ecological effects of endophyte infection (Clay, 1990;Siegel and Schardl, 1991;Schardl, 1996;Bush et al., 1997). The physiological aspects of the endophyte-grass interactions have not, however, been well characterized in any system. We are investigating the physiology of the fungus-grass interaction with the long-range objective of eventually being able to manipulate agriculturally important interactions. We are using the Poa ampla cv Service (big bluegrass)/Neotyphodium sp. interaction as a model system for the grass/fungus interaction (Lindstrom et al., 1993). P. ampla is apomictic, so we have a ready supply of plants of identical genotype. We also have uninfected plants of the identical genotype, which were identified in older seed lots in which the endophyte had lost viability.Almost nothing is known of the proteins relevant to the interaction between the plant hosts and the fungal endophytes. We are interested in fungalsecreted proteins because they are likely to be important components of the mutualistic interaction because they are located at the...

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