The Early Stages in the Interaction Between Mycorrhizal Fungi and Plants

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9630842 Hirsch The Sinorhizobium meliloti-alfalfa symbiosis, which leads to the formation of novel structure--the root nodule in which atmospheric nitrogen is reduced to ammonia--has been well studied. On the other hand, the mycorrhizal symbiosis, which enables plants to grow in phosphorous-deficient soil, is less well studied. Chemical signals produced by both the plant and the bacterium are involved in establishing the interaction between the two organisms. Dr. Hirsch and her colleagues have determined that VAM-fungi induce the expression of at least two plant genes in mycorrhizal roots that are usually triggered by inoculation with rhizobia. Alfalfa plants will be studied for their early responses to the VAM fungi. The roots will be inoculated with the spores of the fungi, the progress of infection by fungal hyphae will be followed, and the timing and patterns of expression of selected plant genes will be analyzed. This award supports feasibility of using the expression of these early nodulin genes as molecular indicators for developing a bioassay to detect a putative Myc factor, i.e., a chemical signal that induces the expression of specific plant genes in VA-mycorrhizal roots, and is involved in establishing this important symbiosis.