Most vascular flowering plants are able to form symbiotic associations with arbuscular mycorrhizal (AM) fungi. These associations, named ‘arbuscular mycorrhizas’, develop in the roots, where the fungus colonizes the cortex to access carbon supplied by the plant. The fungal contribution to the symbiosis includes the transfer of mineral nutrients, particularly phosphorus, from the soil to the plant. In many soils, phosphate exists at levels that are limiting for plant growth. Consequently, additional phosphate supplied via AM fungi can have a significant impact on plant development, and this symbiosis influences the structure of plant communities in ecosystems worldwide.
The long-term goals of our research are to understand the mechanisms underlying development of the AM symbiosis and phosphate transfer between the symbionts. A model legume, Medicago truncatula, and arbuscular mycorrhizal fungi, Glomus versiforme, Glomus intraradices and Gigaspora gigantea are used for these analyses. Currently, a combination of molecular, cell biology, genetic and genomics approaches are being used to obtain insights into development of the symbiosis, communication between the plant and fungal symbionts, and symbiotic phosphate transport.
Phosphorus is a critical macronutrient for proper plant growth. While phosphorus deficiencies can be improved by the application of phosphate fertilizers, it is costly, both to the farmer and to the environment. Furthermore, the crops only take up a small percentage of the applied fertilizer; the remainder is either immobilized in the soil, or carried into ground water and rivers, often resulting in pollution.
Interns in the Harrison lab investigate two aspects of plant phosphorus nutrition. The first aspect seeks to understand the basis for the symbiotic relationships between vascular flowering plants and arbuscular mycorrhizal (AM) fungi. The fungi colonize root cells, gaining access to carbon supplied by the plant, while at the same time mobilizing mineral nutrients from the soil, including phosphorus, to be used by the plant. For this work, the lab uses the model legume, Medicago truncatula and the fungus Glomus versiforme. The Harrison lab also studies how plants find and take up phosphorus from the soil when they do not have these symbiotic relationships with fungi. This work toward understanding the mechanisms of perception and acquisition of phosphorus by plants may eventually lead to a more effective usage of fertilizers.