Fluoride is the 13th-most abundant element in the Earth’s crust. Natural and industrial sources contribute to fluoride levels in the soil, water, and air. While there is no biological requirement for fluoride, low concentrations of fluoride enhance teeth quality in animals. However, under certain conditions, fluoride is toxic. Toxicity depends on multiple factors including concentration, exposure time, and the organism itself. Fluoride-sensitive plants like Gladiolus are injured at a concentration of 20 ppm (1 mM), while concentrations above 1200 ppm (63 mM) have no observable effects on the fluoride-tolerant tea plant. Protection against fluoride toxicity in single-celled organisms is achieved by removing fluoride ions from the cell through a membrane channel called FEX (Fluoride Exporter). A gene encoding this fluoride channel has been recently identified in multicellular organisms, including plants. Plants are particularly vulnerable to fluoride because they are exposed to fluoride from the soil, water, and air. In addition, phosphate fertilizers used to enhance plant growth are sources of contaminating fluoride because they are produced from rock phosphate, which contains fluoride. Studying the putative fluoride channel in plants will broaden our understanding of how they avoid fluoride toxicity. This knowledge will help to protect crop plants from fluoride and possibly reduce the concentration of fluoride in specific plant tissues. In cooperation with the Yale Pathways to Science program, middle- and high- school students will explore plant biology and the scientific method through an all-day festival, in-depth workshops, and extensive summer laboratory experiences.
This research investigates how FEX contributes to fluoride tolerance in plants. Putative fluoride channels from several plants have been tested in a yeast FEX knockout and found to provide fluoride tolerance to a level similar to native yeast FEX. In addition, deletion of FEX in Arabidopsis is lethal in normal plant growth conditions. A variety of viability and growth assays will be used to assess the effect of altered levels of FEX in plants. How FEX affects fluoride travels through plants will be monitored using 18F and Positron Emission Tomography (PET). Additionally, the expression of FEX will be manipulated using cell-specific promoters to ascertain whether plants employ, or would benefit from, a coordinated higher-order strategy for fluoride regulation. This work will establish how the plant accumulates and dissipates fluoride and the role of FEX in that process. Information will be obtained on how to improve fluoride detoxification using FEX. It represents the first study of FEX and fluoride efflux in a multicellular organism. These experiments will provide insights into the ability of FEX to direct fluoride to or from specific tissues through differential regulation, create a baseline for characterization of fluoride toxicity in plants, and open up new areas of study for fluoride detoxification and bioremediation.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
