The primary focus of our research is metal and metalloid homeostasis in plants, using a multi-disciplinary approach involving molecular genetics, ionomics and synchrotron x-ray fluorescence imaging.
1. Metal Homeostasis in Arabidopsis. Why do plants need so many ZIP transporters and so many FRO metal reductases? With 15 ZIP family members and 8 FRO family members, we are working to understand the role of each in metal uptake from the soil and transport throughout the plant. We are also interested in understanding which residues contribute to metal specificity as different members of the ZIP family are capable of transporting different metals, including iron, zinc, manganese and cadmium. We have also been investigating the role of an iron transporter that is located on the vacuole membrane and functions to remove iron from the cytoplasm, presumably for storage in the vacuole. These projects all take advantage of the fact that we can easily assay for function in yeast. The newest project in the lab concerns the metal dependent trafficking of ZIP proteins.
2. Ionomics. Understanding the functional connections between genes, proteins, metabolites and mineral ions is one of biology’s greatest challenges in the postgenomic era. As part of a multi-investigator project, we are using ICP-MS [inductively coupled spectroscopy-mass spectroscopy] nutrient and trace element profiling as a tool to determine the biological significance of connections between a plant’s genome and its elemental profile. We are screening loss of function mutants in each of the predicted ORFs in the Arabidopsis genome and have already identified a number of proteins of unknown function that dramatically alter a plant’s elemental composition.
3. Bradyrhizobium japonicum. What is the role of the iron-regulated outer membrane proteins of Bradyrhizobium japonicum in the symbiosis with soybeans? The release of the B. japoniucm genome sequence last December has allowed us to identify all the putative iron uptake systems in this organism. Using reverse genetics, we will determine the role of each of these systems in iron uptake, both when the bacteria are free living in the soil and when they are living in symbiosis with the plant.
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