The Ionome

The objective of the project is to use high throughput ICP-MS technology to identify gene networks that control uptake and accumulation of a wide array of minerals, the 'ionome'. The prioritized list of target genes is based on four criteria. First, all genes have unknown functions. Second, priority has been given to genes expressed primarily in roots, as uptake and translocation functions in the root have a significant influence on leaf and seed ion profiles. Third, priority is given to those genes that show expression profile changes in response to nutrients. A critical hypothesis to be tested is whether expression profiling changes can be used to identify functionally important genes. Fourth, priority will be given to unique genes to test the hypothesis that defects in unique genes are more likely to generate a phenotype than mutations in genes with close homologs in the genome. A complete gene list is available at http://www.cbs.umn.edu/arabidopsis/ionome/. All the ion profiling data will be available and searchable online, with seeds for various lines available through the ABRC. Analysis of the ionome and its interactions with other cellular processes is essential to understand how plants respond to nutrient availability and toxic metals. The collaborative group will serve as a 'Center of Expertise' to test the hypothesis that > 5% of the genome functions in plant mineral nutrition. The long-term goal is to quantify the functional contribution to mineral nutrition and ion homeostasis of every gene in Arabidopsis. The main objectives are to:

o Conduct ion profiling (quantitation of Fe, Zn, Ca, K, Mn, P, S, Se, Na, Pb, As, etc.) in leaves and seeds of 1600 homozygous disruption lines isolated in genes of unknown function, and thousands of additional lines made available by the Arabidopsis community.

o Conduct saturation mutagenesis, using >100,000 fast neutron (FN) mutagenized lines to identify genes that regulate mineral nutrient accumulation.

o Identify the mutant genes in more than 50 ion profile mutants obtained from FN mutagenesis.

o Conduct expression profiling experiments on 10 lines with altered ion profiles. The goal is to correlate ionome and transcriptome profiling results to understand the networks controlling ion homeostasis.

Broader Impacts: There are four key contributions to the Broader Impacts of the proposed research. 1) Educational outreach will include training of undergraduate and graduate students. 2) Information on the contribution of science to human health, agriculture, and bioremediation will be disseminated through museum exhibits and interactions with the PIs' local communities. 3) Research tools will be provided to the public through web sites and seed line deposits at stock centers. 4) Fundamental knowledge will be provided to facilitate future engineering of increased yields and of more nutritious agricultural crops. For most of the world, plants are the major source of essential minerals. Food-based solutions to 'hidden hunger' offer sustainable solutions to problems of malnutrition. Therefore, this project will contribute to increasing bio-available minerals in plants and to solving important problems in human health. Furthermore, understanding the pathways by which toxic metals accumulate in plants will enable the engineering of crops to exclude toxic metals and create healthier food sources, or to extract toxic metals from the soil as a strategy to clean up polluted lands and water.