This project aims to study the genetic control of arsenic (As) homeostasis in plants. This will enable thedevelopment of plants that can selectively exclude As from their tissues, preventing As accumulation in foodcrops and reducing human dietary intake of As. Arsenic is one of the primary metal(loid)s of concern atSuperfund Sites and chronic low-dose exposure is linked to an increased incidence of bladder cancer.Dietary studies of As intake in humans show that after drinking water, white rice is the most significantsource of inorganic As for humans. A market basket survey found higher As concentrations in U.S. grownrice than rice grown in the As-affected regions of the Bengal Delta. In U.S. rice, As is thought to have comefrom arsenical pesticides used in the production of cotton, but As input to soil comes from a variety ofindustrial sources.
We aim to use Arabidopsis, rice and the As-hyperaccumulating brake fern as model plantsystems. They represent two species with a completed genomic sequence; one of the most important staplefood crops plants and an important dietary source of inorganic As for humans, and one of the few plantspecies with intrinsic As resistance. We propose to use an interdisciplinary approach that combines ionomicsurvey techniques, quantitative trait loci (QTL) mapping and spatially resolved metal(loid) analysis andspeciation via synchrotron x-ray microprobe (SXRM). The research strategy consists of gene discovery andgene characterization phases. For gene discovery, approaches include mining an existing dataset ofelemental profiles of 4,000 yeast and 62,000 Arabidopsis samples for those with altered As phenotypes aswell as examining natural accessions of Arabdiospis for differences in As accumulation. We will use highthroughputelemental analysis and DMA microarray-based mapping to identify genes that regulate Asaccumulation in rice, screening 1,790 rice accessions with the USDA's Rice Core Collection and examiningQTLs for As in the Lemont X Teqing mapping population. We will use SXRM to investigate changes in themicron-scale metal(loid) distribution, abundance and/or speciation in plant tissue resulting from the deletionor silencing of selected genes of interest. This technique allowed successful characterization of genefunction in a recent study of iron homeostasis. An important product of the gene characterization phase willbe the online publication of an Elemental Atlas of Arabidopsis available to the wider scientificcommunity.This proposed research expands the application of x-ray techniques beyond a spatially-resolvedanalytical technique into a tool for functionally characterizing ion homeostasis genes, as well as protectinghuman food supplies.
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