Project Summary (2008-2014)

This project studies the genetic control of arsenic (As) homeostasis in plants. This research enables the development of plants that can selectively exclude As from their tissues, preventing As accumulation in food crops, and reducing human dietary intake of As.

Arsenic is one of the primary metal(loid)s of concern at Superfund Sites. Chronic low-dose exposure is linked to an increased incidence of bladder cancer. Dietary studies of As intake in humans demonstrate that after drinking water, white rice is the most significant source of inorganic As for humans. (Note: a market-based survey found higher As concentrations in U.S. grown rice than rice grown in the As-affected regions of the Bengal Delta.) In U.S. rice, As is thought to come from arsenical pesticides used in the production of cotton; however, As found in the soil comes from a variety of industrial sources.

The goal of this project is to use Arabidopsis, rice, and the As-hyperaccumulating brake fern as model plant systems. They represent two species with a completed genomic sequence; one is a most important staple food crops plant, and an important dietary source of inorganic As for humans, and the other is one of the few plant species with intrinsic As resistance.

Project scientists are using an interdisciplinary approach that combines ionomic survey techniques, quantitative trait loci (QTL) mapping, spatially resolved metal(loid) analysis, and speciation via synchrotron x-ray microprobe (SXRM). The research strategy consists of gene discovery and gene characterization phases. For gene discovery, approaches include mining an existing dataset of elemental profiles of 4,000 yeast and 62,000 Arabidopsis samples for those with altered As phenotypes, as well as examining natural accessions of Arabdiospis for differences in As accumulation. The laboratory uses high-throughput elemental analysis and DMA microarray-based mapping to identify genes that regulate As accumulation in rice by screening 1,790 rice accessions with the USDA's Rice Core Collection, and examining QTLs for As in the Lemont X Teqing mapping population.

The laboratory also uses SXRM to investigate changes in the micron-scale metal(loid) distribution and the abundance and/or speciation in plant tissue resulting from the deletion or silencing of selected genes of interest. (This technique previously allowed for the successful characterization of gene function in a study of iron homeostasis.) An important product of the gene characterization phase will be the online publication of an Elemental Atlas of Arabidopsis available to the wider scientific community. This research expands the application of x-ray techniques beyond a spatially-resolved analytical technique into a tool for functionally characterizing ion homeostasis genes, as well as protecting human food supplies.