Superfund Research Program

Arsenic Uptake, Transport and Storage in Plants

Project Leader: Mary L. Guerinot
Grant Number: P42ES007373
Funding Period: 2008-2021

Project-Specific Links

Final Progress Reports

Year:   2020  2013 

Aims: This project aims to characterize genes involved in arsenic homeostasis in plants using a unique combination of molecular genetics and synchrotron X-ray imaging techniques.

Studies and results: Dr. Lanzirotti's lab specializes in characterizing membrane transporters that are important for human health and nutrition. Dr. Lanzirotti and his research team's studies provide the groundwork for the development of crop varieties that resist arsenic uptake, protecting the food supply. In the short-term, these studies provide information about the presence of arsenic in specific plant tissues, which directly inform market basket studies. In the longer term, they provide information about likely locations of expression of genes involved in arsenic homeostasis. The team has completed the arsenic-pulsing study analysis showing the disruption of nutrient transport in rice grains pulsed with DMA as compared to inorganic As in collaboration with Dr. Andrew Meharg, and have a paper in preparation.

These researchers were the first general users to conduct experiments at newly commissioned synchrotron beamline 13-ID-E of the National Synchrotron Light Source, with collaborator Antonio Lanzirotti. Their work has focused on imaging fragile tissue such as plant roots, and also seeds in various stages of germination. They are particularly interested in plant organs that facilitate entry of contaminants and nutrients into the plant and those that represent significant caloric sources such as seeds. The team's imaging work at this beamline has uncovered a dramatic zinc remobilization event during germination in the model plant Arabidopsis, where a widespread distribution throughout the tissues of the embryo is simultaneously mobilized to the peripheral endodermis. This event mirrors that which was recently observed (also by synchrotron imaging) in the initial stages following fertilization of the human egg. The team is preparing their observations for publication in a short communication to Nature.

Dr. Lanzirotti and his team's work using SXRF imaging as a gene characterization tool, which began as a pilot study in the Dartmouth Superfund Program in 2005, has now been fully described in a methodological paper in Metallomics (Punshon et al 2013a). This publication was made possible by Dartmouth graduate trainees Maria Hindt and Amanda Socha and visiting trainee Felipe Richachenevsky, who also assisted in their collaboration on calcium in transgenic Medicago (Punshon et al 2013b). The team's use of SXRF imaging in plant genetics attracted rotating graduate student trainees Joseph Grainger and Hannah Opalko, who attended experimental time at the team's collaborating beamline at the National Synchrotron Light Source X26A. The graduate students worked on zinc distribution in leaf tissue for a publication in collaboration with Felipe Richachenevsky and Suna Kim on the ZIP7 transporter, which is currently in preparation.

The team of researchers continue to collaborate strongly both with the synchrotron community (aiding design and testing new beamlines targeted at life sciences users), as well as with epidemiological studies which focus on the health effects of arsenic in food. Co-PI Punshon was asked to present again at the 2013 BioXFM meeting at Northwestern University (August 8^th-9^th, 2013) and was one of the NSLS users invited to submit a First Experiment Proposal at the sub-micron X-ray spectroscopy (SRX) beamline at NSLS-II, which is due to receive early users in fall 2014. The researchers have proposed to extend their ionomics work on arsenic uptake in plants at this facility. As part of their ongoing research into the nutrient and contaminant metal distribution in rice, they will collect high resolution elemental images and metal binding characteristics from specific cells: particularly from the aleurone layer, the ovular vascular trace and embryonic organs such as the coleoptile, scutellum and radicle. The team expects sample preparation to be far less challenging in these studies, because seeds contain about 80% less water than hydrated tissue and their previous studies demonstrate that they withstand extended periods of X-ray analysis. The team's analyses of interest in these studies are primarily As (as a target of food safety efforts) and Fe (as a target of biofortification efforts). The team has a range of loss-of-function mutant lines and experimental growth conditions to
test in these studies. They include the rice VIT1 loss-of-function mutant osvit1-1, which in Arabidopsis is unable to store Fe in the vacuole of endodermal cells, and transgenic rice grains pulsed via the cut flag leaf with arsenate, arsenite, dimethylarsinic acid, and monomethylarsonic acid. Co-PI Punshon is also now jointly funded to use SXRF imaging to study how As, Cd, Hg and Pb affect placental functioning ("Assessing maternal-fetal exposure pathways using bio-imaging." Center of Biomedical Research Excellence (COBRE) in Molecular Epidemiology P20 GM104416-01), using the combination of SXRF and gene expression approaches developed as part of the Dartmouth Superfund Program.

Significance: These studies continue to show the importance of membrane transporters in enhancing and protecting the nutritional benefits of plant-based staple foods, and this has fundamental impacts on human health.

Plans: In 2014 the research team will continue to map loci associated with variation in grain arsenic. They will also continue their synchrotron studies, emphasizing both developing grain and germinating seedlings.