Poster: Phytoremediation

Abs # 986: Engineered Phytoremediation of Arsenic: Enhancing Arsenic Uptake in Plants by Controlling Endogenous Arsenate Reductase

Presenter:	Dhankher, Om P, parkash@arches.uga.edu
Authors	Dhankher, Om P (A)   Meagher, Richard B (A)
Affiliations:	(A): University of Georgia

We have developed a genetics-based phytoremediation strategy for arsenic, where the oxyanion arsenate is transported aboveground, reduced to arsenite, and sequestered in thiol-peptide complexes. Arabidopsis plants co-expressing the E. coli arsC gene (arsenate reductase) in leaves and the g-ECS genes (g-glutamylcysteine synthetase) constitutively, showed significantly greater arsenic tolerance than g-ECS, ArsC alone or wild-type plants. When grown on arsenic, these plants (g-ECS+ArsC) accumulated 4- to 17-fold greater fresh shoot weight and accumulated 2- to 3-fold more arsenic per gram of tissue (Dhankher et al., 2002, Nature Biotech. 20:1140-1145). Furthermore, to enhance arsenic movement to aboveground tissues, we examined the endogenous plant activity that affects the electrochemical state and binding of arsenic in roots. Arsenate is a phosphate analogue and uptaken along with phosphate transport systems. Arsenite is highly thiol-reactive and stays tightly bound in roots. A major limitation to our arsenic strategy is the activity of an endogenous plant arsenic reductase resulting in arsenite being trapped in roots. We have identified a potential arsenate reductase gene (AtACR2) in the Arabidopsis genome. AtACR2 cDNA coding sequence complements the bacterial arsC gene functions in the E. coli arsenic resistance (ars) operon. AtACR2 confers arsenate sensitivity to E. coli apparently by converting arsenate to more toxic arsenite. Blocking the AtACR2 activity in Arabidopsis plants by RNAi suppression causes arsenate hypersensitivity. These plants accumulated 7-fold more arsenic in shoots than wild type plants. Altering the expression of the endogenous plant arsenate reductase genes will likely play a vital role in the phytoremediation of environmental arsenic pollution.