Hyperaccumulation of arsenic in the shoots of Arabidopsis silenced for arsenate reductase (ACR2)

Endogenous plant arsenate reductase (ACR) activity converts arsenate to arsenite in roots, immobilizing arsenic below ground. By blocking this activity, we hoped to construct plants that would mobilize more arsenate aboveground. We have identified a single gene in theArabidopsis thaliana genome,ACR2 , with moderate sequence homology to yeast arsenate reductase. Expression ofACR2 cDNA inEscherichia coli complemented the arsenate-resistant and arsenate-sensitive phenotypes of various bacterialars operon mutants. RNA interference reduced ACR2 protein expression inArabidopsis to as low as 2% of wild-type levels. The various knockdown plant lines were more sensitive to high concentrations of arsenate, but not arsenite, than wild type. The knockdown lines accumulated 10- to 16-fold more arsenic in shoots (350–500 ppm) and retained less arsenic in roots than wild type, when grown on arsenate medium with <8 ppm arsenic. Reducing expression ofACR2 homologs in tree, shrub, and grass species should play a vital role in the phytoremediation of environmental arsenic contamination.