Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2008
Publication Date: 1/19/2009
Publication URL: http://www3.interscience.wiley.com/journal/121641473/abstract?CRETRY=1&SRETRY=0
Citation: Korenkov, V., King, B., Hirschi, K., Wagner, G.J. 2009. Root-selective expression of "AtCAX4" and "AtCAX2" results in reduced lamina cadmium in field-grown "Nicotiana tabacum L". Plant Biotechnology Journal. 7(3):219-226. Interpretive Summary: Using the non-edible portions of plants as a means of removing metals from the soil is termed phytoremediation. In this work, we have engineered plants to remove the toxic metal cadmium from soils and trap the metal in portions of the plants that are non-edible. The modified plants contain increased amounts of a transporter that can store toxic metals in compartments within the plant cell. In field trials, these modified plants can remove the toxic metals from the soil while the edible portions of the plants show no increased levels of the toxic metal. These field trails strongly suggest this approach can be used to remove toxic metals from soils and keep the toxic metals out of the food supply.
Technical Abstract: To assess the impact of enhanced root vacuole cadmium (Cd) sequestration on leaf Cd accumulation under a low Cd dose, as generally occurs in agriculture, leaf Cd accumulation was examined in field-grown tobacco plants expressing genes encoding the high-capacity-Cd, tonoplast-localized, divalent cation/H antiporters AtCAX4 and AtCAX2 (AtCAX, "Arabidopsis" cation exchanger). It has been shown previously that root tonoplast vesicles isolated from plants expressing these genes, directed by root-selective promoters, show enhanced Cd transport activity, and young plants show enhanced root Cd accumulation when grown in solution culture containing 0.02 micro m Cd, a moderate Cd dose. In this article, we present results that show that the lower leaves of mature plants expressing "AtCAX2" or "AtCAX4", under the control of two different root-selective promoters, accumulate 15–25% less lamina Cd than control plants when grown in the field (3 years, three different collection methods). Reciprocal grafting experiments of AtCAX2 shoots onto control roots (and vice versa), grown in solution culture with 0.005 micro m Cd, indicated that the root controls Cd translocation and accumulation in the shoot in control and AtCAX2 and AtCAX4 tobacco plants exposed to low Cd concentration. The results are consistent with a model in which supplementation of Cd/H antiporter activity in root cell tonoplasts enhances root Cd sequestration, resulting in decreased translocation of Cd to the shoot of field-grown plants. These results suggest that human Cd intake from food and tobacco use could be reduced via the enhancement of root vacuolar sequestration of this pollutant.