Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2006
Publication Date: 1/1/2007
Citation: Koren'kov, V., Park, S., Cheng, N.-H., Sreevidya, C., Lachmansingh, J., Morris, J., Hirschi, K., Wagner, G.J. 2007. Enchanced Cd[2+]-selective root-tonoplast-transport in tobaccos expressing Arabidopsis cation exchangers. Planta. 225(2):403-411. Interpretive Summary: Consumption of toxic metals such as cadmium can be a health risk for humans. Almost 70% of the cadmium that humans consume is from vegetables and other plant products grown in cadmium polluted soils. The objective of this research is to alter the levels of potentially toxic compounds like cadmium in the edible portions of a plant. In this report, we have altered the expression of plant transporters that move cadmium into different parts of the plant, and thus we have altered the way this metal is distributed within the plant. This work changes the way the cadmium is distributed and could be a means to making plants more nutrient dense.
Technical Abstract: Several "Arabidopsis" CAtion eXchangers (CAXs) encode tonoplast-localized transporters that appear to be major contributors to vacuolar accumulation/sequestration of cadmium (Cd[2+]), an undesirable pollutant ion that occurs in man largely as a result of dietary consumption of aerial tissues of food plants. But ion-selectivity of individual CAX transporter types remains largely unknown. Here we transformed "Nicotiana tabacum" with several "CAX" genes driven by the Cauliflower Mosaic Virus (CaMV) 35S promoter and monitored divalent cation transport in root-tonoplast vesicles from these plants in order to select particular "CAX" genes directing high Cd[2+] antiporter activity in root tonoplast. Comparison of seven different "CAX" genes indicated that all transported Cd[2+], Ca[2+], Zn]2+], and Mn]2+] to varying degrees, but that CAX4 and CAX2 had high Cd[2+] transport and selectivity in tonoplast vesicles. "CAX4" driven by the CaMV "35S" and FS3 [figwort mosaic virus (FMV)] promoters increased the magnitude and initial rate of Cd[2+]/H[+] exchange in root-tonoplast vesicles. Ion selectivity of transport in root-tonoplast vesicles isolated from "FS3::CAX4"-expressing plant lines having a range of gene expression was Cd[2+]>Zn[2+]>>Ca[2+]>>Mn[2+] and the ratios of maximal Cd[2+] (and Zn[2+]) versus maximal Ca[2+] and Mn[2+] transport were correlated with the levels of "CAX4" expression. Root Cd accumulation in high "CAX4" and "CAX2" expressing lines was increased in seedlings grown with 0.02 uM Cd. These observations are consistent with a model in which expression of an "Arabidopsis"-gene-encoded, Cd[2+]-efficient antiporter in host plant roots results in greater root vacuole Cd[2+] transport activity, increased root Cd accumulation, and a shift in overall root tonoplast ion transport selectivity towards higher Cd[2+] selectivity. Results support a model in which certain CAX antiporters are somewhat more selective for particular divalent cations.