The phytochelatin transporters AtABCC1 and AtABCC2 mediate tolerance to cadmium and mercury

Abstract

SUMMARYHeavy metals such as cadmium (Cd) and mercury (Hg) are toxic pollutants that are detrimental to living organisms. Plants employ a two-step mechanism to detoxify toxic ions. First, phytochelatins bind to the toxic ion, and then the metal-phytochelatin complex is sequestered in the vacuole. Two ABCC-type transporters, AtABCC1 and AtABCC2, that play a key role in arsenic detoxification, have recently been identified in Arabidopsis thaliana. However, it is unclear whether these transporters are also implicated in phytochelatindependent detoxification of other heavy metals such as Cd(II) and Hg(II). Here, we show that atabcc1 single or atabcc1 atabcc2 double knockout mutants exhibit a hypersensitive phenotype in the presence of Cd(II) and Hg(II). Microscopic analysis using a Cd-sensitive probe revealed that Cd is mostly located in the cytosol of protoplasts of the double mutant, whereas it occurs mainly in the vacuole of wild-type cells. This suggests that the two ABCC transporters are important for vacuolar sequestration of Cd. Heterologous expression of the transporters in Saccharomyces cerevisiae confirmed their role in heavy metal tolerance. Over-expression of AtABCC1 in Arabidopsis resulted in enhanced Cd(II) tolerance and accumulation. Together, these results demonstrate that AtABCC1 and AtABCC2 are important vacuolar transporters that confer tolerance to cadmium and mercury, in addition to their role in arsenic detoxification. These transporters provide useful tools for genetic engineering of plants with enhanced metal tolerance and accumulation, which are desirable characteristics for phytoremediation.

Fission Yeast HMT1 Lowers Seed Cadmium through Phytochelatin-Dependent Vacuolar Sequestration in Arabidopsis

“…Subcellular localization analyses showed that in wild-type Col-0, nearly 100% of the protoplast Cd 2+ was localized in vacuoles, but in protoplasts of the PC-deficient mutant cad1-3, only 35% is present in vacuoles (Fig. 4), comparable to the result in atabcc1 atabcc2 mutant in which PC and possibly GSH transport was disrupted (Park et al, 2012). These data consistently suggest that PCs play a primary role in vacuolar Cd 2+ sequestration in Arabidopsis.…”

“…A most recent study further reported substantial decrease of vacuolar Cd 2+ in the atabcc1 atabcc2 mutant, indicating that AtABCC1 and AtABCC2 play a significant role in vacuolar Cd 2+ sequestration. However, the relative contribution by PCs and GSH to this process remains to be determined, as GSH might possibly be a substrate of AtABCC1 and AtABCC2 under certain conditions (Park et al, 2012).…”

Vacuolar Transport of Abscisic Acid Glucosyl Ester Is Mediated by ATP-Binding Cassette and Proton-Antiport Mechanisms in Arabidopsis

“…S7). Under standard growth conditions, AtABCC1 and AtABCC2 single and double knockout mutants exhibit no mutant phenotypes (Raichaudhuri et al, 2009;Park et al, 2012). We also did not observe growth phenotypes of these mutant seedlings subjected to drought and osmotic stress.…”

Effects of nitrogen on the activity of antioxidant enzymes and gene expression in leaves of Populus plants subjected to cadmium stress

“…Both GSH and PC could bind Cd 2 + to form a stable chelate (GSH-Cd 2 + or PC-Cd 2 + ) and then transfer chelates into vacuoles. Both these direct and indirect methods can efficiently decrease the concentration of Cd and alleviate the damage caused by ROS in plants (Tennstedt et al 2009;Park et al 2012;Wang et al 2012). In our experiment, the gene expression under the N treatment showed no significant difference compared to the control, but these genes were upregulated in Cd and N + Cd treated plants.…”