Sequence analysis showed that this fern protein contains 10 putative transmembrane domains, suggesting a cellular membrane location. Using an antibody that specifically recognizes the ACR3 protein, they showed that ACR3 is found in the membranes of vacuoles, but not in the plasma membrane or in endoplasmic reticulum membranes. This suggests a mechanism for arsenic tolerance in P. vittata tissues: arsenite that enters the cell is transported by ACR3 into the vacuolar compartment, where it is spatially isolated from the cell cytoplasm, the site of many of the cell's arsenic-sensitive metabolic reactions.
Furthermore, the researchers showed that ACR3 gene expression in P. vittata is induced more than 30-fold in the presence of arsenite. To verify that ACR3 is required for arsenic tolerance, the ACR3 gene was silenced using an inhibitory mRNA. In these silenced plants, ACR3 expression was not induced by arsenite, and arsenic significantly reduced the growth rate of these ACR3-deficient plants relative to unsilenced plants.
Sequence analysis showed that, although this gene is found in a wide range of organisms including bacteria, fungi, mosses and gymnosperms, it is absent in angiosperms. By studying the occurrence and function of ACR3 in various plants, including hyperaccumulating and nonaccumulating ferns, the authors hope to provide additional insights into mechanisms of arsenic transport, tolerance, and accumulation. In addition to potential benefits for human health, this research will hopefully lead to strategies for phytoremed
|Contact: Gregory Bertoni|
American Society of Plant Biologists