Life Sciences Division

A new heavy metal transporter identified in plants

A heavy metal transporter function, identified by the analysis of the genome of Arabidopsis thaliana, has been found in a yeast. This transporter suppresses the yeast´s hypersensitivity to cadmium and lead with no modification to the levels of these metals in the cell. Its molecular mechanism may be based on its ability to direct these metals towards the vacuole, the cell´s waste disposal organ. This finding is of particular interest for the implementation of phytoremediation processes.

Heavy metal transporters allow plants both to absorb and distribute the elements they need for their growth, and to absorb and eliminate toxic metals. The accumulation of heavy metals in crops is a problem for agriculture and human health. Conversely, these properties can be exploited for soil decontamination. As part of its Environmental Nuclear Toxicology Programme, the CEA is studying the strategies deployed by living organisms to forestall the toxic effects of these metals for the purpose of developing phytoremediation processes.

The analysis of the genome of Arabidopsis thaliana identified eight genes coding for a subgroup of transporters (P1B-ATPases) involved in the transport of heavy metals. Although these genes were identified, their function remained to be determined. The proteins they code for could participate in the absorption and/or movement of metals in the plant, or they could prevent the absorption of toxic metals in the roots, or they could help to sequester such metals in specialised compartments. To help find out which, the researchers analysed the function of one of these proteins in yeast cells hypersensitive to cadmium and lead.

To find out whether these metals were trapped or quarantined, a mutant of AtHMA3 that did not change the structure of the protein and so its capacity to bind certain substrates was used. The fact that this mutant was unable to suppress the yeast's sensitivity to cadmium suggests that the transporter, rather than trapping the metals itself, places them in quarantine. Fusion of the transporter with a fluorescent protein localised it on the yeast's vacuole, thereby confirming its role in the efflux of cadmium towards this compartment, which acts as a waste disposal organ.

These results provide insight on the role of this transporter. Such information is indispensable for the implementation of phytoremediation processes, which requires knowledge of how metals are accumulated and/or transported at the molecular level.