Heavy Metal Transporters

Written by admin on October 8, 2015

Many transition metals are essential for all forms of life – for example as cofactors in enzymes or in stabilising transcription factors. Examples include Zn, Fe, Cu, Mn and Co, However, when present at high concentrations these metals become toxic. Some other metals (Cd, Hg, Pb) have no known biological function and are highly toxic. Plants therefore face the dilemma of obtaining sufficient metals from the soil for nutritional needs and yet ensuring that amounts accumulated are not toxic.

The extent to which plants accumulate heavy metals has knock-on effects for human health and nutrition. Ultimately, we derive metals esssential for our metabolism from plants. It is conservatively estimated that around 30% of the world’s population suffers from Zn or Fe deficiency and deficiencies in these two metals alone are thought to account for over 1.5M deaths worldwide (nearly all in High Mortality Developing Countries – WHO). The endosperm of many cereals has a low Zn and Fe content, so it will be highly beneficial to breed plants with the capacity to accumulate more of these metals.

The Cation Diffusion Facilitator (CDF) family of membrane transporters is distributed in all three kingdoms of life – Archeae, Bacteria and Eukaryota – where they are involved in the transport of a variety of transition metals.

 


Topographical model of a CDF family member

 

In Arabidopsis, the CDF family is represented by 12 MTP genes. MTP1 is vacuolar in location and responsible for sequestering Zn, thereby conferring Zn tolerance. MTP1 might be considered as a candidate for biofortification of cereals with Zn.


Localisation of MTP1 to the vacuolar membrane by fluorescent protein fusion (Blaudez et al, 2003)

 

We have shown that MTP11 is a Mn transporter that confers tolerance to high concentrations of Mn. Unlike MTP1, MTP11 localises to a vesicular membranes that are likely to be Golgi. It seems likely that MTP11 confers Mn tolerance by loading Mn into the secretory system.

 


AtMTP11 knockout mtp11-1 (B) and 35S::AtMTP11 overexpressors (D) show hypersensitivity and increased resistance respectively to 1 mM and 1.5 mM MnSO4 respectively. Panes A and C are Arabidopsis Col-0 controls. MTP11 confers Mn tolerance on Arabidopsis (Peiter et al, 2007)

 

Current work in the lab is looking at the use of these transporters in the biofortification of crop plants, as a means to improve grain micronutrient content.

 


Lab members currently working on the project:

Millie Stanton

Siegfried Leher

 


Further reading

 

Blaudez, D., Kohler, A., Martin, F., Sanders, D., Chalot, M. (2003) Poplar metal tolerance protein 1 confers zinc tolerance and is an oligomeric vacuolar zinc transporter with an essential leucine zipper motif. Plant Cell 15: 2911-2928

Montanini, B., Blaudez, D., Jeandroz, S., Sanders, D., Chalot, M. (2007) Phylogenetic and functional analysis of the cation diffusion facilitator family: improved signature and prediction of substrate specificity. BMC Genomics 8: 107

Peiter, E., Montanini, B., Gobert, A., Pedas, P., Husted, S., Maathuis, F.J.M., Blaudez, D., Chalot, M., Sanders, D.(2007) A secretory pathway-localised cation diffusion facilitator confers plant manganese tolerance. Proc. Natl. Acad. Sci. USA 104: 8532-8537