Zinc hyperaccumulation: a model to examine metal homeostasis in plants

The plant Arabidopsis halleri exhibits naturally selected metal hypertolerance and extraordinarily high levels of leaf metal accumulation. Metal hyperaccumulator species attract interest as they represent an extreme end of natural variation of the metal homeostasis network. This might be useful to reveal the global functioning of metal homeostasis networks and uncover key nodes whose alterations can drastically modify metal accumulation and tolerance. In addition, metal hyperaccumulation is a compelling model to study adaptation.
In the last few years, major progress has been achieved in our understanding of the mechanisms underlying metal hyperaccumulation in A. halleri. High rates of metal uptake by roots, root-to-shoot translocation and efficient shoot vacuolar sequestration play central roles in determining hyperaccumulation and hypertolerance. Enhanced functions of several metal transporter-encoding genes result from gene copy number amplification and/or (cis)-regulatory changes. We will describe the function of several transporters in zinc and cadmium hyperaccumulation and hypertolerance, and in the adjustment of nutrient homeostasis in A. halleri. Recent work aiming to determine if selection acted during the evolutionary history of A. halleri on a loci required for metal tolerance and accumulation will be presented.