Arabidopsis halleri – a Hyperaccumulator of Zinc, Cadmium and Lead

Metal hyperaccumulation and associated hypertolerance in plants bear great promise for the
development of phytoremediation and phytomining technologies, in addition to serving as
extreme model traits in molecular physiology, evolution and ecology. A metal
hyperaccumulator is defined as a plant species of which any one individual, when grown in its
natural habitat in the wild, contains an extraordinarily high level of a metal or metalloid in aboveground
tissues of > 10,000 μg g-1 Mn, > 3,000 μg g-1 Zn, > 1,000 μg g-1 Ni, Se, As, Co, Pb, Cu,
Th, or Sb, or > 100 μg g-1 Cd in dry biomass. These concentrations are more than an order of
magnitude above the critical toxicity thresholds of ordinary plants. Thus, metal
hyperaccumulation requires extraordinarily efficient and specific mechanisms of metal
extraction from the soil, root-to-shoot metal partitioning, and internal metal detoxification. To
date, metal hyperaccumulation has been identified in more than 500 plant taxa, corresponding
to about 0.5% of all vascular plants.
The goal of our research is to understand the molecular basis of metal hyperaccumulation and
associated metal hypertolerance in plants in an ecological and evolutionary context. To this
end, we study the Zn, Cd and Pb hyperaccumulator Arabidopsis halleri, a close relative of the
classical genetic model A. thaliana. Arabidopsis halleri is a perennial outcrossing diploid (2n =
16), which tolerates 170-fold higher zinc, 35-fold higher cadmium and 2-fold higher lead
concentrations in soil than A. thaliana. The recent published genome assembly of the
Japanese A. halleri ssp. gemmifera suggests a similar genome size and gene number, as well
as a high level of coding sequence similarity to other species of the Arabidopsis genus,
although A. halleri is the only metal hyperaccumulator in this genus. Hence, metal
hyperaccumulation and tolerance naturally evolved uniquely in A. halleri following the
divergence from A. lyrata. This makes A. halleri interesting for genome-wide cross-species
comparative genomic, transcriptomic and genetic approaches. We will present our current
approaches and results from the analysis of genetic variation in relation to extreme metalrelated
phenotypic traits. Our research may help to advance phytoremediation, phytomining
and crop bio-fortification technologies.