Dr. Ute Krämer

Group "Metal Homeostasis"
New Position: Chair of Plant Physiology, Ruhr University, Bochum

The group is interested in the mechanisms plants use to regulate their internal metal ion levels. The pre-eminent plant model Arabidopsis thaliana and its relative Arabidopsis halleri (which accumulates and tolerates very high levels of zinc) are studied, as are the nickel hyper-accumulator plant Alyssum lesbiacum and the yeast Saccharomyces cerevisiae.

The group is funded primarily by an award received through the BioFuture Competition of the Federal Ministry of Education and Research (BMBF). The BioFuture Competition provides financial support for young scientists who work on new approaches in fundamental research.

Traces of both essential (copper, nickel, and zinc) and non-essential (cadmium, lead, and arsenic) heavy metals occur in most soils. Metal homeostasis balances two requirements essential for survival. (1) Adequate amounts of micronutrients need to be supplied to maintain metal-requiring processes in a growing plant. (2) At the same time the accumulation of surplus micronutrients or non-essential metals has to be prevented in locations where metals can be harmful. When one or several metals are present in large excess, for example on metal-contaminated soils, this can result in metal toxicity. Conversely, plants that grow on soils with low bioavailable micronutrient concentrations can exhibit symptoms of metal deficiency. Our group is using a functional genomics approach to understand how plants maintain the homeostasis of metals.

Surprisingly, some plants found on metal-rich soils accumulate metals to concentrations up to four orders of magnitude above those found in "normal" plants. These plants possess very effective metal acquisition and metal homeostasis systems and are thus highly interesting model plants. One example is Arabidopsis halleri which is very closely related to Arabidopsis thaliana. Our aim is to understand how these accumulator plants concentrate and tolerate such high levels of heavy metals.

The strategies we are using include: heterologous screening and expression in Saccharomyces cerevisiae, expression profiling using EST arrays and oligonucleotide microarrays (to identify differentially regulated genes at the transcript level), isolating Arabidopsis mutants deregulated in various aspects of metal ion homeostasis, biochemical analysis/metabolite profiling (to identify high-affinity, low molecular weight metal chelators), and the generation of transgenic plants with enhanced metal tolerance and metal accumulating capabilities. In addition, we are characterizing identified candidate genes employing expression analysis by real-time RT-PCR, confocal microscopy of GFP fusion proteins, expression in E. coli and yeast.