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Publications - Stress and Develop Biology

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Publications

Boch, A.; Trampczynska, A.; Simm, C.; Taudte, N.; Krämer, U.; Clemens, S.; Loss of Zhf and the tightly regulated zinc-uptake system SpZrt1 in Schizosaccharomyces pombe reveals the delicacy of cellular zinc balance FEMS Yeast Res. 8, 883-896, (2008) DOI: 10.1111/j.1567-1364.2008.00414.x

Zinc is an essential micronutrient, and yet it can be toxic when present in excess. Zinc acquisition and distribution are dependent on tightly controlled transport of Zn2+ ions. Schizosaccharomyces pombe represents a second eukaryotic model to study cellular metal homeostasis. In several ways its micronutrient metabolism is fundamentally different from Saccharomyces cerevisiae. We identified the first Zn2+-uptake system in S. pombe and named it SpZrt1. Knock-out strains for all three ZIP (Zrt, Irt-like protein) transporters in fission yeast were constructed. Only zrt1Δ cells were unable to grow at low Zn2+ and showed reduced65Zn2+ uptake. Elemental profiles revealed a strong decrease in zinc accumulation. Cd2+ ions inhibited uptake but Fe2+ or Mn2+ did not. Both mRNA abundance and protein amount are tightly regulated. Zrt1 activity is rapidly shut down upon transfer of zinc-deficient cells to zinc-replete conditions. In cells lacking Zhf, a transporter mediating endoplasmic reticulum storage of zinc, this response is about 100-fold more sensitive. Thus, removal of excess of zinc from the cytosol is largely Zhf dependent. Moreover, cells deficient for both transporters are no longer able to adjust to changing external Zn2+ concentrations. Optimal growth is restricted to a narrow range of Zn2+ concentrations, illustrating the fine balance between micronutrient deficiency and toxicity.
Books and chapters

Krämer, U.; Clemens, S.; Functions and homeostasis of zinc, copper, and nickel in plants Top. Curr. Genet. 14, 215-271, (2006) ISBN: 978-3-540-31719-7 DOI: 10.1007/4735_96

Nutritional micronutrient deficiencies and exposure to pollutant metals threaten human health globally. Plant crops are at the beginning of a food chain that largely determines food metal contents. In order to survive, all organisms have to supply appropriate amounts of each micronutrient to the correct target apometalloproteins and at the same time avoid adventitious metal binding to non-target metal binding sites or other cellular compounds. This requires the operation of metal homeostasis networks, which orchestrate the mobilization, uptake, distribution, intracellular trafficking, chelation, and sequestration of all metal ions. Presumably as a result of time-dependent and local variations in bioavailable soil metal concentrations, plant metal homeostasis networks exhibit a remarkably high degree of plasticity and natural diversity. This is a review covering the current knowledge of metal-dependent processes and proteins, metal homeostasis and its regulation, and the molecular mechanisms underlying naturally selected metal hypertolerance and metal hyperaccumulation in higher plants.
Publications

Clemens, S.; Palmgren, M. G.; Krämer, U.; A long way ahead: understanding and engineering plant metal accumulation Trends Plant Sci. 7, 309-315, (2002) DOI: 10.1016/S1360-1385(02)02295-1

Some plants can hyperaccumulate metal ions that are toxic to virtually all other organisms at low dosages. This trait could be used to clean up metal-contaminated soils. Moreover, the accumulation of heavy metals by plants determines both the micronutrient content and the toxic metal content of our food. Complex interactions of transport and chelating activities control the rates of metal uptake and storage. In recent years, several key steps have been identified at the molecular level, enabling us to initiate transgenic approaches to engineer the transition metal content of plants.
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