Publications - Stress and Develop Biology

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.

IntroductionHistorical OutlineChemical StructuresNomenclature and Structure of MetallothioneinsPhytochelatins and Phytochelatin–Metal ComplexesStructural Properties of MetallochaperonesChemical Analysis and DetectionMetallothioneinsPhytochelatinsOccurrenceMetallothioneinsPhytochelatinsMetallochaperonesFunctionsMetal Homeostasis and the Role of MetallochaperonesBuffering and DetoxificationPhytochelatin FunctionsMetallothionein FunctionsPhysiologyMetallothionein Localization and IsoformsLocalization and Compartmentation of Phytochelatin SynthesisBiochemistryMetal‐binding Characteristics of MetallothioneinsBiochemistry of Phytochelatin SynthesisMolecular GeneticsMetallothionein Genes and Their RegulationPhytochelatin Synthase GenesBiotechnological ApplicationsPatentsOutlook and Perspectives

Sequestration of metal ions by phytochelatins is an important metal tolerance mechanism in a wide range of organisms including plants and certain fungi. Substantial progress in understanding phytochelatin formation at the molecular level has been made in Schizosaccharomyces pombe . The genome of S. pombe has been completely sequenced and all the necessary tools of functional genomics are available. Since most other proteins implicated in plant metal tolerance and homeostasis are also present in this yeast, it represents a very powerful system to elucidate basic mechanisms of metal buffering, sequestration, and toxicity in cells that form phytochelatins. Here, we summarize the work on phytochelatin formation and metal homeostasis in S. pombe . We describe examples of molecular insights obtained from experiments with S. pombe that will be useful in guiding studies with plants. We also provide evidence for the dominance of the phytochelatin pathway in Cd detoxification in S. pombe.