Plant Metabolism of Xenobiotics
Zusammenfassung der Projektergebnisse
In the funding period we established a novel function of phytochelatin synthase (PCS) in initiating a plant-specific pathway of glutathione-conjugate catabolism in Arabidopsis. PCS action has been located to the cytosolic compartment of plant cells providing a major cytosolic activity for processing glutathione-conjugates. Thus, PCS fulfils at least two cellular functions, namely catalysing the biosynthesis of heavy metalbinding phytochelatins (PCs) and the turnover of GS-conjugates. Plant PC biosynthesis and glutathione-conjugate turnover have been reconstructed in Saccharomyces cerevisiae. To this end, endogenous PC biosynthesis in baker's yeast has been examined and two carboxypeptidases identified that are responsible for generating PCs from glutathione. Hence, a second enzyme class has been identified to mediate PC formation in vivo. Yeast lines deficient in endogenous PC biosynthesis offer now an ideal system to reconstruct and study glutathione-conjugate catabolism of plants as a prelude to transfer the insights gained by these analyses back to the plant system. Additionally, we started to functionally analyse plant glutathione-S-transferases (GSTs) in conjugate metabolism. Again, we resorted to yeast as a model system. S. cerevisiae have been studied for endogenous GST activities and multiple GST-knockout strains (up to quintuple mutants) were generated. GST-deficient yeast strains have been used to analyse the substrate specificities of plant GSTs. Plant GSTs comprise a family of 55 members in Arabidopsis. Almost 50 different Arabidopsis GSTs have been inducibly expressed in yeast. The analysis revealed a novel herbicidemetabolising activity of a subclass of plant GSTs. The analysis of xenobiotic catabolism in yeast has been supported by ultrahigh resolution mass spectrometry and stable isotope labelling. The analysis of the sulphur metabolome of Arabidopsis in respect to glutathione and derivatives thereof has been initiated.
Projektbezogene Publikationen (Auswahl)
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(2007). Function of phytochelatin synthase in catabolism of glutathione-conjugates. Plant Journal 49, 740-749
Blum, R., Beck, A., Korte, A., Stengel, A., Letzel, T., Lendzian, K., Grill, E.
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(2007). Phytochelatins are synthesized by two vacuolar serine carboxypeptidases in Saccharomyces cerevisiae. FEBS Letters 581, 1681-1687
Wünschmann, J., Beck, A., Meyer, L., Letzel, T., Grill, E., Lendzian, K.
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(2010). Cytosolic action of phytochelatin synthase. Plant Physiol. 153, 159-169
Blum R., Meyer K.C., Wünschmann J., Lendzian K.J., Grill E.
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(2010). Dissection of glutathione conjugate turnover in yeast. Phytochem. 71, 54-61
Wünschmann, J., Krajewski, M., Letzel, T., Huber E.M., Ehrmann, A., Grill, E. Lendzian, K.J.
