ZMBP Project Group Ulrike Zentgraf

Leaf senescence of annual plants

 

  

     

 

Ulrike Zentgraf


 Department of Genetics
 University of Tübingen
 Auf der Morgenstelle 28
 72076 Tübingen
 Germany

 

Tel: 07071/29-78833
 Fax: 07071/29-5042
 e-mail: ulrike.zentgraf(at)uni-tuebingen.de

 

Research Group Leader Dr. Ulrike Zentgraf

 

 

Research interest

 

 

Senescence is a key process that underpins many important agronomic traits including yield outcomes and pre- and post-harvest quality. Senescence is a highly regulated and organized process during which macromolecules of the mature green leaf are dismantled and remobilized for further use by the plant, either for new growth or for deposition in developing seeds. Efficient senescence is essential for the overall success of the plant and its following generations; however, premature senescence, induced by stress, leads to reduced yield and quality of crop plants. Abiotic stress is estimated to be the primary cause of crop loss worldwide, with the potential to cause a reduction of more than 50% in the average yield of the main crops.

In general, leaf senescence is characterized by the breakdown of macromolecules and the mobilization of nutrients out of the senescing tissues. The rapid loss of chlorophyll, the lowering of protein and RNA levels or the leakiness of the cell membranes are used as senescence markers. The selective activation of gene expression but also the decrease of certain RNAs and/or proteins is likely to initiate and regulate this process. Despite the importance of the senescence processes in plants, our knowledge on regulatory mechanisms of senescence is still poor. 

 

In order to characterize factors which are involved in the onset and regulation of senescence two different approaches are followed.






Research projects

 

     

a) Free radicals are thought to play an essential role in senescence, especially those derived from oxygen. Increased levels of activated oxygen measured in senescing tissues could either occur through an enhanced production of activated species or a decline of the various defense systems that normally afford protection against oxidative injury. Both mechanisms seem to be realized in senescing tissues, so that investigating the regulation of these scavenging systems probably offers an opportunity to characterize factors and parameters regulating senescence. Especially hydrogen peroxide is discussed as being a signaling molecule in Arabidopsis thaliana leaf senescence. Intracellular hydrogen peroxide levels are controlled by the hydrogen peroxide scavenging enzyme catalase in concert with other scavenging and producing systems. The coordinated regulation of these hydrogen peroxide scavenging enzymes on the transcriptional and posttranscriptional level creates a distinct increase of hydrogen peroxide at the time point when the plants start to bolt and a coordinated senescence process of all rosette leaves should be induced. Conversely, it was already shown that the senescence regulating transcription factor WRKY53 and its regulators as well as other senescence-associated transcription factors and SAGs can be induced by hydrogen peroxide, so that the hydrogen peroxide peak during bolting time most likely serves as a signal to induce senescence-associated gene transcription. Since transcriptional down-regulation of CAT2 appears to be the initial step to create this senescence-promoting signal, we identified G-box binding factor 1 (GBF1) as a negative regulator for CAT2 transcription. In gbf1 plants, CAT2 decrease in expression and activity and the thereby created H2O2 peak disappeared. Consequently, gbf1 plants showed a delayed senescence phenotype and an affected expression of SAGs.   

Senescing phenotypes in Arabidobsis

 

b) Senescence associated gene expression. For detailed gene expression analyses during leaf senescence we have designed a hybridization matrix for gene profiling using the Affymetrix high density genome arrays representing approximately 8.200 genes. If we analyze gene expression according to the age of individual leaves of one plant in comparison to leaves harvested from plants with different ages we get very different expression profiles. These data indicate that gene expression is governed by two different parameters, leaf age and plant age.


 

     

Matrix of leaf material used for chip hybridization and cluster analyses



     

 

 

 

The differential expression of genes according to the age of the leaves within one rosette was also analyzed using suppression subtractive hybridization (SSH). A transcription factor of the WRKY family, WRKY53, was isolated in this screen.
 To understand the regulatory role of the senescence related WRKY53 factor, we identified targets of this transcription factor by a pull down assay using genomic DNA and recombinant WRKY53 protein. We isolated a number of candidate target genes including other transcription factors, also of the WRKY family, stress- and defence related genes, and senescence-associated genes (SAGs). WRKY53 protein could bind to these different promoters in vitro and in vivo and it could act either as transcriptional activator or transcriptional repressor depending on the sequences surrounding the W-boxes. WRKY53 can be induced by H2O2 and can regulate its own expression in a negative feed-back loop. Our results suggest that WRKY53 acts in a complex transcription factor signalling network regulating senescence specific gene expression and hydrogen peroxide might be involved in signal transduction. WRKY53 is tightly regulated on different levels: i) activity, positively by phosphorylation (MEKK1) and negatively by blocking the DNA-binding (ESR/ESP), ii) gene expression which is regulated by at least four proteins that bind to the promoter of WRKY53 and iii) degradation of the protein by a HECT E3 ubiquitin ligase.

 

 

 

  


 Characterization of single leaves of a 6-week-old plant of Arabidopsis thaliana.
 A Colour coded rosette leaves.
 B The photochemical efficiency of PSII. (Fv/Fm)
 C Northern blot analysis of single leaves.

 



 

Figure 1 Model of the regulatory network of WRKY53

Group members

 

 


Mara Hartung, Ulrike Zentgraf, Anja Smykowski, Gabi Eggers-Schumacher, Maren Potschin, Stefan Bieker (from left to right)

 

Kerstin Huhn, Ying Miao, Ulrike Zentgraf, Stefan Bieker, Maren Potschin Gabi Eggers-Schumacher, Carles Marco Llorca, Lena Riester (from left to right)

 




Prof. Dr. Ulrike Zentgraf (Project Group leader)
 Tel: 07071/29-78833
 Fax: 07071/29-5042
 e-mail: ulrike.zentgraf(at)uni-tuebingen.de
 
 
 Dr . Anja Smykowski
 Tel: 07071/29-75358
 Fax: 07071/29-5042
 e-mail: anja.smykowski(at)zmbp.uni-tuebingen.de

Dr. Ying Miao (Postdoc)

Tel: 07071/29-78832
 Fax: 07071/29-5042
 e-mail: ying.miao(at)zmbp.uni-tuebingen.de

Stefan Bieker

Tel: 07071/29-78832
 Fax: 07071/29-5042
 e-mail: stefan.bieker(at)zmbp.uni-tuebingen.de

Lena Riester

Tel: 07071/29-78832
 Fax: 07071/29-5042
 e-mail: Lena.Riester(at)student.uni-tuebingen.de

Maren Potschin
 Tel: 07071/29-74608
 Fax: 07071/29-5042
 e-mail: maren.potschin(at)zmbp.uni-tuebingen.de

Kerstin Huhn
 Tel: 07071/29-74608
 Fax: 07071/29-5042
 e-mail: kerstin.huhn(at)student.uni-tuebingen.de

Carles Marco Llorca
 Tel: 07071/29-78854
 Fax: 07071/29-5042
 e-mail: carles.marco-llorca(at)zmbp.uni-tuebingen.de

Gabi Eggers-Schumacher (technician)
 Tel: 07071/29-75358
 Fax: 07071/29-5042

Former group members

 

 Dr. Katrin Hinderhofer
 
 Dr. Gaby Orendi
 
 Dr. Corinna Dost
 
 Dr. Petra Zimmermann

Dr. Thomas Laun
 
 
 

Publications:

 

  • Zentgraf, U., Zimmermann, P. & Smykowski, A.: Role of intracellular hydrogen peroxide as signalling molecule for plant senescence, In-tech open access publishing, accepted
  • Wierer, S., Elgass, K., Bieker, S., Zentgraf, U., Meixner, A. J., Schleifenbaum, F. : Determination of the in vivo redox potential using roGFP and fluorescence spectra obtained from one-wavelength excitation. Proc. SPIE 7902, 790211 , doi:10.1117/12.873753 (2011)
  •  Smykowski, A., Zimmermann, P., Zentgraf, U.: G-Box Binding Factor1 reduces CATALASE2 expression and regulates the onset of leaf senescence in Arabidopsis. Plant Physiology 153, 1321-1331 (2010)
  • Miao, Y., Zentgraf, U.: A HECT E3 ubiquitin ligase negatively regulates Arabidopsis leaf senescence through degradation of the transcription factor WRKY53. The Plant Journal 63, 179–188 (2010)
  • Zentgraf, U., Laun, T., Miao, Y.: The complex regulation of WRKY53 during leaf senescence of Arabidopsis thaliana. Eur J Cell Biol 89, 133-137 (2009)
  • Zentgraf, U.: Catalase regulation during leaf senescence of Arabidopsis. In: Redox Metabolism and longevity relationships in animals and plants. Eds: Foyer C, Faraghar R, Thornalley P J, Garland Science, London (2009)
  • Zentgraf, U.: Mit Netz und doppeltem Boden: ein molekulares Regulationsnetzwerk der pflanzlichen Senesezenz im Modellsystem Arabidopsis. Biospektrum 14, 465-468 (2008)
  • Miao, Y., Smykowski, A., Zentgraf, U.: A novel upstream regulator of the WRKY53 transcription during leaf senescence of Arabidopsis thaliana. Plant Biol. 10 (Suppl.1) 110-120 (2008)
  • Zentgraf, U,  Hemleben V: Molecular cell biology: Are reactive oxygen species regulators of leaf senescence? In: Progress in Botany, Vol. 69, Springer Verlag, Berlin, Heidelberg, New York, pp 117-137 (2008)
  • Miao, Y., Laun, T., Smykowski, A., Zentgraf, U.: Arabidopsis MEKK1 can take a short cut: it can directly interact with senescence-related WRKY53 transcription factor on the protein level and can bind to its promoter. Plant Mol Biol. 65: 63-76.  (2007) 
  • Miao, Y., Zentgraf U.: The antagonist function of Arabidopsis WRKY53 and ESR/ESP in leaf senescence is modulated by the jasmonic and salicylic acid equilibrium. The Plant Cell 19: 819-830 (2007)
  • Zentgraf, U.: Oxidative stress and leaf senescence. In: Senescence processes in plants. Ed: Gan, S. Annual Plant Reviews Vol. 26, Blackwell Publishing, ISBN: 9781405139847, pp 69-86 (2007) 
  • Dost, C.K., Saraiva, J., Zentgraf, U., Monesi, N., Engels, W., Albuquerque, S.: Is nitric oxide involved in the tolerance of Calomys callosus as a reservoir host towards Trypanosoma cruzi infection? J Infect. 52 :49-55 (2006).
  • Zimmermann, P., Heinlein, C., Orendi, G., Zentgraf, U.: Senescence specific regulation of catalases in Arabidopsis thaliana (L.) Heynh. Plant Cell Environ. 29: 1049-1060 (2006)
  • Volkov, R.A., Komarova, N.Y., Zentgraf, U., Hemleben, V.: Molecular cell biology: epigenetic gene silencing in plants. In: Progr. Botany (Esser, K., Lüttge, U., Beyschlag, W. & Murata, J., Eds.) Progress in Botany Vol. 67, Springer Verlag, Berlin, Heidelberg, New York, pp. 101-133 (2006) 
  • Zimmerman, P., Zentgraf, U.: The Correlation between oxidative stress and leaf senescence during plant development. Mol. Cell. Biol. Lett. 10: 515-534 (2005)
  • Panchuk, I.I., Zentgraf U., Volkov R.A.: Expression of the APX gene family during leaf senescence of Arabidopsis thaliana. Planta 222: 926-32 (2005)
  • Zimmermann, P., Zentgraf, U. : Pflanzliche Seneszenz – geordnetes Chaos? Bioforum 28 (6): 30-31 (2005)
  • Miao, Y., Laun, T., Zimmermann P., Zentgraf, U.:Targets of the WRKY53 transcription factor and its role during leaf senescence in Arabidopsis thaliana. Plant Mol. Biol. 55 (6): 853-867 (2004)
  • Zimmermann, P., Zentgraf, U. : Der Zusammenhang zwischen oxidativem Stress und Blattseneszenz während der Entwicklung von Pflanzen. Gesunde Pflanzen 56: 208-217 (2004)
  • Dost, C..K., Saraiva, J., Monesi, N., Zentgraf, U., Engels, W., Albuquerque, S.: Six Trypanosoma cruzi strains characterized by specific gene expression patterns. Parasitol. Res 94: 134-140 (2004)
  • Zentgraf, U., Jobst, J., Kolb, D., Rentsch, D.: Senescence related gene expression profiles of rosette leaves of Arabidopsis thaliana: leaf age versus plant age. Plant Biol. 6, 178-183 (2004)
  • Volkov, R.A., Medina, F.J., Zentgraf, U., Hemleben, V.: Molecular Cell Biology: Organization and Molecular Evolution of rDNA, Nucleolar Dominanz, and Nucleolus structure. In: Progress in Botany Vol.65, 106-146, Springer Verlag, Berlin, Heidelberg, 2004
  • Fajkus, J., Zentgraf, U.: Structure and maintenance of chromosome ends. In: Telomeres and Telomerases: Cancer and Biology (Eds. Krupp, G., Parwaresch, R.), www.eurekah.com, Bioscience, Gen-Expression, 2002
  • Hemleben, V., Hinderhofer, H., Zentgraf, U.: Molecular Cell Biology: Mechanisms and regulation of protein import into the plant cell nucleus. In: Progress in Botany Vol.63, 132-162, Springer Verlag, Berlin, Heidelberg, New York, (2002)
  • Orendi, G., Zimmermann, P., Baar, C., Zentgraf, U.: Loss of stress-induced expression of catalase3 during leaf senescence of Arabidopsis thaliana is restricted to oxidative stress. Plant Sci. 161, 301-314 (2001)
  • Hinderhofer, K., Zentgraf, U.: Identification of a transcription factor specially expressed at the onset of leaf senescence. Planta 213, 469-473 (2001)
  • Hemleben, V., Torres-Ruiz, RA, Schmidt, T., Zentgraf, U.: Molecular Cell Biology: Role of repetitive DNA in nuclear architecture and chromosome structure. In: Progress in Botany Vol.61, 91-117, Springer Verlag, Berlin, Heidelberg, New York, 2000
  • Zentgraf, U., Hinderhofer, K., Kolb, D.: Specific association of a small protein with the telomeric DNA-protein complex during the onset of leaf senescence in Arabidopsis thaliana. Plant Mol. Biol. 42, 429-438 (2000)
  • Zentgraf, U., Velasco, R., Hemleben, V.: Molecular Cell Biology: Different Transcriptional Activities in the Nucleus. In: Progress in Botany (Behnke et al., eds.) pp. 131-168, Vol. 59, Springer Verlag, Berlin, Heidelberg, New York, 1998
  • Zentgraf, U., Hemleben, V.: Molecular Cell Biology: Signal Transduction in Plants. In: Progress in Botany, Vol. 57, 218-234, Springer-Verlag Berlin Heidelberg 1996
  • Zentgraf, U., Zinkernagel, I.: A gene encoding a catalase isoform from Arabidopsis thaliana (PGR 96-005). Plant Physiol. 110, 1047 (1996)
  • Zentgraf, U.: Telomere-binding proteins of Arabidopsis thaliana. Plant Mol. Biol. 27: 467-475 (1995)
  • Hemleben, V., Zentgraf, U.: Structural organization and regulation of transcription by RNA polymerase I of plant nuclear ribosomal RNA genes. In: Plant Promoters and Transcription Factors. Nover, L. (Ed), Results and Problems in Cell Differentiation. pp. 3 - 24, Vol. 20, Springer, Berlin Heidelberg 1994
  • Fischer, T.C., Groner, S., Zentgraf, U., Hemleben, V.: Evidence for nucleosomal phasing and a novel protein specifically binding to cucumber satellite DNA. J. Biosciences 49c, 79-86 (1994)
  • Zentgraf, U., Hemleben, V.: Nuclear proteins interact with RNA polymerase I promoter and repeated elements of the 5'external transcribed spacer of the rDNA of cucumber in a single-stranded stage. Plant Mol. Biol. 22, 1153-1156 (1993) 
  • King, K., Torres, R.A., Zentgraf, U., Hemleben, V.: Molecular evolution of the intergenic spacer in the nuclear ribosomal RNA genes of ucurbitaceae. J. Mol. Evol. 36, 144-152 (1993) 
  • Hemleben, V., Zentgraf, U., King, K., Borisjuk, N., Schweizer, G.: Middle repetitive and highly repetitive sequences detect polymorphisms in plants. In: DNA-polymorphisms in Eukaryotic Genomes. Kahl, G., Appelhans, H., Kömpf, J., Driesel, A.J. (Eds.). BioTechForum (BTF), Advances in Molecular Genetics, Vol. 5, pp. 157 - 170, Huethig Verlag, Heidelberg, 1992
  • Zentgraf, U., Hemleben, V.: Complex formation of nuclear proteins with the RNA polymerase I promoter and repeated elements in the external transcribed spacer of Cucumis sativus ribosomal DNA. Nucl. Acids Res. 20, 3685-3691 (1992)
  • Zentgraf, U., King, K., Hemleben, V.: Repetitive sequences are valuable as molecular markers in studies of phylogenetic relationships within the genus Cucumis. Acta Bot. Neerl. 41, 397-406 (1992)
  • Zentgraf, U, Ganal, M., Hemleben, V.: Length heterogeneity of the rRNA precursor in cucumber (Cucumis sativus). Plant Mol. Biol. 15, 465-474 (1990)
  • Zentgraf, U.: Wechselwirkung von Kernproteinen mit funktionellen und repetitiven Strukturen des intergenen Spacers der rRNA-Gene von Cucumis sativus L. Dissertation, Tübingen (1990)
  • Torres, R.A., Zentgraf, U., Hemleben, V.: Species and genus specificity of the intergenic spacer (IGS) in the ribosomal RNA genes of Cucurbitaceae. J. Biosciences 44c, 1029-1034 (1989)
  • Zentgraf U.: Sequenzierung und Sequenzvergleich der 5´ externen ribosomalen Spacerregion der Gurke, Diplomarbeit, Tübingen (1987)