Universität zu Köln 

Prof. Dr. George Coupland

Max-Planck-Institut für Pflanzenzüchtungsforschung, Köln
email: coupland@mpipz.mpg.de
phone: +49-(0)221 5062 205
website

This project studies the significance of post-translational modifications of transcriptional regulators in controlling flowering of Arabidopsis. Transcription of a key determinant of flowering, FLOWERING LOCUS T (FT), will be studied. Two MADS box transcription factors, SHORT VEGETATIVE PHASE (SVP) and FLOWERING LOCUS C (FLC), act in a complex to repress FT transcription. We showed that these two proteins are SUMOylated in a heterologous E. coli system. We will test for this SUMOylation in plants by using derivatives of these proteins that prevent SUMOylation or act as constitutively SUMOylated forms. These derivatives will be used to test whether SUMOylation is required for heterodimerisation of SVP/FLC and/or their ability to repress transcription. Furthermore, we will determine whether heterodimerisation of SVP/FLC influences binding to target genes by carrying out chromatin immunoprecipitation for each protein in the wildtype background as well as in svp or flc mutants. In contrast to SVP and FLC, the B-box protein CONSTANS (CO) activates FT transcription. We have shown that CO stability is regulated by ubiquitination, that it is phosphorylated and that it is SUMOylated in a heterologous E.coli system. Here we will study the relationship between phosphorylation, SUMOylation and ubiquitination of CO. We will examine whether the phosphorylated form is the preferred substrate for the ubiquitin ligase COP1, whether mutant CO forms that cannot be phosphorylated are more stable and the effect of preventing SUMOylation on CO activity. These approaches will provide a deeper understanding of the mechanisms by which SVP/FLC and CO antagonistically regulate FT transcription.

Running time: 07/2003 – 06/2015

Recent publications:

Tomanov, K., Hardtke, C., Budhiraja, R., Hermkes, R., Coupland, G. and Bachmair, A. (2013). Small ubiquitin-like modifier conjugating enzyme with active site mutation acts as dominant negative inhibitor of SUMO conjugation in Arabidopsis. J Integr Plant Biol 55, 75-82.

Hermkes, R., Fu, Y.F., Nürrenberg, K., Budhiraja, R., Schmelzer, E., Elrouby, N., Dohmen, R.J., Bachmair, A., and Coupland, G. (2011). Distinct roles for Arabidopsis SUMO protease and its closest homolog ELS1. Planta 233, 63-73.

Elrouby, N. and Coupland, G. (2010). Proteome-wide screens for small ubiquitin-like modifier (SUMO) substrates identify Arabidopsis proteins implicated in diverse biological processes. Proc. Natl. Acad. Sci. U.S.A. 107, 17415-17420.

Fornara, F., de Montaigu, A. and Coupland, G. (2010). SnapShot: Control of flowering in Arabidopsis. Cell 141, 550-550.e2.

Budhiraja, R., Hermkes, R., Müller, S., Schmidt, J., Colby, J., Panigrahi, K., Coupland, G., and Bachmair, A. (2009). Substrates related to chromatin and to RNA-dependent processes are modified by Arabidopsis SUMO isoforms that differ in a conserved residue with influence on de-sumoylation. Plant Physiol. 149, 1529-1540.

Fornara, F., Panigrahi, K.C.S., Gissot, L., Sauerbrunn, N., Rühl, M., Jarillo, J., and Coupland, G. (2009). Arabidopsis DOF transcription factors act redundantly to reduce CONSTANS expression and are essential for a photoperiodic flowering response. Dev. Cell 17, 75-86.

Jang, S., Marchal, V., Panigrahi, K.C., Wenkel, S., Soppe, W., Deng, X.-W., Valverde, F., and Coupland, G. (2008). Arabidopsis COP1 shapes the temporal pattern of CO accumulation conferring a photoperiodic flowering response. EMBO J. 27, 1277-1288.

Fujiwara, S; Oda, A., Yoshida, R. Niinuma, K., Miyata, K., Tomozoe, Y., Tajima, T., Nakagawa, M., Hayashi, K., Coupland, G., and Mizoguchi, T. (2008). Circadian clock proteins LHY and CCA1 regulate SVP protein accumulation to control flowering in Arabidopsis. Plant Cell 20, 2960-2971.

Farrona, S., Coupland, G., Turck, F. (2008). The impact of chromatin regulation on the floral transition. Sem. Cell Developm. Biol. 19, 560-573.