Seminars with Ferenc Nagy and Sascha Laubinger – University of Copenhagen

Center for Synthetic Biology > News > Seminars with Ferenc N...

26 May 2015

Seminars with Ferenc Nagy and Sascha Laubinger

TIME: 3 June 2015, 10-12
PLACE: Room R645 and R646, Dept of Plant and Environmental Sciences, Thorvaldsensvej 40

Professor Ferenc Nagy
Institute of Plant Biology, Biological Research Centre (BRC) at the Hungarian Academy of Sciences

Post-translational modifications of the photoreceptor phytochrome-B modulate light induced signalling and development

Abstract: The red/far-red light absorbing phytochromes cycle between their biologically inactive Pr (λmax = 660 nm) and active Pfr (λmax = 730 nm) forms and act as light quality/quantity dependent molecular switches to control photomorphogenesis. Phytochrome signaling is launched by the Pfr conformer and mediated by specific protein-protein interactions between phyA-E Pfr and their downstream regulatory partners. We showed that phyB is phosphorylated at Ser-86 and that phosphorylation of Ser-86 negatively regulates all phyB-regulated photomorphogenic responses. Phosphorylation of Ser-86 (i) does not affect the stability, photoconversion or spectral properties of phyB, (ii) strongly enhances dark/thermal reversion of the phyB Pfr into Pr and (iii) attenuates interaction of phyB Pfr with the negative regulator PIF3 (Plant Cell 2013). More recently we found that phyB is also target of  another post-translational modification. Our data demonstrate that phyB is SUMOylated at its C-terminal domain, accumulation of SUMOylated phyB is enhanced by red light and it displays a diurnal pattern in plants grown under light/dark cycles. Moreover we show that (i) transgenic plants expressing the mutant phyB- K996R-YFP photoreceptor are hypersensitive to red light, (ii) light induced SUMOylation of the mutant phyB is drastically decreased as compared to phyB-YFP and (iii) SUMOylation of phyB inhibits binding of PIF5 to phyB Pfr. phyB is hyperSUMOylated in the ots1/ots2 genetic background and the double mutant is hyposensitive to red light. Taken together we conclude that reversible SUMOylation of phyB is mediated at least partly by the action of these SUMO proteases and SUMOylation of this photoreceptor negatively regulates red light induced signaling. 

Group leader Sascha Laubinger
Center for Plant Molecular Biology, University of Tübingen

Uncovering the functions of Arabidopsis SERRATE in RNA metabolism

Abstract: Plant microRNAs (miRNA) are released from longer primary-miRNA (pri-miRNA) transcripts by a miRNA processing complex comprising several proteins including DICER-LIKE1 (DCL1), , HYPONASTIC LEAVES1 (HYL1) and SERRATE (SE). In addition, the nuclear cap-binding complex (CBC) consisting of CAP-BINDING PROTEIN 20 (CBP20) and CBP80 binds to the 5'-cap of pri-miRNA transcripts and interacts with SE to facilitate miRNA processing. Interestingly, SE and the CBC also ensure proper splicing of introns and therefore fulfill a more general function in RNA metabolism that is distinct from specialized miRNA-processing factors. To gain insights into the mechanistic functions of SE in general RNA, we conducted (1) extensive yeast two-hybrid screens, (2) mass-spec analysis of the SE complex purified form Arabidopsis, and (3) an in depth transcriptome analysis of wild type and se mutant plants. Our results show that SE interacts with additional miRNAs factors, it communicates with the spliceosome and has additional functions in RNA metabolism other than miRNA processing and splicing. Furthermore, interaction between SE and transciprional regulators suggest a role for SE in regulating transcription as well. Taken together, our results reveal the important functions of SE in shaping the Arabidopsis transcriptome.

The professors are in Copenhagen as opponents for the PhD defense of Samir Ben Chaabane