Kerstin Huhn, Ying Miao, Ulrike Zentgraf, Stefan Bieker, Maren Potschin, Gabi Eggers-Schumacher, Carles Llorca (Merit-fellow), Lena Riester (from left to right) on a tour to the “Nebelhöhle”


Our group is interested in the regulatory network involved in senescence regulation. Developmental as well as dark-induced leaf senescence is accompanied by a massive change in the transcriptome clearly implying an important role of transcription factors in these overlapping processes. We could show that G-box binding factor1 (GBF1), belonging to the G-group bZIP transcription factors, is involved in the induction of developmental leaf senescence since gbf1 mutant plants exhibit a delayed senescence phenotype. GBF1 expression is not transcriptionally up-regulated during leaf senescence and therefore GBF1 is presumed to be post-transcriptionally regulated, possibly by the formation of specific heterodimers with other bZIP factors. Another possibility is that GBF1 is modified e.g. by specific kinases such as SnRK1 or that it is regulated at the level of translation or its intracellular localization in analogy with bZIP10. The aim of this project will be to characterize the senescence-specific activation of GBF1 and the crosstalk to low energy stress in more detail. Methodology will include bimolecular fluorescence complementation assays (BiFC) and FACS analyses, Yeast-two-hybrid, phosphorylation assays, site-directed mutagenesis, senescence phenotyping and expression analyses, ELISA-based DNA-binding assays, transient protoplast transformation, intracellular hydrogen peroxide measurements.


1) Target genes and localization of GBF1/bZIP63 dimers.

We will test the influence of GBF1/bZIP63 dimer formation on its DNA-binding activity and on the expression of the reporter genes CAT2 and RUBISCO. We will follow up the intracellular localization of the proteins and the complex over plant development. New target genes should be isolated by ChIPSeq.

2) Influence of SnRK1 on GBF1/bZIP63 dimers.

bZIP63 is affected by SnRK1, which is related to starvation and the LES in plants. Over-expressing a SnRK1 catalytic subunit increased the expression of sugar-repressed and autophagy genes and showed a delayed flowering and senescence phenotype (Wingler et al. (2009) J Ex. Bot 60 1063-1066). Therefore, we will analyze the interaction of bZIP63/GBF1 in the snrk1 mutant background and SnRK1 over-expressing lines and test the expression of reporter genes and senescence induction. Conversely dark-induced senescence will be compared between wild type plants and gbf1 mutants. In addition, a direct interaction between SnRK1 and GBF1/bZIP63 will be tested by means of Y2H, BiFC and Co-IP.

3) Identification of new interacting partners.

We will identify other bZIP protein interaction partners forming heterodimers with GBF1 using a protoplast-based high through-put system.