Polycomb group proteins. Polycomb group proteins are master regulators of cell identity and development in plants and animals, and faulty Polycomb group protein function contributes to tumor formation in animals. We study how Polycomb group proteins function in plants and how they control regular plant development. For instance, we found that Arabidopsis Like Heterochromatin Protein 1 (LHP1) must bind to modified histones (histone H3 trimethylated at lysine 27) for the Polycomb Group protein system being able to repress target genes (Exner et al., 2009). An important implication of this work is to understand to which extend cell identity is maintained by the same mechanisms in animals and plants.
Chromatin assembly and composition. Establishment and maintenance of cell identity depends on functional chromatin and correct propagation of chromatin states during replication of the genome. We study which histones and histone modifications exist in plants and how histones are guided into newly formed chromatin. For example, we found that chromatin assembly factor 1 is needed to control genome replication at multiple steps of development (Exner et al. 2006).
Control of flowering time. To flower or not to flower is a crucial decision for plants. The time to initiate flowering greatly affects the reproductive success of plants and the yield of many crops. Therefore, timing of flowering is tightly regulated not only by internal signals but also by many environmental factors. We study how the control of flowering time integrates diverse environmental signals and which role epigenetic mechanisms play in this process. For example, we found that vernalization, i.e. the increased competence to flower after prolonged cold periods such as experienced during winter, involves the repression of the flowering activator AGL19 by Polycomb group proteins (Schönrock et al., 2006).
Epigenomics and transcriptomics. Genome-wide profiling such as possible with microarrays or next generation sequencing can generate global pictures of genome states and function. We exploit various OMICS technologies to establish a comprehensive, system-wide under-standing of chromatin function in plant development. We have developed Gene- vestigator, a widely used portal to published expression data (Zimmermann et al., 2005), and we have established cell type-specific epigenome maps (i.e. genome-wide distribution of histone modifications) (Weinhofer et al. 2010).
Weinhofer, I., Hehenberger, E., Roszak, P., Hennig, L., Köhler, C. (2010) H3K27me3 profiling of the endosperm implies exclusion of Polycomb group protein targeting by DNA methylation. PLoS Genetics 6, e100115
Exner, V., Aichinger, E., Shu, H., Wildhaber, T., Alfarano, P., Caflisch, A., Gruissem, W., Köhler, C., Hennig, L. (2009) The chromodomain of LIKE HETEROCHROMATIN PROTEIN 1 is essential for H3K27me3 binding and function during Arabidopsis development. PLOS ONE 4, e5335
Exner, V., Taranto, P., Schonrock, N., Gruissem, W., and Hennig, L. (2006). Chromatin assembly factor CAF-1 is required for cellular differentiation during plant development. Development 133, 4163-4172
Schönrock, N., Bouveret, R., Gruissem, W., and Hennig, L. (2006) Polycomb Group proteins repress the floral activator AGL19 in the FLC-independent vernalization pathway. Genes & Development 20, 1667-1678 (MEDLINE)
Zimmermann, P, Hirsch-Hoffmann, M., Hennig, L., and Gruissem, W. (2004) GENEVESTIGATOR: Arabidopsis thaliana microarray database and analysis toolbox. Plant Physioloy 136, 2621-2632