LHP1 nuclear localisation
LHP1, the Drosophila heterochromatin protein 1 (HP1) homologue, controls developmental pathways by being involved in organ and cell size, in plant architecture, in the vegetative to reproductive phase transition and in floral morphogenesis (Figure 1) (Gaudin et al., 2001). LHP1 contains a chromo and chromo shadow domains that are central to the function of HP1-like proteins and to the recognition of epigenetic marks allowing to establish specific chromatin states.
We have studied its localization in both A. thaliana and Nicotiana tabacum to unravel its function (Libault et al., 2005). Our data indicate that LHP1 is mainly involved in euchromatin organization in A. thaliana. Indeed, in A. thaliana interphase nuclei, LHP1 was predominantly located outside the heterochromatic chromocenters (Figure 2). Furthermore, no major aberrations were observed in heterochromatin content or chromocenter organization in lhp1 plants. However, in tobacco BY-2 cells, the LHP1 distribution, although in nuclear foci, slightly differed suggesting that LHP1 localization is determined by the underlying genome organization of plant species. Truncated LHP1 proteins expressed in vivo allowed us to determine the function of the different domains in directing the localization. Finally, using transgenic plants expressing the LHP1-GFP fusion protein, we could observe two major localization patterns according to cell types suggesting that localization evolves with age or differentiation states.

DamID, a new tool for studying plant chromatin profiling in vivo, and its use to identify putative LHP1 target loci.
To identify target sites of chromatin proteins on the genome we have adapted the in vivo methylation-based tagging technique, DamID (DNA adenine methyltransferase identification) initially designed for chromatin profiling in animals (http://www.nki.nl/nkidep/vansteensel). Using DamID, we have shown that LHP1 was targeted to the promoter and transcribed regions of four floral regulatory genes, AG, AP3, FT and PI. Our data also demonstrate that LHP1-containing complexes (like its animal homologues) have a high-binding affinity for A/T-rich regions, localizing to the large regulatory introns of AG and PI (Germann et al., 2006). Using DamID-chip in collaboration with S. Jacobsen, we established a genome-wide LHP1 profiling (http://epigenomics.mcdb.ucla.edu/LHP1/). We could show that LHP1 localizes to chromatin associated with H3K27me3 genome-wide. Furthermore, the LHP1 chromodomain binds H3K27me3 with high affinity. These results suggest that LHP1 shares similar functions with POLYCOMB and would be part of a PRC1 complex (Zhang et al., 2007).