Arabidopsis TFL2/LHP1 Specifically Associates with Genes Marked by Trimethylation of Histone H3 Lysine 27
TERMINAL FLOWER 2/LIKE HETEROCHROMATIN PROTEIN 1 (TFL2/LHP1) is the only Arabidopsis protein with overall sequence similarity to the HETEROCHROMATIN PROTEIN 1 (HP1) family of metazoans and S. pombe. TFL2/LHP1 represses transcription of numerous genes, including the flowering time genes FLOWERING LOCUS T (FT) and FLOWERING LOCUS C (FLC) as well as the floral organ identity genes AGAMOUS (AG) and APETALA 3 (AP3) These genes are also regulated by proteins of the Polycomb repressive complex 2 (PRC2) and it has been proposed that TFL2/LHP1 represents a potential stabilizing factor of PRC2 activity. Here we show by chromatin immunoprecipitation and hybridization to an Arabidopsis Chromosome 4 tiling array (ChIP chip) that TFL2/LHP1 associates with hundreds of small domains, almost all of which correspond to genes located within euchromatin. We investigated the chromatin marks to which TFL2/LHP1 binds and show that, in vitro, TFL2/LHP1 binds to histone H3 di or tri methylated at lysine 9 (H3K9me2 or H3K9me3) the marks recognized by HP1, and to histone H3 trimethylated at lysine 27 (H3K27me3) the mark deposited by PRC2. However, in vivo TFL2/LHP1 association with chromatin occurs almost exclusively and co extensively with domains marked by H3K27me3, but not H3K9me2 or 3. Moreover, the distribution of H3K27me3 is unaffected in lhp1 mutant plants, indicating that unlike PRC2 components, TFL2/LHP1 is not involved in the deposition of this mark. Rather, our data suggest that TFL2/LHP1 recognizes specifically H3K27me3 in vivo as part of a mechanism that represses the expression of many genes targeted by PRC2.
PLoS genetics