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ABSTRACT: The chromatin modifying Polycomb group (PcG) and trithorax group (trxG) proteins are central regulators of cell identity that maintain a tightly controlled balance between cell proliferation and cell differentiation. The opposing activities of PcG and trxG proteins ensure the correct expression of specific transcriptional programs at defined developmental stages. Here, we report that the chromatin remodeling factor PICKLE (PKL) and the PcG protein CURLY LEAF (CLF) antagonistically determine root meristem activity. Whereas loss of PKL function caused a decrease in meristematic activity, loss of CLF function increased meristematic activity. Alterations of meristematic activity in pkl and clf mutants were not connected with changes in auxin concentration but correlated with decreased or increased expression of root stem cell and meristem marker genes, respectively. Root stem cell and meristem marker genes are modified by the PcG-mediated trimethylation of histone H3 on lysine 27 (H3K27me3). Decreased expression levels of root stem cell and meristem marker genes in pkl correlated with increased levels of H3K27me3, indicating that root meristem activity is largely controlled by the antagonistic activity of PcG proteins and PKL.
The Plant Cell 03/2011; 23(3):1047-60. · 8.99 Impact Factor
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ABSTRACT: Cellular identity is maintained by epigenetic processes that prevent changes of cell-type specific transcriptional programs. Polycomb group (PcG) proteins are evolutionary conserved key players of cellular identity that repress central developmental regulators by modifying chromatin structure. PcG-mediated repression is antagonized by trithorax group (trxG) proteins that prevent inappropriate repression by PcG proteins. The molecular basis for this antagonistic activity is unclear. So far, only few chromatin regulatory proteins have been associated with trxG function in Arabidopsis. Recent work revealed that ATP-dependent chromatin remodeling factors of the Chromodomain-Helicase-DNA-binding (CHD) subfamily have trxG-like functions in Arabidopsis. Here we will discuss the implications of these findings that point towards an evolutionary conservation of PcG/trxG mediated gene regulation in higher eukaryotes.
Epigenetics: official journal of the DNA Methylation Society 01/2010; 5(1):20-3. · 4.58 Impact Factor
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ABSTRACT: DNA methylation is a prominent epigenetic mark and extensively found within plant genomes. It has two major roles- first, defending the genome against invasive DNA and second, regulation of gene expression. Since the first report of 5-methylcytosine found in wheat germ, many improvements in detection of methylated cytosine residues have been made and genome-wide methylation maps for Arabidopsis thaliana are now available. The development of fast, reproducible, and single-base pair resolving detection methods for DNA methylation at defined loci advanced our understanding of the establishment and maintenance of DNA methylation patterns. Bisulphite conversion of unmethylated cytosine residues followed by detection methods such as sequencing of distinct loci has become accepted as the gold standard for detecting 5-methylcytosines. Treatment of single-stranded DNA with bisulphite under acidic conditions leads to the conversion of cytosine residues to uracil whereas 5-methylcytosine is less sensitive and remains unchanged. Here, a detailed protocol for bisulphite conversion, primer design, and optimization of PCR conditions is given. Specific requirements for plant DNA are discussed.
Methods in molecular biology (Clifton, N.J.) 01/2010; 655:433-43.
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ABSTRACT: Dynamic regulation of chromatin structure is of fundamental importance for modulating genomic activities in higher eukaryotes. The opposing activities of Polycomb group (PcG) and trithorax group (trxG) proteins are part of a chromatin-based cellular memory system ensuring the correct expression of specific transcriptional programs at defined developmental stages. The default silencing activity of PcG proteins is counteracted by trxG proteins that activate PcG target genes and prevent PcG mediated silencing activities. Therefore, the timely expression and regulation of PcG proteins and counteracting trxG proteins is likely to be of fundamental importance for establishing cell identity. Here, we report that the chromodomain/helicase/DNA-binding domain CHD3 proteins PICKLE (PKL) and PICKLE RELATED2 (PKR2) have trxG-like functions in plants and are required for the expression of many genes that are repressed by PcG proteins. The pkl mutant could partly suppress the leaf and flower phenotype of the PcG mutant curly leaf, supporting the idea that CHD3 proteins and PcG proteins antagonistically determine cell identity in plants. The direct targets of PKL in roots include the PcG genes SWINGER and EMBRYONIC FLOWER2 that encode subunits of Polycomb repressive complexes responsible for trimethylating histone H3 at lysine 27 (H3K27me3). Similar to mutants lacking PcG proteins, lack of PKL and PKR2 caused reduced H3K27me3 levels and, therefore, increased expression of a set of PcG protein target genes in roots. Thus, PKL and PKR2 are directly required for activation of PcG protein target genes and in roots are also indirectly required for repression of PcG protein target genes. Reduced PcG protein activity can lead to cell de-differentiation and callus-like tissue formation in pkl pkr2 mutants. Thus, in contrast to mammals, where PcG proteins are required to maintain pluripotency and to prevent cell differentiation, in plants PcG proteins are required to promote cell differentiation by suppressing embryonic development.
PLoS Genetics 09/2009; 5(8):e1000605. · 8.69 Impact Factor
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ABSTRACT: Polycomb group (PcG) proteins are essential to maintain gene expression patterns during development. Transcriptional repression by PcG proteins involves trimethylation of H3K27 (H3K27me3) by Polycomb Repressive Complex 2 (PRC2) in animals and plants. PRC1 binds to H3K27me3 and is required for transcriptional repression in animals, but in plants PRC1-like activities have remained elusive. One candidate protein that could be involved in PRC1-like functions in plants is LIKE HETEROCHROMATIN PROTEIN 1 (LHP1), because LHP1 associates with genes marked by H3K27me3 in vivo and has a chromodomain that binds H3K27me3 in vitro. Here, we show that disruption of the chromodomain of Arabidopsis thaliana LHP1 abolishes H3K27me3 recognition, releases gene silencing and causes similar phenotypic alterations as transcriptional lhp1 null mutants. Therefore, binding to H3K27me3 is essential for LHP1 protein function.
PLoS ONE 02/2009; 4(4):e5335. · 4.09 Impact Factor
