Polycomb silencing of KNOX genes confines shoot stem cell niches in Arabidopsis.

Institut de Biologie Moleculaire des Plantes (IBMP), Centre National de la Recherche Scientifique (CNRS), Universite Louis Pasteur de Strasbourg (ULP), Strasbourg Cedex, France.
Most plant organs develop postembryonically from stem cells in the shoot and root meristems. In Arabidopsis, Class I KNOTTED-like homeobox (KNOX) transcription factors are specifically expressed in shoot meristems and play a primary role in the maintenance of meristem function. Although suppression of KNOX was shown to associate with histone H3K27-methylation, the molecular mechanism underlying this suppression is not well understood. Here, we provide genetic, molecular, and functional evidence that an Arabidopsis POLYCOMB REPRESSIVE COMPLEX1 (PRC1)-like complex acts in conjunction with PRC2 in KNOX suppression. We identified AtRING1a and AtRING1b as homologs of the animal PRC1 core component RING1. Loss-of-function mutant Atring1a(-/-)Atring1b(-/-) shows release of KNOX suppression and ectopic-meristem formation. AtRING1a and AtRING1b proteins are localized in the nucleus. AtRING1a binds to itself and to AtRING1b, to CURLY LEAF (CLF), a PRC2 core component catalyzing H3K27-methylation, and to LIKE HETEROCHROMATIN PROTEIN1 (LHP1), a chromodomain protein binding trimethyl-H3K27. We further show that clf(-/-) and lhp1(-/-) enhance Atring1a(-/-)Atring1b(-/-) in release of KNOX suppression and mutant phenotypes. We propose a model in which AtRING1a, AtRING1b, and LHP1 form a PRC1-like complex, which binds trimethyl-H3K27 marked by the CLF-containing PRC2, resulting in transcriptional suppression of KNOX.
Mesh Terms:
Arabidopsis, Arabidopsis Proteins, Gene Silencing, Genes, Homeobox, Genes, Plant, Histones, Meristem, Models, Biological, Models, Genetic, Multigene Family, Mutation, Phenotype, Plant Shoots, Repressor Proteins, Stem Cells
Curr. Biol. Dec. 23, 2008; 18(24);1966-71 [PUBMED:19097900]
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