title: Polycomb silencing of KNOX genes confines shoot stem cell niches in Arabidopsis.
abstract: 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.
authors.affiliation: Institut de Biologie Moléculaire des Plantes (IBMP), Centre National de la Recherche Scientifique (CNRS), Université Louis Pasteur de Strasbourg (ULP), Strasbourg Cédex, France.
authors.forename: Lin
authors.initials: L
authors.lastname: Xu
authors.forename: Wen-Hui
authors.initials: WH
authors.lastname: Shen
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D020868:Gene Silencing; D005801:Genes, Homeobox; D017343:Genes, Plant; D006657:Histones / Q000378:metabolism; D018519:Meristem / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D008954:Models, Biological; D008957:Models, Genetic; D005810:Multigene Family; D009154:Mutation; D010641:Phenotype; D018520:Plant Shoots / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D006657:Histones; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins