title: Control of Paternally Expressed Imprinted UPWARD CURLY LEAF1, a Gene Encoding an F-Box Protein That Regulates CURLY LEAF Polycomb Protein, in the Arabidopsis Endosperm.
abstract: Genomic imprinting, an epigenetic process in mammals and flowering plants, refers to the differential expression of alleles of the same genes in a parent-of-origin-specific manner. In Arabidopsis, imprinting occurs primarily in the endosperm, which nourishes the developing embryo. Recent high-throughput sequencing analyses revealed that more than 200 loci are imprinted in Arabidopsis; however, only a few of these imprinted genes and their imprinting mechanisms have been examined in detail. Whereas most imprinted loci characterized to date are maternally expressed imprinted genes (MEGs), PHERES1 (PHE1) and ADMETOS (ADM) are paternally expressed imprinted genes (PEGs). Here, we report that UPWARD CURLY LEAF1 (UCL1), a gene encoding an E3 ligase that degrades the CURLY LEAF (CLF) polycomb protein, is a PEG. After fertilization, paternally inherited UCL1 is expressed in the endosperm, but not in the embryo. The expression pattern of a β-glucuronidase (GUS) reporter gene driven by the UCL1 promoter suggests that the imprinting control region (ICR) of UCL1 is adjacent to a transposable element in the UCL1 5'-upstream region. Polycomb Repressive Complex 2 (PRC2) silences the maternal UCL1 allele in the central cell prior to fertilization and in the endosperm after fertilization. The UCL1 imprinting pattern was not affected in paternal PRC2 mutants. We found unexpectedly that the maternal UCL1 allele is reactivated in the endosperm of Arabidopsis lines with mutations in cytosine DNA METHYLTRANSFERASE 1 (MET1) or the DNA glycosylase DEMETER (DME), which antagonistically regulate CpG methylation of DNA. By contrast, maternal UCL1 silencing was not altered in mutants with defects in non-CpG methylation. Thus, silencing of the maternal UCL1 allele is regulated by both MET1 and DME as well as by PRC2, suggesting that divergent mechanisms for the regulation of PEGs evolved in Arabidopsis.
authors.affiliation: School of Biological Sciences, Seoul National University, Seoul, Korea.
authors.forename: Cheol Woong
authors.initials: CW
authors.lastname: Jeong
authors.affiliation: School of Biological Sciences, Seoul National University, Seoul, Korea.
authors.forename: Guen Tae
authors.initials: GT
authors.lastname: Park
authors.affiliation: School of Biological Sciences, Seoul National University, Seoul, Korea.
authors.forename: Hyein
authors.initials: H
authors.lastname: Yun
authors.affiliation: Plants for Human Health Institute & Department of Plant and Microbial Biology, North Carolina State University, Kannapolis, North Carolina, United State of America.
authors.forename: Tzung-Fu
authors.initials: TF
authors.lastname: Hsieh
authors.affiliation: Department of Agricultural Biotechnology, Seoul National University, Seoul, Korea.
authors.forename: Yang Do
authors.initials: YD
authors.lastname: Choi
authors.affiliation: School of Biological Sciences, Seoul National University, Seoul, Korea.
authors.forename: Yeonhee
authors.initials: Y
authors.lastname: Choi
authors.affiliation: School of Biological Sciences, Seoul National University, Seoul, Korea.
authors.forename: Jong Seob
authors.initials: JS
authors.lastname: Lee
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics*; D001483:Base Sequence; D019175:DNA Methylation; D056625:Endosperm / Q000378:metabolism*; D044783:F-Box Proteins / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D018392:Genomic Imprinting; D063146:Polycomb-Group Proteins / Q000378:metabolism*; D019076:Transgenes / Q000235:genetics; D044767:Ubiquitin-Protein Ligases / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; D044783:F-Box Proteins; D063146:Polycomb-Group Proteins; C000604003:UPWARD CURLY LEAF1 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases