title: DNA demethylation is initiated in the central cells of Arabidopsis and rice.
abstract: Cytosine methylation is a DNA modification with important regulatory functions in eukaryotes. In flowering plants, sexual reproduction is accompanied by extensive DNA demethylation, which is required for proper gene expression in the endosperm, a nutritive extraembryonic seed tissue. Endosperm arises from a fusion of a sperm cell carried in the pollen and a female central cell. Endosperm DNA demethylation is observed specifically on the chromosomes inherited from the central cell in Arabidopsis thaliana, rice, and maize, and requires the DEMETER DNA demethylase in Arabidopsis DEMETER is expressed in the central cell before fertilization, suggesting that endosperm demethylation patterns are inherited from the central cell. Down-regulation of the MET1 DNA methyltransferase has also been proposed to contribute to central cell demethylation. However, with the exception of three maize genes, central cell DNA methylation has not been directly measured, leaving the origin and mechanism of endosperm demethylation uncertain. Here, we report genome-wide analysis of DNA methylation in the central cells of Arabidopsis and rice-species that diverged 150 million years ago-as well as in rice egg cells. We find that DNA demethylation in both species is initiated in central cells, which requires DEMETER in Arabidopsis However, we do not observe a global reduction of CG methylation that would be indicative of lowered MET1 activity; on the contrary, CG methylation efficiency is elevated in female gametes compared with nonsexual tissues. Our results demonstrate that locus-specific, active DNA demethylation in the central cell is the origin of maternal chromosome hypomethylation in the endosperm.
authors.affiliation: Department of Biological Sciences, Seoul National University, 151-742 Seoul, South Korea.
authors.forename: Kyunghyuk
authors.initials: K
authors.lastname: Park
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720.
authors.forename: M Yvonne
authors.initials: MY
authors.lastname: Kim
authors.affiliation: Department of Cell and Developmental Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Vickers
authors.affiliation: Department of Biological Sciences, Seoul National University, 151-742 Seoul, South Korea.
authors.forename: Jin-Sup
authors.initials: JS
authors.lastname: Park
authors.affiliation: Department of Biological Sciences, Seoul National University, 151-742 Seoul, South Korea.
authors.forename: Youbong
authors.initials: Y
authors.lastname: Hyun
authors.affiliation: Tokyo Metropolitan University, 192-0397 Tokyo, Japan; okamoto-takashi@tmu.ac.jp danielz@berkeley.edu rfischer@berkeley.edu xiaoqi.feng@jic.ac.uk yhc@snu.ac.kr stefan.scholten@uni-hamburg.de.
authors.forename: Takashi
authors.initials: T
authors.lastname: Okamoto
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720; okamoto-takashi@tmu.ac.jp danielz@berkeley.edu rfischer@berkeley.edu xiaoqi.feng@jic.ac.uk yhc@snu.ac.kr stefan.scholten@uni-hamburg.de.
authors.forename: Daniel
authors.initials: D
authors.lastname: Zilberman
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720; okamoto-takashi@tmu.ac.jp danielz@berkeley.edu rfischer@berkeley.edu xiaoqi.feng@jic.ac.uk yhc@snu.ac.kr stefan.scholten@uni-hamburg.de.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Fischer
authors.affiliation: Department of Cell and Developmental Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom; okamoto-takashi@tmu.ac.jp danielz@berkeley.edu rfischer@berkeley.edu xiaoqi.feng@jic.ac.uk yhc@snu.ac.kr stefan.scholten@uni-hamburg.de.
authors.forename: Xiaoqi
authors.initials: X
authors.lastname: Feng
authors.affiliation: Department of Biological Sciences, Seoul National University, 151-742 Seoul, South Korea; okamoto-takashi@tmu.ac.jp danielz@berkeley.edu rfischer@berkeley.edu xiaoqi.feng@jic.ac.uk yhc@snu.ac.kr stefan.scholten@uni-hamburg.de.
authors.forename: Yeonhee
authors.initials: Y
authors.lastname: Choi
authors.affiliation: University of Hamburg, 22609 Hamburg, Germany okamoto-takashi@tmu.ac.jp danielz@berkeley.edu rfischer@berkeley.edu xiaoqi.feng@jic.ac.uk yhc@snu.ac.kr stefan.scholten@uni-hamburg.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Scholten
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000378:metabolism; D019175:DNA Methylation; D018744:DNA, Plant / Q000235:genetics; D000073398:Demethylation; D056625:Endosperm / Q000378:metabolism; D044127:Epigenesis, Genetic; D035264:Flowers / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018745:Genome, Plant; D018392:Genomic Imprinting; D006720:Homozygote; D012275:Oryza / Q000235:genetics*; D018749:RNA, Plant / Q000378:metabolism; D012639:Seeds / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D018749:RNA, Plant
keywords: DNA methylation; central cell; egg cell; epigenetics; gene imprinting