title: Loss of function mutations in the rice chromomethylase OsCMT3a cause a burst of transposition.
abstract: Methylation patterns of plants are unique as, in addition to the methylation at CG dinucleotides that occurs in mammals, methylation also occurs at non-CG sites. Genes are methylated at CG sites, but transposable elements (TEs) are methylated at both CG and non-CG sites. The role of non-CG methylation in transcriptional silencing of TEs is being extensively studied at this time, but only very rare transpositions have been reported when non-CG methylation machineries have been compromised. To understand the role of non-CG methylation in TE suppression and in plant development, we characterized rice mutants with changes in the chromomethylase gene, OsCMT3a. oscmt3a mutants exhibited a dramatic decrease in CHG methylation, changes in the expression of some genes and TEs, and pleiotropic developmental abnormalities. Genome resequencing identified eight TE families mobilized in oscmt3a during normal propagation. These TEs included tissue culture-activated copia retrotransposons Tos17 and Tos19 (Lullaby), a pericentromeric clustered high-copy-number non-autonomous gypsy retrotransposon Dasheng, two copia retrotransposons Osr4 and Osr13, a hAT-tip100 transposon DaiZ, a MITE transposon mPing, and a LINE element LINE1-6_OS. We confirmed the transposition of these TEs by polymerase chain reaction (PCR) and/or Southern blot analysis, and showed that transposition was dependent on the oscmt3a mutation. These results demonstrated that OsCMT3a-mediated non-CG DNA methylation plays a critical role in development and in the suppression of a wide spectrum of TEs. These in planta mobile TEs are important for studying the interaction between TEs and the host genome, and for rice functional genomics.
authors.affiliation: National Institute of Genetics, Yata 1111, Mishima, Shizuoka, 411-8540, Japan.|National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Chaoyang
authors.initials: C
authors.lastname: Cheng
authors.affiliation: National Institute of Genetics, Yata 1111, Mishima, Shizuoka, 411-8540, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Tarutani
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Miyao
authors.affiliation: National Institute of Genetics, Yata 1111, Mishima, Shizuoka, 411-8540, Japan.
authors.forename: Tasuku
authors.initials: T
authors.lastname: Ito
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Muneo
authors.initials: M
authors.lastname: Yamazaki
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Sakai
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Eigo
authors.initials: E
authors.lastname: Fukai
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Hirochika
mesh_terms: D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D004251:DNA Transposable Elements; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000096:biosynthesis / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000235:genetics* / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018626:Retroelements
chemical_list: D004251:DNA Transposable Elements; D005875:Gibberellins; D010940:Plant Proteins; D018626:Retroelements; D004248:DNA (Cytosine-5-)-Methyltransferases; C112810:chromomethylase
keywords: DNA methylation; chromomethylase; genome dynamics; rice; silencing; transposable elements; transposition