title: Strict de novo methylation of the 35S enhancer sequence in gentian.
abstract: A novel transgene silencing phenomenon was found in the ornamental plant, gentian (Gentiana triflora x G. scabra), in which the introduced Cauliflower mosaic virus (CaMV) 35S promoter region was strictly methylated, irrespective of the transgene copy number and integrated loci. Transgenic tobacco having the same vector did not show the silencing behavior. Not only unmodified, but also modified 35S promoters containing a 35S enhancer sequence were found to be highly methylated in the single copy transgenic gentian lines. The 35S core promoter (-90)-introduced transgenic lines showed a small degree of methylation, implying that the 35S enhancer sequence was involved in the methylation machinery. The rigorous silencing phenomenon enabled us to analyze methylation in a number of the transgenic lines in parallel, which led to the discovery of a consensus target region for de novo methylation, which comprised an asymmetric cytosine (CpHpH; H is A, C or T) sequence. Consequently, distinct footprints of de novo methylation were detected in each (modified) 35S promoter sequence, and the enhancer region (-148 to -85) was identified as a crucial target for de novo methylation. Electrophoretic mobility shift assay (EMSA) showed that complexes formed in gentian nuclear extract with the -149 to -124 and -107 to -83 region probes were distinct from those of tobacco nuclear extracts, suggesting that the complexes might contribute to de novo methylation. Our results provide insights into the phenomenon of sequence- and species- specific gene silencing in higher plants.
authors.affiliation: Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan. mishiba@plant.osakafu-u.ac.jp
authors.forename: Kei-ichiro
authors.initials: K
authors.lastname: Mishiba
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamasaki
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakatsuka
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Abe
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Daimon
authors.forename: Masayuki
authors.initials: M
authors.lastname: Oda
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nishihara
mesh_terms: D017796:Caulimovirus / Q000235:genetics*; D018899:CpG Islands; D019175:DNA Methylation; D004742:Enhancer Elements, Genetic; D044127:Epigenesis, Genetic; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D030012:Gentiana / Q000235:genetics* / Q000821:virology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D009841:Oligonucleotides / Q000235:genetics; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D019076:Transgenes
chemical_list: D009841:Oligonucleotides; D049452:Green Fluorescent Proteins