title: Invasion of the Arabidopsis genome by the tobacco retrotransposon Tnt1 is controlled by reversible transcriptional gene silencing.
abstract: Long terminal repeat (LTR) retrotransposons are generally silent in plant genomes. However, they often constitute a large proportion of repeated sequences in plants. This suggests that their silencing is set up after a certain copy number is reached and/or that it can be released in some circumstances. We introduced the tobacco (Nicotiana tabacum) LTR retrotransposon Tnt1 into Arabidopsis (Arabidopsis thaliana), thus mimicking the horizontal transfer of a retrotransposon into a new host species and allowing us to study the regulatory mechanisms controlling its amplification. Tnt1 is transcriptionally silenced in Arabidopsis in a copy number-dependent manner. This silencing is associated with 24-nucleotide short-interfering RNAs targeting the promoter localized in the LTR region and with the non-CG site methylation of these sequences. Consequently, the silencing of Tnt1 is not released in methyltransferase1 mutants, in contrast to decrease in DNA methylation1 or polymerase IVa mutants. Stable reversion of Tnt1 silencing is obtained when the number of Tnt1 elements is reduced to two by genetic segregation. Our results support a model in which Tnt1 silencing in Arabidopsis occurs via an RNA-directed DNA methylation process. We further show that silencing can be partially overcome by some stresses.
authors.affiliation: Station de Génétique et d'Amélioration des Plantes, UR254, INRA, F-78026 Versailles, France.
authors.forename: Javier
authors.initials: J
authors.lastname: Pérez-Hormaeche
authors.forename: Frédérique
authors.initials: F
authors.lastname: Potet
authors.forename: Linda
authors.initials: L
authors.lastname: Beauclair
authors.forename: Ivan
authors.initials: I
authors.lastname: Le Masson
authors.forename: Béatrice
authors.initials: B
authors.lastname: Courtial
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bouché
authors.forename: Hélène
authors.initials: H
authors.lastname: Lucas
mesh_terms: D000222:Adaptation, Physiological; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D029681:Arabidopsis Proteins / Q000378:metabolism; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D018628:Gene Dosage; D020868:Gene Silencing; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000378:metabolism; D018626:Retroelements; D020079:Terminal Repeat Sequences; D014026:Nicotiana / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C118957:DDM1 protein, Arabidopsis; D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; D018626:Retroelements; D014157:Transcription Factors; C499608:MET1 protein, Arabidopsis; D004248:DNA (Cytosine-5-)-Methyltransferases; C499181:RNA polymerase IV, Arabidopsis; D012321:DNA-Directed RNA Polymerases