Invasion of the Arabidopsis genome by the tobacco retrotransposon Tnt1 is controlled by reversible transcriptional gene silencing.
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.
Pérez-Hormaeche
Javier
J
Station de Génétique et d'Amélioration des Plantes, UR254, INRA, F-78026 Versailles, France.
Potet
Frédérique
F
Beauclair
Linda
L
Le Masson
Ivan
I
Courtial
Béatrice
B
Bouché
Nicolas
N
Lucas
Hélène
H
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
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