title: Transitive RNA silencing signals induce cytosine methylation of a transgenic but not an endogenous target.
abstract: Post-transcriptional gene silencing of a primary target gene in plants can coincide with the production of secondary small interfering RNAs (siRNAs) of coding sequences adjacent to the target region and with de novo RNA-directed DNA methylation (RdDM) thereof. Here, we analyzed the susceptibility of transgenic and endogenous targets to RdDM induced by primary and secondary silencing signals. In three different configurations, primary silencing signals were able to direct in trans methylation of chimeric transgenes and the CATALASE2 (CAT2) endogene; however, extensive spreading of methylation occurred only in the transgene, resulting in the methylation of the flanking CAT2 sequence, whereas methylation of the CAT2 endogene was restricted to the target region and the enclosed introns. The secondary silencing signals arising from this transgenic primary target simultaneously silenced a secondary transgene target and the CAT2 endogene, but were only capable of directing RdDM to the transgene. Our data indicate that RdDM is correlated with the in situ generation of secondary siRNAs, occurring in P35S-driven transgenes but not in most endogenes. We conclude that although both endogenes and transgenes are equally sensitive to transitive silencing, differences exist in their susceptibility to undergo secondary RdDM.
authors.affiliation: Department of Plant Systems Biology, VIB, 9052 Gent, Belgium.
authors.forename: Leen
authors.initials: L
authors.lastname: Vermeersch
authors.forename: Nancy
authors.initials: N
authors.lastname: De Winne
authors.forename: Jonah
authors.initials: J
authors.lastname: Nolf
authors.forename: Annick
authors.initials: A
authors.lastname: Bleys
authors.forename: Aleš
authors.initials: A
authors.lastname: Kovařík
authors.forename: Ann
authors.initials: A
authors.lastname: Depicker
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics; D015139:Blotting, Southern; D002374:Catalase / Q000235:genetics; D003596:Cytosine / Q000378:metabolism; D019175:DNA Methylation; D005966:Glucuronidase / Q000235:genetics; D030821:Plants, Genetically Modified; D034622:RNA Interference; D015398:Signal Transduction / Q000235:genetics*; D019076:Transgenes / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D003596:Cytosine; D002374:Catalase; D005966:Glucuronidase