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Exogenous Transposable Elements Circumvent Homology Permitting the Dissection of Expression Dependent Silencing

ABSTRACT: The propagation of epigenetic marks has received a great deal of attention, yet the initiation of epigenetic silencing on a new transgene, virus, or transposable element remains incompletely characterized. The overlapping function of multiple silencing mechanisms has obscured this area of investigation. Here, we have revealed two broad mechanisms that are both able to initiate silencing independently: homology-based silencing and expression-dependent silencing. By transforming exogenous transposable elements into Arabidopsis, we circumvented homology-based silencing allowing us to isolate and investigate the molecular mechanism of expression-dependent silencing. We found that several small RNA-generating mechanisms all trigger de novo expression-dependent RNA-directed DNA methylation (RdDM) through RNA Polymerase V. In addition, the silencing of transposable elements fragments stalls at the RdDM phase, while full-length elements quickly progress through RdDM to maintenance methylation and heterochromatin formation. We found that there is a narrow window of time for the transition to a fully silenced state. Transformation into a mutant genotype followed by introgression into wild-type does not result in the same level of silencing as direct transformation into wild-type. This demonstrates that the genotype of transposable element insertion or transgene transformation is key for establishing the transgenerational extent of epigenetic silencing.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE86787 | GEO | 2017/08/25

SECONDARY ACCESSION(S): PRJNA342506

REPOSITORIES: GEO

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