Maintaining genome integrity is necessary for the survival of organisms. Genomes face continuous threats not only from external mutagenic factors but also intrinsically from mobile genetic elements known as transposable elements (TEs). Although potentially deleterious, TEs are a major component of plant and animal genomes and have contributed to genome evolution through their mobility.

The RdDM (RNA-directed DNA methylation) pathway inhibits TE expression in plants. This inactivation also extends to adjacent genes, leading to transcriptional repression that is propagated over several generations via so-called epigenetic mechanisms. RNA polymerase IV (Pol IV) initiates the RdDM pathway by transcribing TEs in the nucleus. The resulting non-coding RNAs are recognised by the RNA-dependent RNA polymerase RDR2, which generates double-stranded RNAs (dsRNAs). These are then cut into small interfering RNAs (siRNAs) of 24 nucleotides that guide DNA methylation towards TEs throughout the genome.

This talk will focus on the functional assembly of the RNA Polymerase IV (Pol IV) complex in plants, emphasizing the roles of associated proteins in small RNA biogenesis and transposon silencing. Recent insights into the molecular interactions that guide Pol IV recruitment and activity will also be presented.

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