Figure 4

Proposed model for the action of the DRB2 containing complex, and the resulting situation in the drb2 mutant. (a) In wild type plants, both the RdDM and the DRB2 containing complex act independently to negatively regulate TE transcription. RdDM uses siRNA-mediated DNA methylation to induce silencing while targeting of the DRB2 complex to TE nascent transcript would directly result in an increase in chromatin repressive marks at these loci. (b) In a drb2 plant, targeting efficiency of the complex to nascent transcripts decreases leading to and increase in TE transcription. As no components of the RdDM are impaired, these transcripts are routed to DCL3/RDR2 for p4-siRNA biogenesis leading to the symptomatic over-accumulation of p4-siRNAs observed in the drb2 mutant without changing the steady state level of TE RNAs.