Pol IV complex precludes the spread of aberrant silencing. (A) Transcription by Pol IV produces sRNAs that guide silencing via DNA methylation at euchromatic TEs. Its activity also suppresses ungauged transcription by other polymerases and optimal distribution of H3K27me3 over coding genes. (B) Upon loss of Pol IV, distributions of H3K27me3, H3K9me2 marks are perturbed, and several transposons and genes are marked by H3K27me3. In addition, upon loss of Pol IV, ungauged aberrant transcription leads to production of Pol IV–suppressed sRNAs, partly dependent on RDR6 (post-transcriptionally) and DDM1 (transcriptionally). In rice, these transcripts are loaded into AGO1 and can target genes.
