Pol IV and RDR2: A two-RNA-polymerase machine that produces double-stranded RNA

DNA methylation affects gene expression and maintains genome integrity. The DNA-dependent RNA polymerase IV (Pol IV), together with the RNA-dependent RNA polymerase RDR2, produces double-stranded small interfering RNA precursors essential for establishing and maintaining DNA methylation in plants. We determined the cryo-electron microscopy structures of the Pol IV-RDR2 holoenzyme and the backtracked transcription elongation complex. These structures reveal that Pol IV and RDR2 form a complex with their active sites connected by an interpolymerase channel, through which the Pol IV-generated transcript is handed over to the RDR2 active site after being backtracked, where it is used as the template for double-stranded RNA (dsRNA) synthesis. Our results describe a 'backtracking-triggered RNA channeling' mechanism underlying dsRNA synthesis and also shed light on the evolutionary trajectory of eukaryotic RNA polymerases.

Automated summary

DNA methylation plays a crucial role in gene expression and genome integrity in plants. The complex formed by Pol IV and RDR2 is involved in dsRNA synthesis, revealing a mechanism of "backtracking-triggered RNA channeling".