DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Component of RNA polymerases IV and V which mediate short-interfering RNAs (siRNA) accumulation and subsequent RNA-directed DNA methylation-dependent (RdDM) transcriptional gene silencing (TGS) of endogenous repeated sequences, including transposable elements. Component of the RNA polymerase IV and V complexes. Interacts with NRPD1. Expressed inleaves, flower buds, flowers and siliques. Belongs to the archaeal Rpo5/eukaryotic RPB5 RNA polymerase subunit family.