In plants, unorthodox multisubunit RNA polymerases (RNAPs) play key roles in small interfering RNA (siRNA) genesis and function. In a recent issue of Molecular Cell, Ream et al. (2009) established a 12-subunit composition for Arabidopsis RNAPIV and RNAPV. Subunit and sequence divergence between RNAPIV-V and RNAPI-III suggests significant functional deviation of these intriguing RNAPs.