DTF1 is a core component of RNA-directed DNA methylation and may assist in the recruitment of Pol IV
DNA methylation is an important epigenetic mark in many eukaryotic organisms.  De novo DNA methylation in plants can be achieved by the RNA-directed DNA methylation (RdDM) pathway, where the plant-specific DNA-dependent RNA polymerase Pol IV transcribes target sequences to initiate 24-nt siRNA production and action.  The Arabidopsis DTF1/SHH1 has been shown to associate with Pol IV and is required for 24-nt siRNA accumulation and transcriptional silencing at several RdDM target loci.  However, the extent and mechanism of DTF1 function in RdDM is unclear.  We show here that DTF1 is necessary for the accumulation of the majority of Pol IV-dependent 24-nt siRNAs.  It is also required for a large proportion of Pol IV-dependent de novo DNA methylation.  Interestingly, there is a group of RdDM target loci where 24-nt siRNA accumulation but not DNA methylation is dependent on DTF1.  Taken together, our results show that DTF1 is a core component of the RdDM pathway. Our results also suggest the involvement of DTF1 in an important negative feedback mechanism for DNA methylation at some RdDM target loci. Overall design: Examination of whole-genome DNA methylation and small RNA in 12-day-old Col-0, dtf1-2, nrpd1-3 and nrpe1-11 seedlings