Characteristics and processing of Pol IV-dependent transcripts in Arabidopsis.

RNAi is a highly conserved machinery in eukaryotes for transcriptional or post-transcriptional silencing. In plants, RNA-directed DNA Methylation (RdDM) pathway deploys small interfering RNAs (siRNAs) to target DNA methylation. This process is initiated by the plant-specific RNA polymerase IV (Pol IV) to produce RNA precursors that are later processed into siRNAs. Until recently, characterization of Pol IV transcript had been difficult due to its presumed rapid turnover. This review summarizes five recent reports on Pol IV-dependent RNAs that explore the biogenesis and features of Pol IV transcripts, as well as alternative dicer-independent processing of Pol IV products.

DNA methylome of the 20-gigabase Norway spruce genome.

DNA methylation plays important roles in many biological processes, such as silencing of transposable elements, imprinting, and regulating gene expression. Many studies of DNA methylation have shown its essential roles in angiosperms (flowering plants). However, few studies have examined the roles and patterns of DNA methylation in gymnosperms. Here, we present genome-wide high coverage single-base resolution methylation maps of Norway spruce (Picea abies) from both needles and somatic embryogenesis culture cells via whole genome bisulfite sequencing. On average, DNA methylation levels of CG and CHG of Norway spruce were higher than most other plants studied. CHH methylation was found at a relatively low level; however, at least one copy of most of the RNA-directed DNA methylation pathway genes was found in Norway spruce, and CHH methylation was correlated with levels of siRNAs. In comparison with needles, somatic embryogenesis culture cells that are used for clonally propagating spruce trees showed lower levels of CG and CHG methylation but higher level of CHH methylation, suggesting that like in other species, these culture cells show abnormal methylation patterns.