The RNA export factor ALY1 enables genome-wide RNA-directed DNA methylation (Plant Cell)

The epigenetic control of gene expression is crucial for genomic stability and allows the defence against invading DNA that for instance could be derived from viruses or transposable elements. In this context, the RNA-directed DNA methylation (RdDM) plays an essential role in silencing of genes via epigenetically modifying the DNA. Here, small RNA molecules direct a protein complex to a target region that finally catalyses the methylation of cysteine residues thus leading to a transcriptional repression. The RdDM-pathways involves several components including the endoribonuclease DICER-like 3, the ARGONAUTE proteins 4 and 6 as well as the RNA Polymerase V and methylases. Choudury et al. describe an Arabidopsis thaliana mutant that is deficient in the RdDM-mechanism and thus vulnerable to the expression of foreign DNA. They identify the corresponding gene, ALY1, which is involved in the export of RNA from the nucleus. In aly1, the mRNA of several factors such as ARGONAUTE6 and Pol V cannot be efficiently exported leading to a decreased abundance of these proteins thus to a damaged RdDM-pathway. (Summary by Florian Ahloumessou) Plant Cell 10.1105/tpc.18.00624