Last week PNAS has published something which would apparently contribute to future textbooks: Mobile small RNAs regulate genome-wide DNA methylation. You think that cutting / physical joining of different plants (grafting) will leave their genomes unaffected, right? Think twice! Authors show that mobile RNA travels between the two species and regulate methylation level of thousands of loci of the “foreign” species… Does it result in actual changes in gene expression? Authors say: Yes! (see pages 4-6 of the paper).