European scientists have discovered a new type of signal molecule in plants. In two papers published online in Science (23 April 2010) the investigators have shown that small RNA molecules, known as small interfering RNAs, can migrate long distances in plants and can direct chemical modification of DNA in the recipient cells. This modification – DNA methylation – normally results in the silencing of gene expression that persists through cell divisions even if the mobile RNA is no longer present. The newly discovered signal could explain many mysterious phenomena in plant biology in which a local stimulus induces a long term and persistent effect in the recipient tissues. The discoveries are an outcome of the SIROCCO (Silencing RNAs: organisers and coordinators of complexity in eukaryotic organisms') project, which received EUR 11.8 million under the 'Life sciences, genomics and biotechnology for health' thematic area of the EU's Sixth Framework Programme (FP6). SIROCCO aims to characterise the small RNA populations in plants and animals and reveal how they target specific genes for silencing. The SIROCCO consortium is made up of 21 partners (18 academic research institutes and 3 companies) from 10 European countries.