Stem cells are undifferentiated cells that can give rise to different cell types in multicellular organisms. Plant and animal stem cells are usually not specified by the same subset of genes, even though the niche organizations are very similar. The Retinoblastoma (Rb) protein and its plant homologue RETINOBLASTOMA-RELATED (RBR) in stem cell identity however constitutes a possible common pathway in both kingdoms (1). We want to further explore possible similarities in stem cell control, so we focused on RBR interactors in order to find conserved mechanisms. RBR shares two main protein-protein interaction domains with its animal homologs; one interacts with the transcription factor E2F and the other with LxCxE containing motif proteins (such as viral proteins and histone deacetylases). Interestingly, we have found that two proteins implicated in siRNA mediated silencing contain LxCxE domains, and both mutants show a root phenotype. Our aim is to characterize the role of siRNA-mediated silencing in the root meristem stem cells, and to identify the role of RBR in this pathway. It has been found that small inhibitory RNAs control the shoot apical meristem and flowering transition as well as root cap cell formation and lateral root formation (2,3). We will try to identify the role that siRNAs have in stem cell identity.