A chromatin link that couples cell division to root epidermis patterning in Arabidopsis

Cell proliferation and cell fate decisions are strictly coupled processes during plant embryogenesis and organogenesis(1-5). In the Arabidopsis thaliana root epidermis, expression of the homeobox GLABRA2 (GL2) gene determines hair/non-hair cell fate(6,7). This requires signalling of positional information from the underlying cortical layer(8,9), complex transcriptional regulation(10,11) and a change in chromatin accessibility(12). However, the molecular connections among these factors and with cell division are not known. Here we have identified a GL2-expression modulator, GEM, as an interactor of CDT1, a DNA replication protein. GEM also interacts with TTG1 ( TRANSPARENT TESTA GLABRA1), a WD40-repeat protein involved in GL2-dependent cell fate decision, and modulates both cell division and GL2 expression. Here we show that GEM participates in the maintenance of the repressor histone H3K9 methylation status of root patterning genes, providing a link between cell division, fate and differentiation during Arabidopsis root development.