Proteasomal degradation of poly-ubiquitylated proteins plays a crucial role in controlling the cell cycle during development, thus ensuring that adult tissues contain the right number of cells. Recently, an alternative pathway for cell-cycle control, in which monoubiquitylated proteins are sorted into lysosomes in animal cells or vacuoles in yeast cells for degradation, was identified. Now, on , Spitzer and colleagues report that this pathway is involved in the development of trichomes - hair-like bristles - in Arabidopsis. Wild-type trichomes are single polyploid cells with three to four branches. The researchers report that the oddly shaped trichomes seen in Arabidopsis elc mutants have multiple nuclei. This indicates that ELC - the Arabidopsis homolog of yeast Vps23, a component of the endosomal sorting complex required for transport (ESCRT) - is involved in cytokinesis. Other genetic and biochemical data suggest that ELC regulates cytokinesis through a mono-ubiquitin-dependent proteinsorting pathway, possibly by regulating the microtubule cytoskeleton, thus providing the first evidence that the ESCRT pathway operates in plants.
