Specific cell types are generated partly by differential growth (when certain cell regions rapidly expand). In animal cells, this requires the actin cytoskeleton. Mathur et al. now report, on , that an actin-based mechanism might also regulate differential growth in plants, with their discovery that a mutation in the plant orthologue of ARPC5 causes random cell expansion and aberrant cell shape in Arabidopsis CROOKEDmutants. ARPC5 is a subunit of the ARP2/3 complex – an actin polymerization modulator in many organisms that generates fine F-actin arrays. By studying polarized cells in mutant and normal plants, the authors found that localized cell expansion occurs only where fine F-actin is maintained,implicating F-actin density as a likely determinant of cell shape. Importantly, the rescue of CROOKED cells with human ARPC5 provides the first evidence that this complex is functionally conserved in higher plants.
