Rho of plant (ROP) proteins belong to the sole family of Rho-like GTPases in plants and have been suggested to regulate the polarised growth of tip-growing cells by modulating interactions between the actin and microtubule cytoskeletons. However, most studies performed to date have relied on the overexpression of proteins, including constitutively active or dominant-negative isoforms, and therefore Magdalena Bezanilla and colleagues (p. ) took advantage of the ease of reverse genetics and the low number of highly similar ROP proteins (ROP1–4) in the model moss Physcomitrella patens to analyse the role of ROPs using a loss-of-function approach. Knockdown of all four ROP genes by RNAi resulted in dwarf plants comprising small spherical cells that had a significantly smaller area, compared with control plants. The authors also observed that, surprisingly, ROP-knockdown plants had strongly reduced cell adhesion and an altered cell wall structure, suggesting that ROPs might have previously unappreciated roles. Importantly, the authors found that actin filaments were more dynamic and that actin arrays were more disordered in ROP-knockdown cells, but that there was no ROP-specific effect on the dynamics of the microtubule cytoskeleton. In summary, this extensive study provides important new insights into the functions of ROP proteins in cell adhesion, cell wall assembly and polarised cell growth – roles they possibly exert by suppressing actin dynamics.
