Involved in cell polarity control during the actin-dependent tip growth of root hairs, thus regulating root hair length and root hair initiation. Inactive GDP-bound Rho GTPases reside in the cytosol, are found in a complex with Rho GDP-dissociation inhibitors (Rho GDIs), and are released from the GDI protein in order to translocate to membranes upon activation. Interacts with GDI1 and ROPGEF8 homodimer (PubMed:10798620, PubMed:17218277, PubMed:19335195). Binds to SPK1 (PubMed:18308939). Associated with the membrane when activated. The localization to the plasma membrane requires YIP4A and YIP4B (By similarity). Ubiquitous. Preferentially expressed at the tip of root hairs. In root trichoblasts, accumulates into patches at the basal end of the cell before a hair bulge is visible and remain concentrated at the tip of the bulge and in the growing hair. Fewer and shorter root hairs. Belongs to the small GTPase superfamily. Rho family.