GTP-binding protein that functions in the development of root systems, which are mediated by auxin. Acts as a cell cycle regulator during root development. Proteasome-mediated degradation of the protein is necessary for the transition of metaphase to anaphase in mitosis. Interacts with RPT4. During mitosis, associates with mitotic spindles. Specifically expressed in the apical meristem, the elongation zone of root tip, steles of the branch zone, and the young lateral root. Also expressed in spikes. Expressed in roots and spikes (at protein level). By auxin. D-box [RxxLxx(L/I)xN] is the common motif recognized by the E3 ubiquitin ligase APC specifically acting during transition from metaphase to anaphase. Ubiquitinated. RPT4 mediates its proteasome-dependent degradation. RNAi mutants display reduced seedling height phenotype, because of abnormal cell division. Overexpression results in reduced growth of the primary root, an increased number of adventitious roots, a helix primary root and a delayed gravitropic response of roots in seedlings. Belongs to the FPF1 family.