Guanine-nucleotide exchange factor (GEF) that acts as an activator of Rop (Rho of plants) GTPases by promoting the exchange of GDP for GTP. Interacts with ARC10/ROP11. Expressed in the vascular tissues of roots, leaves, sepals, petals and siliques. The PRONE (plant-specific Rop nucleotide exchanger) domain is responsible for the GEF activity.