Guanine-nucleotide exchange factor (GEF) that acts as an activator of Rop (Rho of plants) GTPases by promoting the exchange of GDP for GTP. May be recruited by PRK2 at the plasma membrane to maintain polar Rop activity in the pollen tube and control polarized pollen tube growth. Phosphorylation at Ser-510 by PRK2 may release ROPGEF12 auto-inhibition, thereby activating ROPGEF12 and downstream Rop signaling. Interacts (via C-terminus) with PRK2. Interacts with PRK6 (PubMed:26961657). ROPGEF12 colocalizes with PRK2 at the apical plasma membrane of pollen tube. Expressed in pollen grains. The PRONE (plant-specific Rop nucleotide exchanger) domain is responsible for the GEF activity.