Guanine-nucleotide exchange factor (GEF) that acts as an activator of Rop (Rho of plants) GTPases by promoting the exchange of GDP for GTP. Acts downstream of PRK2 in the control of polarized pollen tube growth by activating ARAC11/ROP1. In association with ROPGEF4, acts as specific regulator of ARAC10/ROP11 function in ABA-mediated stomatal closure. May play a role in the Rac/Rop-signaling pathway that controls ROS-mediated root hair development. Phosphorylation at Ser-460 and Ser-480 by PRK2 releases ROPGEF1 auto-inhibition, thereby activating ROPGEF1, which in turn activates ARAC11/ROP1. Interacts with ARAC10/ROP11 and FER. Forms a complex with ARAC11/ROP1 and PRK2 (PubMed:23024212). Interacts in vitro (via PRONE domain) with PRK1, PRK2, PRK3 and PRK4 (PubMed:23024212). The C-terminal region is also important for the interaction with PRK2 (PubMed:23024212). Localizes to the apical region of the pollen tube plasma membrane to activate ARAC11/ROP1 and interacts with ARAC10/ROP11 on plasma membrane in guard cells. Expressed in roots, cotyledons, leaves, stems, sepals, petals, anthers, pollen grains, stigmas and siliques. The PRONE (plant-specific Rop nucleotide exchanger) domain is responsible for the GEF activity. The intrinsic dissociation of ROP4-GDP is stimulated 15-fold by the PRONE domain (PubMed:15980860), whereas that of ROP1-GDP is increased 350-fold (PubMed:16415208). Phosphorylated at Ser-460 and Ser-480 by PRK2. No visible phenotype under normal growth conditions. Plants overexpressing ROPGEF1 or ROPGEF4 are relatively insensitive to ABA-induced stomatal closure and become severely wilted during drought stress. A similar phenotype is observed in plants expressing a constitutively active ARAC10/ROP11 (PubMed:22500990).