Functions as downstream effector of Rho-related GTP binding proteins of the 'Rho of Plants' (ROPs) family. Participates in the propagation of ROP GTPase signals in specific cellular responses. Required for cortical microtubule organization. Promotes microtubule bundling and formation of well-ordered microtubule arrays in the neck region of pavement cells. This restricts cell lateral expansion to generate the narrow neck morphology of pavement cells. Its function is inhibited when it interacts with activated ARAC4/ROP2. Represses ARAC4/ROP2 activation and antagonizes the RIC4-actin pathway that promotes the assembly of cortical actin microfilaments. Acts as downstream effector of ARAC3/ROP6 which functions in a signaling pathway that negatively regulates clathrin-mediated endocytosis and internalization of PIN1 and PIN2. Required for the asymmetric auxin distribution during root gravitropism and vascular patterning. Positively regulates auxin responses, but negatively regulates ABA responses during lateral root development and primary root elongation. Interacts with ARAC11/ROP1. Associates with and promotes the organization of cortical microtubules in leaf epidermal pavement cells. Localizes to punctate loci in the cytoplasm of root cells. Expressed in columella cells from the root tip and epidermal cells at the base of lateral roots, leaves, stems, flowers, anthers, pollen and siliques. By auxin and abscisic acid (ABA) in roots. Reduced primary root elongation. Over-expression of RIC1 in tobacco germinating pollen reduces pollen tube elongation.