Acts as component of the peripheral membrane COG complex that is involved in intra-Golgi protein trafficking (PubMed:27448097). Involved in pollen tube growth by modulating Golgi morphology and vesicle trafficking homeostasis leading to the deposition of cell wall components and proteins at the pollen tube tip (PubMed:27448097). Required for sporophytic development (PubMed:27448097). Homodimer (PubMed:27448097). Component of the conserved oligomeric Golgi complex which is composed of eight different subunits and is required for normal Golgi morphology and localization (Probable). Interacts with COG1, COG2, COG4, COG5 and COG8 (PubMed:27448097). Male-specific transmission defect due to incorrect deposition of cell wall components and proteins during pollen tube elongation, thus leading to disrupted pollen tube growth (PubMed:27448097). Embryo- and seedling-lethal associated with white seeds in siliques, delayed embryo development from the early stages, arrested at heart stages and resulting in abnormal curled cotyledons (PubMed:27448097). Altered Golgi bodies morphology (PubMed:27448097). Impaired Gamma-COP and TMN1/EMP12 tight association with the Golgi (PubMed:27448097). Belongs to the COG3 family.