Specific subunit of the TRAPP II complex, a highly conserved vesicle tethering complex that is required for the proper transport of proteins in post-Golgi trafficking pathways to the growing cell plate in mitotic active cells (PubMed:20609115, PubMed:21689172). Required for the polarized and selective transport of PIN2, but not PIN1, to the plasma membrane. Not required for ER-to-Golgi as well as biosynthetic and endocytic vacuolar transport (PubMed:21689172). Part of the multisubunit TRAPP (transport protein particle) II complex composed of BET3, BET5, TRS20, TRS23, TRS31, TRS33, TRS65, TRS85, TRS120 and TRS130. Cytokinesis-defective and seedling-lethal phenotype. Belongs to the TMEM1 family.