Together with either SYP41 or SYP61, required for membrane fusion; the fusion of phospholipid vesicles containing SYP41 or SYP61 and VTI12 is triggered by YKT61 and YKT62 (PubMed:15919093). Functions as a v-SNARE responsible for the docking or fusion of transport vesicles within the trans-Golgi network (TGN) and mediates liposome fusion (PubMed:24021022, PubMed:15797025). Necessary to deliver proteins to the protein storage vacuole (PSV) (PubMed:17360696). May be also involved in retrograde traffic to the cis-Golgi (By similarity). Forms SNARE complexes with the t-SNAREs SYP61 and either SYP41 or SYP42, and with a much lower affinity with SYP51 in the TGN (PubMed:11739776, PubMed:15919093). Interacts also with VPS45, a Sec1 protein, but not with SYP21 or SYP22 (PubMed:10888666). Binds to EPSIN2 (PubMed:17277094). Core constituent of the SNARE complex required for membrane fusion at the trans-Golgi network (PubMed:15919093). Interacts with SCYL2B (PubMed:28751315). Accumulates in structural sterols-containing apical and subapical compartments of developing root hairs tips. Expressed in roots, stems, flowers and leaves. Altered transport of storage proteins to the protein storage vacuole (PSV). Belongs to the VTI1 family.