Essential protein required during embryogenesis. Believed to act as a core component of the putative HOPS endosomal tethering complex and of the class C core vacuole/endosome tethering (CORVET) complex. CORVET is required for vacuolar transport of SYP22. HOPS is required for the central vacuole formation. Involved in root development (PubMed:29463724). Plays a role in vesicle-mediated protein trafficking to lysosomal compartments including the endocytic membrane transport pathways (By similarity). Core component of at least two putative endosomal tethering complexes, the homotypic fusion and vacuole protein sorting (HOPS) complex and the class C core vacuole/endosome tethering (CORVET) complex. Their common core is composed of the class C Vps proteins VPS11, VCL1, VPS18 and VPS33, which in HOPS further associates with VPS39 and VPS41 and in CORVET with VPS3. Co-localizes with VPS39 at subdomains of the vacuolar membrane, and with VPS3 and RABF2B at punctate compartments in the cytoplasm, with faintly dispersed distribution in the cytosol. Sometimes observed at the vertex zone, the ring-shaped edge of vacuole-vacuole contact sites. Co-localizes with RABG3F. Embryonic lethality (PubMed:29463724). Heterozygous mutants produce some yellowish seeds with developmentally retarded or abnormally shaped embryos. Conditional dexamethasone (DEX)-inducible mutants exhibit abnormal root morphology (PubMed:29463724). Belongs to the VPS18 family.