Contributes to the regulation of secretory and vacuolar transport pathways in the post-Golgi network, and to the maintenance of the Golgi apparatus and trans-Golgi network (TGN) morphologies (PubMed:22307646). Vesicle trafficking protein that functions in the secretory pathway and mediates liposome fusion (PubMed:24021022). Required for extracellular resistance responses to a fungal pathogen (PubMed:22307646). Also involved in the protection of chloroplasts from salicylic acid-dependent biotic stress (PubMed:22307646). Also involved in the protection of chloroplasts from salicylic acid-dependent biotic stress (PubMed:22307646). Part of the t-SNARE complex. Expressed at low levels in roots, stems, flowers and leaves. The double mutant syp42 syp43 exhibits severe pleiotropic defects, including short roots, a large number of lateral roots, semi dwarfism and early senescence (PubMed:22307646). Plants lacking the three genes SYP41 SYP42 and SYP43 are seedling lethals (PubMed:22307646). Belongs to the syntaxin family.