Component of the biogenesis of lysosome-related organelles complex-1 (BLOC-1), a complex that mediates the vacuolar degradative transport via the intracellular vesicle trafficking from the endosome to the vacuole. Probably regulates the PIN1 and PIN2 homeostasis through its interaction with SNX1. Component of the biogenesis of lysosome-related organelles complex-1 (BLOC-1) (By similarity). Interacts with BLOS2 and SNX1. Expressed in the whole plant (at protein level). Longer primary roots and more lateral roots in the RNAi mutant. Belongs to the BLOC1S1 family.