AbstractBackgroundTwo-pore channels (TPCs) release Ca²⁺from acidic intracellular stores and are implicated in a number of diseases, but their role in development is unclear. The social amoebaDictyostelium discoideumproliferates as single cells that aggregate to form a multicellular organism on starvation. Starvation is sensed by the mTORC1 complex which, like TPC proteins, is found on acidic vesicles. Here, we address the role of TPCs in development and under starvation.ResultsWe report that disruption of the gene encoding the singleDictyosteliumTPC protein, TPC2, leads to a delay in early development and prolonged growth in culture with delayed expression of early developmental genes, although a rapid starvation-induced increase in autophagy is still apparent. Ca²⁺signals induced by extracellular cAMP are delayed in developingtpc2⁻cells, and aggregation shows increased sensitivity to weak bases, consistent with reduced acidity of the vesicles. In mammalian cells, the mTORC1 protein kinase has been proposed to suppress TPC channel opening. Here, we show a reciprocal effect astpc2⁻cells show an increased level of phosphorylation of an mTORC1 substrate, 4E-BP1. mTORC1 inhibition reverses the prolonged growth and increases the efficiency of aggregation oftpc2⁻cells.ConclusionTPC2 is required for efficient growth development transition inDictyosteliumand acts through modulation of mTORC1 activity revealing a novel mode of regulation.