Plasma membrane H-ATPases promote TORC1 activation in plant suspension cells.

The TORC1 (Target of Rapamycin Complex 1) kinase complex plays a pivotal role in controlling cell growth in probably all eukaryotic species. The signals and mechanisms regulating TORC1 have been intensely studied in mammals but those of fungi and plants are much less known. We have previously reported that the yeast plasma membrane H-ATPase Pma1 promotes TORC1 activation when stimulated by cytosolic acidification or nutrient-uptake-coupled H influx. Furthermore, a homologous plant H-ATPase can substitute for yeast Pma1 to promote this H-elicited TORC1 activation. We here report that TORC1 activity in BY-2 cells is also strongly influenced by the activity of plasma membrane H-ATPases. In particular, stimulation of H-ATPases by fusicoccin activates TORC1, and this response is also observed in cells transferred to a nutrient-free and auxin-free medium. Our results suggest that plant H-ATPases, known to be regulated by practically all factors controlling cell growth, contribute to TOR signaling.