FYVE1/FREE1 is involved in glutamine-responsive TORC1 activation in plants

Target of rapamycin complex 1 (TORC1) integrates nutrient availability, growth factors, and stress signals to regulate cellular metabolism according to its environment. Similar to mammals, amino acids have been shown to activate TORC1 in plants. However, as the Rag complex that controls amino acid-responsive TORC1 activation mechanisms in many eukaryotes is not conserved in plants, the amino acid-sensing mechanisms upstream of TORC1 in plants remain unknown. In this study, we report that Arabidopsis FYVE1/FREE1 is involved in glutamine-induced TORC1 activation, independent of its previously reported function in ESCRT-dependent processes. FYVE1/FREE1 has a domain structure similar to that of the yeast glutamine sensor Pib2 that directly activates TORC1. Similar to Pib2, FYVE1/FREE1 interacts with TORC1 in response to glutamine. Furthermore, overexpression of a <i>FYVE1/FREE1</i> variant lacking the presumptive TORC1 activation motif hindered the glutamine-responsive activation of TORC1. Overall, these observations suggest that FYVE1/FREE1 acts as an intracellular amino acid sensor that triggers TORC1 activation in plants.