Mechanisms of Vacuolar Phosphate Efflux Supporting Soybean Root Hair Growth in Response to Phosphate Deficiency

The study investigates how soybean plants maintain root hair growth under phosphate (Pi) deficiency by examining the role of vacuole-stored Pi. It identifies two vacuolar Pi efflux transporters, GmVPE1 and GmVPE2, which help remobilize Pi to sustain cytosolic Pi levels in root hair cells. Double mutants of these transporters showed reduced root hair growth under low Pi conditions. The expression of GmVPE1 and GmVPE2 is upregulated by low Pi and is promoted by the transcription factor GmRSL2, which binds to their promoter regions. Mutants lacking GmRSL2 and its homolog GmRSL3 had impaired root hair growth under low Pi stress, which was rescued by overexpressing GmVPE1 or GmVPE2. This study identifies a module of vacuolar Pi exporters and transcription factors that support root hair growth in response to Pi deficiency in soybean.