P1BS, a conserved motif involved in tolerance to phosphate starvation in soybean.

Available phosphate (Pi) is a major limiting factor for plant growth, development, and productivity. Phosphate starvation response 1 (PHR1) is a binding dimer that binds to an imperfect palindromic sequence. PHR1-binding sequences (GnATATnC) exist in the promoter of Pi starvation-responsive structural genes, indicating an effect occurring downstream in the Pi starvation signaling pathway. These sequences are referred to as PHR1-binding site (P1BS) structures. In this study, the sequences of GmPHR1 and GmSPX1 from Glycine max (L.) Merr. soybean were determined and analyzed. We found that GmPHR1 is an MYB-related transcription factor. In addition, GmSPX1 contained a P1BS structure, which is an important cis-regulatory motif in the phosphate signaling pathway. We found that GmPHR1 can physically interact with GmSPX1 through the cis-element, which may be a major pathway for the GmPHR1-mediated Pi starvation stress response. Thus, the P1BS structure in the Pi starvation signaling pathway is an important cis-regulatory motif that improves the tolerance to low phosphorus conditions in soybean.