Molecular mechanism underlying phosphate distribution by SULTR family transporter SPDT in Oryza sativa

Abstract

Phosphorus (P) limitation severely affects crop yields. To address the molecular basis of inorganic phosphate (Pi) specific transport within the sulfate transporter (SULTR) family, we determined the cryo–electron microscopy structures of Oryza sativa SULTR-like phosphorus distribution transporter (OsSPDT), a key Pi transporter for grain allocation, in apo- and Pi-binding states. OsSPDT forms a domain-swapped homodimer with each protomer containing an N-terminal domain (NTD), a transmembrane domain (TMD) divided into core and gate subdomains, and a C-terminal sulfate transporter and antisigma factor (STAS) domain. The structure adopts a cytoplasm-facing conformation with Pi coordinated at the core-gate interface. Key residues, including SPDT-unique Ser¹⁷⁰, mediate Pi specificity within the binding pocket, distinguishing it evolutionarily from sulfate transporters within the SULTR family. Domain-swapping and mutational studies demonstrate functional interdependence of the NTD, TMD, and STAS domains. This work elucidates Pi selectivity in plant SULTR transporters and provides a molecular basis for developing low-phytate rice via OsSPDT gene editing.