Molecular mechanism underlying phosphate distribution by SULTR family transporter SPDT in <i>Oryza sativa</i>.

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 <i>Oryza sativa</i> 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.