The Sulfate Transporter (SULTR) gene family encodes integral membrane proteins that function as ion transporters. Early work characterized SULTR transporters for their involvement in root sulfate uptake from the soil and sulfate re-distribution within plant tissues. The proteins encoded by the SULTR gene family form 4 sub-groups based on amino acid sequence identity that correlate with localization and function. Despite these seemingly clear distinctions, SULTR3 protein isoforms have evaded a clear functional description. The genome of Oryza sativa encodes six SULTR3 isoforms, and several contribute to unique, agronomically relevant roles, including phosphate transport. OsSULTR3 isoforms lack in-depth functional analysis and, therefore, their full contribution to plant mineral nutrition is unknown. In this dissertation the protein structure-function connection of this clade was investigated, with a specific focus on OsSULTR3;6 and OsSULTR3;4. The use of heterologous expression systems and stable, OsSULTR3;6 CRISPR-edited rice lines demonstrate that OsSULTR3;6 is a phosphate transporter that regulates phosphorus and sulfur nutrition of the rice grain and vegetative shoot. The use of 3-dimensional SULTR structural models identified the Sulfate Transport Motif 1 (SD1) as a region underlying substrate specificity within the SULTR family of transporters.