A node-localized transporter TaSPDT is responsible for the distribution of phosphorus to grains in wheat

Wheat (Triticum aestivum L.) is one of the world's main food crops and the largest phosphorus (P) fertilizer consumer globally. However, the molecular mechanism of P distribution in wheat remains largely unknown. This study investigated the TaSULTR gene family and functionally characterized TaSPDT (TaSULTR3;4). Thirty-three TaSULTR genes were identified and divided into four groups. These genes contained three tandem duplications and 28 segmental duplications. TaSPDT was localized on the plasma membrane and demonstrated P transport activity. TaSPDT was mainly expressed at nodes, and its expression was elevated under low P conditions. TaSPDT was distributed on the xylem and phloem of enlarged and diffuse vascular bundles at nodes, as well as on the parenchyma cell bridge between vascular bundles. TaSPDT knockout reduced P distribution to young leaves but increased it in older leaves during the vegetative stage under low P availability. P uptake by roots, transfer to above-ground tissues, and redistribution within aerial organs were unaffected. At the reproductive stage, TaSPDT knockout notably diminished P allocation to grains, resulting in a significant decrease in grain yield, particularly under P-deficient conditions. These results suggest that TaSPDT mediates the transmembrane transport of P from the xylem to the phloem at the nodes, resulting in the preferential distribution of P to grains. This study enables a better understanding of the TaSULTR gene family and P distribution in wheat.