Phosphate transporter OsPHT2;1 regulates Cd accumulation in rice via the regulation of phosphorus homeostasis

While rice (Oryza sativa) phosphate (Pi) transporter 2;1 (OsPHT2;1) has been characterized as a low-affinity Pi transporter critical for phosphorus (P) accumulation and translocation in rice leaves, its function in modulating cadmium (Cd) accumulation remains unclear. Here, we show that OsPHT2;1 regulates rice's Cd resistance and influences Cd accumulation in grains. Cd stress significantly downregulated its transcript levels in roots and shoots, decreasing by 17.6-18.8% after 0.5 h of 1 μM Cd exposure. Under 1 μM Cd stress, the inhibition of root elongation in the ospht2;1 mutant was somewhat alleviated (13.9-19.8% vs. 37.9% in wild-type ZH11), and exhibited markedly lower Cd concentrations in roots (20-26%), shoots (15-25%), xylem sap (24-28%). In contrast, OsPHT2;1 overexpression lines exhibited enhanced Cd sensitivity and increased Cd concentrations in xylem sap (23-28%). Field trials further demonstrated that ospht2;1 mutants maintain normal yield while reducing grain Cd levels by 26-35% in Cd-contaminated soil. Mechanistically, we found that the loss of OsPHT2;1 disrupts chloroplast P homeostasis, which triggers an intensified systemic P-starvation signal mediated by the regulators OsPHO2 and OsPHR2. This shoot-to-root signaling cascade coordinates the transcriptional repression of root Cd transporters (OsNRAMP5 and OsHMA3), thereby restricting Cd uptake across physiological P gradients. Haplotype analysis further identified Hap1 as an elite variant of OsPHT2;1 associated with low Cd accumulation. Collectively, these results identify OsPHT2;1 as a key target for breeding Cd-tolerant and low-Cd-accumulating rice varieties.