Elevated CO₂ reinforces PT11-dependent symbiotic phosphate uptake to reprogram root nutrient acquisition in rice

Plants acquire inorganic phosphate (Pi) either directly through their roots or through symbiosis with arbuscular mycorrhizal (AM) fungi, and the direct uptake pathway is downregulated when the symbiosis establishes. As atmospheric CO₂ concentrations rise, it is critical to understand how increased carbon availability alters plant nutrient acquisition strategies, with implications for crop productivity and carbon sequestration alike. Here, we investigated the interaction between elevated CO₂, soil Pi availability, and AM symbiosis in the major cereal crop rice. Elevated CO₂ enhanced mycorrhizal colonization, phosphorus uptake, and crop biomass. We employed the rice pt11 mutant, which is defective in symbiotic Pi transport, in combination with split-root and radiotracer approaches to demonstrate that suppression of the direct Pi uptake pathways occurs locally in colonized roots, requiring functional symbiotic Pi transport. Likewise, changes in root architecture-notably reduced fine lateral root development-occur with local regulation dependent on processes downstream of PT11. Transcriptomic analyses identify symbiotic Pi transport as a regulatory checkpoint of the suppression of direct nutrient uptake and the progression of the mycorrhizal transcriptional program. Together, these findings reveal that in rice, rising CO₂ enhances AM symbiosis not necessarily by activating canonical symbiosis signaling pathways, but rather by reinforcing symbiotic Pi uptake through enhanced carbon availability, thereby reshaping root nutrient acquisition. This work provides a mechanistic framework for integrating plant-microbe interactions into strategies aimed at sustaining crop productivity and managing carbon in a high-CO₂ world.