Nonredundant Regulation of Rice Arbuscular Mycorrhizal Symbiosis by Two Members of the Phosphate Transporter 1 Gene Family

Pi acquisition of crops via arbuscular mycorrhizal (AM) symbiosis is becoming increasingly important due to limited highgrade
rock Pi reserves and a demand for environmentally sustainable agriculture. Here, we show that 70% of the overall Pi
acquired by rice (Oryza sativa) is delivered via the symbiotic route. To better understand this pathway, we combined genetic,
molecular, and physiological approaches to determine the specific functions of two symbiosis-specific members of the
PHOSPHATE TRANSPORTER1 (PHT1) gene family from rice, ORYsa;PHT1;11 (PT11) and ORYsa;PHT1;13 (PT13). The PT11
lineage of proteins from mono- and dicotyledons is most closely related to homologs from the ancient moss, indicating an
early evolutionary origin. By contrast, PT13 arose in the Poaceae, suggesting that grasses acquired a particular strategy for
the acquisition of symbiotic Pi. Surprisingly, mutations in either PT11 or PT13 affected the development of the symbiosis,
demonstrating that both genes are important for AM symbiosis. For symbiotic Pi uptake, however, only PT11 is necessary and
sufficient. Consequently, our results demonstrate that mycorrhizal rice depends on the AM symbiosis to satisfy its Pi
demands, which is mediated by a single functional Pi transporter, PT11.