Abstract
Nitrogen (N) is the most important essential nutrient required by plants. Most land plants have evolved two N uptake pathways, a direct root pathway and a symbiotic pathway, via association with arbuscular mycorrhizal (AM) fungi. However, the interaction between the two pathways is ambiguous. Here, we report that OsNAR2.1-OsNRT2s, the nitrate (NO(3)(-)) transporter complexes with crucial roles in direct NO(3)(-) uptake, are also recruited for symbiotic NO(3)(-) uptake. OsNAR2.1 and OsNRT2.1/2.2 are coregulated by NIN-like protein 3 (OsNLP3), a key regulator in NO(3)(-) signaling, and OsPHR2, a major regulator of phosphate starvation responses. More importantly, AM symbiosis induces expression of OsNAR2.1-OsNRT2s, OsNLP3, and OsSPX4, encoding an intracellular Pi sensor, in arbuscular-containing cells, but weakens their expression in the epidermis. OsNAR2.1 and OsNLP3 can activate both mycorrhizal NO(3)(-) uptake and mycorrhization efficiency. Overall, we demonstrate that OsNLP3 and OsPHR2 orchestrate the direct and mycorrhizal NO(3)(-) uptake pathways by regulating the NAR2.1-NRT2s complexes in rice.