OsNLP3 and OsPHR2 orchestrate direct and mycorrhizal pathways for nitrate uptake by regulating NAR2.1-NRT2s complexes in rice.

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 (NO₃^-) transporter complexes with crucial roles in direct NO₃^- uptake, are also recruited for symbiotic NO₃^- uptake. OsNAR2.1 and OsNRT2.1/2.2 are coregulated by NIN-like protein 3 (OsNLP3), a key regulator in NO₃^- 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 NO₃^- uptake and mycorrhization efficiency. Overall, we demonstrate that OsNLP3 and OsPHR2 orchestrate the direct and mycorrhizal NO₃^- uptake pathways by regulating the NAR2.1-NRT2s complexes in rice.