Functional Analysis of the OsNPF4.5 Nitrate Transporter Reveals a Conserved Mycorrhizal Pathway of Nitrogen Acquisition in Plants

Low availability of nitrogen (N) is often a major limiting factor to crop yield in most nutrient-poor soils. Arbuscular mycorrhizal (AM) fungi are beneficial symbionts of most land plants that enhance plant nutrient uptake, particularly of phosphate. A growing number of reports point to the substantially increased N accumulation in many mycorrhizal plants; however, the contribution of AM symbiosis to plant N nutrition and the mechanisms underlying the AM-mediated N acquisition are still in the early stages of being understood. Here, we report that inoculation with AM fungus remarkably promoted rice () growth and N acquisition, and about 42% of the overall N acquired by rice roots could be delivered via the symbiotic route under N-NO supply condition. Mycorrhizal colonization strongly induced expression of the putative nitrate transporter gene in rice roots, and its orthologs in and in OsNPF4.5 is exclusively expressed in the cells containing arbuscules and displayed a low-affinity NO transport activity when expressed in oocytes. Moreover, knockout of resulted in a 45% decrease in symbiotic N uptake and a significant reduction in arbuscule incidence when NO was supplied as an N source. Based on our results, we propose that the NPF4.5 plays a key role in mycorrhizal NO acquisition, a symbiotic N uptake route that might be highly conserved in gramineous species.