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 Rhizophagus irregularis remarkably promoted rice (Oryza sativa) growth and N acquisition, and about 42% of the overall N acquired by rice roots could be delivered via the symbiotic route under N-NO₃⁻ supply condition. Mycorrhizal colonization strongly induced expression of the putative nitrate transporter gene OsNPF4.5 in rice roots, and its orthologs ZmNPF4.5 in Zea mays and SbNPF4.5 in Sorghum bicolor. OsNPF4.5 is exclusively expressed in the cells containing arbuscules and displayed a low-affinity NO₃⁻ transport activity when expressed in Xenopus laevis oocytes. Moreover, knockout of OsNPF4.5 resulted in a 45% decrease in symbiotic N uptake and a significant reduction in arbuscule incidence when NO₃⁻ was supplied as an N source. Based on our results, we propose that the NPF4.5 plays a key role in mycorrhizal NO₃⁻ acquisition, a symbiotic N uptake route that might be highly conserved in gramineous species.

在大多数营养贫瘠的土壤中，氮素的低利用率通常是限制作物产量的主要因素。丛枝菌根（AM）真菌是大多数陆地植物的有益共生体，可增强植物对养分的吸收，尤其是对磷酸盐的吸收。越来越多的报告指出，许多菌根植物中氮的积累显着增加。但是，AM共生对植物氮素营养的贡献以及AM介导的N吸收的潜在机制仍处于早期了解之中。在这里，我们报道了不规则AM真菌根瘤菌的接种显着促进了水稻（Oryza sativa）的生长和氮素的吸收，在N-NO ₃下，通过根系共生途径可输送约42％的水稻根系氮素。⁻供应状况。菌根定植强烈诱导水稻根系中假定的硝酸盐转运蛋白基因OsNPF4.5的表达，其直系同源物ZmNPF4.5在玉米中的表达和SbNPF4.5在高粱中的表达。OsNPF4.5在含有丛枝细胞特异表达和显示的低亲和力NO ₃ ^-中表达时转运活性非洲爪蟾卵母细胞。此外，敲除OsNPF4.5导致共生氮吸收和在丛枝入射NO当显著减少了45％的减少₃ ^-作为N源提供。根据我们的结果，我们建议NPF4.5起着菌根NO关键作用，₃ ^-采集，共生氮的吸收途径可能在禾本科物种中高度保守。