![]() An increasing number of reports suggest that AM fungi can take up both NO 3 − and NH 4 +, as well as organic N forms, from the surrounding soils ( 6– 13). The primary forms of N absorbed by plant roots are nitrate (NO 3 −) in aerobic upland soil and ammonium (NH 4 +) in flooding soil. ![]() Nitrogen (N) is the most important nutrient for plant growth and development. It has been demonstrated that AM fungi dominates Pi uptake in symbiotic plants ( 4, 5). Upon the formation of AM symbiosis, mycorrhizal plants have two pathways for nutrient uptake, either direct uptake from the soil via root hairs and root epidermis or indirectly through the AM fungal hyphae at the plant–fungus interface. Cortical cells develop a specialized membrane, the periarbuscular membrane (PAM), to envelop each branching hypha to separate the fungus from the plant cell cytoplasm, resulting in an extensive plant–fungal interface specialized for nutrient exchange ( 3). In the AM symbiosis, the fungal hyphae penetrate the root epidermis, grow through the intercellular spaces of the root, and subsequently invade cortical cells, developing highly branched tree-like structures called arbuscules ( 2). AM association is an endosymbiotic process that requires the differentiation of both symbionts to create novel contact interfaces within the cells of plant roots. In a natural soil ecosystem, the majority of land plants can form mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi of Glomeromycotina to better adapt to limited nutrient supplies ( 1). Based on our results, we propose that the NPF4.5 plays a key role in mycorrhizal NO 3 − acquisition, a symbiotic N uptake route that might be highly conserved in gramineous species. Moreover, knockout of OsNPF4.5 resulted in a 45% decrease in symbiotic N uptake and a significant reduction in arbuscule incidence when NO 3 − was supplied as an N source. OsNPF4.5 is exclusively expressed in the cells containing arbuscules and displayed a low-affinity NO 3 − transport activity when expressed in Xenopus laevis oocytes. 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. 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-NO 3 − supply condition. 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. ![]() Arbuscular mycorrhizal (AM) fungi are beneficial symbionts of most land plants that enhance plant nutrient uptake, particularly of phosphate. Low availability of nitrogen (N) is often a major limiting factor to crop yield in most nutrient-poor soils. ![]()
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