College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, MOE, China Agricultural University, Beijing, 100193, China.
Department of Nutritional Crop Physiology, Institute of Crop Science, University of Hohenheim, Stuttgart, 70593, Germany.
Plant Cell. 2022 Sep 27;34(10):4066-4087. doi: 10.1093/plcell/koac225.
Most plant species can form symbioses with arbuscular mycorrhizal fungi (AMFs), which may enhance the host plant's acquisition of soil nutrients. In contrast to phosphorus nutrition, the molecular mechanism of mycorrhizal nitrogen (N) uptake remains largely unknown, and its physiological relevance is unclear. Here, we identified a gene encoding an AMF-inducible ammonium transporter, ZmAMT3;1, in maize (Zea mays) roots. ZmAMT3;1 was specifically expressed in arbuscule-containing cortical cells and the encoded protein was localized at the peri-arbuscular membrane. Functional analysis in yeast and Xenopus oocytes indicated that ZmAMT3;1 mediated high-affinity ammonium transport, with the substrate NH4+ being accessed, but likely translocating uncharged NH3. Phosphorylation of ZmAMT3;1 at the C-terminus suppressed transport activity. Using ZmAMT3;1-RNAi transgenic maize lines grown in compartmented pot experiments, we demonstrated that substantial quantities of N were transferred from AMF to plants, and 68%-74% of this capacity was conferred by ZmAMT3;1. Under field conditions, the ZmAMT3;1-dependent mycorrhizal N pathway contributed >30% of postsilking N uptake. Furthermore, AMFs downregulated ZmAMT1;1a and ZmAMT1;3 protein abundance and transport activities expressed in the root epidermis, suggesting a trade-off between mycorrhizal and direct root N-uptake pathways. Taken together, our results provide a comprehensive understanding of mycorrhiza-dependent N uptake in maize and present a promising approach to improve N-acquisition efficiency via plant-microbe interactions.
大多数植物物种可以与丛枝菌根真菌（AMF）形成共生关系，这可能增强宿主植物对土壤养分的获取。与磷营养不同，丛枝菌根氮（N）吸收的分子机制在很大程度上仍然未知，其生理相关性也不清楚。在这里，我们在玉米（Zea mays）根中鉴定了一个编码 AMF 诱导的铵转运体基因 ZmAMT3;1。ZmAMT3;1 在含有丛枝的皮质细胞中特异性表达，并且编码的蛋白质定位于周丛膜。酵母和非洲爪蟾卵母细胞中的功能分析表明，ZmAMT3;1 介导高亲和力铵转运，其底物 NH4+可被访问，但可能转运不带电荷的 NH3。ZmAMT3;1 的 C 端磷酸化抑制转运活性。使用在分隔盆栽实验中生长的 ZmAMT3;1-RNAi 转基因玉米株系，我们证明了大量的 N 从 AMF 转移到植物中，并且这种能力的 68%-74%由 ZmAMT3;1 赋予。在田间条件下，ZmAMT3;1 依赖的丛枝菌根 N 途径贡献了超过 postsilking N 吸收的 30%。此外，AMF 下调了在根表皮中表达的 ZmAMT1;1a 和 ZmAMT1;3 蛋白丰度和转运活性，表明丛枝菌根和直接根 N 吸收途径之间存在权衡。总之，我们的结果提供了对玉米中丛枝菌根依赖的 N 吸收的全面理解，并提出了一种通过植物-微生物相互作用提高 N 获取效率的有前途的方法。
