ZmNRT1.1B (ZmNPF6.6) determines nitrogen use efficiency via regulation of nitrate transport and signalling in maize.

Nitrate (NO ) is crucial for optimal plant growth and development and often limits crop productivity under low availability. In comparison with model plant Arabidopsis, the molecular mechanisms underlying NO acquisition and utilization remain largely unclear in maize. In particular, only a few genes have been exploited to improve nitrogen use efficiency (NUE). Here, we demonstrated that NO -inducible ZmNRT1.1B (ZmNPF6.6) positively regulated NO -dependent growth and NUE in maize. We showed that the tandem duplicated proteoform ZmNRT1.1C is irrelevant to maize seedling growth under NO supply; however, the loss of function of ZmNRT1.1B significantly weakened plant growth under adequate NO supply under both hydroponic and field conditions. The N-labelled NO absorption assay indicated that ZmNRT1.1B mediated the high-affinity NO -transport and root-to-shoot NO translocation. Transcriptome analysis further showed, upon NO supply, ZmNRT1.1B promotes cytoplasmic-to-nuclear shuttling of ZmNLP3.1 (ZmNLP8), which co-regulates the expression of genes involved in NO response, cytokinin biosynthesis and carbon metabolism. Remarkably, overexpression of ZmNRT1.1B in modern maize hybrids improved grain yield under N-limiting fields. Taken together, our study revealed a crucial role of ZmNRT1.1B in high-affinity NO transport and signalling and offers valuable genetic resource for breeding N use efficient high-yield cultivars.