Coordinated regulation of nitrogen transport and assimilation drives high nitrogen use efficiency in sugarcane

Improving nitrogen use efficiency (NUE) is essential for sustainable sugarcane production. Breeding high-NUE varieties enables high yields under low nitrogen (N) input, and identifying NUE-related genes is a critical step for molecular breeding. In this study, we compared two sugarcane genotypes, AS108 (high NUE) and GT11 (low NUE), under normal N (NN) and low N (LN) conditions. AS108 maintained significantly higher biomass, nitrogen content, and NUE under nitrogen limitation. Integrative analyses of enzyme activity, gene expression, and correlation networks indicated that its superior performance results from coordinated, organ-specific enhancement of nitrogen transport and assimilation. AS108 displayed consistently higher Glutamine synthetasec (GS) and glutamate synthase (GOGAT) activities, earlier and stronger induction of high-affinity transporters NRT2 and NRT2.2, and dynamic network reorganization under low nitrogen conditions. Network analysis identified NRT2/NRT2.2 as central hubs coupling nitrate uptake with GS/GOGAT-mediated assimilation. Notably, key nitrate transporter genes peaked 30-60 days earlier in AS108, highlighting the importance of temporal coordination. Together, these findings define a systems-level mechanism in which early-activated nitrate transport drives downstream assimilation to sustain growth under nitrogen limitation, providing molecular targets for breeding high NUE sugarcane cultivars.