Abstract
Excessive application of nitrogen (N) fertilizers in modern agriculture causes serious environmental problems. Sorghum is recognized as a crop with high tolerance to low-fertility soil; however, the molecular mechanisms underlying its nitrate uptake and utilization remain largely unclear. In this study, we identified the sorghum putative nitrate transporter (NRT) gene SbNRT1.1A (Sobic.007G044300), and we generated two independent SbNRT1.1A-overexpression lines (OE-A1 and OE-A2) using the rice cultivar ZH11. Compared with wild-type (WT) plants, the OE lines exhibited significantly improved growth under low-nitrogen (LN) conditions, characterized by increased shoot and root lengths, higher tiller and panicle numbers, greater grain counts per panicle, a larger aboveground biomass, and an elevated total N content. Transcriptome analysis identified 10,549 differentially expressed genes (DEGs). Under LN stress, the OE lines exhibited coordinated upregulation of genes involved in nitrate transport (NRTs), nitrate reduction (NR), glutamate synthesis (GOGAT), and glutamate dehydrogenase (GDH), indicating enhanced N uptake and assimilation. Moreover, genes encoding photosynthetic light reaction components (LHC-II, PSII, PSI and electron transfer proteins), glycolytic enzymes (UGPase, FRK, PGM, and PGI), and tricarboxylic acid (TCA) cycle enzymes (succinate dehydrogenase complex) were consistently upregulated in the OE lines. This metabolic shift likely provides sufficient ATP, NADPH and carbon skeletons (α-ketoglutarate) to fuel N assimilation. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses further revealed that SbNRT1.1A overexpression alleviated N-deficiency-induced oxidative stress and defence responses while specifically activating hypoxia-related pathways. Our results demonstrate that SbNRT1.1A is a promising genetic resource for improving growth under low-N conditions in crops, Its overexpression systemically reprograms carbon–N metabolic networks, leading to superior growth under low-N conditions, thereby providing a valuable target and a mechanistic framework for sustainable crop improvement.