Shining light on Arabidopsis regulatory networks integrating nitrogen use and photosynthesis.

Nitrogen and light availability are well-known to influence photosynthesis, having both individual and synergistic effects. However, the regulatory interactions between these signaling pathways, especially the transcription factors (TFs) that perceive and integrate these cues, remain to be elucidated. Arabidopsis grown in a matrix of nitrogen and light treatments exhibited distinct physiological and transcriptomic responses. Notably, the effect of nitrogen dose on biomass, nitrogen use efficiency, carbon-to-nitrogen ratio, and gene expression was highly dependent on light intensity. Genes differentially expressed across the treatments were enriched for photosynthetic processes, including the pentose-phosphate cycle, light-harvesting, and chlorophyll biosynthesis. TFs coordinating photosynthesis, carbon-to-nitrogen balance, and nitrogen uptake were identified based on motif enrichment, validated binding data, and gene regulatory network analysis. Dynamic light-by-nitrogen responses were found for TFs previously linked to either nitrogen or light signaling, which now emerge as regulatory hubs that integrate these signals. Among these TFs, we identified bZIP and MYB-related family transcription factors as pivotal players in harmonizing photosynthesis, nitrogen assimilation, and light responses. The transcription factors unveiled in this study have the potential to unlock new strategies for optimizing photosynthetic activity and nutrient-use efficiency in plants.