Transcriptomic insights into nitrogen-regulated cadmium absorption and accumulation in Spirodela polyrhiza: Toward...

To reveal the molecular mechanism by which nitrogen (N) regulates cadmium (Cd) uptake and accumulation in Spirodela polyrhiza, transcriptome analysis was performed on S. polyrhiza 7498 under low nitrogen (0.25N) and high nitrogen (1N) conditions combined with 50 μM CdCl₂ stress. We systematically investigated the effects of N on metabolic pathways and key regulatory factors in S. polyrhiza under Cd stress. A total of 19,325 genes were identified, and the number of differentially expressed genes (DEGs) increased significantly with prolonged treatment time. These DEGs were mainly enriched in pathways related to oxidative stress, metal ion binding, photosynthesis, and sugar metabolism. N enhanced Cd transport and detoxification by upregulating the expression of heavy metal transporter genes including IRT, MTP, HMA, and HIPP26. Meanwhile, it increased the expression of genes associated with chlorophyll synthesis, photosystems, and ATP synthesis to alleviate Cd-induced inhibition of photosynthesis, and regulated sugar metabolism to promote starch degradation and sucrose transport, thereby providing carbon skeletons to support Cd stress responses. In addition, transcription factors such as bHLH56, bHLH47 and WRKY4 played crucial regulatory roles in N-Cd crosstalk. Among them, GATA22, as a hub gene in the co-expression network, coordinately regulated genes involved in N metabolism, photosynthesis, and Cd tolerance. This study provides a theoretical basis for illustrating the molecular mechanism of N-Cd interaction in aquatic plants, and offers genetic resources and technical insights for enhancing phytoremediation of Cd-contaminated water bodies using S. polyrhiza combined with N management.