Superabsorbent polymers seed coatings modulate transcriptomic and physiological responses to drought in rapeseed

Drought stress is a major constraint on rapeseed (Brassica napus L.) production, particularly during germination and early seedling development, and its impact is intensifying with climate change. Superabsorbent polymers (SAPs) have emerged as a promising strategy to mitigate water limitation by enhancing moisture availability. This study conducted a comparative analysis of three SAP types, two fossil-based (MERCK, SWT) and one natural-based (ABG), applied via seed coating to evaluate their effects on germination, sodium uptake, total phenol content mitigation, and transcriptomic profiles under drought stress. While all SAPs increased seedling sodium content, the MERCK treatment produced the highest rate of normal germination, the lowest Na⁺ accumulation, and reduced oxidative stress, closely resembling the well-watered control (CN). Transcriptome sequencing revealed distinct expression profiles across treatments. MERCK seedlings showed expression of key stress-responsive genes (PER45, ABI1, STM) most similar to CN. In contrast, ABG seedlings exhibited significant downregulation of important genes (especially transcription factor (TF) genes) such as WRKY33, MYB77, CIPK17, and STZ, consistent with their poor performance. Functional enrichment analysis indicated the induction of phenylpropanoid biosynthesis, antioxidant activity, and hormonal signaling pathways, with MERCK and ABG showing contrasting signatures. These findings demonstrate that SAP composition influences drought adaptation in rapeseed by modulating molecular stress-response pathways. The integration of physiological and transcriptomic analyses not only identifies effective SAP formulations for seed coating but also provides candidate genes to support breeding programs aimed at developing stress-resilient cultivars.