Table 3_Transcriptomic and physiological effects of superabsorbent polymer seed coating on maize under drought stress.docx

Drought stress severely impairs maize germination and early seedling growth, posing a significant threat to global food security. To address this, superabsorbent polymers (SAPs) are being explored as an effective seed-coating method to improve water availability during the crucial germination phase. However, their comparative efficacy and underlying molecular mechanisms remain insufficiently understood. In this study, we evaluated the effects of three distinct SAPs, two fossil-based (MERCK, SWT) and one natural-based (ABG), on maize germination and seedling development under controlled drought conditions. We integrated physiological (germination rate and NA+), biochemical (total phenol content), and transcriptomic (mRNA-seq) analyses to provide a comprehensive multi-level assessment. Physiologically, among all SAPs, the MERCK was the most effective, resulting in the highest proportion of normal seedlings and the fewest abnormal seedlings. In contrast, the SWT treatment was detrimental, increasing the proportion of abnormal seedlings, suggesting phytotoxic effects. Biochemically, all SAP treatments resulted in elevated seedling sodium (Na+) content, indicating potential secondary ionic stress. Transcriptomic analysis further elucidated these observations, revealing a set of differentially expressed genes, including those involved in stress response (BADH, FACT, XCP2), SAP-specific response (DRB5, RAF35, EDR1), and combined salt/drought stress (WRKY47, DTX20), as promising candidate biomarkers for stress assessment and breeding. Our research highlights the nuanced efficacy of SAPs; specifically, the MERCK SAP yielded more favorable outcomes, while other formulations occasionally caused unexpected phytotoxicity. The identified gene expression patterns not only mechanistically explain the observed physiological responses but also offer a valuable panel of molecular biomarkers. These markers can be used to screen novel SAP applications, such as seed coatings, and to breed stress-resilient maize cultivars.

干旱胁迫会严重抑制玉米萌发与幼苗早期生长，对全球粮食安全构成重大威胁。针对这一问题，高吸水性聚合物（superabsorbent polymers, SAPs）作为一种有效的种子包衣手段，正被研究用于提升关键萌发阶段的水分供给。然而，不同SAPs的相对功效及其潜在分子机制仍未得到充分阐释。本研究在可控干旱条件下，评估了3种不同类型SAPs的效果：2种为化石基SAPs（MERCK、SWT），1种为天然基SAPs（ABG），覆盖玉米萌发与幼苗生长两个层面。本研究整合了生理学（萌发率与钠离子（Na⁺）含量）、生物化学（总酚含量）以及转录组学（mRNA测序（mRNA-seq））分析，以开展全面的多维度评估。生理学层面的结果显示，在所有供试SAPs中，MERCK的效果最为优异，可使正常幼苗占比达到最高，同时异常幼苗占比最低。与之相反，SWT处理则表现出有害性，会提升异常幼苗占比，提示其存在植物毒性效应。生物化学层面的分析表明，所有SAP处理组的幼苗钠离子（Na⁺）含量均有所升高，提示存在潜在的继发性离子胁迫。转录组学分析进一步阐明了上述观测结果，筛选出一批差异表达基因，其中包括参与胁迫响应（BADH、FACT、XCP2）、SAP特异性响应（DRB5、RAF35、EDR1）以及盐/干旱复合胁迫响应（WRKY47、DTX20）的基因，这些基因均可作为用于胁迫评估与品种选育的潜在候选生物标志物。本研究凸显了SAPs功效的细微差异：具体而言，MERCK型SAP可带来更优的应用效果，而其他配方则偶尔会引发未预期的植物毒性。本次鉴定得到的基因表达模式不仅从机制层面解释了观测到的生理学响应，还提供了一组极具应用价值的分子生物标志物。这些标志物可用于筛选新型SAP应用场景（如种子包衣），以及培育抗胁迫玉米品种。