Integrated physiological, transcriptomic, and metabolomic investigation reveals that MgO NPs mediate the alleviation of cadmium stress in tobacco seedlings through ABA-regulated lignin synthesis.

The harmful influence caused by cadmium (Cd) to agriculture is severe and enduring. Efforts to reduce the damage by Cd to crop is an important topic. In this study, we investigated the effect of MgO NPs on tobacco seedlings' growth under Cd stress and explored its mechanism. Results showed Cd inhibited seedling growth, but MgO NPs alleviated this toxicity. With MgO NPs, shoot and root fresh weight increased by 35.12 % and 45.73 %. This was mainly due to MgO NPs reducing Cd accumulation by 40 % in root and 20.48 % in shoot compared to Cd treatment. MgO NPs not only reduced Cd accumulation but redistributed it to inactive cell walls: up to 55 % in shoot and 22 % in root (compared to 47 % and 22 % in Cd treatment). The primary mechanism was the change in cell wall's main ingredient: lignin. MgO NPs increased lignin content by 50.62 % compared to Cd treatment. To further investigate the underlying molecular mechanism, multi-omics analysis was conducted. Comparing Cd + MgO NPs with Cd, 1358 DEGs (694 up, 664 down) and 160 DEMs (44 up, 116 down) were identified. Furthermore, we identified ABA-regulated phenylpropanoid pathway as the key mechanism for lignin synthesis. MgO NPs boosted ABA levels by 6.72 % compared to Cd treatment. The multi-omics analysis revealed upregulation of ABA synthesis and signal transduction, leading to increased phenylpropanoid pathway metabolites and gene expressions. Notably, POD, a key enzyme, increased by 92.05 %. It was concluded that MgO NPs represent a highly efficient alternative for enhancing plant resistance to Cd.