Metabolomics and Transcriptomic Analysis Revealed the Response Mechanism of Maize to Saline-Alkali Stress

Saline-alkali stress inhibited the normal growth and development of plants, which seriously restricted the yield of crops. Maize is one of the most important crops in the world. However, the mechanism of maize in response to saline-alkali stress is still largely unknown. Through the observation of growth parameters and the detection of physiological and biochemical indicators in saline-alkali tolerant (22KN3894) and saline-alkali sensitive (H23146) maize inbred lines, this study found that compared with H23146, 22KN3894 accumulated less ROS content and more total flavonoids content, while the degree of root damage and ion toxicity was relatively small. Full-length transcriptome and broadly targeted metabolome were used to analyse the response mechanism of extreme maize inbred lines to saline-alkali stress. 22KN3894 accumulated more metabolites such as sugars and flavonoids. There were significant differences in the contents of flavonoid metabolites and genes related to flavonoid synthesis between the two materials. Weighted gene co-expression network analysis and co-expression network analysis based on RNA-Seq data suggested that the ZmWRKY82 gene might respond to saline-alkali stress by regulating the flavonoid biosynthesis pathway. ZmWRKY82 directly bound to the W-box in the ZmCHI6 promoter and promoted its expression. The above results showed that ZmWRKY82 could improve the antioxidant capacity by promoting the transcription of ZmCHI6 and the synthesis of flavonoids, thereby resisting saline-alkali stress. These findings provided novel insights for improving maize saline-alkali stress tolerance, demonstrating that flavonoids played pivotal roles in plant stress adaptation, and laid the foundation for future mechanistic studies and breeding improvement.