Lipidomic and transcriptomic analyses reveal that the gene ZmLACS9 enhances salt stress tolerance by regulating chloroplast lipid metabolism and maintaining photosynthetic performance in maize

Salt stress is a major environmental factor limiting crop growth and productivity. We found a long-chain acyl-CoA synthetase (LACS) gene ZmLACS9 that was associated with salt tolerance traits in maize (Zea mays). Mutation of ZmLACS9 impaired plant growth, while overexpression of ZmLACS9 improved plant growth vigour under salt stress conditions. Metabolome and transcriptome analyses indicated that ZmLACS9 may regulate the expression of lipid trafficking-related genes, thereby influencing the concentrations of galactolipids and phospholipid in the photosynthetic membrane under salt stress. Under salt stress conditions, ultrastructural observation and chlorophyll fluorescence parameters showed that the mutation of ZmLACS9 led to significant impairment of the number of thylakoid layer structures and PSII activity, while overexpression of ZmLACS9 markedly improved the number of chloroplast thylakoid grana lamella and PSII activity. Furthermore, yeast one-hybrid and LUC transient expression assays found that ZmWRKY17 could bind to the promoter of ZmLACS9. Collectively, our study provides candidate genes for breeding maize varieties with higher stress resistance.