Transcriptomic analysis of the cysteine-induced cadmium tolerance in maize (Zea mays L.) seedlings

Cadmium (Cd) is a highly toxic heavy metal that can accumulate in the soil, posing a serious threat to plant growth and development. Cysteine (Cys), a sulfur−containing amino acid, has been shown to play a crucial role in the detoxification of cadmium in plants. However, the molecular mechanisms underlying Cys-mediated Cd tolerance in maize seedlings has not been well understood. In this study, therefore, the possible molecular mechanisms of the Cys−mediated Cd detoxification in maize (Zea mays L. cv. Capuzi) seedlings by physiological and transcriptomic analyses were investigated. Hydroponically grown maize seedlings were subjected to 75 M Cd and 250 M Cys treatments. After 10 d, the treated maize seedlings were harvested to analyze the metal tolerance mechanism via examining growth, Cd accumulation, chlorophyll content, enzymatic antioxidants and differentially expressed genes (DEGs). Cd stres decreased seedling growth and chlorophyll content due to greater Cd accumulation. Moreover Cd stresi enhanced oxidative stress markers such as lipid peroxidation due to decrease in superoxide dismutase and catalase activities. It has been determined that exogenous Cys application has a protective effect on plant growth by reducing Cd accumulation and lipid peroxidation and improving the activities of photosynthetic pigments and antioxidant enzymes. Comparative transcriptome analysis showed that the expression levels of 2422 genes changed (953 up−regulated and 1469 down−regulated) under Cd stress. Whereas the expression levels of 2577 genes changed by Cys+Cd application (1540 up−regulated and 1037 down−regulated). In gene ontology (GO) classification, many DEGs related to small molecule metabolic process, transmembrane transport and carbohydrate metabolic process were enriched in the control/Cd comparison, and transmembrane transport, photosynthesis and carbohydrate metabolic process were enriched in the Cd/Cys+Cd comparison. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis reveals that DEGs in control/Cd comparison are related to the metabolic pathways, photosynthesis, and biosynthesis of secondary metabolites, while in Cd/Cys+Cd comparison, DEGs are related to the photosynthesis, metabolic pathways, and phenylpropanoid biosynthesis. The results indicated that exogenous application of Cys improved the Cd tolerance of maize seedlings by regulating the expression of genes in different pathways, such as photosynthesis, chlorophyll biosynthesis, membrane transport, antioxidant enzyme system, and secondary metabolite biosynthesis. This research has the potential to contribute to the development of innovative strategies for improving the tolerance of crops to heavy metal stress, ultimately benefiting agricultural productivity and environmental sustainability.