Transcriptomic and proteomic analysis of thiourea-induced salt tolerance in maize (Zea mays L.) seedlings

Salt stress is one of the major constraints to crop production. In this study, physiological, biochemical, transcriptomic and proteomic analyses were carried out to reveal the mechanism of action of thiourea (TU) to induce salt stress tolerance in maize (Zea mays L.). In the present study, maize seedlings were exposed to control, TU (35 μM), NaCl (100 mM), and TU+NaCl treatments. Salt stress caused a significant decrease in stem fresh and dry weight of maize seedlings, while the addition of TU to the medium significantly increased stem fresh and dry weight. Salt stress increased MDA content and altered the expression levels of antioxidant enzymes in the leaves of maize seedlings. TU+NaCl treatment caused a decrease in MDA content and promoted antioxidant enzyme activity. Salt stress caused a significant increase in leaf proline content, and the addition of TU to the medium significantly reduced leaf proline accumulation. Transcriptomic and proteomic analyses allow the identification of genes and proteins whose expression changes depending on plant developmental stages or different environmental factors. Numerous genes and proteins whose expressions increased or decreased in maize leaf tissue when NaCl was applied alone or in combination with TU were identified. RNAseq analysis revealed changes in the expression profiles of 49 genes, most of which are markers of stress response, in the leaves of maize seedlings exposed to TU+NaCl treatments compared to NaCl. According to gene ontology (GO) analysis, DEGs were found to be genes related to stress response, secondary metabolite biosynthesis, carbohydrate metabolism, cell wall synthesis and hormone biosynthesis in TU+NaCl treatment compared to NaCl. nLCMS/MS analysis revealed that 145 proteins showed changes in their expression levels in NaCl and TU+NaCl treatments compared to control. According to GO analysis, DEPs were identified as proteins related to photosynthesis, transport system, antioxidant system, protein metabolism and tricarboxylic acid cycle and electron transport system. The results of qPCR validation of nine genes with altered expression correlated with RNAseq data. TU application was found to regulate different signaling and effector mechanisms to alleviate salt stress at the early seedling development stage of maize. These results suggest that TU may have the potential to be used as an effective bioregulator for the acquisition of salt tolerance in plants.