Physiological and transcriptomic analyses reveal that exogenous silicon alleviate the response of tomato to salt stress

Salt stress is a primary abiotic constraint that adversely affects the growth and development of tomato plants. Silicon, a beneficial element, has shown potential in mitigating various abiotic stresses. However, although numerous studies have been conducted in this field, the precise mechanism by which exogenous silicon mitigates salt stress in tomato seedlings remains to be fully elucidated. In this study, we analyzed the physiological responses and underlying molecular mechanisms in tomato seedlings under NaCl stress with or without silicon application. The results showed that salt stress severely inhibited seedling growth, as indicated by reductions in shoot and root fresh weight and plant height, while this damage was markedly alleviated by the application of exogenous silicon. Compared to the treatment with NaCl alone (Na), salt stress plus silicon treatment (Na + Si) improved plant growth, the leaf chlorophyll a content, the net photosynthetic rate (Pn), and the proline content and decreased the contents of reactive oxygen species (ROS) and malondialdehyde (MDA) in tomato seedlings. Transcriptomic analysis showed that there were 435 differentially expressed genes (DEGs) (397 upregulated and 38 downregulated) between Na + Si and Na treatments. Further enrichment analysis showed that the upregulated DEGs in Na + Si treatment were enriched in response to salt stress, ethylene and abscisic acid biosynthesis process, lignin catabolic process, cell wall biogenesis and the MAPK signaling pathway. Additionally, exogenous silicon application (Na + Si) upregulated the expression of key families of transcription factors, notably the AP2/ERF, WRKY and NAC families. Taken together, our study preliminarily revealed candidate genes and metabolic pathways affected by exogenous silicon treatment, which may provide a strategy for improving the adaptation of tomato to salt stress.