Salinity stress is a major obstacle that limits plant growth and productivity. However, plants possess robust defense mechanisms to mitigate its adverse effects. In this study, we found that overexpression of SlPSAN (photosystem I reaction center subunit N) conferred salt stress resistance in both yeast and tomato seedlings. The results showed that the T-DNA mutants were susceptible to salt stress, resulting in a significant decline in seed germination rates and root length in Arabidopsis. Overexpression of SlPSAN enhanced root and shoot fresh weights, as well as root and shoot dry weights, in tomato seedlings under salt stress. In contrast, knockout (psan1 and psan2) lines exhibited increased sensitivity to salt stress and a significant reduction in tomato seedling growth. Moreover, SlPSAN overexpression enhanced nutrient accumulation, chlorophyll content (Chl A, Chl B, Chl A+B, and carotenoids) and enhanced the activities of antioxidant enzymes (APX, SOD, POD, and CAT), while simultaneously decreasing the accumulation of ROS and MDA when compared with WT and knockout lines. Transcriptome analysis revealed that knockout of SlPSAN altered the enrichment of biological processes, including response to stimulus, immune system processes, and detoxification pathways, under salt stress in to mato. These findings suggested that SlPSAN positively regulates salt stress in tomato seedlings. This study un locks an innovative research direction for identifying candidate genes for improving salinity stress tolerance and protecting horticultural crop production.
