PLAC8 is a cysteine-rich protein that serves as a central mediator of tumor evolution in mammals. PLAC8 motif-containing proteins widely distribute in fungi, algae, higher plants and animals that have been described to be implicated in fruit size, cell number and the transport of heavy metals such as cadmium or zinc. In tomatoes, FW2.2 is a PLAC8 motif-containing gene that negatively controls fruit size by regulating cell division and expansion in the carpel ovary during fruit development. However, despite FW2.2, other FWL (FW2.2-Like) genes in tomatoes have not been investigated. In this study, we identified the 21 SlFWL genes, including FW2.2, examined their expression profiles under various abiotic adversity-related conditions. The SlFWL gene structures and motif compositions are conserved, indicating that tomato SlFWL genes may have similar roles. Cis-acting element analysis revealed that the SlFWL genes may participate in light and abiotic stress responses, and they also interacted with a variety of phytohormone-responsive proteins and plant development elements. Phylogenetic analyses were performed on five additional plant species, including Arabidopsis, pepper, soybean, rice and maize, these genes were classified into five subfamilies. Based on the results of collinearity analyses, the SlFWL genes have a tighter homologous evolutionary relationship with soybean, and these orthologous FWL gene pairs might have the common ancestor. Expression profiling of SlFWL genes show that they were all responsive to abiotic stresses, each subgroup of genes exhibited a different expression trend. Our findings provide a strong foundation for investigating the function and abiotic stress responses of the SlFWL family genes.

Ascorbic acid (AsA), an essential non-enzymatic antioxidant in plants, regulates development growth and responses to abiotic and biotic stresses. However, research on AsA’s role in cold tolerance remains largely unknown. Here, our study uncovered the positive role of AsA in improving cold stress tolerance in tomato seedlings. Physiological analysis showed that AsA significantly enhanced the enzyme activity of the antioxidant defense system in tomato seedling leaves and increased the contents of proline, sugar, abscisic acid (ABA), and endogenous AsA. In addition, we found that AsA is able to protect the photosynthetic system of tomato seedlings, thereby relieving the declining rate of chlorophyll fluorescence parameters. qRT-PCR analysis indicated that AsA significantly increased the expression of genes encoding antioxidant enzymes and involved in AsA synthesis, ABA biosynthesis/signal transduction, and low-temperature responses in tomato. In conclusion, the application of exogenous AsA enhances cold stress tolerance in tomato seedlings through various molecular and physiological responses. This provides a theoretical foundation for exploring the regulatory mechanisms underlying cold tolerance in tomato and offers practical guidance for enhancing cold tolerance in tomato cultivation.