Genome-wide identification and characterization of the thioredoxin (TRX) gene family in tomato (Solanum lycopersicum) and a functional analysis of SlTRX2 under salt stress.

Thioredoxin is a multifunctional acidic protein widely presented in organisms that regulates intracellular redox processes, participating in a series of biochemical reactions in cells to affect the growth and development of plants. Although the thioredoxin (TRX) gene family has been widespread recognized across various plant species, and the tomato genome has been sequenced for years now, of tomato (Solanum lycopersicum) has remained largely uncharted in terms of identifying and unraveling the functional intricacies of is TRX genes. In this study, 53 SlTRX genes were identified, unevenly distributed across 11 of the 12 tomato chromosomes. These 53 SlTRX genes were categorized into 4 distinct subfamilies based on their evolutionary kinship and phylogenetic development. Expression profiling reveals that most of SlTRX genes exhibited distinct expression patterns across various tissues and developmental stages. In addition, the gene structure, conserved protein motifs and cis-elements of 53 SlTRX genes were analyzed simultaneously. In our rigorous in silico expression analysis, 8 SlTRX genes were meticulously selected for subsequent experiments. Subcellular localization indicated that these 8 SlTRX genes were localized in chloroplasts. Furthermore, these 8 SlTRX genes were responsive to abiotic stress (salt, drought and cold stress) under the qRT-PCR analysis, and their different expression patterns under diverse types of treatments indicated their possible roles in stress tolerance in tomato. Based on these results, SlTRX2, whose expression level continued to increase under salt stress, was selected for silencing to further investigate its function, and furthermore, silencing SlTRX2 inhibited plant growth and led to a significant reduction in photosynthesis under salt stress. Yeast two-hybrid and luciferase complementation imaging assays demonstrated that SlTRX2 may regulate tomato salt resistance by affecting related photosynthetic genes. Thus, our study establishes a valuable resource for further analysis on biological functions of SlTRX genes and will provide important insights in the mechanism of action under stress.