SlHY5 is a necessary regulator of the cold acclimation response in tomato

HY5, a bZIP transcription factor, plays a key role in the light- and cold-stress signaling pathways. In this study, the tomato HY5 gene (SlHY5) was isolated and characterized with respect to its function in cold-stress tolerance. The expression level of SlHY5 was similar in the root, stem, leaf, flower, and fruit of tomato. SlHY5 was upregulated gradually during cold stress and was induced in response to NaCl and the plant hormone abscisic acid. Overexpression of SlHY5 in tomato markedly increased cold stress tolerance. In addition, the SlHY5-overexpressing lines exhibited enhanced expression of genes related to antioxidant defense systems (SOD and CAT) and anthocyanin biosynthesis (CHS, CHI, and F3H) under cold stress compared to the wild-type plants, which suggested that overexpression of SlHY5 alleviated oxidative damage and lipid peroxidation, relieved membrane injuries induced by cold stress, enhanced anthocyanin accumulation, and thereby enhanced the cold-stress tolerance of SlHY5-overexpressing tomato plants. Furthermore, SlHY5 was involved in the regulation of several cold-induced genes, including PR1, CYSb, LEA, Osmotin, and ICE1, suggesting that constitutive overexpression of SlHY5 in tomato modulates the expression of other stress-responsive genes, thereby imparting cold tolerance. In conclusion, these results indicate that SlHY5 enhances plant tolerance to cold stress and that it may be used to facilitate the enhancement of stress tolerance in tomato.