Function Of Tomato SlHY5 Gene Under Cold Stress

HY5 is a b ZIP transcription factor, which has a pivotal role both in light signaling and cold signaling pathways. Since HY5 was identified from Arabidopsis, its structure, function and molecular mechanism have been clarified. Current research on HY5 has mainly been focused on light signaling. However, the function of HY5 under cold stress still remains unclear. In this study,tomato HY5 gene(Sl HY5) was isolated and characterized for its function under cold stress, which may provide a basis for vegetable breeding in the future. The main findings are as follows:Subcellular localization study showed that tomato HY5 was a nuclear-localized protein.Real-time quantitative PCR showed that Sl HY5 was constitutively expressed in the root, stem, leaf,flower and mature fruit. Sl HY5 was up-regulated during cold stress and it was also induced by Na Cl and plant hormone ABA. Overexpression of Sl HY5 in tomato increased the tolerance to cold stress, and the transgene expression level was correlated well with the degree of cold tolerance.These results suggest that Sl HY5 might play important roles under various abiotic stresses.Under cold treatment, the gene expressions of antioxidant enzymes(SOD and POX) were significantly higher in the Sl HY5-overexpressing lines, while the ROS content, relative electrolyte leakage and MDA level in the transgenic lines were significantly lower compared with the wild-type. These results indicate that overexpression of Sl HY5 could enhance the gene expressions of antioxidant defense enzymes and reduce the ROS level, which alleviated oxidative damage and lipid peroxidation, and ultimately enhanced the cold-stress tolerance in the transgenic tomato.During cold stress, the expressions of cold-inducible genes CHALCONE SYNTHASE(CHS), CHALCONE ISOMERASE(CHI), and FLAVANONE 3-HYDROXYLASE(F3H), which encode key enzymes in the anthocyanin biosynthetic pathway, were obviously induced in cold-treated Sl HY5 overexpressing tomato plants compared with the wild-type. Consistently,Sl HY5 overexpressing tomato plants had significantly higher accumulation of anthocyanins than wild-type. Meanwhile, Sl HY5 overexpressing tomato plants accumulated significantly lower level of ROS than wild-type plants in cold stress conditions. These data imply that Sl HY5 might operate under cold stress by inducing anthocyanin biosynthesis to restrain ROS accumulation, and Sl HY5 maybe integrate cold and light signaling to regulate the antioxidant defense mechanisms and ultimately enhance the cold-stress tolerance in the transgenic tomato.As several cold-inducible genes including PR1, CYSb, LEA1, Osmotin, and ICE1 are involved in regulation of transcription, osmotic adjustment, antioxidant defense and metabolite contents, which could enhance the stress tolerance of plants. Sl HY5 gene regulated the expressions of these genes. Thus, the results suggest that overexpression of Sl HY5 in tomato maybe modulate the expressions of other stress responsive genes, thereby enhancing cold tolerance.Taken together, these results indicate that Sl HY5 had an important role in improving the adaptation of plants to cold stress, and it possesses a potential use in genetic improvement for stress tolerance in tomato.