A homeobox7 transcription factor from Mesembryanthemum crystallinum enhanced salt tolerance

Mesembryanthemum crystallinum (common ice plant) is a facultative halophyte species, which has adapted to extreme conditions. In this study, we cloned a McHB7 transcription factor gene from the ice plant. The expression of McHB7 was significantly induced by 500 mM NaCl and it reached the peak under salt treatment for 7 days. The McHB7 protein was targeted to the nucleus. Overexpression of McHB7 gene in ice plant leaves by Agrobacterium-mediated transformation led to 25 times more McHB7 transcripts than the non-transformed control wild type (WT). After 500 mM NaCl treatment for 7 days, SOD, POD activities and water content of the transgenic plants were significantly higher than WT, while MDA content was decreased in the transgenic plants. Proteomics results showed that a total of 1082 and 1072 proteins were profiled under control and salt treatment, respectively. 22 (2%) and 11 (1%) proteins were uniquely identified under control and salt stress conditions, respectively. Among these 11 proteins, 7 were increased and 4 were decreased. Most identified proteins involved in the processes of regulation of biological, transporter and catalytic activity, biosynthesis of secondary metabolties and response to stimulus were significantly increased in the McHB7 overexpression ice plants under high salinity. All the results demonstrate that the McHB7 transcription factor plays a positive role in improving plant salt tolerance.