Project description:Background: The halophyte Mesembryanthemum crystallinum (ice plant) is a model for studying salt tolerance. The morphology, physiology, metabolism, and gene expression of ice plant have been studied for over 40 years. Although the complete genome sequence has not been revealed, large-scale analyses of gene expression profiling have drawn an outline of salt tolerance in ice plant. Despite ample information in the transcriptome, miRNA information has not been documented. Results: We examined responses to a sudden increase in salinity in ice plant seedlings. Using a fluorescent dye to detect Na+, we found that ice plant roots respond to an increased flux of Na+ by either secreting or storing Na+ in specialized cells. High-throughput sequencing was used to identify small RNA profiles in three-day-old seedlings treated with or without 200 mM NaCl. Totally 132 conserved miRNAs belonging to 22 families were found. The hairpin precursor of 19 conserved mcr-miRNAs and 12 novel mcr-miRNAs were identified. Target genes are involved in a broad range of biological processes: transcription factors that regulate growth and development, enzymes that catalyze miRNA biogenesis for the most conserved mcr-miRNA, and proteins that are involved in ion homeostasis and drought-stress responses for some novel mcr-miRNAs. After 6 h of salt stress, the expressions of most mcr-miRNAs were down-regulated, whereas the expressions of their corresponding target genes were up-regulated. Analyses of the functions of target genes revealed that cellular processes, including growth and development, metabolism, and ion transport activity were up-regulated in roots under salt stress. Conclusions: Analyses of small RNA profile of ice plant seedlings identified many conserved miRNA families and several novel miRNAs. The expression of ten conserved miRNAs and three novel miRNAs were reciprocally correlated to predicted targets hourly after salt stress. Based on the expression pattern of miRNA and target genes in combination with the observation of Na+ distribution, we suggest that ice plant roots respond effectively to increased salinity by using Na+ as an osmoticum for cell expansion and guard cell opening. Excessive Na+ could either be secreted through root epidermis or stored in specialized leaf epidermal cells. These responses are partially regulated at the miRNA-mediated post-transcriptional level.
Project description:Mesembryanthemum crystallinum (common ice plant) is one of the facultative halophyte plants, and it serves as a model for investigating the molecular mechanisms underlying its salt stress response and tolerance. Here we cloned one of homeobox transcription factor (TF) gene McHB7 from ice plant, which has 60% similarity with the Arabidopsis AtHB7. Overexpression of McHB7 in Arabidopsis (OE) showed that the plants had significantly elevated relative water content (RWC), chlorophyll content, superoxide dismutase (SOD) and peroxidase (POD) activities after salt stress treatment. Proteomics analysis identified 145 to be significantly changed in abundance, and 66 were exclusively increased in the OE plants compared to wild type (WT). After salt treatment, 979 and 959 metabolites were significantly increased and decreased in OE plants compared to the WT, respectively. The results demonstrated McHB7 can improve photosynthesis and increase the leaf chlorophyll content, and affect TCA cycle by regulating metabolites (e.g., pyruvate) and proteins (e.g., citrate synthase). Also, McHB7 modulates the expression of stress-related proteins (e.g., superoxide dismutase, dehydroascorbate reductase and pyrroline-5-carboxylate synthase B) to scavenge reactive oxygen species and enhance plant salt tolerance.
Project description: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.