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Molecular mechanisms underpinning physiological tolerances to salinity and alkaline salinity in Brassica juncea

ABSTRACT: In low rainfall regions soils are naturally conditioned with frequent co-occurrence of salinity and alkalinity. Plant salinity responses both at physiological and molecular level have been extensively researched. However, effects of the combined treatment of alkaline salinity that could greatly reduce plant growth and the mechanisms responsible for tolerance remain indeterminate. In Brassica juncea, large reductions in biomass and increased leaf Na+ concentration under alkaline salinity indicates that the combined treatment had greater negative effect than salinity on both growth and the physiological responses of the plant. To determine molecular mechanisms potentially controlling adaptive tolerance responses to salinity and alkaline salinity, the moderately tolerant genotype NDR 8501 was further investigated using microarray analysis. The transcripts of treated leaf tissues verses those of the untreated control sample were analysed after prolonged stress of four weeks. In total, 528 salinity responsive and 1245 alkaline salinity responsive genes were indentified and only 101 genes were expressed jointly in either of the two treatments. Transcription of 37% more genes involved in response to alkaline salinity than salinity alone, which suggests the increased impact and severity of the combined stress on the plant, indicating the transcription of a far greater number of genes likely involved in mitigation and damage control. Transcription of KUP2 and KUP7 genes involved in potassium homeostasis under salinity alone and NHX1 and ENH1 genes for ion (K+ and Na+) homeostasis under alkaline salinity, clearly demonstrated that different genes and genetic pathways are involved in response to each stress. They further provide supporting evidence for the physiological responses that occur in the plant, with massive reprogramming of the transcriptome leading to partial ion exclusion, shuttling and compartmentation.

ORGANISM(S): Brassica napus Brassica juncea

PROVIDER: GSE38905 | GEO | 2012/06/26

SECONDARY ACCESSION(S): PRJNA169393

REPOSITORIES: GEO

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Project description:In low rainfall regions soils are naturally conditioned with frequent co-occurrence of salinity and alkalinity. Plant salinity responses both at physiological and molecular level have been extensively researched. However, effects of the combined treatment of alkaline salinity that could greatly reduce plant growth and the mechanisms responsible for tolerance remain indeterminate. In Brassica juncea, large reductions in biomass and increased leaf Na+ concentration under alkaline salinity indicates that the combined treatment had greater negative effect than salinity on both growth and the physiological responses of the plant. To determine molecular mechanisms potentially controlling adaptive tolerance responses to salinity and alkaline salinity, the moderately tolerant genotype NDR 8501 was further investigated using microarray analysis. The transcripts of treated leaf tissues verses those of the untreated control sample were analysed after prolonged stress of four weeks. In total, 528 salinity responsive and 1245 alkaline salinity responsive genes were indentified and only 101 genes were expressed jointly in either of the two treatments. Transcription of 37% more genes involved in response to alkaline salinity than salinity alone, which suggests the increased impact and severity of the combined stress on the plant, indicating the transcription of a far greater number of genes likely involved in mitigation and damage control. Transcription of KUP2 and KUP7 genes involved in potassium homeostasis under salinity alone and NHX1 and ENH1 genes for ion (K+ and Na+) homeostasis under alkaline salinity, clearly demonstrated that different genes and genetic pathways are involved in response to each stress. They further provide supporting evidence for the physiological responses that occur in the plant, with massive reprogramming of the transcriptome leading to partial ion exclusion, shuttling and compartmentation. Salinity and alkaline salinity induced gene expression in Brassica juncea leaf was measured at 4 weeks of prolonged treatment of 50 mM NaCl alone and combined with 2.5 mM HCO3- versus non-stressed control. A single experiment was conducted using Brassica juncea genotype NDR 8501 at a single time point (fours weeks after treatment) with three replications per treatment.

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:Yield losses as a result of abiotic stress factors present a significant challenge for the future of global food production. While breeding technologies provide potential to combat negative stress-mediated outcomes over time, interventions which act to prime plant tolerance to stress, via the use of phytohormone-based elicitors for example, could act as a valuable tool for crop protection. However, the translation of fundamental biology into functioning solution is often constrained by knowledge-gaps. Photosynthetic and transcriptomic responses were characterised in young tomato (Solanum lycopersicum) seedlings in response to pre-treatment with a new plant health activator technology, M-bM-^@M-^XAlethea,M-bM-^@M-^Y followed by a subsequent 100 mM salinity stress. Salinity treatment led to a maximal 47% reduction in net photosynthetic rate 8 d following NaCl treatment. In Alethea pre-treated seedlings, sensitivity to salinity stress was markedly reduced during the experimental period. Microarray analysis of leaf transcriptional responses showed that while salinity stress and Alethea individually impacted on largely non-overlapping, distinct groups of genes, Alethea pre-treatment substantially modified the response to salinity. Alethea affected the expression of genes related to biotic stress, ethylene signalling, cell wall synthesis, redox signalling and photosynthetic processes. Since Alethea had clear effects on photosynthesis/chloroplastic function at the physiological and molecular levels, we also investigated the ability of Alethea to protect plants against methyl viologen, a potent generator of oxidative stress in chloroplasts. Alethea pre-treatment produced dramatic reductions in visible foliar necrosis caused by methyl viologen compared with non-primed controls. Tomato leaves from four groups of treated plants were harvested at a single point following treatment for RNA extraction and hybridization on Affymetrix microarrays. Plants came from two initial groups, pre-treated either with water (control) or the Alethea product. Equal numbers of plants from within these groups were subsequently treated either with water (control) or salinity (100 mM NaCl), generating 4 main experimental groups in a 2x2 factorial design. Samples were collected from 3 biological replicate experiments, and each sample included leaves pooled from 3 individual plants from each treatment group.

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Molecular mechanisms underpinning physiological tolerances to salinity and alkaline salinity in Brassica juncea

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