Sulian Lv

Multiple compartmentalization of sodium conferred salt tolerance in Salicornia europaea

Euhalophyte Salicornia europaea L., one of the most salt-tolerant plant species in the world, can tolerate more than 1000 mM NaCl. To study the salt tolerance mechanism of this plant, the effects of different NaCl concentrations on plant growth, as well as Na(+) accumulation and distribution at organ, tissue, and subcellular levels, were investigated. Optimal growth and an improved photosynthetic rate were observed with the plant treated with 200-400 mM NaCl. The Na(+) content in the shoots was considerably higher than that in the roots of S. europaea. The Na(+) in S. europaea cells may act as an effective osmotic adjuster to maintain cell turgor, promoting photosynthetic competence and plant growth. The results from the SEM-X-ray and TEM-X-ray microanalyses demonstrate that Na(+) was compartmentalized predominantly into the cell vacuoles of shoot endodermis tissues. Accordingly, the transcript amounts of SeNHX1, SeVHA-A, and SeVP1 increased significantly with increased NaCl concentration, suggesting their important roles in Na(+) sequestration into the vacuoles. Therefore, a multiple sodium compartmentalization mechanism is proposed to enhance further the salt tolerance of S. europaea.

Transformation of β-Lycopene Cyclase Genes from Salicornia europaea and Arabidopsis Conferred Salt Tolerance in Arabidopsis and Tobacco

Inhibition of lycopene cyclization decreased the salt tolerance of the euhalophyte Salicornia europaea L. We isolated a β-lycopene cyclase gene SeLCY from S. europaea and transformed it into Arabidopsis with stable expression. Transgenic Arabidopsis on post-germination exhibited enhanced tolerance to oxidative and salt stress. After 8 and 21 d recovery from 200 mM NaCl treatment, transgenic lines had a higher survival ratio than wild-type (WT) plants. Three-week-old transgenic plants treated with 200 mM NaCl showed better growth than the WT with higher photosystem activity and less H(2)O(2) accumulation. Determination of endogenous pigments of Arabidopsis treated with 200 mM NaCl for 0, 2 or 4 d demonstrated that the transgenic plants retained higher contents of carotenoids than the WT. Furthermore, to compare the difference between SeLCY and AtLCY from Arabidopsis, we used viral vector mediating ectopic expression of SeLCY and AtLCY in Nicotiana benthamiana. Although LCY genes transformation increased the salt tolerance in tobacco, there is no significant difference between SeLCY- and AtLCY-transformed plants. These findings indicate that SeLCY transgenic Arabidopsis improved salt tolerance by increasing synthesis of carotenoids, which impairs reactive oxygen species and protects the photosynthesis system under salt stress, and as a single gene, SeLCY functionally showed no advantage for salt tolerance improvement compared with AtLCY.

Coordination of carbon fixation and nitrogen metabolism in Salicornia europaea under salinity: Comparative proteomic analysis on chloroplast proteins

Halophyte, like Salicornia europaea, could make full use of marginal saline land for carbon fixation. How the photosynthesis of S. europaea is regulated under high salinity implicates a significant aspect to exploit this pioneer plant in future. Measurement of photosynthesis parameters demonstrated the reduction of photosynthesis for the 0 and 800 mM NaCl treated plants are more likely due to non‐stomatal limitation, which might be caused by changes in the enzymes associated with photosynthesis. Different salinity induced ultrastructure changes other than photosynthetic apparatus damage, suggesting the photosynthesis of S. europaea might be affected via biochemical regulation. Comparative proteomics analysis of chloroplast proteins by 2‐D gel electrophoresis reproducibly detected 90 differentially expressed proteins, among which 66 proteins were identified by nanoLC MS/MS. Further study of thylakoid membrane proteins by Blue‐Native PAGE proved the increase in abundance of light reaction proteins under salinity. Analysis of gene expression patterns of 12 selected proteins provides evidence for the correlations between transcription and proteomics data. Based on our results, a putative model of photosynthesis regulatory network figured out proper coordination of carbon fixation and nitrogen metabolism in chloroplast of S. europaea under salinity, which provided subcellular level insight into salt tolerance mechanism in S. europaea.

High-throughput deep sequencing reveals that microRNAs play important roles in salt tolerance of euhalophyte Salicornia europaea.

BackgroundmicroRNAs (miRNAs) are implicated in plant development processes and play pivotal roles in plant adaptation to environmental stresses. Salicornia europaea, a salt mash euhalophyte, is a suitable model plant to study salt adaptation mechanisms. S. europaea is also a vegetable, forage, and oilseed that can be used for saline land reclamation and biofuel precursor production on marginal lands. Despite its importance, no miRNA has been identified from S. europaea thus far.ResultsDeep sequencing was performed to investigate small RNA transcriptome of S. europaea. Two hundred and ten conserved miRNAs comprising 51 families and 31 novel miRNAs (including seven miRNA star sequences) belonging to 30 families were identified. About half (13 out of 31) of the novel miRNAs were only detected in salt-treated samples. The expression of 43 conserved and 13 novel miRNAs significantly changed in response to salinity. In addition, 53 conserved and 13 novel miRNAs were differentially expressed between the shoots and roots. Furthermore, 306 and 195 S. europaea unigenes were predicted to be targets of 41 conserved and 29 novel miRNA families, respectively. These targets encoded a wide range of proteins, and genes involved in transcription regulation constituted the largest category. Four of these genes encoding laccase, F-box family protein, SAC3/GANP family protein, and NADPH cytochrome P-450 reductase were validated using 5′-RACE.ConclusionsOur results indicate that specific miRNAs are tightly regulated by salinity in the shoots and/or roots of S. europaea, which may play important roles in salt tolerance of this euhalophyte. The S. europaea salt-responsive miRNAs and miRNAs that target transcription factors, nucleotide binding site-leucine-rich repeat proteins and enzymes involved in lignin biosynthesis as well as carbon and nitrogen metabolism may be applied in genetic engineering of crops with high stress tolerance, and genetic modification of biofuel crops with high biomass and regulatable lignin biosynthesis.

Virus‐induced gene silencing reveals control of reactive oxygen species accumulation and salt tolerance in tomato by γ‐aminobutyric acid metabolic pathway

γ-Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress. However, the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. Here, the genes, including glutamate decarboxylases (SlGADs), GABA transaminases (SlGABA-Ts) and succinic semialdehyde dehydrogenase (SlSSADH), controlling three steps of the metabolic pathway of GABA, were studied through virus-induced gene silencing approach in tomato. Silencing of SlGADs (GABA biosynthetic genes) and SlGABA-Ts (GABA catabolic genes) led to increased accumulation of reactive oxygen species (ROS) as well as salt sensitivity under 200 mm NaCl treatment. Targeted quantitative analysis of metabolites revealed that GABA decreased and increased in the SlGADs- and SlGABA-Ts-silenced plants, respectively, whereas succinate (the final product of GABA metabolism) decreased in both silenced plants. Contrarily, SlSSADH-silenced plants, also defective in GABA degradation process, showed dwarf phenotype, curled leaves and enhanced accumulation of ROS in normal conditions, suggesting the involvement of a bypath for succinic semialdehyde catabolism to γ-hydroxybutyrate as reported previously in Arabidopsis, were less sensitive to salt stress. These results suggest that GABA shunt is involved in salt tolerance of tomato, probably by affecting the homeostasis of metabolites such as succinate and γ-hydroxybutyrate and subsequent ROS accumulation under salt stress.

Sodium plays a more important role than potassium and chloride in growth of Salicornia europaea

Salicornia europaea is a succulent euhalophyte that belongs to the Chenopodiaceae family. It is found that moderate concentration of NaCl can dramatically stimulate the growth of S. europaea plants. To elucidate the mechanism underlying the phenomenon, morphological and physiological changes of S. europaea in response to different ions, including cations (Na+, K+, Li+, Cs+) and anions (Cl−, NO3−, CH3COO−) were investigated, and the effects of Na+, Cl− and K+ on the growth of S. europaea were also studied. Na+ was more effective than K+ and Cl− in stimulating shoot succulence, cell expansion, and stomatal opening. Plants treated with Na+ (including NaCl, Na+, NaNO3) showed better plant growth, increased photosynthesis and less cell membrane damage than those untreated and treated with 200 mM of Cl− and K+ (including KCl and KNO3). Both SEM-X-Ray microanalysis and flame emission results revealed that well developed S. europaea plants had a higher content of sodium but lower potassium and chlorine. It is concluded that sodium plays a more important role in the growth and development of S. europaea than potassium and chloride.

Chloroplast-targeted Hsp90 plays essential roles in plastid development and embryogenesis in Arabidopsis possibly linking with VIPP1

The Arabidopsis genome contains seven members of Hsp90. Mutations in plastid AtHsp90.5 were reported to cause defects in chloroplast development and embryogenesis. However, the exact function of plastid AtHsp90.5 has not yet been defined. In this study, albino seedlings were found among AtHsp90.5 transformed Arabidopsis, which were revealed to be AtHsp90.5 co-suppressed plants. The accumulation of photosynthetic super-complexes in the albinos was decreased, and expression of genes involved in photosynthesis was significantly down-regulated. AtHsp90.5 T-DNA insertion mutants were embryo-lethal with embryo arrested at the heart stage. Further investigation showed AtHsp90.5 expression was up-regulated in the siliques at 4 days post anthesis (DPA). Confocal microscopy proved AtHsp90.5 was located in the chloroplasts. Plastid development in the AtHsp90.5 mutants and co-suppressed plants was seriously impaired, and few thylakoid membranes were observed, indicating the involvement of AtHsp90.5 in chloroplast biogenesis. AtHsp90.5 was found to interact with vesicle-inducing protein in plastids 1 (VIPP1) by bimolecular fluorescence complementation system. The ratio between VIPP1 oligomers and monomers in AtHsp90.5 co-suppressed plants drastically shifted toward the oligomeric state. Our study confirmed that AtHsp90.5 is vital for chloroplast biogenesis and embryogenesis. Further evidence also suggested that AtHsp90.5 may help in the disassembly of VIPP1 for thylakoid membrane formation and/or maintenance.

Transcriptome analysis of Salicornia europaea under saline conditions revealed the adaptive primary metabolic pathways as early events to facilitate salt adaptation.

Background Halophytes such as Salicornia europaea have evolved to exhibit unique mechanisms controlled by complex networks and regulated by numerous genes and interactions to adapt to habitats with high salinity. However, these mechanisms remain unknown. Methods To investigate the mechanism by which halophytes tolerate salt based on changes in the whole transcriptome, we performed transcriptome sequencing and functional annotation by database search. Using the unigene database, we conducted digital gene expression analysis of S. europaea at various time points after these materials were treated with NaCl. We also quantified ion uptakes. Gene functional enrichment analysis was performed to determine the important pathways involved in this process. Results A total of 57,151 unigenes with lengths of >300 bp were assembled, in which 57.5% of these unigenes were functionally annotated. Differentially expressed genes indicated that cell wall metabolism and lignin biosynthetic pathways were significantly enriched in S. europaea to promote the development of the xylem under saline conditions. This result is consistent with the increase in sodium uptake as ions pass through the xylem. Given that PSII efficiency remained unaltered, salt treatment activated the expression of electron transfer-related genes encoded by the chloroplast chromosome. Chlorophyll biosynthesis was also inhibited, indicating the energy-efficient state of the electron transfer system of S. europaea. Conclusions The key function of adjusting important primary metabolic pathways in salt adaption was identified by analyzing the changes in the transcriptome of S. europaea. These pathways could involve unique salt tolerance mechanisms in halophytes. This study also provided information as the basis of future investigations on salt response genes in S. europaea. Ample gene resources were also provided to improve the genes responsible for the salt tolerance ability of crops.

Roles, Regulation, and Agricultural Application of Plant Phosphate Transporters

Phosphorus (P) is an essential mineral nutrient for plant growth and development. Low availability of inorganic phosphate (orthophosphate; Pi) in soil seriously restricts the crop production, while excessive fertilization has caused environmental pollution. Pi acquisition and homeostasis depend on transport processes controlled Pi transporters, which are grouped into five families so far: PHT1, PHT2, PHT3, PHT4, and PHT5. This review summarizes the current understanding on plant PHT families, including phylogenetic analysis, function, and regulation. The potential application of Pi transporters and the related regulatory factors for developing genetically modified crops with high phosphorus use efficiency (PUE) are also discussed in this review. At last, we provide some potential strategies for developing high PUE crops under salt or drought stress conditions, which can be valuable for improving crop yields challenged by global scarcity of water resources and increasing soil salinization.

Na+/H+ exchanger 1 participates in tobacco disease defence against Phytophthora parasitica var. nicotianae by affecting vacuolar pH and priming the antioxidative system

Summary NbNHX1 affects the cellular pH and oxidation state by regulating the vacuolar H+ flux, which primes the antioxidative system associated with Phytophthora parasitica var. nicotianae resistance in tobacco.