Cell size and xylem differentiation regulating genes from Salicornia europaea contribute to plant salt tolerance.

Cell wall is involved in plant growth and plays pivotal roles in plant adaptation to environmental stresses. Cell wall remodelling may be crucial to salt adaptation in the euhalophyte Salicornia europaea. However, the mechanism underlying this process is still unclear. Here, full-length transcriptome indicated cell wall-related genes were comprehensively regulated under salinity. The morphology and cell wall components in S. europaea shoot were largely modified under salinity. Through the weighted gene co-expression network analysis, SeXTH2 encoding xyloglucan endotransglucosylase/hydrolases, and two SeLACs encoding laccases were focused. Meanwhile, SeEXPB was focused according to expansin activity and the expression profiling. Function analysis in Arabidopsis validated the functions of these genes in enhancing salt tolerance. SeXTH2 and SeEXPB overexpression led to larger cells and leaves with hemicellulose and pectin content alteration. SeLAC1 and SeLAC2 overexpression led to more xylem vessels, increased secondary cell wall thickness and lignin content. Notably, SeXTH2 transgenic rice exhibited enhanced salt tolerance and higher grain yield. Altogether, these genes may function in the succulence and lignification process in S. europaea. This work throws light on the regulatory mechanism of cell wall remodelling in S. europaea under salinity and provides potential strategies for improving crop salt tolerance and yields.

PHT1;5 Repressed by ANT Mediates Pi Acquisition and Distribution under Low Pi and Salinity in Salt Cress.

Salinity and phosphate (Pi) starvation are the most common abiotic stresses that threaten crop productivity. Salt cress (Eutrema salsugineum) displays good tolerance to both salinity and Pi limitation. Previously, we found several Phosphate Transporter (PHT) genes in salt cress upregulated under salinity. Here, EsPHT1;5 induced by both low Pi (LP) and salinity was further characterized. Overexpression of EsPHT1;5 in salt cress enhanced plant tolerance to LP and salinity, while the knock-down lines exhibited growth retardation. The analysis of phosphorus (P) content and shoot/root ratio of total P in EsPHT1;5-overexpressing salt cress seedlings and the knock-down lines as well as arsenate uptake assays suggested the role of EsPHT1;5 in Pi acquisition and root-shoot translocation under Pi limitation. In addition, overexpression of EsPHT1;5 driven by the native promoter in salt cress enhanced Pi mobilization from rosettes to siliques upon a long-term salt treatment. Particularly, the promoter of EsPHT1;5 outperformed that of AtPHT1;5 in driving gene expression under salinity. We further identified a transcription factor EsANT, which negatively regulated EsPHT1;5 expression and plant tolerance to LP and salinity. Taken together, EsPHT1;5 plays an integral role in Pi acquisition and distribution in plant response to LP and salt stress. Further, EsANT may be involved in the cross-talk between Pi starvation and salinity signaling pathways. This work provides further insight into the mechanism underlying high P use efficiency in salt cress in its natural habitat, and evidence for a link between Pi and salt signaling.

Comparative analysis of sRNAs, degradome and transcriptomics in sweet sorghum reveals the regulatory roles of miRNAs in Cd accumulation and tolerance.

MAIN CONCLUSION: Key miRNAs including sbi-miR169p/q, sbi-miR171g/j, sbi-miR172a/c/d, sbi-miR172e, sbi-miR319a/b, sbi-miR396a/b, miR408, sbi-miR5384, sbi-miR5565e and nov_23 were identified to function in the regulation of Cd accumulation and tolerance. As an energy plant, sweet sorghum shows great potential in the phytoremediation of Cd-contaminated soils. However, few studies have focused on the regulatory roles of miRNAs and their targets under Cd stress. In this study, comparative analysis of sRNAs, degradome and transcriptomics was conducted in high-Cd accumulation (H18) and low-Cd accumulation (L69) genotypes of sweet sorghum. A total of 38 conserved and 23 novel miRNAs with differential expressions were identified under Cd stress or between H18 and L69, and 114 target genes of 41 miRNAs were validated. Furthermore, 25 miRNA-mRNA pairs exhibited negatively correlated expression profiles and sbi-miR172e together with its target might participate in the distinct Cd tolerance between H18 and L69 as well as sbi-miR172a/c/d. Additionally, two groups of them: miR169p/q-nov_23 and miR408 were focused through the co-expression analysis, which might be involved in Cd uptake and tolerance by regulating their targets associated with transmembrane transportation, cytoskeleton activity, cell wall construction and ROS (reactive oxygen species) homeostasis. Further experiments exhibited that cell wall components of H18 and L69 were different when exposed to cadmium, which might be regulated by miR169p/q, miR171g/j, miR319a/b, miR396a/b, miR5384 and miR5565e through their targets. Through this study, we aim to reveal the potential miRNAs involved in sweet sorghum in response to Cd stress and provide references for developing high-Cd accumulation or high Cd-resistant germplasm of sweet sorghum that can be used in phytoremediation.

Variation of PHT families adapts salt cress to phosphate limitation under salinity.

Salt cress (Eutrema salsugineum) presents relatively high phosphate (Pi) use efficiency cy in its natural habitat. Phosphate Transporters (PHTs) play critical roles in Pi acquisition and homeostasis. Here, a comparative study of PHT families between salt cress and Arabidopsis was performed. A total of 27 putative PHT genes were identified in E. salsugineum genome. Notably, seven tandem genes encoding PHT1;3 were found, and function analysis in Arabidopsis indicated at least six EsPHT1;3s participated in Pi uptake. Meanwhile, different expression profiles of PHT genes between the two species under Pi limitation and salt stress were documented. Most PHT1 genes were down-regulated in Arabidopsis while up-regulated in salt cress under salinity, among which EsPHT1;9 was further characterized. EsPHT1;9 was involved in root-to-shoot Pi translocation. Particularly, the promoter of EsPHT1;9 outperformed that of AtPHT1;9 in promoting Pi translocation, K+ /Na+ ratio, thereby salt tolerance. Through cis-element analysis, we identified a bZIP transcription factor EsABF5 negatively regulating EsPHT1;9 and plant tolerance to low-Pi and salt stress. Altogether, more copies and divergent transcriptional regulation of PHT genes contribute to salt cress adaptation to the co-occurrence of salinity and Pi limitation, which add our knowledge on the evolutionary and molecular component of multistress- tolerance of this species.

Phosphatidylserine Synthase from Salicornia europaea Is Involved in Plant Salt Tolerance by Regulating Plasma Membrane Stability.

Salinity-induced lipid alterations have been reported in many plant species; however, how lipid biosynthesis and metabolism are regulated and how lipids work in plant salt tolerance are much less studied. Here, a constitutively much higher phosphatidylserine (PS) content in the plasma membrane (PM) was found in the euhalophyte Salicornia europaea than in Arabidopsis. A gene encoding PS synthase (PSS) was subsequently isolated from S. europaea, named SePSS, which was induced by salinity. Multiple alignments and phylogenetic analysis suggested that SePSS belongs to a base exchange-type PSS, which localises to the endoplasmic reticulum. Knockdown of SePSS in S. europaea suspension cells resulted in reduced PS content, decreased cell survival rate, and increased PM depolarization and K+ efflux under 400 or 800 mM NaCl. By contrast, the upregulation of SePSS leads to increased PS and phosphatidylethanolamine levels and enhanced salt tolerance in Arabidopsis, along with a lower accumulation of reactive oxygen species, less membrane injury, less PM depolarization and higher K+/Na+ in the transgenic lines than in wild-type (WT). These results suggest a positive correlation between PS levels and plant salt tolerance, and that SePSS participates in plant salt tolerance by regulating PS levels, hence PM potential and permeability, which help maintain ion homeostasis. Our work provides a potential strategy for improving plant growth under multiple stresses.

Identification for the capability of Cd-tolerance, accumulation and translocation of 96 sorghum genotypes.

Cadmium (Cd) pollution is a worldwide environmental problem which heavily threatens human health and food security. Sorghum, as one of the most promising energy crop, has been considered to be the source of high-quality feedstock for ethanol fuel. Ninety-six sorghum genotypes were investigated under hydroponic conditions to compare their capabilities of Cd-tolerance, accumulation and translocation for their potential in remediation of Cd contamination. Different genotypes varied largely in the tolerance to Cd stress with tolerance indexes ranked from 0.107 to 0.933. Great difference was also found in Cd uptake and accumulation with concentrations ranging from 19.0 to 202.4mg/kg in shoots and 277.0-898.3mg/kg in roots. The total amounts of Cd ranked from 6.1 to 25.8µg per plant and the highest translocation factor was over 4 times higher than the lowest one. The correlation analysis demonstrated that Cd concentration in shoot reflected the ability of Cd translocation and tolerance of sorghum, and the path coefficient analysis indicated that root biomass could be taken as a biomarker to evaluate Cd extraction ability of sorghum. The results in this study can facilitate the restoring of Cd contaminated areas by sorghum.

The V-ATPase subunit A is essential for salt tolerance through participating in vacuolar Na+ compartmentalization in Salicornia europaea.

MAIN CONCLUSION: The V-ATPase subunit A participates in vacuolar Na + compartmentalization in Salicornia europaea regulating V-ATPase and V-PPase activities. Na+ sequestration into the vacuole is an efficient strategy in response to salinity in many halophytes. However, it is not yet fully understood how this process is achieved. Particularly, the role of vacuolar H+-ATPase (V-ATPase) in this process is controversial. Our previous proteomic investigation in the euhalophyte Salicornia europaea L. found a significant increase of the abundance of V-ATPase subunit A under salinity. Here, the gene encoding this subunit named SeVHA-A was characterized, and its role in salt tolerance was demonstrated by RNAi directed downregulation in suspension-cultured cells of S. europaea. The transcripts of genes encoding vacuolar H+-PPase (V-PPase) and vacuolar Na+/H+ antiporter (SeNHX1) also decreased significantly in the RNAi cells. Knockdown of SeVHA-A resulted in a reduction in both V-ATPase and vacuolar H+-PPase (V-PPase) activities. Accordingly, the SeVHA-A-RNAi cells showed increased vacuolar pH and decreased cell viability under different NaCl concentrations. Further Na+ staining showed the reduced vacuolar Na+ sequestration in RNAi cells. Taken together, our results evidenced that SeVHA-A participates in vacuolar Na+ sequestration regulating V-ATPase and V-PPase activities and thereby vacuolar pH in S. europaea. The possible mechanisms underlying the reduction of vacuolar V-PPase activity in SeVHA-A-RNAi cells were also discussed.

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.

H(+)-pyrophosphatase from Salicornia europaea enhances tolerance to low phosphate under salinity in Arabidopsis.

Increasing soil salinity threatens crop productivity worldwide. High soil salinity is usually accompanied by the low availability of many mineral nutrients. Here, we investigated the potential role that the H(+)- PPase could play in optimizing P use efficiency under salinity in plants. Transgenic Arabidopsis plants overexpressing either SeVP1 or SeVP2 from Salicornia europaea outperformed the wild-types under low phosphate (Pi) as well as low Pi plus salt conditions. Our results suggested that H(+)-PPase could increase external Pi acquisition through promoting root development and upregulating phosphate transporters, thus to protect plants from Pi limiting stress. This study provides a potential strategy for improving crop yields challenged by the co-occurrence of abiotic stresses.

H(+) -pyrophosphatase from Salicornia europaea confers tolerance to simultaneously occurring salt stress and nitrogen deficiency in Arabidopsis and wheat.

High salinity and nitrogen (N) deficiency in soil are two key factors limiting crop productivity, and they usually occur simultaneously. Here we firstly found that H(+) -PPase is involved in salt-stimulated NO3 (-) uptake in the euhalophyte Salicornia europaea. Then, two genes (named SeVP1 and SeVP2) encoding H(+) -PPase from S. europaea were characterized. The expression of SeVP1 and SeVP2 was induced by salt stress and N starvation. Both SeVP1 or SeVP2 transgenic Arabidopsis and wheat plants outperformed the wild types (WTs) when high salt and low N occur simultaneously. The transgenic Arabidopsis plants maintained higher K(+) /Na(+) ratio in leaves and exhibited increased NO3 (-) uptake, inorganic pyrophosphate-dependent vacuolar nitrate efflux and assimilation capacity under this double stresses. Furthermore, they had more soluble sugars in shoots and roots and less starch accumulation in shoots than WT. These performances can be explained by the up-regulated expression of ion, nitrate and sugar transporter genes in transgenic plants. Taken together, our results suggest that up-regulation of H(+) -PPase favours the transport of photosynthates to root, which could promote root growth and integrate N and carbon metabolism in plant. This work provides potential strategies for improving crop yields challenged by increasing soil salinization and shrinking farmland.