Dissecting the Molecular Regulation of Natural Variation in Growth and Senescence of Two Eutrema salsugineum Ecotypes.

Salt cress (Eutrema salsugineum, aka Thellungiella salsuginea) is an extremophile and a close relative of Arabidopsis thaliana. To understand the mechanism of selection of complex traits under natural variation, we analyzed the physiological and proteomic differences between Shandong (SD) and Xinjiang (XJ) ecotypes. The SD ecotype has dark green leaves, short and flat leaves, and more conspicuous taproots, and the XJ ecotype had greater biomass and showed clear signs of senescence or leaf shedding with age. After 2-DE separation and ESI-MS/MS identification, between 25 and 28 differentially expressed protein spots were identified in shoots and roots, respectively. The proteins identified in shoots are mainly involved in cellular metabolic processes, stress responses, responses to abiotic stimuli, and aging responses, while those identified in roots are mainly involved in small-molecule metabolic processes, oxidation-reduction processes, and responses to abiotic stimuli. Our data revealed the evolutionary differences at the protein level between these two ecotypes. Namely, in the evolution of salt tolerance, the SD ecotype highly expressed some stress-related proteins to structurally adapt to the high salt environment in the Yellow River Delta, whereas the XJ ecotype utilizes the specialized energy metabolism to support this evolution of the short-lived xerophytes in the Xinjiang region.

Plant Dehydrins: Expression, Regulatory Networks, and Protective Roles in Plants Challenged by Abiotic Stress.

Dehydrins, also known as Group II late embryogenesis abundant (LEA) proteins, are classic intrinsically disordered proteins, which have high hydrophilicity. A wide range of hostile environmental conditions including low temperature, drought, and high salinity stimulate dehydrin expression. Numerous studies have furnished evidence for the protective role played by dehydrins in plants exposed to abiotic stress. Furthermore, dehydrins play important roles in seed maturation and plant stress tolerance. Hence, dehydrins might also protect plasma membranes and proteins and stabilize DNA conformations. In the present review, we discuss the regulatory networks of dehydrin gene expression including the abscisic acid (ABA), mitogen-activated protein (MAP) kinase cascade, and Ca2+ signaling pathways. Crosstalk among these molecules and pathways may form a complex, diverse regulatory network, which may be implicated in regulating the same dehydrin.

Hyperuricemia is associated with impaired intestinal permeability in mice.

Hyperuricemia is associated with many metabolic diseases. However, the underlying mechanism remains unknown. The gut microbiota has been demonstrated to play significant roles in the immunity and metabolism of the host. In the present study, we constructed a hyperuricemic mouse model to investigate whether the metabolic disorder caused by hyperuricemia is related to intestinal dysbiosis. A significantly increased intestinal permeability was detected in hyperuricemic mice. The difference in microflora between wild-type and hyperuricemic mice accompanies the translocation of gut microbiota to the extraintestinal tissues. Such a process is followed by an increase in innate immune system activation. We observed increased LPS and TNF-α levels in the hyperuricemic mice, indicating that hyperuricemic mice were in a state of low-grade systemic inflammation. In addition, hyperuricemic mice presented early injury of parenteral tissue and disordered lipid metabolism. These findings suggest that intestinal dysbiosis due to an impaired intestinal barrier may be the key cause of metabolic disorders in hyperuricemic mice. Our findings should aid in paving a new way of preventing and treating hyperuricemia and its complications.NEW & NOTEWORTHY Hyperuricemia is associated with many metabolic diseases. However, the underlying mechanism remains unknown. We constructed a hyperuricemic mouse model to explore the relationship between intestinal dysbiosis and metabolic disorder caused by hyperuricemia.

Transcriptomic profiling revealed an important role of cell wall remodeling and ethylene signaling pathway during salt acclimation in Arabidopsis.

Plants can successfully improve their resistance to previously lethal salinity stress by a short exposure to low levels of salt stress, a process known as salt acclimation (SA). In spite of its fundamental significance in theoretical study and agricultural practice, the molecular mechanisms underlying plant SA remain elusive. In this study, we found that salt acclimated Arabidopsis young seedlings can survive subsequent 200 mM NaCl stress. RNA-seq was performed to analyze the genome-wide transcriptional response under SA conditions. Among 518 differentially expressed genes (DEGs) under SA, 366 up-regulated genes were enriched for cell wall biosynthesis, osmoregulation, oxidative stress, or transcription factors. Seven DEGs participate in the synthesis of lignin and 24 DEGs encode plant cell wall proteins, suggesting the importance of cell wall remodeling under SA. Furthermore, in comparison to non-acclimated salt stress, 228 of 245 DEGs were repressed by acclimated salt stress, including many genes related to ethylene biosynthesis and signaling pathway. In addition, MAPK6, a major component of the ethylene signaling pathway, was found to play a crucial role in SA. Our transcriptomic analysis has provided important insight on the roles of transcription factors, cell wall remodeling, and the ethylene biosynthesis and signaling pathways during SA in Arabidopsis.

Light induced shoot-sourced transcription factor HY5 regulates the nitrate uptake of cotton by shoot-to-root signal transport.

Elongated hypocotyls 5 (HY5) is a transcription factor that can be induced by illumination and promotes nitrate uptake in Arabidopsis. However, whether GhHY5 regulates nitrate uptake in cotton is unknown. In this study, the cotton seedlings growing in light and dark conditions were treated with 15N-labeled nutrient solution to study whether the GhHY5 regulates nitrate uptake in cotton. The results showed that the 15N content and GhNRT1.1 expression in the light condition were higher than that in the dark condition, indicating that light induced the expression of GhNRT1.1 and subsequently promoted N uptake. Additionally, the expression of GhHY5 in the leaf and root of cotton was induced by light and the expression pattern of GhHY5 in the root was similar to that of GhNRT1.1. Furthermore, when the GhHY5 expression in the root was reduced, the 15N content and GhNRT1.1 expression were both decreased, indicating that the GhNRT1.1 expression was regulated by GhHY5. The root expression of GhHY5 was decreased in the grafted seedlings which the GhHY5 in the shoot was silenced by VIGS or the seedlings which the hypocotyl was girdled, but the expression of GhHY5 on one side root of the grafted cotton seedling was not changed if the GhHY5 was silenced on the other side root. Thus, we proposed that the light induced shoot-derived GhHY5 gene or GhHY5 protein may be transported from the xylem to the root, regulating the expression of GhHY5 and GhNRT1.1, and thus regulating N uptake at the root of cotton.

Transcriptomic Profiling Provides Molecular Insights Into Hydrogen Peroxide-Enhanced Arabidopsis Growth and Its Salt Tolerance.

Salt stress is an important environmental factor limiting plant growth and crop production. Plant adaptation to salt stress can be improved by chemical pretreatment. This study aims to identify whether hydrogen peroxide (H2O2) pretreatment of seedlings affects the stress tolerance of Arabidopsis thaliana seedlings. The results show that pretreatment with H2O2 at appropriate concentrations enhances the salt tolerance ability of Arabidopsis seedlings, as revealed by lower Na+ levels, greater K+ levels, and improved K+/Na+ ratios in leaves. Furthermore, H2O2 pretreatment improves the membrane properties by reducing the relative membrane permeability (RMP) and malonaldehyde (MDA) content in addition to improving the activities of antioxidant enzymes, including superoxide dismutase, and glutathione peroxidase. Our transcription data show that exogenous H2O2 pretreatment leads to the induced expression of cell cycle, redox regulation, and cell wall organization-related genes in Arabidopsis, which may accelerate cell proliferation, enhance tolerance to osmotic stress, maintain the redox balance, and remodel the cell walls of plants in subsequent high-salt environments.

Natural variation in stress response induced by low CO2 in Arabidopsis thaliana.

Variation in atmospheric carbon dioxide (CO2) concentration can dictate plant growth and development and shape plant evolution. For paired populations of 31 Arabidopsis accessions, respectively, grown under 100 or 380 ppm CO2, we compared phenotypic traits related to vegetative growth and flowering time. Four accessions showed the least variation in measured growth traits between 100 ppm CO2 and 380 ppm CO2 conditions, though all accessions exhibited a dwarf stature with reduced biomass under low CO2. Our comparison of accessions also incorporated the altitude (indicated in meters) above sea level at which they were originally collected. Notably, An-1 (50 m), Est (50 m), Ws-0 (150 m), and Ler-0 (600 m) showed the least differences (lower decrease or increase) between treatments in flowering time, rosette leaf number, specific leaf weight, stomatal density, and less negative δ13C values. When variations for all traits and seedset were considered together, Ws-0 exhibited the least change between treatments. Our results showed that physiological and phenotypic responses to low CO2 varied among these accessions and did not correlate linearly with altitude, thus suggesting that slower growth or smaller stature under ambient CO2 may potentially belie a fitness advantage for sustainable growth under low CO2 availability.

The altered gut microbiota of high-purine-induced hyperuricemia rats and its correlation with hyperuricemia.

Some studies on the hyperuricemia (HUA) have focused on intestinal bacteria. To better understand the correlation between gut microbiota and HUA, we established a HUA rat model with high-purine diet, and used 16S rRNA genes sequencing to analyze gut microbiota changes in HUA rats. To analyze the potential role played by gut microbiota in HUA, we altered the gut microbiota of HUA rats with antibiotics, and compared the degree of uric acid elevation between HUA and antibiotic-fed HUA rats (Ab+HUA). Finally, we established a recipient rat model, in which we transplanted fecal microbiota of HUA and normal rats into recipient rats. Three weeks later, we compared the uric acid content of recipient rats. As a result, the diversity and abundance of the gut microbiota had changed in HUA rats. The Ab-fed HUA rats had significantly lower uric acid content compared to the HUA rats, and gut microbiota from HUA rats increased uric acid content of recipient rats. The genera Vallitalea, Christensenella and Insolitispirillum may associate with HUA. Our findings highlight the association between gut microbiota and HUA, and the potential role played by gut microbiota in HUA. We hope that this finding will promote the isolation and culture of HUA-related bacteria and orient HUA-related studies from being correlational to mechanistic. These steps will therefore make it possible for us to treat HUA using gut microbiota as the target.

Overexpression of TsGOLS2, a galactinol synthase, in Arabidopsis thaliana enhances tolerance to high salinity and osmotic stresses.

Galactinol synthase (GOLS, EC 2.4.1.123), a key enzyme in the synthesis of raffinose family oligosaccharides (RFOs), catalyzes the condensation of UDP-galactose with myo-inositol to produce galactinol as the sole donor for the synthesis of RFOs. RFOs have been implicated in mitigating effects of environmental stresses on plants. TsGOLS2, was cloned from Thellungiella salsuginea with high homology to AtGOLS2. TsGOLS2 was up-regulated by several abiotic stresses. We overexpressed TsGOLS2 in Arabidopsis thaliana. The contents of galactinol, raffinose, and α-ketoglutaric acid were significantly increased in transgenic plants. Compared to wild type plants, salt-stressed transgenic A. thaliana exhibited higher germination rate, photosynthesis ability, and seedling growth. After being treated with osmotic stress by high concentration of sorbitol, transgenic plants retained high germination rates and grew well during early development. These results indicated that overexpression of TsGOLS2 in A. thaliana improved the tolerance of transgenic plants to high salinity and osmotic stress.

A simple and effective method for detecting phosphopeptides for phosphoproteomic analysis.

An immuno-dot blot method for detecting phosphopeptides is described. This method allows detection of phosphopeptides prior to analysis by mass spectrometry, and does not require specialized equipment. Further, this method allows peptides containing a given phosphoamino acid to be selectively detected by using phosphoamino acid-specific antibody. This phosphopeptide assay should be useful for researchers who do not have direct access to the mass spectrometers to prepare high quality samples by optimizing phosphopeptide enrichment procedures prior to mass spectrometry analysis.

Analysis of the physiological mechanism of salt-tolerant transgenic rice carrying a vacuolar Na+/H + antiporter gene from Suaeda salsa.

Salt stress is one of the most serious factors limiting the productivity of agricultural crops. Increasing evidence has demonstrated that vacuolar Na+/H+ antiporters play a crucial role in plant salt tolerance. In the present study, we expressed the Suaeda salsa vacuolar Na+/H+ antiporter SsNHX1 in transgenic rice to investigate whether this can increase the salt tolerance of rice, and to study how overexpression of this gene affected other salt-tolerant mechanisms. It was found that transgenic rice plants showed markedly enhanced tolerance to salt stress and to water deprivation compared with non-transgenic controls upon salt stress imposition under outdoor conditions. Measurements of ion levels indicated that K+, Ca2+ and Mg2+ contents were all higher in transgenic plants than in non-transformed controls. Furthermore, shoot V-ATPase hydrolytic activity was dramatically increased in transgenics compared to that of non-transformed controls under salt stress conditions. Physiological analysis also showed that the photosynthetic activity of the transformed plants was higher whereas the same plants had reduced reactive oxygen species generation. In addition, the soluble sugar content increased in the transgenics compared with that in non-transgenics. These results imply that up-regulation of a vacuolar Na+/H+ antiporter gene in transgenic rice might cause pleiotropic up-regulation of other salt-resistance-related mechanisms to improve salt tolerance.

Salt cress. A halophyte and cryophyte Arabidopsis relative model system and its applicability to molecular genetic analyses of growth and development of extremophiles.

Salt cress (Thellungiella halophila) is a small winter annual crucifer with a short life cycle. It has a small genome (about 2 x Arabidopsis) with high sequence identity (average 92%) with Arabidopsis, and can be genetically transformed by the simple floral dip procedure. It is capable of copious seed production. Salt cress is an extremophile native to harsh environments and can reproduce after exposure to extreme salinity (500 mm NaCl) or cold to -15 degrees C. It is a typical halophyte that accumulates NaCl at controlled rates and also dramatic levels of Pro (>150 mm) during exposure to high salinity. Stomata of salt cress are distributed on the leaf surface at higher density, but are less open than the stomata of Arabidopsis and respond to salt stress by closing more tightly. Leaves of salt cress are more succulent-like, have a second layer of palisade mesophyll cells, and are frequently shed during extreme salt stress. Roots of salt cress develop both an extra endodermis and cortex cell layer compared to Arabidopsis. Salt cress, although salt and cold tolerant, is not exceptionally tolerant of soil desiccation. We have isolated several ethyl methanesulfonate mutants of salt cress that have reduced salinity tolerance, which provide evidence that salt tolerance in this halophyte can be significantly affected by individual genetic loci. Analysis of salt cress expressed sequence tags provides evidence for the presence of paralogs, missing in the Arabidopsis genome, and for genes with abiotic stress-relevant functions. Hybridizations of salt cress RNA targets to an Arabidopsis whole-genome oligonucleotide array indicate that commonly stress-associated transcripts are expressed at a noticeably higher level in unstressed salt cress plants and are induced rapidly under stress. Efficient transformation of salt cress allows for simple gene exchange between Arabidopsis and salt cress. In addition, the generation of T-DNA-tagged mutant collections of salt cress, already in progress, will open the door to a new era of forward and reverse genetic studies of extremophile plant biology.