Productivity–species richness relationship changes from unimodal to positive linear with increasing spatial scale in the Inner Mongolia steppe

Productivity–species diversity relationships have been a controversial research topic in ecology with scale believed to be among the main reasons for discovering different relationships. We collected data on species diversity (richness) and productivity (peak above-ground biomass) of the Stipa breviflora association in the Inner Mongolia grassland to examine spatial scale dependency and possible underlying mechanisms responsible for the relationships found. One local and seven different landscape scales (the first level corresponds in extent to a 100 × 100 km area, which is increased consecutively by 100 km resulting in the 700 × 700 km area at the highest level) were considered. We found that: (1) unimodal relationships dominated the local scale, but this varied depending on the position along successional gradients; (2) a positive linear relationship was common at larger spatial scales; (3) biotic processes were the most likely primary factor underlying local scale unimodal relationships, but environmental heterogeneity (precipitation patterns) was the main determinant of relationships found at larger spatial scales; (4) our study contributed to other empirical evidence and predictions of theoretical models regarding scale dependency of productivity–species richness relationships; (5) while earlier research demonstrated positive linear species richness–productivity relationships across a number of ecological scales in the Inner Mongolia steppe, our study specifically tested a spectrum of geographical scales to confirm the scale-dependency of this relationship. Lastly, our study emphasized the critical role played by precipitation patterns in controlling biodiversity and grassland ecosystem functioning, which maintains the relatively high level of biodiversity and stable ecosystem processes.     

Synthesis and evaluation of new iRGD peptide analogs for tumor optical imaging

Recently, a disulfide-based cyclic RGD peptide called iRGD, that is, c(CRGDKGPDC), has been reported to interact with both integrin and neuropilin-1 receptors for cellular and deep tissue penetration to improve the imaging sensitivity and therapeutic efficacy. In this study, two new near-infrared fluorescent iRGD conjugates, that is, Ac-Cys(IRDye®800CW)-iRGD (1), and its dual labeling analog DOTA-Cys(IRDye®800CW)-iRGD (2) were synthesized via the specific mercapto-maleimide reaction for tumor imaging. Both 1 and 2 showed significant tumor localization in optical imaging of MDA-MB-435 tumor-bearing mice. The potential of such iRGD compounds in tumor-targeted imaging and drug delivery deserves further exploration.     

Discovery of novel mGluR1 antagonists: a multistep virtual screening approach based on an SVM model and a pharmacophore hypothesis significantly increases the hit rate and enrichment factor

Development of glutamate non-competitive antagonists of mGluR1 (Metabotropic glutamate receptor subtype 1) has increasingly attracted much attention in recent years due to their potential therapeutic application for various nervous disorders. Since there is no crystal structure reported for mGluR1, ligand-based virtual screening (VS) methods, typically pharmacophore-based VS (PB-VS), are often used for the discovery of mGluR1 antagonists. Nevertheless, PB-VS usually suffers a lower hit rate and enrichment factor. In this investigation, we established a multistep ligand-based VS approach that is based on a support vector machine (SVM) classification model and a pharmacophore model. Performance evaluation of these methods in virtual screening against a large independent test set, M-MDDR, show that the multistep VS approach significantly increases the hit rate and enrichment factor compared with the individual SB-VS and PB-VS methods. The multistep VS approach was then used to screen several large chemical libraries including PubChem, Specs, and Enamine. Finally a total of 20 compounds were selected from the top ranking compounds, and shifted to the subsequent in vitro and in vivo studies, which results will be reported in the near future.     

Structural basis of γH2AX recognition by human PTIP BRCT5-BRCT6 domains in the DNA damage response pathway

Human Pax2 transactivation domain-interacting protein (hPTIP), containing six BRCT domains, is an essential protein required for the IR induced DDR process with an unclear role. Here we report that the tandem BRCT5–BRCT6 domain of hPTIP recognizes the γH2AX tail, and this interaction depends on the phosphorylation of H2AX Ser139 and binding with the carboxyl ending peptide to the aminoacyl ending peptide. The 2.15 Å crystal structure of hPTIP BRCT5/6–γH2AX complex and mutation analysis provide molecular evidence for direct interactions between PTIP and γH2AX. This interaction proffers a new clue to identify the role of PTIP in DDR pathways.

Structured summary of protein interactions

PTIP and gamma H2AXbind by fluorescence polarization spectroscopy (View Interaction: 1, 2, 3, 4, 5, 6).PTIP and gamma H2AXbind by X-ray crystallography (View interaction).     

Targeted introgression of a wheat stem rust resistance gene by DNA marker-assisted chromosome engineering

Chromosome engineering is a useful strategy for transfer of alien genes from wild relatives into modern crops. However, this strategy has not been extensively used for alien gene introgression in most crops due to low efficiency of conventional cytogenetic techniques. Here, we report an improved scheme of chromosome engineering for efficient elimination of a large amount of goatgrass (Aegilops speltoides) chromatin surrounding Sr39, a gene that provides resistance to multiple stem rust races, including Ug99 (TTKSK) in wheat. The wheat ph1b mutation, which promotes meiotic pairing between homoeologous chromosomes, was employed to induce recombination between wheat chromosome 2B and goatgrass 2S chromatin using a backcross scheme favorable for inducing and detecting the homoeologous recombinants with small goatgrass chromosome segments. Forty recombinants with Sr39 with reduced surrounding goatgrass chromatin were quickly identified from 1048 backcross progenies through disease screening and molecular marker analysis. Four of the recombinants carrying Sr39 with a minimal amount of goatgrass chromatin (2.87-9.15% of the translocated chromosomes) were verified using genomic in situ hybridization. Approximately 97% of the goatgrass chromatin was eliminated in one of the recombinants, in which a tiny goatgrass chromosome segment containing Sr39 was retained in the wheat genome. Localization of the goatgrass chromatin in the recombinants led to rapid development of three molecular markers tightly linked to Sr39. The new wheat lines and markers provide useful resources for the ongoing global effort to combat Ug99. This study has demonstrated great potential of chromosome engineering in genome manipulation for plant improvement.     

IFN-γ acts on the airway epithelium to inhibit local and systemic pathology in allergic airway disease

Inhibiting allergic airway inflammation is the goal of therapy in persistent asthma. Administration of medication via the airways delivers drug directly to the site of inflammation and avoids systemic side effects but often fails to modulate systemic features of asthma. We have shown that Th1 cells, through production of IFN-γ, inhibit many Th2-induced effector functions that promote disease. Using a newly generated mouse that expresses IFN-γR only on airway epithelial cells, we show that the airway epithelium controls a range of pathological responses in asthma. IFN-γ acting only through the airway epithelium inhibits mucus, chitinases, and eosinophilia, independent of Th2 cell activation. IFN-γ signaling through the airway epithelium inhibits eosinophil generation in the bone marrow, indicating that signals on the airway mucosal surface can regulate distant functions to inhibit disease. IFN-γ actions through the airway epithelium will limit airway obstruction and inflammation and may be therapeutic in refractory asthma.     

PSI-driven cyclic electron flow allows intertidal macro-algae Ulva sp. (Chlorophyta) to survive in desiccated conditions

Ulva sp. (Chlorophyta) is a representative species of the intertidal macro-algae responsible for the green tides that occurred along the shores of Qingdao in 2008 and had detrimental effects on the preparation for the 2008 Beijing Olympic Games sailing competition. In view of its significance, we have investigated the photosynthetic performance of the photosystems and the changes in photosynthetic electron transport that occur during desiccation and rehydration of Ulva sp. The PSII activity in Ulva sp. declined gradually during the course of desiccation, which was reflected by the decreased maximum quantum yield and effective quantum yield, whereas the PSI activity fluctuated significantly. In contrast, the electron transport rates of PSII approached zero at severe levels of desiccation, but the electron transport of PSI, which still operated, could be suppressed effectively by a specific inhibitor. Furthermore, the electron transport of PSI during rehydration of desiccated thalli was recovered faster than that of PSII. All these results implied that the linear electron flow was abolished in desiccated Ulva sp., whereas the cyclic PSI activity was significantly elevated, was still active at severe levels of desiccation and could be restored faster than PSII activity. Based on these results, we concluded the PSI-driven cyclic electron flow might provide desiccation tolerance and additional flexibility for the cell physiology of Ulva sp. under desiccation conditions, which might be one of the most important factors that make Ulva sp. well suited to experience daily cycles of desiccation at low tide and rehydration at high tide.     

Resource availability, species composition and sown density effects on productivity of experimental plant communities

Productivity of artificial grassland communities was investigated in a 6-year field experiment on the Qinghai-Tibetan Plateau. In the experiment, assemblages varying in seven species compositions and four density gradients were grown in fertilized and non-fertilized subplots. We measured biomass of sown species as an indicator of community productivity. In general, 6-years of experiments indicated that: (i) species composition had a significant influence on community productivity. During the initial phase of the experiment, sown density significantly affected community productivity, but the effects disappear with the increase of grown years. This productivity increased with biodiversity increase and fertilization, while the biodiversity effects disappeared when the influence of composition was removed. (ii) The increase of community productivity with biodiversity was resulted from joint effects of selection and complementarity. (iii) With an increase of growth time, the selection effects become weaker while complementarities become enhanced. Influence of density on both effects was significantly different in early stages, but ultimately this all became insignificant. Fertilization dramatically increased the complementarity effects in all experiment processes, but had different influences on selection effects during different experimental period.     

Scalable High-Permittivity Polyimide Copolymer with Ultrahigh High-Temperature Capacitive Performance Enabled by Molecular Engineering

Polymer capacitors are essential components of advanced electronic and power systems. However, the deficient high-temperature capacitive performance of polymer dielectrics fails to meet the demand for harsh condition applications, due to the mutually restrictive relationships in permittivity (ε_r), glass transition temperature (T_g), and bandgap (E_g). Here, a modularized molecular engineering strategy is reported to enhance the high-temperature capacitive performance of polymer dielectrics. First, the potential influences of multiple structural units on ε_r, T_g, and E_g of polymers are elucidated by comparing a set of polyimides (PIs). After screening out an excellent sulfonated PI with concurrently high ε_r (4.2), E_g (3.4 eV), and T_g (311.2 °C), a semi-alicyclic sulfonyl-containing PI copolymer is further synthesized that exhibits a superior discharged energy density of 4.3 J cm⁻³ above 90% efficiency at 200 °C and 485 MV m⁻¹. Density functional theory calculations demonstrate that the combination of polar sulfonyl group, ether linkage, and alicyclic group in the backbones of the copolymer decouples the dipole orientation and the segmental motion of backbones, and reduces conjugation effects of aromatic groups, thereby minimizing the polarization relaxation loss and the conduction loss while retaining excellent thermal stability and high permittivity.