Overexpression of the glutamine synthetase gene modulates oxidative stress response in rice after exposure to cadmium stress

Key message

Overexpression of OsGS gene modulates oxidative stress response in rice after exposure to cadmium stress. Our results describe the features of transformants with enhanced tolerance to Cd and abiotic stresses.

Abstract

Glutamine synthetase (GS) (EC 6.3.1.2) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine. Exposure of plants to cadmium (Cd) has been reported to decrease GS activity in maize, pea, bean, and rice. To better understand the function of the GS gene under Cd stress in rice, we constructed a recombinant pART vector carrying the GS gene under the control of the CaMV 35S promoter and OCS terminator and transformed using Agrobacterium tumefaciens. We then investigated GS overexpressing rice lines at the physiological and molecular levels under Cd toxicity and abiotic stress conditions. We observed a decrease in GS enzyme activity and mRNA expression among transgenic and wild-type plants subjected to Cd stress. The decrease, however, was significantly lower in the wild type than in the transgenic plants. This was further validated by the high GS mRNA expression and enzyme activity in most of the transgenic lines. Moreover, after 10 days of exposure to Cd stress, increase in the glutamine reductase activity and low or no malondialdehyde contents were observed. These results showed that overexpression of the GS gene in rice modulated the expression of enzymes responsible for membrane peroxidation that may result in plant death.     

The Homologous Tripartite Viral RNA Polymerase of A/Swine/Korea/CT1204/2009(H1N2) Influenza Virus Synergistically Drives Efficient Replication and Promotes Respiratory Droplet Transmission in Ferrets

We previously reported that influenza A/swine/Korea/1204/2009(H1N2) virus was virulent and transmissible in ferrets in which the respiratory-droplet-transmissible virus (CT-Sw/1204) had acquired simultaneous hemagglutinin (HA_D225G) and neuraminidase (NA_S315N) mutations. Incorporating these mutations into the nonpathogenic A/swine/Korea/1130/2009(H1N2, Sw/1130) virus consequently altered pathogenicity and growth in animal models but could not establish efficient transmission or noticeable disease. We therefore exploited various reassortants of these two viruses to better understand and identify other viral factors responsible for pathogenicity, transmissibility, or both. We found that possession of the CT-Sw/1204 tripartite viral polymerase enhanced replicative ability and pathogenicity in mice more significantly than did expression of individual polymerase subunit proteins. In ferrets, homologous expression of viral RNA polymerase complex genes in the context of the mutant Sw/1130 carrying the HA_225G and NA_315N modifications induced optimal replication in the upper nasal and lower respiratory tracts and also promoted efficient aerosol transmission to respiratory droplet contact ferrets. These data show that the synergistic function of the tripartite polymerase gene complex of CT-Sw/1204 is critically important for virulence and transmission independent of the surface glycoproteins. Sequence comparison results reveal putative differences that are likely to be responsible for variation in disease. Our findings may help elucidate previously undefined viral factors that could expand the host range and disease severity induced by triple-reassortant swine viruses, including the A(H1N1)pdm09 virus, and therefore further justify the ongoing development of novel antiviral drugs targeting the viral polymerase complex subunits.     

Stable,high‐affinity streptavidin monomer for protein labeling and monovalent biotin detection

The coupling between the quaternary structure, stability and function of streptavidin makes it difficult to engineer a stable, high affinity monomer for biotechnology applications. For example, the binding pocket of streptavidin tetramer is comprised of residues from multiple subunits, which cannot be replicated in a single domain protein. However, rhizavidin from Rhizobium etli was recently shown to bind biotin with high affinity as a dimer without the hydrophobic tryptophan lid donated by an adjacent subunit. In particular, the binding site of rhizavidin uses residues from a single subunit to interact with bound biotin. We therefore postulated that replacing the binding site residues of streptavidin monomer with corresponding rhizavidin residues would lead to the design of a high affinity monomer useful for biotechnology applications. Here, we report the construction and characterization of a structural monomer, mSA, which combines the streptavidin and rhizavidin sequences to achieve optimized biophysical properties. First, the biotin affinity of mSA (K_d = 2.8 nM) is the highest among nontetrameric streptavidin, allowing sensitive monovalent detection of biotinylated ligands. The monomer also has significantly higher stability (T_m = 59.8°C) and solubility than all other previously engineered monomers to ensure the molecule remains folded and functional during its application. Using fluorescence correlation spectroscopy, we show that mSA binds biotinylated targets as a monomer. We also show that the molecule can be used as a genetic tag to introduce biotin binding capability to a heterologous protein. For example, recombinantly fusing the monomer to a cell surface receptor allows direct labeling and imaging of transfected cells using biotinylated fluorophores. A stable and functional streptavidin monomer, such as mSA, should be a useful reagent for designing novel detection systems based on monovalent biotin interaction. Biotechnol. Bioeng. 2013; 110: 57–67. © 2012 Wiley Periodicals, Inc.     

Ribosomal protein S3 is secreted as a homodimer in cancer cells

Protein secretion is a general phenomenon by which cells communicate with the extracellular environment. Secretory proteins, including hormones, enzymes, toxins, and antimicrobial peptides have various functions in extracellular environments. Here, we determined that ribosomal protein S3 (rpS3) is homodimerized and secreted in several cancer cell lines such as HT1080 (human fibrosarcoma) and MPC11 (mouse plasmacytoma). Moreover, we found that the secreted rpS3 protein increased in doxorubicin-resistant MPC11 cells compared to that in MPC11 cells. In addition, we also detected that the level of secreted rpS3 increased in more malignant cells, which were established with continuous exposure of cigarette smoke condensate. These findings suggest that the secreted rpS3 protein is an indicator of malignant tumors.     

β-cyclodextrin production by the cyclodextrin glucanotransferase from Paenibacillus illinoisensis ZY-08: cloning, purification, and properties

The gene encoding the cyclodextrin glucanotransferase (CGTase, EC2.4.1.19) of Paenibacillus illinoisensis was isolated, cloned, sequenced and expressed in Escherichia coli. Sequence analysis showed that the mature enzyme (684 amino acids) was preceded by a signal peptide of 34-residues. The deduced amino acid sequence of the CGTase from P. illinoisensis ZY-08 exhibited highest identity (99 %) to the CGTase sequence from Bacillus licheniformis (P14014). The four consensus regions of carbohydrate converting domain and Ca²⁺ binding domain could be identified in the sequence. The CGTase was purified by using cold expression vector, pCold I, and His-tag affinity chromatography. The molecular weight of the purified enzyme was about 74 kDa. The optimum temperature and pH of the enzyme were 40 °C and pH 7.4, respectively. The enzyme activity was increased by the addition of Ca²⁺ and inhibited by Ba²⁺, Cu²⁺, and Hg²⁺. The K _m and V _max values calculated were 0.48 mg/ml and 51.38 mg of β-cyclodextrin/ml/min. The ZY-08 and recombinant readily converted soluble starch to β-cyclodextrin but ZY-08 did not convert king oyster mushroom powder and enoki mushroom powder. However the recombinant CGTase converted king oyster mushroom powder and enoki mushroom powder to β-cyclodextrin.     

A molecular level prototype for mechanoelectrical transducer in mammalian hair cells

The mechanoelectrical transducer (MET) is a crucial component of mammalian auditory system. The gating mechanism of the MET channel remains a puzzling issue, though there are many speculations, due to the lack of essential molecular building blocks. To understand the working principle of mammalian MET, we propose a molecular level prototype which constitutes a charged blocker, a realistic ion channel and its surrounding membrane. To validate the proposed prototype, we make use of a well-established ion channel theory, the Poisson–Nernst–Planck equations, for three-dimensional (3D) numerical simulations. A wide variety of model parameters, including bulk ion concentration, applied external voltage, blocker charge and blocker displacement, are explored to understand the basic function of the proposed MET prototype. We show that our prototype prediction of channel open probability in response to blocker relative displacement is in remarkable accordance with experimental observation of rat cochlea outer hair cells. Our results appear to suggest that tip links which connect hair bundles gate MET channels.     

Development of cyan fluorescent protein (CFP) reporter system in green alga Chlamydomonas reinhardtii and macroalgae Pyropia sp.

Various fluorescent proteins have been developed for in vivo reporter systems in diverse prokaryotes and eukaryotes. However, few in vivo imaging systems have been reported for the model algae Chlamydomonas reinhardtii or Pyropia sp. In this study, an effective imaging system using cyan fluorescent protein (CFP) was developed for the green alga C. reinhardtii, and its application was also successful in the red macroalgae Pyropia tenera and P. yezoensis. For optimization of CFP expression in C. reinhardtii and Pyropia sp., we modified codon usage in the CFP gene (CFP), generating PtCrCFP (Pyropia tenera/Chlamydomonas reinhardtii CFP). PtCrCFP was successfully expressed in PtCrCFP-expressing UVM11 transgenic lines, and high accumulation levels of PtCrCFP were found by western blotting. Consistent with these results, PtCrCFP fluorescence was clearly detected with a low level of chlorophyll background fluorescence in PtCrCFP-expressing UVM11 transgenic lines. In Pyropia sp. gametophytic cells, transient expression of PtCrCFP fluorescence was distinctly visualized. PtCrCFP fluorescence was also observed during the regeneration of monospores and young gametophytes from PtCrCFP-expressing P. yezoensis gametophytic cells. These results suggest that PtCrCFP may be useful as an in vivo reporter in green algae due to the short emission wavelength of CFP, which provides a low level of chlorophyll background fluorescence. This study also presents the possibility of PtCrCFP’s use as a visible selection marker for the generation of transgenic lines in the red algae Pyropia sp. Thus, PtCrCFP as an in vivo visualization tool may offer new opportunities for the functional analysis of genetic studies in both green and red algae.     

A Modified Entropy-Based Approach for Identifying Gene-Gene Interactions in Case-Control Study

Gene-gene interactions may play an important role in the genetics of a complex disease. Detection and characterization of gene-gene interactions is a challenging issue that has stimulated the development of various statistical methods to address it. In this study, we introduce a method to measure gene interactions using entropy-based statistics from a contingency table of trait and genotype combinations. We also developed an exploration procedure by using graphs. We propose a standardized relative information gain (RIG) measure to evaluate the interactions between single nucleotide polymorphism (SNP) combinations. To identify the k ^th order interactions, contingency tables of trait and genotype combinations of k SNPs are constructed, with which RIGs are calculated. The RIGs are standardized using the mean and standard deviation from the permuted datasets. SNP combinations yielding high standardized RIG are chosen for gene-gene interactions. Detection of high-order interactions and comparison of interaction strengths between different orders are made possible by using standardized RIG. We have applied the proposed standardized entropy-based method to two types of data sets from a simulation study and a real genetic association study. We have compared our method and the multifactor dimensionality reduction (MDR) method through power analysis of eight different genetic models with varying penetrance rates, number of SNPs, and sample sizes. Our method shows successful identification of genetic associations and gene-gene interactions both in simulation and real genetic data. Simulation results suggest that the proposed entropy-based method is better able to detect high-order interactions and is superior to the MDR method in most cases. The proposed method is well suited for detecting interactions without main effects as well as for models including main effects.