A study of the galvanic replacement reaction at surfaces and the role of lateral charge propagation

The galvanic replacement of isolated nanostructures of copper and silver on conducting supports as well as continuous films of copper with gold is reported. The surface morphology was characterized by scanning electron microscopy and the replacement with gold was confirmed by EDX analysis. It was found that lateral charge propagation during the replacement reaction had a significant effect in all cases. For the isolated nanostructures the deposition of gold was observed not only at the sacrificial template but also at the surrounding unmodified areas of the conducting substrate. In the case of copper films the role of lateral charge propagation was also confirmed by connecting it to an ITO electrode through an external circuit upon which gold deposition was also observed to occur. Interestingly, by inhibiting the rate of charge propagation, through the introduction of a series resistor, the morphology of gold on the copper substrate could be changed from discrete surface decoration with cube like nanoparticles to a more porous rough surface.

Lateral charge propagation effects during the galvanic replacement of electrodeposited MTCNQ (M= Cu, Ag) microstructures with gold and its influence on catalysed electron transfer reactions

The galvanic replacement of isolated electrodeposited semiconducting CuTCNQ microstructures on a glassy carbon (GC) substrate with gold is investigated. It is found that anisotropic metal nanoparticles are formed which are not solely confined to the redox active sites on the semiconducting materials but are also observed on the GC substrate which occurs via a lateral charge propagation mechanism. We also demonstrate that this galvanic replacement approach can be used for the formation of isolated AgTCNQ/Au microwire composites which occurs via an analogous mechanism. The resultant MTCNQ/Au (M = Cu, Ag) composite materials are characterized by Raman, spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and investigated for their catalytic properties for the reduction of ferricyanide ions with thiosulphate ions in aqueous solution. Significantly it is demonstrated that gold loading, nanoparticle shape and in particular the MTCNQ–Au interface are important factors that influence the reaction rate. It is shown that there is a synergistic effect at the CuTCNQ/Au composite when compared to AgTCNQ/Au at similar gold loadings.

Description of plant tRNA-derived RNA fragments (tRFs) associated with argonaute and identification of their putative targets

tRNA-derived RNA fragments (tRFs) are 19mer small RNAs that associate with Argonaute (AGO) proteins in humans. However, in plants, it is unknown if tRFs bind with AGO proteins. Here, using public deep sequencing libraries of immunoprecipitated Argonaute proteins (AGO-IP) and bioinformatics approaches, we identified the Arabidopsis thaliana AGO-IP tRFs. Moreover, using three degradome deep sequencing libraries, we identified four putative tRF targets. The expression pattern of tRFs, based on deep sequencing data, was also analyzed under abiotic and biotic stresses. The results obtained here represent a useful starting point for future studies on tRFs in plants. © 2013 Loss-Morais et al.; licensee BioMed Central Ltd.

Defense and counterdefense in the plant world

An important role of RNA interference (RNAi)-like pathways in plants is defense against viral infection. Viruses can overcome this defense by expressing proteins that suppress the pathway. A new study of Agrobacterium tumefaciens infection reveals that this plant pathogen, although a bacterium, also induces and then suppresses the host RNAi response. © 2006 Nature Publishing Group.

Exploring plant genomes by RNA-induced gene silencing

The nucleotide sequences of several animal, plant and bacterial genomes are now known, but the functions of many of the proteins that they are predicted to encode remain unclear. RNA interference is a gene-silencing technology that is being used successfully to investigate gene function in several organisms - for example, Caenorhabditis elegans. We discuss here that RNA-induced gene silencing approaches are also likely to be effective for investigating plant gene function in a high-throughput, genome-wide manner.

Viruses face a double defense by plant small RNAs

Plants fight viral infections with enzymes that digest viral RNA, but viruses retaliate with proteins that suppress these enzymes. To boost their antiviral response plants deploy enzymes with redundant functions.

Synthesis of complementary RNA by RNA-dependent RNA polymerases in plant extracts is independent of an RNA primer

RNA-dependent RNA polymerase (RDR) activities were readily detected in extracts from cauliflower and broccoli florets, Arabidopsis thaliana (L.) Heynh callus tissue and broccoli nuclei. The synthesis of complementary RNA (cRNA) was independent of a RNA primer, whether or not the primer contained a 3′ terminal 2′-O-methyl group or was phosphorylated at the 5′ terminus. cRNA synthesis in plant extracts was not affected by loss-of-function mutations in the DICER-LIKE (DCL) proteins DCL2, DCL3, and DCL4, indicating that RDRs function independently of these DCL proteins. A loss-of-function mutation in RDR1, RDR2 or RDR6 did not significantly reduce the amount of cRNA synthesis. This indicates that these RDRs did not account for the bulk RDR activities in plant extracts, and suggest that either the individual RDRs each contribute a fraction of polymerase activity or another RDR(s) is predominant in the plant extract. © CSIRO 2008.

The roles of plant dsRNA-binding proteins in RNAi-like pathways

Dicers are associated with double-stranded RNA-binding proteins (dsRBPs) in animals. In the plant, Arabidopsis, there are four dicer-like (DCL) proteins and five potential dsRBPs. These DCLs act redundantly and hierarchically. However, we show there is little or no redundancy or hierarchy amongst the DRBs in their DCL interactions. DCL1 operates exclusively with DRB1 to produce micro (mi)RNAs, DCL4 operates exclusively with DRB4 to produce trans-acting (ta) siRNAs and 21nt siRNAs from viral RNA. DCL2 and DCL3 produce viral siRNAs without requiring assistance from any dsRBP. DRB2, DRB3 and DRB5 appear unnecessary for mi-, tasi-, viral si-, or heterochromatinising siRNA production but act redundantly in a developmental pathway. © 2008 Federation of European Biochemical Societies.

Plant and animal microRNAs : similarities and differences

Plant and animal microRNAs (miRNAs) are evolutionarily ancient small RNAs, ∼19-24 nucleotides in length, that are generated by cleavage from larger highly structured precursor molecules. In both plants and animals, miRNAs posttranscriptionally regulate gene expression through interactions with their target mRNAs, and these targets are often genes involved with regulating key developmental events. Despite these similarities, plant and animal miRNAs exert their control in fundamentally different ways. Generally, animal miRNAs repress gene expression by mediating translational attenuation through (multiple) miRNA-binding sites located within the 3′ untranslated region of the target gene. In contrast, almost all plant miRNAs regulate their targets by directing mRNA cleavage at single sites in the coding regions. These and other differences suggest that the two systems may have originated independently, possibly as a prerequisite to the development of complex body plans. © Springer-Verlag 2005.

A suite of novel promoters and terminators for plant biotechnology II. The pPLEX series for use in monocots

A suite of plant expression vectors (pPLEX), constructed from the gene regulation signals from subterranean clover stunt virus (SCSV) genome, has previously been used in dicot transformation for a variety of applications in plant biotechnology. To assess their use for the transformation of monocots, a number of modifications were made to the basic vector series and assessed in rice. In their unmodified forms, the SCSV promoters directed low levels of gene expression, however, insertion of an intron between the promoter and the transgene open reading frame (analogous to the rice actin and maize ubiquitin promoter systems) increased transgene expression 50-fold. The expression patterns from the intron-modified SCSV (segments 4 and 7) promoters were very similar to those directed by the actin or ubiquitin promoters. All promoter systems investigated directed expression that appeared to be constitutive within leaf tissue, and localised to the epidermal and vascular tissues of the root. The pPLEX vectors described here are an important counterpart to the dicot pPLEX series and have the potential to be useful in monocot research and biotechnology.

A suite of novel promoters and terminators for plant biotechnology

The gene regulation signals from subterranean clover stunt virus (SCSV) were investigated for their expression in dicot plants. The SCSV genome has at least eight circular DNA molecules. Each circular DNA component contains a promoter element, a single open reading frame and a terminator. The promoters from seven of the segments were examined for their strength and tissue specificity in transgenic tobacco (Nicotiana tabacum L.), potato (Solanum tuberosum L.) and cotton (Gossypium hirsutum L.) using a GUS reporter gene assay system. While the promoters of many of the segments were poorly expressed, promoters derived from segments 4 and 7 were shown to direct high levels of expression in various plant tissues and organs. The segment 1 promoter directs predominantly callus-specific expression and, when used to control a selectable marker gene, facilitated the transformation of all three species (tobacco, potato and cotton). From the results, a suite of plant expression vectors (pPLEX) derived from the SCSV genome were constructed and used here to produce herbicide- and insect-resistant cotton, demonstrating their utility in the expression of foreign genes in dicot crop species and their potential for use in agricultural biotechnology.

Intron-mediated improvement of a selectable marker gene for plant transformation using Agrobacterium tumefaciens

In binary vectors, the antibiotic resistance gene used for selection of transformed plant cells is also usually expressed in the transforming Agrobacterium cells. This expression gives the bacterium antibiotic resistance, an unnecessary advantage on selective medium containing the antibiotic. Insertion of a castor bean catalase-1 (CAT-1) gene intron or a Parasponia andersonii haemoglobin gene intron into the coding region of the selectable marker gene, hph, completely abolished the expression of the gene in Agrobacterium, rendering it susceptible to hygromycin B. Use of these modified binary vectors minimized the overgrowth of Agrobacterium during plant transformation. Both of the introns were correctly spliced in plant cells and significantly enhanced hph gene expression in transformed rice tissue. The presence of these introns in the hph coding sequence not only maintained the selection efficiency of the hph gene, but with the CAT-1 intron also substantially increased the frequency of rice transformation. Transgenic lines with an intron-hph gene generally contained fewer gene copies and produced substantially more mRNA of the predicted size. Our results also indicate that transgenic plants with many copies of the transgene were more likely to show gene silencing than plants with 1-3 copies.

Role of electromechanical wave propagation in power systems

In a large interconnected power system, disturbances initiated by a fault or other events cause acceleration in the generator rotors with respect to their synchronous reference frame. This acceleration of rotors can be described by two different dynamic phenomena, as shown in existing literature. One of the phenomena is simultaneous acceleration and the other is electromechanical wave propagation, which is characterized by travelling waves in terms of a wave equation. This paper demonstrates that depending on the structure of the system, the exhibited dynamic response will be dominated by one phenomenon or the other or a mixture of both. Two system structures of choice are examined, with each structure exemplifying each phenomenon present to different degrees in their dynamic responses. Prediction of dominance of either dynamic phenomenon in a particular system can be determined by taking into account the relative sizes of the values of its reduced admittance matrix.

Nucleotide sequence of coat protein gene for GPV isolate of barley yellow dwarf virus and construction of expression plasmid for plant

GPV is a Chinese serotype isolate of barley yellow dwarf virus (BYDV) that has no reaction with antiserum of MAV, PAV, SGV, RPV and RMV The sequence of the coat protein (CP) of GPV isolate of BYDV was identified and its amino acid sequence was deduced. The coding region for the putative GPV CP is 603 bases nucleotides and encodes a Mr 22 218 (22 ku) protein. The same as MAV, PAV and RPV, GPV contained a second ORF within the coat protein coding region. This protein of 17 024 Mr (17 ku) is thought to correspond to the Virion protein genome linked (Vpg). Sequence comparisons of the CP coding region between the GPV isolate of BYDV and other isolates of BYDV have been done. The nucleotide and amino acid sequence homology of GPV has a greater identity to the sequence of RPV than those of PAV and MAV. The GPV CP sequence stored 83.7% of nucleotide similarity and 77.5% of deduced amino acid similarity, whereas that of the PAV and MAV shared 56.9%, 53.2% and 44.1%, 43.8% respectively. According to BYDV-GPV CP sequence, two primers were designed. The cDNA of CP was produced by RT-PCR. Full-length cDNA of CP was inserted into plasmid to construct expression plasmids named pPPI1, pPPI2 and pPPI5 based on different promoters. The recombinant plasmids were identified by using α-32P-dATP labelled CP probe, α-32P-ATP labelled GPV RNA probe and sequencing to confirm real GPV CP gene cDNA in plasmids.