Geminivirus sequences as bidirectional transcription termination/polyadenylation signals for economic construction of stably expressed transgenes

Bidirectional, convergent transcription of transgenes in transgenic plants can occur due to leaky transcription termination of separate convergent genes or from genomic promoters. It might also be engineered with the purpose of generating double-stranded RNA to downregulate genes by RNA interference. We have tested the effects of convergent transcription on expression levels and analysed the potential of geminivirus derived DNA sequences to act as bidirectional transcription termination/polyadenylation signals in transgenes to counteract such negative effects. Convergent, overlapping transcription decreased expression, however, no increased propensity for induction of gene silencing was observed. The geminivirus terminators in both orientations supported efficient expression of single genes and of convergent genes, whereas a unidirectional terminator allowed only reduced expression in this latter situation. Geminivirus terminators could be used as efficient transcription control element for the expression of two genes simultaneously or, with single genes, could afford protection of the gene against unwanted anti-sense transcription from transcription units downstream of the gene, e.g. in the integration locus. Our results also suggest that flanking of a given sequence by two convergent promoters would not be an efficient way to generate double-stranded RNA and induce gene silencing by RNA

Surge Wave Propagation in a Common Tailrace Channel for Two Large Pumped-Storage Plants

Sudden starting and stopping of turbines and pumps lead to highly unsteady flow in tailrace channels of hydropower plants (HPP). Submergence of Pelton turbines and air entrainment in pumps due to surge waves must be avoided by technical measures. The existing 240 MW Veytaux pumped-storage plant in Switzerland will be enlarged by a new powerhouse adding another 240 MW, using the same tailrace channel and intake. Therefore, surge waves, induced by the two combined HPPs’ operation, were investigated using a physical model. For its validation, the flow behavior of the present scheme was tested and compared to prototype measurements. The enhanced scheme was investigated to analyze critical scenarios, to optimize the plant operation rules, and to define its limits. The effect of the layout on wave reflection in pump mode is highlighted and compared to theoretical approaches

Upstream and downstream sequence elements determine the specificity of the rice tungro bacilliform virus promoter and influence RNA production after transcription initiation

The contribution of sequences upstream and downstream of the transcription start site to the strength and specificity of the promoter of rice tungro bacilliform virus was analysed in transgenic rice plants. The promoter is strongly stimulated by downstream sequences which include an intron and is active in all vascular and epidermal cells. Expression in the vascular tissue requires a promoter element located between −100 and −164 to which protein(s) from rice nuclear extracts bind. Elimination of this region leads to specificity for the epidermis. Due to the presence of a polyadenylation signal in the intron, short-stop RNA is produced from the promoter in addition to full-length primary transcript and its spliced derivatives. The ratio between short-stop RNA and full-length or spliced RNA is determined by upstream promoter sequences, suggesting the assembly of RNA polymerase complexes with different processivity on this promote

Optimization of a Shared Tailrace Channel of Two Pumped-Storage Plants by Physical and Numerical Modeling

Pump and turbine operations lead to head losses in the tailrace channel. Pumping discharge may be limited due to potential air entrainment into the pump shaft when the downstream reservoir is at its lowest level and the head losses are too high. Regarding turbine operations, the limit is given by the maximum level in the Pelton turbine chamber due to high water level in the downstream reservoir and head losses. The rapid starting and stopping of turbines and pumps lead to highly unsteady flow in the tailrace channel system of the two connected hydropower plants. Negative and positive surges may lead to similar consequences as for stationary operations such as sudden air entrainment into the pump shaft and submerging of the Pelton runner under operation. Therefore, flow and head losses test were conducted on a physical model at 1:30 scale together with numerical simulations using FLOW-3D. On-site measurement of the existing power plant allows validating the results. Representative and extreme operational scenarios have been simulated; the main results are discussed and presented

Flow and waves in a common tailrace channel of two pump-storage plants - physical and numerical simulation

Pump and turbine operations lead to head losses in the tailrace channel. Pumping discharge may be limited due to potential air entrainment into the pump shaft when the downstream reservoir is at its lowest level and the head losses are high. Regarding turbine operations, the limit is given by the maximum level in the Pelton turbine chamber due to high water level in the downstream reservoir and head losses. For the extended Hongrin-Léman pumped-storage scheme in Switzerland, the rapid operations of turbines and pumps lead to highly unsteady flow in the tailrace channel system of the two connected hydropower plants. Negative and positive surges may lead to similar consequences as for stationary operations such as sudden air entrainment into the pump shaft and submerging of the Pelton runner under operation. Therefore flow and head losses tests were performed on a physical model at 1:30 scale together with numerical simulations using the FLOW-3D software. On site measurement of the existing power plant allowed validation of the results. Representative and extreme operational scenarios have been simulated; the main results are discussed and presented

Geminivirus sequences as bidirectional transcription termination/polyadenylation signals for economic construction of stably expressed transgenes

ISSN:1380-3743ISSN:1572-978

Type Ia supernova explosion models are inherently multidimensional

Theoretical and observational approaches to settling the important questions surrounding the progenitor systems and the explosion mechanism of normal Type Ia supernovae have thus far failed. With its unique capability to obtain continuous spectra through the near- and mid-infrared, JWST now offers completely new insights into Type Ia supernovae. In particular, observing them in the nebular phase allows us to directly see the central ejecta and thereby constrain the explosion mechanism. We aim to understand and quantify differences in the structure and composition of the central ejecta of various Type Ia supernova explosion models. We examined the currently most popular explosion scenarios using self-consistent multidimensional explosion simulations of delayed-detonation and pulsationally assisted, gravitationally confined delayed detonation Chandrasekhar-mass models and double-detonation sub-Chandrasekhar-mass and violent merger models. We find that the distribution of radioactive and stable nickel in the final ejecta, both observable in nebular spectra, are significantly different between different explosion scenarios. Therefore, comparing synthetic nebular spectra with JWST observations should allow us to distinguish between explosion models. We show that the explosion ejecta are inherently multidimensional for all models, and the Chandrasekhar-mass explosions simulated in spherical symmetry in particular lead to a fundamentally unphysical ejecta structure. Moreover, we show that radioactive and stable nickel cover a significant range of densities at a fixed velocity of the homologously expanding ejecta. Any radiation transfer postprocessing has to take these variations into account to obtain faithful synthetic observables; this will likely require multidimensional radiation transport simulations