40 results on '"Mehrshahi P"'
Search Results
2. A Novel Method Based on Sequential Unconstrained Programming for Transmit Beamforming in Colocated MIMO Radars
- Author
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Elahe Faghand, Giorgio Guerzoni, Esfandiar Mehrshahi, Giorgio Matteo Vitetta, and Shokrollah Karimian
- Subjects
Colocated multiple-input multiple-output radar ,covariance matrix design ,transmit beampattern matching ,unconstrained programming ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
The design of the waveform covariance matrix for beampattern matching in colocated multiple-input multiple-output (MIMO) radars represents a challenging problem because of its large number of variables and the presence of multiple constraints. The solutions available in the technical literature are computationally intensive and usually rely on iterative procedures that minimize a constrained mean square error (MSE). In this manuscript, a new computationally efficient method for beampattern matching design is proposed. This method, called sequential weight-shift unconstrained programming (SWSUP), allows to compute the covariance matrix of the probing signals achieving a desired beampattern at the transmit side of a colocated MIMO radar. Its derivation is based on the idea of reformulating the beampattern matching problem in an unconstrained form that can be tackled by breaking it into two subproblems. The first subproblem admits a closed-form solution, whose accuracy, in terms of MSE, is comparable to provided by other known methods. The solution of the second subproblem, instead, is evaluated through an iterative procedure and allows to achieve further improvement. Our numerical results evidence that the SWSUP method achieves precise beampattern matching with a substantially lower computational effort and computing time with respect to various existing alternatives.
- Published
- 2024
- Full Text
- View/download PDF
3. Publisher Correction: Naked clams to open a new sector in sustainable nutritious food production
- Author
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Willer, David F., Aldridge, David C., Mehrshahi, Payam, Papadopoulos, Konstantinos P., Archer, Lorraine, Smith, Alison G., Lancaster, Max, Strachan, Alex, and Shipway, J. Reuben
- Published
- 2023
- Full Text
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4. Naked Clams to open a new sector in sustainable nutritious food production
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Willer, David F., Aldridge, David C., Mehrshahi, Payam, Papadopoulos, Konstantinos P., Archer, Lorraine, Smith, Alison G., Lancaster, Max, Strachan, Alex, and Shipway, J. Reuben
- Published
- 2023
- Full Text
- View/download PDF
5. Novel Movement-Based Methods for the Calibration of Colocated Multiple-Input Multiple-Output Radars
- Author
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Giorgio Guerzoni, Elahe Faghand, Giorgio Matteo Vitetta, Loris Vincenzi, and Esfandiar Mehrshahi
- Subjects
Calibration ,multiple-input multiple-output ,radar ,synthetic aperture radar ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
It is well-known that the availability of transmit and receive arrays in colocated multiple-input multiple-output radar systems can be exploited to detect multiple targets, and estimate their range and angular coordinates. Unluckily, the accuracy achieved in the estimation of target parameters can be severely affected by hardware nonidealities. The impact of these nonidealities can be mitigated through the adoption of specific methods explicitly developed to estimate and compensate for them, i.e., briefly, of calibration methods. As far as we know, until now, most of the calibration techniques proposed in the technical literature for colocated multiple-input multiple-output radars are based on the idea of placing one or more reference targets in front of the considered radar device at perfectly known and fixed locations, and quantifying the difference between the expected radar image and the measured one. In this manuscript, two novel calibration methods are proposed. Both exploit the measurements captured by a colocated multiple-input multiple-output radar device at multiple positions; for this reason, the acquisition of such measurements involves the movement of the radar. The first one does not require any knowledge about the nature, number, position or radar cross section of the reference targets, provided that all these are in far-field; the second one, instead, needs a single reference target in near-field conditions, with the only constraints for it to be pointwise and isolated from stray targets in the range domain. This drastically simplifies the experimental setup to be employed for radar calibration. The proposed methods are tested on a commercial radar device and compared with a traditional method for radar calibration.
- Published
- 2023
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6. Overexpression of PSR1 in Chlamydomonas reinhardtii induces luxury phosphorus uptake
- Author
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Stephen P. Slocombe, Tatiana Zúñiga-Burgos, Lili Chu, Payam Mehrshahi, Matthew P. Davey, Alison G. Smith, Miller Alonso Camargo-Valero, and Alison Baker
- Subjects
biomass ,micro-algae ,polyphosphate ,transcription factor ,wastewater remediation ,Plant culture ,SB1-1110 - Abstract
Remediation using micro-algae offers an attractive solution to environmental phosphate (PO43-) pollution. However, for maximum efficiency, pre-conditioning of algae to induce ‘luxury phosphorus (P) uptake’ is needed. To replicate this process, we targeted the global regulator PSR1 (Myb transcription factor: Phosphate Starvation Response 1) for over-expression in algae. Manipulating a single gene (PSR1) drove uptake of both PO43- and a Mg2+ counter-ion leading to increased PolyP granule size, raising P levels 4-fold to 8% dry cell weight, and accelerated removal of PO43- from the medium. Examination of the gene expression profile showed that the P-starvation response was mimicked under P-replete conditions, switching on luxury uptake. Hyper-accumulation of P depended on a feed-forward mechanism, where a small set of ‘Class I’ P-transporter genes were activated despite abundant external PO43- levels. The transporters drove a reduction in external PO43- levels, permitting more genes to be expressed (Class II), leading to more P-uptake. Our data pointed toward a PSR1-independent mechanism for detection of external PO43- which suppressed Class II genes. This model provided a plausible mechanism for P-overplus where prior P-starvation elevates PSR1 and on P-resupply causes luxury P-uptake. This is because the Class I genes, which include P-transporter genes, are not suppressed by the excess PO43-. Taken together, these discoveries facilitate a bio-circular approach of recycling nutrients from wastewater back to agriculture.
- Published
- 2023
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7. A Compressive Method for Centralized PSD Map Construction with Imperfect Reporting Channel
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Eslami, Mohammad, Safavi, Seyed Hamid, Torkamani-Azar, Farah, and Mehrshahi, Esfandiar
- Subjects
Computer Science - Information Theory ,Computer Science - Networking and Internet Architecture - Abstract
Spectrum resources management of growing demands is a challenging problem and Cognitive Radio (CR) known to be capable of improving the spectrum utilization. Recently, Power Spectral Density (PSD) map is defined to enable the CR to reuse the frequency resources regarding to the area. For this reason, the sensed PSDs are collected by the distributed sensors in the area and fused by a Fusion Center (FC). But, for a given zone, the sensed PSDs by neighbor CR sensors may contain a shared common component for a while. This component can be exploited in the theory of the Distributed Source Coding (DSC) to make the sensors transmission data more compressed. However, uncertain channel fading and random shadowing would lead to varying signal strength at different CRs, even placed close to each other. Hence, existence of some perturbations in the transmission procedure yields to some imperfection in the reporting channel and as a result it degrades the performance remarkably. The main focus of this paper is to be able to reconstruct the PSDs of sensors \textit{robustly} based on the Distributed Compressive Sensing (DCS) when the data transmission is slightly imperfect. Simulation results verify the robustness of the proposed scheme., Comment: Submitted to the 25th European Signal Processing Conference (EUSIPCO 2017). arXiv admin note: text overlap with arXiv:1612.02892
- Published
- 2017
8. A Compressive Method for Centralized PSD Map Construction
- Author
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Eslami, Mohammad, Torkamani-Azar, Farah, and Mehrshahi, Esfandiar
- Subjects
Computer Science - Information Theory - Abstract
Spectrum resources are facing huge demands and cognitive radio (CR) can improve the spectrum utilization. Recently, power spectral density (PSD) map is defined to enable the CR to reuse the frequency resources regarding to the area. For this reason, the sensed PSDs are fused by a Fusion Center (FC) which the sensed PSDs are collected by the distributed sensors in the area. But, for a given zone, the sensed PSD by neighbor CR sensors may contain a shared common component for a while. This component can be exploited in the theory of the distributed source coding (DSC) to compress sensing data more. In this paper based on the distributed compressive sensing (DCS) a method is proposed to compress and reconstruct the PSDs of the sensors when the data transmission is slightly imperfect. Simulation results show the advantages of using proposed method in compressing, reducing overhead and also recovering PSDs. % Proposed method can be used to develop a framework when the holding times of the users are large in comparison with the rate of the spectrum sensing., Comment: The 42nd IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP 2017), Ph.D. Forum
- Published
- 2016
9. Performance evaluation of a surcharge preloading project based on back-analysis of field monitoring and numerical assessment
- Author
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Alielahi, Hamid, Maleki, Mohammad, and Mehrshahi, Khosrow
- Published
- 2021
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10. Accurate off-axis magnetic field calculation of axisymmetric cylindrical current distributions
- Author
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S. Karimian and G. Mehrshahi
- Subjects
Physics ,QC1-999 - Abstract
This paper proposes an accurate, simple, and versatile approach for calculation of the off-axis magnetic field of any axisymmetric cylindrical current distribution, eliminating the need for complicated elliptical integrals and sophisticated numerical methods, e.g., finite element method. The results obtained from both integral and series forms not only confirm the validity of the proposed method against well-established analytical techniques but also outperform them in terms of accuracy, simplicity, and calculation time. The integral method yields greater convergence (14 decimal places) compared to the ill-posed series method, which depends on the highest order of derivatives; this would yield an error below 1% at the highest order of derivatives (i.e., 14 for axial-H and 11 for radial-H in the range of 0 < ρ < 0.8R). The off-axis solution to the case of a thin shell of finite length with cylindrical current distribution is calculated using the proposed method irrespective of the current density function, though only the most common case of uniform current has been included in the solved special cases. Given that no known formula is available to solve this case, the results of this work have been validated against the results of the well-known software ANSYS Maxwell simulator.
- Published
- 2021
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11. Collocated ULA-MIMO Radar Waveform Design with Coherent Detection of Targets in Background Clutter
- Author
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Haghnegahdar, Mohammad, Mehrshahi, Esfandiar, and Ghorashi, Seyed Ali
- Published
- 2018
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12. Geomorphology and dating of the sand ramp (Kouh Rig) in Farashah, Taft, on the purpose of determining the last quaternary features of the northern slopes of Shirkouh
- Author
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Morteza Fattahi and Dariush Mehrshahi
- Subjects
sand ramp ,geomorphology and dating ,quaternary ,farashâh ,Commerce ,HF1-6182 ,Human ecology. Anthropogeography ,GF1-900 - Abstract
The sand ramp (or Kouh Rig as in Farsi) is a phenomenon formed by accumulation of sand and other materials in the upwind side or leeside of a mountain slope. This formation is due to the multiple interactions of extreme wind actions, feeding and displacement of sand, physical obstacles, and slope-induced processes. Unfortunately, the phenomenon is not well-known in the physical geography studies of Iran. The sand ramp, about five km west of Taft city, was selected to be investigated due to its relative intactness. Some sand samples were extracted from the depth of 0.4m and 4.2m on the top of the sand ramp. The samples were cleaned several times to provide pure quartz particles that were then analysed using the Optically Stimulated Luminescence (OSL) dating method. The results of dating indicated that the top half section of Farashâh sand ramp was probably accumulated during or near the last glacial maximum phase (something between 18000 to 24000 years ago). The results also emphasize that, in contrast to the theory of cold and wet conditions, with more rain during the glacial phases of Quaternary on the Iranian plateau, at least for parts of the glacial (cold) phases, colder and drier environments with very active winds were dominant on the central Iran.
- Published
- 2018
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13. Exploring the Impact of Terminators on Transgene Expression in Chlamydomonas reinhardtii with a Synthetic Biology Approach
- Author
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Katrin Geisler, Mark A. Scaife, Paweł M. Mordaka, Andre Holzer, Eleanor V. Tomsett, Payam Mehrshahi, Gonzalo I. Mendoza Ochoa, and Alison G. Smith
- Subjects
algae ,heterologous protein expression ,modular assembly ,quantification of transgene expression ,standardized workflow ,terminator ,Science - Abstract
Chlamydomonas reinhardtii has many attractive features for use as a model organism for both fundamental studies and as a biotechnological platform. Nonetheless, despite the many molecular tools and resources that have been developed, there are challenges for its successful engineering, in particular to obtain reproducible and high levels of transgene expression. Here we describe a synthetic biology approach to screen several hundred independent transformants using standardised parts to explore different parameters that might affect transgene expression. We focused on terminators and, using a standardised workflow and quantitative outputs, tested 9 different elements representing three different size classes of native terminators to determine their ability to support high level expression of a GFP reporter gene. We found that the optimal size reflected the median size of element found in the C. reinhardtii genome. The behaviour of the terminator parts was similar with different promoters, in different host strains and with different transgenes. This approach is applicable to the systematic testing of other genetic elements, facilitating comparison to determine optimal transgene design.
- Published
- 2021
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14. Antenna Array and Waveform Design for 4-D-Imaging mmWave MIMO Radar Sensors
- Author
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Karimian-Sichani, Nazila, Alaee-Kerahroodi, Mohammad, Mysore Rama Rao, Bhavani Shankar, Mehrshahi, Esfandiar, and Ghorashi, Seyed Ali
- Abstract
4D-Imaging mmWave multiple-input-multiple-output (MIMO) radars have significant advantages over conventional radar sensors. However, the physical placement of transmit and receive antennas to achieve the desired virtual array, while considering cost and efficiency is not intuitive. Furthermore, due to the large number of transmit elements in such systems, they necessitate an appropriate strategy for transmit waveforms design. These waveforms should be separable on the receive side while also having low auto-correlation sidelobes. In this paper, we propose a general optimization framework based on Coordinate Descent (CD), to solve the problems of antenna array and waveform design for 4D-imaging radars. First, we propose the CD approach for an optimal array configuration design to obtain a sequence of optimal antenna placements. The objective function converges to a solution that guarantees the desired number of transmit and receive antennas, while the obtained virtual array is as close to the desired one as possible. We, then, propose an entry-based optimization framework based on CD, to jointly design a phase-modulated waveform set optimized based on weighted integrated sidelobe level and spectrum shaping, considering the radar operates adjacent to communication systems. Finally, the simulation results are provided to assess the validity of our proposed methods for both array and waveform design. The former is validated by simulating the virtual array of several commercially available 4D-Imaging radar products. The latter demonstrates that our proposed waveform design can outperform conventional MIMOFMCW approaches, by performing comparative simulations. Finally we show that it can also provide compatibility with other communication systems.
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- 2024
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15. A New Iterative Approach in SINR Improvement of MIMO Radars by Using Combination of Orthogonal Waveforms
- Author
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Haghnegahdar, Mohamad, Imani, Sadjad, Ghorashi, Seyed Ali, and Mehrshahi, Esfandiar
- Published
- 2017
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16. A Fast Frequency Sweep – Green’s Function Based Analysis of Substrate Integrated Waveguide
- Author
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E. Abaei, G. Amendola, E. Arnieri, S. Costanzo, and E. Mehrshahi
- Subjects
Green's function methods ,Substrate integrated waveguide ,SIW ,Asymptotic Waveform Evaluation ,AWE ,Complex Frequency Hopping ,CFH ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
In this paper, a fast frequency sweep technique is applied to the analysis of Substrate Integrated Waveguides performed with a Green’s function technique. The well-known Asymptotic Waveform Evaluation technique is used to extract the Padè approximation of the frequency response of Substrate Integrated Waveguides devices. The analysis is extended to a large frequency range by adopting the Complex Frequency Hopping algorithm. It is shown that, with this technique, CPU time can be reduced of almost one order of magnitude with respect to a point by point computation.
- Published
- 2012
17. A Novel Method Describing the Space Charge Limited Region in a Planar Diode
- Author
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Mitra Ghergherehchi, Esfandiar Mehrshahi, and hesam ahmady
- Subjects
space-charge region ,space-charge limited current ,planar diode ,initial velocity ,Physics ,QC1-999 - Abstract
A novel and rather simple method is presented to describe the physics of space-charge region in a planar diode. The method deals with the issue in the time domain and as a consequence transient time behavior can be achieved. Potential distributions and currents obtained using this technique, supposing zero initial velocity for electrons, reveal absolute agreement with Child's results. Moreover, applying the method for non-zero uniform initial velocity for electrons, gives results which are in good agreement with previous works
- Published
- 2017
18. Folate Polyglutamylation is Required for Rice Seed Development
- Author
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Anukul, Nampeung, Ramos, Riza Abilgos, Mehrshahi, Payam, Castelazo, Anahi Santoyo, Parker, Helen, Diévart, Anne, Lanau, Nadège, Mieulet, Delphine, Tucker, Gregory, Guiderdoni, Emmanuel, Barrett, David A., and Bennett, Malcolm J.
- Published
- 2010
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19. A Closed-Form Transient Response of Coupled Transmission Lines
- Author
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Zahedi, Fatemeh, Mehrshahi, Esfandiar, and Jahanian, Ali
- Abstract
There is a growing interest in analysis of crosstalk noise and delay in coupled transmission lines in various fields. Due to the large number of interconnections and associated compression, this analysis is particularly significant in large integrated circuits. There are various ways to analyze crosstalk noise and delay considering the compromise between accuracy and complexity. This article presents closed-form expressions in the Laplace domain based on transmission line theory to obtain crosstalk noise and delay of identical and nonidentical coupled interconnections. To this end, a simple model is proposed, which encompasses both capacitive and inductive coupling features in coupled interconnections. Moreover, it serves to handle both functional and dynamic crosstalk. The crosstalk noise voltage and propagation delay at the far-end of coupled lines are observed. The transient response of coupled transmission lines is demonstrated for various case studies. The obtained results are compared with Advanced Design System simulations indicating that the proposed model computes crosstalk noise and captures waveform shapes with desired accuracy. Moreover, the derived form is scalable for the analysis of N coupled multiconductors, opening new horizons to analyze the complex integrated circuit interconnections with decent accuracy and high computation speed.
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- 2022
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20. Vitamin B12 bioaccumulation in Chlorella vulgaris grown on food waste-derived anaerobic digestate.
- Author
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Papadopoulos, Konstantinos P., de Souza, Marcella Fernandes, Archer, Lorraine, Illanes, Ana Camila Zenteno, Harrison, Ellen L., Taylor, Fiona, Davey, Matthew P., Gallardo, Daniela Ahuatzin, Komakech, Allan J., Radmehr, Shahla, Holzer, Andre, Meers, Erik, Smith, Alison G., and Mehrshahi, Payam
- Abstract
Anaerobic digestion plays a pivotal role in the modern circular economy, as it offers a sustainable solution for converting organic waste into biogas (methane). It also results in a nutrient-rich liquid stream, referred to as digestate. This digestate is extensively applied to agricultural land as fertilizer due to its high macronutrient (N, P) content, but the bioactive micronutrients it contains and their significance for downstream applications remain largely unknown. Here, we investigate whether digestate generated from a vitamin B 12 -deficient substrate (fruit and vegetable waste) can be enriched in this vitamin through anaerobic digestion, and explore the capability of the microalga Chlorella vulgaris to grow in this medium and bioaccumulate B 12. Our findings uncover, for the first time, that substantial amounts of B 12 are synthesized during anaerobic digestion, and that C. vulgaris can effectively be enriched with this vitamin when grown in the digestate (10.6 μg Β 12 ·g
−1 dry weight). Additionally, we identified that pH-induced ammonia toxicity was the main inhibitor when growing microalgae in the digestate, which allowed us to significantly enhance productivity at lab- and pilot-scale through pH control. The case of B 12 synthesis in digestate and accumulation in microalgae highlights the potential for enhancing the value of these waste streams through the identification and utilization of bioactive compounds. [Display omitted] • Anaerobic digestion produces substantial amounts of vitamin B 12 , a bioactive compound. • Chlorella vulgaris effectively grows and accumulates B 12 when cultivated in digestate. • pH control boosts microalgae productivity in digestate, overcoming ammonia toxicity. • Digestate-grown Chlorella vulgaris can be a high-value feed in aquaculture. • Utilizing bioactive compounds like vitamin B 12 expands the applications of digestate. [ABSTRACT FROM AUTHOR]- Published
- 2023
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21. Functional analysis of folate polyglutamylation and its essential role in plant metabolism and development
- Author
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Mehrshahi, P., Gonzalez-Jorge, S., Akhtar, T. A., Ward, J. L., Santoyo-Castelazo, A., Marcus, S. E., Lara-Nunez, A., Ravanel, S., Hawkins, N. D., Beale, M. H., Barrett, D. A., Knox, J. P., Gregory, J. F. Iii, Hanson, A. D., Bennett, M. J., and Dellapenna, D.
- Published
- 2010
22. Characterising the functional importance of folate polyglutamylation in plants
- Author
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Mehrshahi, P., primary, Tucker, G., additional, and J. Bennett, M., additional
- Published
- 2007
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23. Dissecting the genetic control of folate homeostasis in plants
- Author
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Gonzalez-Jorge, S., primary, Mehrshahi, P., additional, and Bennett, M.J., additional
- Published
- 2007
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24. A Fast Frequency Sweep -- Green's Function Based Analysis of Substrate Integrated Waveguide.
- Author
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ABAEI, Elnaz, AMENDOLA, Giandomenico, ARNIERI, Emilio, COSTANZO, Sandra, and MEHRSHAHI, Esfandiar
- Subjects
GREEN'S functions ,SUBSTRATE integrated waveguides ,PERFORMANCE evaluation ,MATHEMATICAL complexes ,MOTHERBOARDS ,COMPUTER algorithms - Abstract
In this paper, a fast frequency sweep technique is applied to the analysis of Substrate Integrated Waveguides performed with a Green's Junction technique. The well-known Asymptotic Waveform Evaluation technique is used to extract the Padè approximation of the frequency response of Substrate Integrated Waveguides devices. The analysis is extended to a large frequency range by adopting the Complex Frequency Hopping algorithm. It is shown that, with this technique, CPU time can be reduced by almost one order of magnitude with respect to a point by point computation. [ABSTRACT FROM AUTHOR]
- Published
- 2012
25. Development and Environmental Significance of an Eolian Sand Ramp of Last-Glacial Age, Central Iran
- Author
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Thomas, David S.G., Bateman, Mark D., Mehrshahi, Daryoush, and O'hara, Sarah L.
- Abstract
A 25-m-thick section of mostly eolian sediment is exposed in the stream-cut flank of a sand ramp accumulated in a mountain saddle near Ardakan playa, central Iran. The well-sorted eolian sediments of the ramp contain talus beds and incipient paleosols. Morphology and bedding structures imply that southeasterly winds were primarily responsible for deposition of the eolian sand. Optical dating shows that the sand was deposited near the last glacial maximum within about 5000 yr. Surface stabilization, lack of surface scree, and the development of a stream cut between the mountain and the ramp show that sediment accumulation ceased after this time. The Siberian high pressure system may have been established over central Iran during the last glacial maximum, causing cooler temperatures and a prevalence of southeasterly winds. These colder, windier conditions would have led to frost shattering and eolian transport, both of which are not significant processes today but which are evident as past processes from the ramp sediments.
- Published
- 1997
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26. Conserved cobalamin acquisition protein 1 is essential for vitamin B12 uptake in both Chlamydomonas and Phaeodactylum.
- Author
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Sayer AP, Llavero-Pasquina M, Geisler K, Holzer A, Bunbury F, Mendoza-Ochoa GI, Lawrence AD, Warren MJ, Mehrshahi P, and Smith AG
- Subjects
- Humans, Vitamin B 12 genetics, Vitamin B 12 metabolism, Bacteria metabolism, Chlamydomonas metabolism, Diatoms genetics, Diatoms metabolism, Chlamydomonas reinhardtii genetics, Chlamydomonas reinhardtii metabolism
- Abstract
Microalgae play an essential role in global net primary productivity and global biogeochemical cycling. Despite their phototrophic lifestyle, over half of algal species depend for growth on acquiring an external supply of the corrinoid vitamin B12 (cobalamin), a micronutrient produced only by a subset of prokaryotic organisms. Previous studies have identified protein components involved in vitamin B12 uptake in bacterial species and humans. However, little is known about its uptake in algae. Here, we demonstrate the essential role of a protein, cobalamin acquisition protein 1 (CBA1), in B12 uptake in Phaeodactylum tricornutum using CRISPR-Cas9 to generate targeted knockouts and in Chlamydomonas reinhardtii by insertional mutagenesis. In both cases, CBA1 knockout lines could not take up exogenous vitamin B12. Complementation of the C. reinhardtii mutants with the wild-type CBA1 gene restored B12 uptake, and regulation of CBA1 expression via a riboswitch element enabled control of the phenotype. When visualized by confocal microscopy, a YFP-fusion with C. reinhardtii CBA1 showed association with membranes. Bioinformatics analysis found that CBA1-like sequences are present in all major eukaryotic phyla. In algal taxa, the majority that encoded CBA1 also had genes for B12-dependent enzymes, suggesting CBA1 plays a conserved role. Our results thus provide insight into the molecular basis of algal B12 acquisition, a process that likely underpins many interactions in aquatic microbial communities., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2023. Published by Oxford University Press on behalf of American Society of Plant Biologists.)
- Published
- 2024
- Full Text
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27. Overexpression of PSR1 in Chlamydomonas reinhardtii induces luxury phosphorus uptake.
- Author
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Slocombe SP, Zúñiga-Burgos T, Chu L, Mehrshahi P, Davey MP, Smith AG, Camargo-Valero MA, and Baker A
- Abstract
Remediation using micro-algae offers an attractive solution to environmental phosphate (PO
4 ) pollution. However, for maximum efficiency, pre-conditioning of algae to induce 'luxury phosphorus (P) uptake' is needed. To replicate this process, we targeted the global regulator PSR1 (Myb transcription factor: Phosphate Starvation Response 1) for over-expression in algae. Manipulating a single gene (PSR1) drove uptake of both PO3- ) pollution. However, for maximum efficiency, pre-conditioning of algae to induce 'luxury phosphorus (P) uptake' is needed. To replicate this process, we targeted the global regulator PSR1 (Myb transcription factor: Phosphate Starvation Response 1) for over-expression in algae. Manipulating a single gene (PSR1) drove uptake of both PO4 counter-ion leading to increased PolyP granule size, raising P levels 4-fold to 8% dry cell weight, and accelerated removal of PO3- from the medium. Examination of the gene expression profile showed that the P-starvation response was mimicked under P-replete conditions, switching on luxury uptake. Hyper-accumulation of P depended on a feed-forward mechanism, where a small set of 'Class I' P-transporter genes were activated despite abundant external PO2+ counter-ion leading to increased PolyP granule size, raising P levels 4-fold to 8% dry cell weight, and accelerated removal of PO4 levels, permitting more genes to be expressed (Class II), leading to more P-uptake. Our data pointed toward a PSR1-independent mechanism for detection of external PO3- which suppressed Class II genes. This model provided a plausible mechanism for P-overplus where prior P-starvation elevates PSR1 and on P-resupply causes luxury P-uptake. This is because the Class I genes, which include P-transporter genes, are not suppressed by the excess PO4 3- levels. The transporters drove a reduction in external PO4 3- levels, permitting more genes to be expressed (Class II), leading to more P-uptake. Our data pointed toward a PSR1-independent mechanism for detection of external PO4 3- which suppressed Class II genes. This model provided a plausible mechanism for P-overplus where prior P-starvation elevates PSR1 and on P-resupply causes luxury P-uptake. This is because the Class I genes, which include P-transporter genes, are not suppressed by the excess PO4 3- . Taken together, these discoveries facilitate a bio-circular approach of recycling nutrients from wastewater back to agriculture., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Slocombe, Zúñiga-Burgos, Chu, Mehrshahi, Davey, Smith, Camargo-Valero and Baker.)- Published
- 2023
- Full Text
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28. Thiamine metabolism genes in diatoms are not regulated by thiamine despite the presence of predicted riboswitches.
- Author
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Llavero-Pasquina M, Geisler K, Holzer A, Mehrshahi P, Mendoza-Ochoa GI, Newsad SA, Davey MP, and Smith AG
- Subjects
- Fungi genetics, Thiamine chemistry, Thiamine metabolism, Thiamine Pyrophosphate genetics, Thiamine Pyrophosphate metabolism, Diatoms genetics, Diatoms metabolism, Riboswitch genetics
- Abstract
Thiamine pyrophosphate (TPP), an essential co-factor for all species, is biosynthesised through a metabolically expensive pathway regulated by TPP riboswitches in bacteria, fungi, plants and green algae. Diatoms are microalgae responsible for c. 20% of global primary production. They have been predicted to contain TPP aptamers in the 3'UTR of some thiamine metabolism-related genes, but little information is known about their function and regulation. We used bioinformatics, antimetabolite growth assays, RT-qPCR, targeted mutagenesis and reporter constructs to test whether the predicted TPP riboswitches respond to thiamine supplementation in diatoms. Gene editing was used to investigate the functions of the genes with associated TPP riboswitches in Phaeodactylum tricornutum. We found that thiamine-related genes with putative TPP aptamers are not responsive to supplementation with thiamine or its precursor 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP), and targeted mutation of the TPP aptamer in the THIC gene encoding HMP-P synthase does not deregulate thiamine biosynthesis in P. tricornutum. Through genome editing we established that PtTHIC is essential for thiamine biosynthesis and another gene, PtSSSP, is necessary for thiamine uptake. Our results highlight the importance of experimentally testing bioinformatic aptamer predictions and provide new insights into the thiamine metabolism shaping the structure of marine microbial communities with global biogeochemical importance., (© 2022 The Authors. New Phytologist © 2022 New Phytologist Foundation.)
- Published
- 2022
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29. Exploring the Impact of Terminators on Transgene Expression in Chlamydomonas reinhardtii with a Synthetic Biology Approach.
- Author
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Geisler K, Scaife MA, Mordaka PM, Holzer A, Tomsett EV, Mehrshahi P, Mendoza Ochoa GI, and Smith AG
- Abstract
Chlamydomonas reinhardtii has many attractive features for use as a model organism for both fundamental studies and as a biotechnological platform. Nonetheless, despite the many molecular tools and resources that have been developed, there are challenges for its successful engineering, in particular to obtain reproducible and high levels of transgene expression. Here we describe a synthetic biology approach to screen several hundred independent transformants using standardised parts to explore different parameters that might affect transgene expression. We focused on terminators and, using a standardised workflow and quantitative outputs, tested 9 different elements representing three different size classes of native terminators to determine their ability to support high level expression of a GFP reporter gene. We found that the optimal size reflected the median size of element found in the C. reinhardtii genome. The behaviour of the terminator parts was similar with different promoters, in different host strains and with different transgenes. This approach is applicable to the systematic testing of other genetic elements, facilitating comparison to determine optimal transgene design.
- Published
- 2021
- Full Text
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30. Development of Novel Riboswitches for Synthetic Biology in the Green Alga Chlamydomonas.
- Author
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Mehrshahi P, Nguyen GTDT, Gorchs Rovira A, Sayer A, Llavero-Pasquina M, Lim Huei Sin M, Medcalf EJ, Mendoza-Ochoa GI, Scaife MA, and Smith AG
- Subjects
- 5' Untranslated Regions, Algal Proteins genetics, Algal Proteins metabolism, Aptamers, Nucleotide genetics, Aptamers, Nucleotide metabolism, Gene Expression, Mutagenesis, Thiamine Pyrophosphate metabolism, Ultraviolet Rays, Chlamydomonas metabolism, Metabolic Engineering methods, Riboswitch genetics
- Abstract
Riboswitches are RNA regulatory elements that bind specific ligands to control gene expression. Because of their modular composition, where a ligand-sensing aptamer domain is combined with an expression platform, riboswitches offer unique tools for synthetic biology applications. Here we took a mutational approach to determine functionally important nucleotide residues in the thiamine pyrophosphate (TPP) riboswitch in the THI4 gene of the model alga Chlamydomonas reinhardtii , allowing us to carry out aptamer swap using THIC aptamers from Chlamydomonas and Arabidopsis thaliana . These chimeric riboswitches displayed a distinct specificity and dynamic range of responses to different ligands. Our studies demonstrate ease of assembly as 5'UTR DNA parts, predictability of output, and utility for controlled production of a high-value compound in Chlamydomonas . The simplicity of riboswitch incorporation in current design platforms will facilitate the generation of genetic circuits to advance synthetic biology and metabolic engineering of microalgae.
- Published
- 2020
- Full Text
- View/download PDF
31. Responses of a Newly Evolved Auxotroph of Chlamydomonas to B 12 Deprivation.
- Author
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Bunbury F, Helliwell KE, Mehrshahi P, Davey MP, Salmon DL, Holzer A, Smirnoff N, and Smith AG
- Subjects
- Corrinoids metabolism, Nitrogen metabolism, Reactive Oxygen Species metabolism, Chlamydomonas metabolism, Chlamydomonas reinhardtii metabolism
- Abstract
The corrinoid B
12 is synthesized only by prokaryotes yet is widely required by eukaryotes as an enzyme cofactor. Microalgae have evolved B12 dependence on multiple occasions, and we previously demonstrated that experimental evolution of the non-B12 -requiring alga Chlamydomonas reinhardtii in media supplemented with B12 generated a B12 -dependent mutant (hereafter metE7). This clone provides a unique opportunity to study the physiology of a nascent B12 auxotroph. Our analyses demonstrate that B12 deprivation of metE7 disrupts C1 metabolism, causes an accumulation of starch and triacylglycerides, and leads to a decrease in photosynthetic pigments, proteins, and free amino acids. B12 deprivation also caused a substantial increase in reactive oxygen species, which preceded rapid cell death. Survival could be improved without compromising growth by simultaneously depriving the cells of nitrogen, suggesting a type of cross protection. Significantly, we found further improvements in survival under B12 limitation and an increase in B12 use efficiency after metE7 underwent a further period of experimental evolution, this time in coculture with a B12 -producing bacterium. Therefore, although an early B12 -dependent alga would likely be poorly adapted to coping with B12 deprivation, association with B12 -producers can ensure long-term survival whilst also providing a suitable environment for evolving mechanisms to tolerate B12 limitation better., (© 2020 The authors. All Rights Reserved.)- Published
- 2020
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32. Birth of a Photosynthetic Chassis: A MoClo Toolkit Enabling Synthetic Biology in the Microalga Chlamydomonas reinhardtii.
- Author
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Crozet P, Navarro FJ, Willmund F, Mehrshahi P, Bakowski K, Lauersen KJ, Pérez-Pérez ME, Auroy P, Gorchs Rovira A, Sauret-Gueto S, Niemeyer J, Spaniol B, Theis J, Trösch R, Westrich LD, Vavitsas K, Baier T, Hübner W, de Carpentier F, Cassarini M, Danon A, Henri J, Marchand CH, de Mia M, Sarkissian K, Baulcombe DC, Peltier G, Crespo JL, Kruse O, Jensen PE, Schroda M, Smith AG, and Lemaire SD
- Subjects
- Biotechnology, Chlamydomonas reinhardtii genetics, Gene Expression, Genes, Reporter genetics, Green Fluorescent Proteins genetics, Green Fluorescent Proteins metabolism, Plasmids genetics, Promoter Regions, Genetic, Chlamydomonas reinhardtii metabolism, Photosynthesis, Plasmids metabolism, Synthetic Biology methods
- Abstract
Microalgae are regarded as promising organisms to develop innovative concepts based on their photosynthetic capacity that offers more sustainable production than heterotrophic hosts. However, to realize their potential as green cell factories, a major challenge is to make microalgae easier to engineer. A promising approach for rapid and predictable genetic manipulation is to use standardized synthetic biology tools and workflows. To this end we have developed a Modular Cloning toolkit for the green microalga Chlamydomonas reinhardtii. It is based on Golden Gate cloning with standard syntax, and comprises 119 openly distributed genetic parts, most of which have been functionally validated in several strains. It contains promoters, UTRs, terminators, tags, reporters, antibiotic resistance genes, and introns cloned in various positions to allow maximum modularity. The toolkit enables rapid building of engineered cells for both fundamental research and algal biotechnology. This work will make Chlamydomonas the next chassis for sustainable synthetic biology.
- Published
- 2018
- Full Text
- View/download PDF
33. Synthetic biology approaches for the production of plant metabolites in unicellular organisms.
- Author
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Moses T, Mehrshahi P, Smith AG, and Goossens A
- Subjects
- Bacteria metabolism, Microalgae metabolism, Yeasts metabolism, Plants metabolism, Synthetic Biology
- Abstract
Synthetic biology is the repurposing of biological systems for novel objectives and applications. Through the co-ordinated and balanced expression of genes, both native and those introduced from other organisms, resources within an industrial chassis can be siphoned for the commercial production of high-value commodities. This developing interdisciplinary field has the potential to revolutionize natural product discovery from higher plants, by providing a diverse array of tools, technologies, and strategies for exploring the large chemically complex space of plant natural products using unicellular organisms. In this review, we emphasize the key features that influence the generation of biorefineries and highlight technologies and strategic solutions that can be used to overcome engineering pitfalls with rational design. Also presented is a succinct guide to assist the selection of unicellular chassis most suited for the engineering and subsequent production of the desired natural product, in order to meet the global demand for plant natural products in a safe and sustainable manner., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)
- Published
- 2017
- Full Text
- View/download PDF
34. ZEAXANTHIN EPOXIDASE Activity Potentiates Carotenoid Degradation in Maturing Seed.
- Author
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Gonzalez-Jorge S, Mehrshahi P, Magallanes-Lundback M, Lipka AE, Angelovici R, Gore MA, and DellaPenna D
- Subjects
- Arabidopsis growth & development, Arabidopsis Proteins genetics, Carotenoids genetics, Dioxygenases genetics, Dioxygenases metabolism, Gene Expression Regulation, Plant, Genome-Wide Association Study, Haplotypes, Mutation, Oxidoreductases genetics, Quantitative Trait Loci, Seeds genetics, Seeds growth & development, Xanthophylls genetics, Xanthophylls metabolism, Arabidopsis metabolism, Arabidopsis Proteins metabolism, Carotenoids metabolism, Oxidoreductases metabolism, Seeds metabolism
- Abstract
Elucidation of the carotenoid biosynthetic pathway has enabled altering the composition and content of carotenoids in various plants, but to achieve desired nutritional impacts, the genetic components regulating carotenoid homeostasis in seed, the plant organ consumed in greatest abundance, must be elucidated. We used a combination of linkage mapping, genome-wide association studies (GWAS), and pathway-level analysis to identify nine loci that impact the natural variation of seed carotenoids in Arabidopsis (Arabidopsis thaliana). ZEAXANTHIN EPOXIDASE (ZEP) was the major contributor to carotenoid composition, with mutants lacking ZEP activity showing a remarkable 6-fold increase in total seed carotenoids relative to the wild type. Natural variation in ZEP gene expression during seed development was identified as the underlying mechanism for fine-tuning carotenoid composition, stability, and ultimately content in Arabidopsis seed. We previously showed that two CAROTENOID CLEAVAGE DIOXYGENASE enzymes, CCD1 and CCD4, are the primary mediators of seed carotenoid degradation, and here we demonstrate that ZEP acts as an upstream control point of carotenoid homeostasis, with ZEP-mediated epoxidation targeting carotenoids for degradation by CCD enzymes. Finally, four of the nine loci/enzymatic activities identified as underlying natural variation in Arabidopsis seed carotenoids also were identified in a recent GWAS of maize (Zea mays) kernel carotenoid variation. This first comparison of the natural variation in seed carotenoids in monocots and dicots suggests a surprising overlap in the genetic architecture of these traits between the two lineages and provides a list of likely candidates to target for selecting seed carotenoid variation in other species., (© 2016 American Society of Plant Biologists. All Rights Reserved.)
- Published
- 2016
- Full Text
- View/download PDF
35. Redefining the metabolic continuity of chloroplasts and ER.
- Author
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Mehrshahi P, Johnny C, and DellaPenna D
- Subjects
- Biological Evolution, Membrane Fusion, Models, Biological, Plant Cells metabolism, Chloroplasts metabolism, Endoplasmic Reticulum metabolism
- Abstract
As a hub for plant metabolism, plastids extensively exchange metabolites with the extraplastid environment. For polar metabolites, membrane transporters mediate this exchange, but for many plastid-synthesized nonpolar compounds, such transporters remain elusive. Here, we discuss recent data from transorganellar complementation studies that demonstrate that enzymes in one organelle can directly access nonpolar metabolites from a companion organelle. We propose that a mechanism, based on hemifused-membranes at plastid-endoplasmic reticulum (ER) contact sites, facilitates interorganellar interactions and allows enzymes direct, transporter-independent access to a range of nonpolar compounds in both organelle membranes. In a wider context, interorganellar metabolism at hemifusion interfaces would allow evolution of membrane-spanning pathways for the many thousands of nonpolar metabolites in the plant kingdom to be uncoupled from coevolution with nonpolar metabolite transporters., (Copyright © 2014 Elsevier Ltd. All rights reserved.)
- Published
- 2014
- Full Text
- View/download PDF
36. Transorganellar complementation redefines the biochemical continuity of endoplasmic reticulum and chloroplasts.
- Author
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Mehrshahi P, Stefano G, Andaloro JM, Brandizzi F, Froehlich JE, and DellaPenna D
- Subjects
- Arabidopsis, Carotenoids biosynthesis, Carotenoids metabolism, Cloning, Molecular, Image Processing, Computer-Assisted, Immunoblotting, Microscopy, Fluorescence, Biosynthetic Pathways genetics, Chloroplasts metabolism, Endoplasmic Reticulum metabolism, Enzymes metabolism, Genetic Complementation Test methods, Tocopherols metabolism
- Abstract
Tocopherols are nonpolar compounds synthesized and localized in plastids but whose genetic elimination specifically impacts fatty acid desaturation in the endoplasmic reticulum (ER), suggesting a direct interaction with ER-resident enzymes. To functionally probe for such interactions, we developed transorganellar complementation, where mutated pathway activities in one organelle are experimentally tested for substrate accessibility and complementation by active enzymes retargeted to a companion organelle. Mutations disrupting three plastid-resident activities in tocopherol and carotenoid synthesis were complemented from the ER in this fashion, demonstrating transorganellar access to at least seven nonpolar, plastid envelope-localized substrates from the lumen of the ER, likely through plastid:ER membrane interaction domains. The ability of enzymes in either organelle to access shared, nonpolar plastid metabolite pools redefines our understanding of the biochemical continuity of the ER and chloroplast with profound implications for the integration and regulation of organelle-spanning pathways that synthesize nonpolar metabolites in plants.
- Published
- 2013
- Full Text
- View/download PDF
37. Engineering starch accumulation by manipulation of phosphate metabolism of starch.
- Author
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Weise SE, Aung K, Jarou ZJ, Mehrshahi P, Li Z, Hardy AC, Carr DJ, and Sharkey TD
- Subjects
- Arabidopsis metabolism, Arabidopsis Proteins genetics, Biomass, Computational Biology, Dual-Specificity Phosphatases genetics, Gene Expression Regulation, Plant, Phosphorylation, Phosphotransferases (Paired Acceptors) genetics, Plant Leaves metabolism, Plants, Genetically Modified genetics, Plants, Genetically Modified metabolism, Promoter Regions, Genetic, RNA Interference, Zea mays genetics, Zea mays metabolism, Arabidopsis genetics, Arabidopsis Proteins metabolism, Dual-Specificity Phosphatases metabolism, Phosphates metabolism, Phosphotransferases (Paired Acceptors) metabolism, Starch metabolism
- Abstract
A new understanding of leaf starch degradation has emerged in the last 10 years. It has been shown that starch phosphorylation and dephosphorylation are critical components of this process. Glucan, water dikinase (GWD) (and phosphoglucan, water dikinase) adds phosphate to starch, and phosphoglucan phosphatase (SEX4) removes these phosphates. To explore the use of this metabolism to manipulate starch accumulation, Arabidopsis (Arabidopsis thaliana) plants were engineered by introducing RNAi constructs designed to reduce expression of AtGWD and AtSEX4. The timing of starch build-up was altered with ethanol-inducible and senescence-induced gene promoters. Ethanol induction of RNAi lines reduced transcript for AtGWD and AtSEX4 by 50%. The transgenic lines had seven times more starch than wild type at the end of the dark period but similar growth rates and total biomass. Elevated leaf starch content in maize leaves was engineered by making an RNAi construct against a gene in maize that appeared to be homologous to AtGWD. The RNAi construct was expressed using the constitutive ubiquitin promoter. Leaf starch content at the end of a night period in engineered maize plants was 20-fold higher than in untransformed plants with no impact on total plant biomass. We conclude that plants can be engineered to accumulate starch in the leaves with little impact on vegetative biomass., (© 2012 The Authors. Plant Biotechnology Journal © 2012 Society for Experimental Biology, Association of Applied Biologists and Blackwell Publishing Ltd.)
- Published
- 2012
- Full Text
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38. Functional analysis of folate polyglutamylation and its essential role in plant metabolism and development.
- Author
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Mehrshahi P, Gonzalez-Jorge S, Akhtar TA, Ward JL, Santoyo-Castelazo A, Marcus SE, Lara-Núñez A, Ravanel S, Hawkins ND, Beale MH, Barrett DA, Knox JP, Gregory JF 3rd, Hanson AD, Bennett MJ, and Dellapenna D
- Subjects
- Arabidopsis genetics, Arabidopsis growth & development, Arabidopsis Proteins genetics, Homeostasis, Isoenzymes genetics, Isoenzymes metabolism, Multigene Family, Pantothenic Acid, Pectins metabolism, Peptide Synthases genetics, Phenotype, Seeds enzymology, Sucrose, Arabidopsis enzymology, Arabidopsis Proteins metabolism, Folic Acid metabolism, Peptide Synthases metabolism
- Abstract
Cellular folates function as co-enzymes in one-carbon metabolism and are predominantly decorated with a polyglutamate tail that enhances co-enzyme affinity, subcellular compartmentation and stability. Polyglutamylation is catalysed by folylpolyglutamate synthetases (FPGSs) that are specified by three genes in Arabidopsis, FPGS1, 2 and 3, which reportedly encode plastidic, mitochondrial and cytosolic isoforms, respectively. A mutational approach was used to probe the functional importance of folate polyglutamylation in one-carbon metabolism and development. Biochemical analysis of single FPGS loss-of-function mutants established that folate polyglutamylation is essential for organellar and whole-plant folate homeostasis. However, polyglutamylated folates were still detectable, albeit at lower levels, in organelles isolated from the corresponding isozyme knockout lines, e.g. in plastids and mitochondria of the fpgs1 (plastidial) and fpgs2 (mitochondrial) mutants. This result is surprising given the purported single-compartment targeting of each FPGS isozyme. These results indicate redundancy in compartmentalised FPGS activity, which in turn explains the lack of anticipated phenotypic defects for the single FPGS mutants. In agreement with this hypothesis, fpgs1 fpgs2 double mutants were embryo-lethal, fpgs2 fpgs3 mutants exhibited seedling lethality, and fpgs1 fpgs3 mutants were dwarfed with reduced fertility. These phenotypic, metabolic and genetic observations are consistent with targeting of one or more FPGS isozymes to multiple organelles. These data confirm the importance of polyglutamylation in folate compartmentation, folate homeostasis and folate-dependent metabolic processes, including photorespiration, methionine and pantothenate biosynthesis., (© 2010 The Authors. Journal compilation © 2010 Blackwell Publishing Ltd.)
- Published
- 2010
- Full Text
- View/download PDF
39. A central role for gamma-glutamyl hydrolases in plant folate homeostasis.
- Author
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Akhtar TA, Orsomando G, Mehrshahi P, Lara-Núñez A, Bennett MJ, Gregory JF 3rd, and Hanson AD
- Subjects
- Arabidopsis genetics, DNA, Bacterial, Fruit enzymology, Homeostasis, Solanum lycopersicum genetics, Multigene Family, Mutagenesis, Insertional, Plant Leaves metabolism, Plant Proteins genetics, Polyglutamic Acid metabolism, RNA Interference, Vacuoles metabolism, gamma-Glutamyl Hydrolase genetics, Arabidopsis enzymology, Folic Acid metabolism, Solanum lycopersicum enzymology, Plant Proteins metabolism, gamma-Glutamyl Hydrolase metabolism
- Abstract
Most cellular folates carry a short poly-γ-glutamate tail, and this tail is believed to affect their efficacy and stability. The tail can be removed by γ-glutamyl hydrolase (GGH; EC 3.4.19.9), a vacuolar enzyme whose role in folate homeostasis remains unclear. In order to probe the function of GGH, we modulated its level of expression and subcellular location in Arabidopsis plants and tomato fruit. Three-fold overexpression of GGH in vacuoles caused extensive deglutamylation of folate polyglutamates and lowered the total folate content by approximately 40% in Arabidopsis and tomato. No such effects were seen when GGH was overexpressed to a similar extent in the cytosol. Ablation of either of the major Arabidopsis GGH genes (AtGGH1 and AtGGH2) alone did not significantly affect folate status. However, a combination of ablation of one gene plus RNA interference (RNAi)-mediated suppression of the other (which lowered total GGH activity by 99%) increased total folate content by 34%. The excess folate accumulated as polyglutamate derivatives in the vacuole. Taken together, these results suggest a model in which: (i) folates continuously enter the vacuole as polyglutamates, accumulate there, are hydrolyzed by GGH, and exit as monoglutamates; and (ii) GGH consequently has an important influence on polyglutamyl tail length and hence on folate stability and cellular folate content., (© 2010 The Authors. Journal compilation © 2010 Blackwell Publishing Ltd.)
- Published
- 2010
- Full Text
- View/download PDF
40. Folate biofortification in food plants.
- Author
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Bekaert S, Storozhenko S, Mehrshahi P, Bennett MJ, Lambert W, Gregory JF 3rd, Schubert K, Hugenholtz J, Van Der Straeten D, and Hanson AD
- Subjects
- Carbon-Nitrogen Ligases genetics, Carbon-Nitrogen Ligases metabolism, GTP Cyclohydrolase genetics, GTP Cyclohydrolase metabolism, Models, Biological, Plants, Edible enzymology, Transaminases, Folic Acid biosynthesis, Plants, Edible genetics, Plants, Edible metabolism, Plants, Genetically Modified
- Abstract
Folate deficiency is a global health problem affecting many people in the developing and developed world. Current interventions (industrial food fortification and supplementation by folic acid pills) are effective if they can be used but might not be possible in less developed countries. Recent advances demonstrate that folate biofortification of food crops is now a feasible complementary strategy to fight folate deficiency worldwide. The genes and enzymes of folate synthesis are sufficiently understood to enable metabolic engineering of the pathway, and results from pilot engineering studies in plants (and bacteria) are encouraging. Here, we review the current status of investigations in the field of folate enhancement on the eve of a new era in food fortification.
- Published
- 2008
- Full Text
- View/download PDF
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