Genetic engineering of osmoregulation impact on plant productivity for food, chemicals, and energy.
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Genetic Engineering↗
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Engineering salt tolerance in plants.
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Biological Transport↗
Evaluating genetic containment strategies for transgenic plants.
One of the primary concerns about genetically engineered crop plants is that they will hybridize with wild relatives, permitting the transgene to escape into the environment. The likelihood that a transgene will spread in the environment depends on its potential fitness impact. The fitness conferred by various transgenes to crop and/or wild-type hybrids has been evaluated in several species. Different strategies have been developed for reducing the probability and impact of gene flow, including physical separation from wild relatives and genetic engineering. Mathematical models and empirical experimental evidence suggest that genetic approaches have the potential to effectively prevent transgenes from incorporating into wild relatives and becoming established in wild populations that are not reproductively isolated from genetically engineered crops.
Chimera↗
Medical molecular farming: production of antibodies, biopharmaceuticals and edible vaccines in plants.
The use of plants for medicinal purposes dates back thousands of years but genetic engineering of plants to produce desired biopharmaceuticals is much more recent. As the demand for biopharmaceuticals is expected to increase, it would be wise to ensure that they will be available in significantly larger amounts, on a cost-effective basis. Currently, the cost of biopharmaceuticals limits their availability. Plant-derived biopharmaceuticals are cheap to produce and store, easy to scale up for mass production, and safer than those derived from animals. Here, we discuss recent developments in this field and possible environmental concerns.
Antibodies↗
The production of long chain polyunsaturated fatty acids in transgenic plants by reverse-engineering.
The nutritional importance of long chain polyunsaturated fatty acids (LC-PUFAs) is now well-established, with these lipids playing roles in human development and the prevention of various diseases. In particular, n-3 polyunsaturated fatty acids are protective against cardiovascular disease (CVD) and risks associated with metabolic syndrome. In view of the decline in marine fish stocks, which represent the predominant natural reserves of n-3 long chain polyunsaturates, alternative sources are urgently required. One approach may be to express the LC-PUFA-biosynthetic pathway in transgenic plants. Recent progress in validating this approach has now emerged, demonstrating the feasibility of using transgenic plants to synthesise these important human nutrients.
Animals↗
A simple plant and tissue culture growth chamber for the regeneration of tobacco mesophyll protoplasts.
The isolation and regeneration of tobacco mesophyll protoplasts from fully developed leaves, an important methodological step in plant genetic engineering as well as in plant cell biology and physiology, has been proven unreliable to the extent that it has become a significant setback to basic research. This unfortunate situation is primarily due to the suboptimal physiological state of greenhouse-grown protoplast donor plants. A technically simple and inexpensive method, based on the utilization of commercial Phototron units, is described for the production of suitable tobacco donor plants. Furthermore, a modified version of such a culture unit can be used to regenerate plants from protoplast-derived calli.
Atmosphere Exposure Chambers↗
Engineering photoassimilate partitioning in tobacco plants improves growth and productivity and provides pathogen resistance.
Expression of pathogenesis-related (PR) genes is part of the plant's natural defense response against pathogen attack. To study the in vivo role and function of the maize PRms protein, tobacco plants were transformed with the PRms cDNA under the control of the CaMV35S promoter. Transgenic tobacco plants grow faster and yield more leaf and seed biomass. By using immunoelectron microscopy, we found that PRms is associated with plasmodesmata in leaves of transgenic tobacco plants. Furthermore, we found that activation of sucrose efflux from photosynthetically active leaves and accumulation of higher levels of sucrose in leaf tissues are characteristic features of PRms tobacco plants. This, in turn, results in the constitutive expression of endogenous tobacco PR genes and resistance to phytopathogens. The expression of multiple plant defense genes can then be achieved by using a single transgene. These data provide a new approach for engineering disease-resistant plants while simultaneously improving plant yield and productivity through the modification of photoassimilate partitioning.
Carbohydrate Metabolism↗
[Advances in the research of genetic engineering of heavy metal resistance and accumulation in plants].
Using plants to remove or inactivate heavy metal pollutants from soils and surface waters provide a cheap and sustainable approach of Phytoremediation. However, field trials suggested that the efficiency of contaminant removal using natural hyperaccumulators is insufficient, due to that many of these species are slow growing and produce little shoot biomass. These factors severely constrain their potential for large-scale decontamination of polluted soils. Moreover, both the micronutrient and toxic metal content accumulated in crops determine the quality and safety of our food-chain. By a transgenic approach, the introduction of novel genes responsible for hyperaccumulating phenotype into high biomass plants and/or stable crops uptaking minerals as food is a promising strategy for the development of effective techniques of phytoremediation and improvement of nutritional value of stable food through a viable commercialization. Recently, the progress at molecular level for heavy metal uptaking, detoxification and hyperaccumulation in plants, and also the clarification of some functional genes in bacteria, yeasts, plants and animals, have advanced the research on genetic engineering plants of heavy metal resistance and accumulation, and on the functional genes (e . g. gsh1, MerA and ArsC) and their genetic transformated plants. These studies demonstrated commercialization potentials of phytoremediation. In this paper, the molecular approach, effects and problems in gene transformation were discussed in details, and also the strategy and emphases were probed into the future research.
Biodegradation, Environmental↗
Restoration of fertility by antisense RNA in genetically engineered male sterile tobacco plants.
Transgenic tobacco plants (Nicotiana tabacum L.) expressing the rolC gene of Agrobacterium rhizogenes under the transcriptional control of the 35S RNA promoter are male sterile. When these plants are genetically crossed with others containing the rolC gene linked in antisense orientation to the 35S RNA promoter, hybrid progeny display restoration of male fertility. Moreover, hybrid progeny are revertant for other features of the rolC phenotype, such as restoration of plant height, leaf pigment content and female fertility. The level of restoration of the characteristics of untransformed tobacco appeared to be independent of the steady-state level of antisense RNA. Addition of six transcriptional enhancer sequences upstream of the 35S transcriptional start region in the antisense construct led to a higher steady-state level of antisense RNA than that produced using a promoter linked to a single enhancer sequence. However no significant difference was observed in the level of attenuation of the rolC phenotype in the progeny of crosses with either one or six transcriptional enhancers linked to the antisense rolC gene. Antisense constructs comprising only 189 bp of the rolC 5' coding region appeared less efficient in attenuating the rolC phenotype than those including the whole rolC coding region as well as its 3' untranslated region. Furthermore, results from experiments on light-controlled rolC gene expression indicate that microsporogenesis is sensitive to rolC gene action during the early stages of flower development.
Bacterial Proteins↗
Genetically engineered microorganisms to rescue plants from frost injury.
Ice nucleation active bacteria belonging to genera Pseudomonas, Xanthomonas and Erwinia contribute to frost damage to plants by initiating the formation of ice in plants that would otherwise supercool and avoid the damaging ice formation. The biological control of frost injury can be achieved by the application of non-ice nucleation active bacteria to the plant surfaces before they become colonized by Ice+ species. ice genes have been cloned from Pseudomonas and isogenic Ice- derivatives constructed via genetic manipulations. These genetically engineered microorganisms (GEMs) have been released into the environment to control the frost damage. The incidence of frost injury to the plants has, thereby, been reduced by 50-85% during natural frosts. These GEMs do not survive in soil and show no aerial dispersal in the environment.
Amino Acid Sequence↗
Engineering pathogen resistance in crop plants.
As the world population continues to increase, food supplies must also grow to meet nutritional requirements. One means of ensuring the stability and plentitude of the food supply is to mitigate crop loss caused by plant pathogens. Strategies for combating disease include traditional technologies such as plant breeding and chemical applications; current technologies such as generating transgenic plants that express components of known defense signaling pathways; and the adaptation of newer technologies such as RNA silencing of pathogen and plant transcripts. Breeding has been used to pyramid resistance (R) genes into many different plants including rice. Chemical strategies include application of salicylic acid (SA) analogs to stimulate systemic acquired resistance (SAR) responses. Genetic screens in Arabidopsis have identified genes controlling SAR and these genes have been manipulated and used to engineer crop plants. The diseases caused by plant viruses are being thwarted through the initiation of endogenous RNA silencing mechanisms. Many of these strategies show great promise, some limitations, and exciting opportunities to develop many new tools for combating plant pests.
Crops, Agricultural↗
Plastid biotechnology: prospects for herbicide and insect resistance, metabolic engineering and molecular farming.
Transgene expression from the chloroplast (plastid) genome offers several attractions to plant biotechnologists, including high-level accumulation of foreign proteins, transgene stacking in operons and a lack of epigenetic interference with the stability of transgene expression. In addition, the technology provides an environmentally benign method of plant genetic engineering, because plastids and their genetic information are maternally inherited in most crops and thus are largely excluded from pollen transmission. During the past few years, researchers in both the public and private sectors have begun to explore possible areas of application of plastid transformation in plant biotechnology as a viable alternative to conventional nuclear transgenic technologies. Recent proof-of-concept studies highlight the potential of plastid genome engineering for the expression of resistance traits, the production of biopharmaceuticals and metabolic pathway engineering in plants.
Agriculture↗
Guard cell abscisic acid signalling and engineering drought hardiness in plants.
Guard cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants through transpiration to the atmosphere. Guard cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of guard cell abscisic acid signalling have been discovered. The molecular understanding of the guard cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.
Abscisic Acid↗
Agrobacterium is not alone: gene transfer to plants by viruses and other bacteria.
Agrobacterium-mediated genetic transformation is the most widely used technology for obtaining the overexpression of recombinant proteins in plants. However, complex patent issues related to the use of Agrobacterium as a tool for plant genetic engineering and the general requirement of establishing transgenic plants can create obstacles in using this technology for speedy research and development and for agricultural improvements in many plant species. Recent studies addressing these issues have shown that virus-based vectors can be efficiently used for high transient expression of foreign proteins in transfected plants and that non-Agrobacterium bacterial species can be used for the production of transgenic plants, laying the foundation for alternative tools for future plant biotechnology.
Gene Transfer Techniques↗
Engineered male sterility in plants.
We constructed two chimaeric ribonuclease genes that are specifically expressed in anthers of tobacco and rapeseed plants. The expression of these genes affects the production of functional and viable pollen yielding plants that are male sterile. This dominant gene for nuclear male sterility should facilitate the production of hybrid seed in various crops.
Brassica↗
Transgenesis and yield: what are our targets?
Plant metabolic engineering has been used to generate a wide range of transgenic lines in which specific metabolic steps have been targeted. Attempts to increase yield of some agronomically important crops using this approach have highlighted the inherent complexities of modulating plant metabolism. In light of the recent findings by Regierer et al. this article addresses the major challenges faced with respect to enhancing yield through transgenesis.
Gene Expression Regulation, Plant↗
The interaction of Agrobacterium Ti-plasmid DNA and plant cells.
The tumour-inducing plasmids of Agrobacterium tumefaciens (Ti-plasmids) reveal several interesting properties. They are catabolic plasmids, which, instead of rendering Agrobacterium strains capable of catabolizing compounds found in Nature, force a plant to synthesize these catabolites (denoted 'opines'). This situation is obtained by insertion of a segment of the Ti-plasmid (the T-DNA) into the plant nucleus, where T-DNA genes become expressed and intervene in the biosynthesis of these opines. Cells containing the T-DNA behave as neoplasms (crown gall cells). Southern blotting shows that the insertion process responsible for T-DNA transfer probably recognizes special sequences on the T-DNA since the length of the T-DNA segment observed in different, independently isolated tumour lines was found to be similar. For the nopaline Ti-plasmids both left-hand and right-hand borders were found to be constant. For the octopine plasmid the left border was constant and at least two classes of right-hand borders were found. Upon redifferentiation of the transformed plant cells, the T-DNA was found to be conserved in all somatic cells examined. However, small deletions at the border fragments of the T-DNA have been observed. The exact arrangement and copy number of the T-DNA in a nucleus is still under study, but genomic cloning has already revealed that an interspersed tandem arrangement is dominant in nopaline tumours. Clones containing both the right border of one T-DNA and the left border of the neighbouring tandem T-DNA were isolated. In order to identify the different T-plasmid encoded functions an extensive use was made of transposon insertion mutagenesis. When an antibiotic resistance transposon was inserted into the non-essential regions of the T-DNA, a linked transfer to the plant DNA of the transposon together with the T-DNA was observed. This indicates that Ti-plasmids are possible vectors for genetic engineering in plants. A strategy is described for insertion of any cloned DNA segment into the T-DNA.
Amino Acids↗
Performance evaluation of reverse osmosis desalination plants for rural water supply in a developing country--a case study.
Performance evaluation of two reverse osmosis (RO) desalination plants (DSP) at villages: Melasirupodhu (30 m3 day(-1)) and Sikkal (50 m3 day(-1)) in Ramanathpuram district, Tamil Nadu (India) were studied so as to bring out the state-of-art of their operation and maintenance (O&M). Detailed information on plant design and engineering, water quality, plant personnel, and cost of O&M was collected for a period of three years after commissioning of the two plants. Feed water was brackish, the TDS varied in the range of 6500-8500 mg L(-1) at Melasirupodhu and 5300-7100 mg L(-1) at Sikkal villages. The product water quality was observed to be gradually deteriorating as the salt rejection by the membranes decreased with time. The salt rejection was 97-99% at the time of commissioning of the plants, and came down to 89-90% at the end of 3 years of operation. Product water TDS soon after installation of the plants was excellent and within desirable limits of BIS. After three years of operation, few parameters exceeded the desirable limits, however, they were found to be within permissible limits of BIS. The analyses of the data showed that both plants were operated only at 30-36% of the design capacity. Plant shut-down due to inadequate and erratic power supply, and plant break-down and inherent delay in repairs due to lack of adequate infrastructure were found to be the major causes for the low utilization of the plants. Consequently the recurring cost of product water production enhanced to Rs. 25.0/m3 at Melasirupodhu and Rs. 17.5 m(-3) at Sikkal, as against the estimated cost of Rs. 15.0/m3 and Rs. 11.0/m3, respectively, as per the design. Over the years, the energy consumption for the product water output increased reflecting higher operational pressures needed with the aging of the membranes.
Conservation of Energy Resources↗