PLANT TRANSFORMATION

 TRANSFORMATION OF PLANT


Tissue culture of plants

Plant transformation is often accomplished by inserting plasmid constructions or fragments of plasmid constructs into the genome of a plant cell. It is not easy to regrow entire transgenic plants from changed cells. Many plant cells are totipotent, which means they can regenerate an entire plant from a single cell. Tissue culture, on the other hand, is time-consuming, labor-intensive, necessitates specialised skills, and has the potential to trigger DNA changes within plant cells. Plant tissue culture systems in some crops, such as soybean and sunflower, are extremely difficult. Plant-transformation technologies based on tissue culture have mostly been used to develop commercial GM crops.


Transformation technologies that are commonly used

The first plants were transformed utilising Agrobacterium-mediated transformation in the mid-1980s. This approach takes advantage of the crown gall disease-causing agent Agrobacterium tumefaciens' intrinsic proclivity to transfer genes into plant genomes. This approach may be used to consistently change many plant species, including tobacco and Arabidopsis. Most crop plants are not receptive to routine Agrobacterium transformation (19). The gene gun, also known as microprojectile bombardment, was invented in 1987 to address this issue. Microprojectile bombardment employs the utilisation of micrometer-sized particles coated with DNA that are propelled to puncture plant cells at random. This method's efficacy is broader than that of Agrobacterium, but it is less accurate in its transgenic integration patterns.


New genetic modification technologies

Transformation without the use of tissue culture

Beginning in the late 1980s, successful trials were carried out to reduce the reliance on tissue culture in plant transformation. A new gene pistol was employed to bombard genes into soybean seedling meristems in one creative application (6, 42). Following the bombardment, the meristems were put in cytokinin-containing media to produce numerous shoots. This approach did not use any selectable markers, instead relying on the presence of beta-glucuronidase (GUS) in putatively transformed tissues to detect stable transformation. However, in order to identify gene expression and transgenic status, this approach needed damaging tissue sample and an expensive substrate (X-GLUC). Vacuum infiltration of Arabidopsis was the first approach to completely circumvent tissue culture. In this procedure, emerging floral meristems/flowers are placed under vacuum in an Agrobacterium solution, and germ cells are transformed.


Visual selection

Once changed, cells are frequently picked using antibiotics or herbicides, which destroy untransformed cells (negative selection). Positive selection systems are being developed as a result of research. Cells transformed with a gene that permits them to metabolise mannose (28, 64) or to be more receptive to cytokinin (36) for example, allow transformation to occur in the absence of antibiotic or herbicide resistance genes. Selection based on a visible marker gene, such as the one encoding the green fluorescent protein, is another option (GFP).


Chimeraplasty

Plant transformation methods have clearly gotten more efficient, allowing for the production of a large number of transgenic plants and the subsequent commercialization of a diverse range of transgenic crops. Chimeraplasty is a method that allows for precise genetic manipulation of plants without transformation. Chimeric DNA/RNA can be used to introduce point or frameshift mutations (8). This method has proven to be effective on tobacco and corn, but it should hold enormous promise for making precise but minor genetic modifications in nearly any crop.

BIOSAFETY IN THE ENVIRONMENT AND IN HEALTH

The concept of risk assessment in agricultural and food technologies is not new. Each advancement in food production has brought with it its own set of potential hazards. These have included increased pesticide exposure in conventional agriculture as well as increased pathogen exposure in organic farming. The dangers connected with genetically modified organisms are similar to those associated with crop hybridization, which was a cornerstone of the first green revolution. Whereas hybridization involves the transfer of hundreds of genes from one plant to another, resulting in a variety of effects, genetic modification (GM) involves the transfer of one to a few genes, resulting in more predictable consequences. As a result, GM should result in fewer unforeseen consequences. Unfortunately, this is not the message that the general population receives.


BIOSAFETY IN THE ENVIRONMENT

Transgenic crops' increased invasiveness and voluntarism


Crops will have a suite of new abilities and will be cultivated in new geographic areas as new genes are found and used by the biotechnology sector. Some have argued that transgenic and novel traits contained in crops such as alfalfa (Medicago sativa), canola (Brassica napus and Brassica rapa), sunflower (Helianthus annuus), and rice (Oryza sativa) that have some "weed-like" characteristics could allow the crop itself to become weedier and invasive.


Intraspecific hybridization is the formation of hybrids between species.


When transgenic crops are grown in close proximity to non-transgenic kinds, intraspecific hybridization may occur. Saving seed from the previous year's harvest may allow transgenic material to become accidentally persistent. Wind pollinated crops, such as maize and other grain crops, have the capacity to transmit genes to neighbouring conspecifics regardless of whether the crop is GM or conventional.


Interspecific hybridization and the persistence of transgenes

Hybridization between closely related species can be a pathway for transgenes to enter wild populations. Crop plants with weedy wild cousins are especially problematic. A transgene, if expressed in the genetic background of a weed species, could boost the plant's fitness in nature. In the worst-case, albeit improbable, situation, the plant could become more invasive and competitive, causing damage to natural ecosystems in a relatively short period of time.

Interspecific hybridization is dependent on a number of factors in order to allow gene transfer across related species. There must be some naturally occurring wild cousins of the crop growing nearby cultivation.

The ability of transgenic hybrids and backcrosses to promote fitness is dependent on the type of the transgene and the environment. Weeds having a transgene that imparts herbicide resistance, for example, would be a nuisance in agriculture but would have minimal effect in a non-agricultural environment where the chemical is not present.


Non-target organism effects

Transgenic crops that produce insecticidal transgenes to control agricultural pests may have unintended consequences for non-target organisms. Three investigations using corn modified with a Bacillus thuringiensis (Bt) insecticidal transgene found indications of non-target effects. The authors came to the conclusion that Bt corn constituted a risk to non-target monarch populations that ate milkweed near Bt cornfields.


Management of Resistance

Insect pest resistance to transgenic proteins may limit the length of time that an insecticidal transgenic variety can be produced. The diamondback moth, a major pest of Brassica crops around the world, was the first pest to gain resistance to Bt toxins used in microbial formulations in open-field populations. Bt resistance has recently been identified in at least two independent recessive loci with distinct mechanisms of action. To date, no dominantly inherited Bt resistance genes have been identified, but this discovery would severely limit the efficacy of future Bt crops.


BIOSAFETY OF FOOD

Toxicity

Any substance that enters the food supply is subject to rigorous food safety testing. A potentially harmful transgenic product, such as Bt toxin, must, for example, meet the same safety regulations as any biochemical pesticide product. Exceptions to this rule occur when the gene product generated in transgenic plants is essentially identical to a chemical already in the food supply. Food toxicity testing is required when a plant overproduces inherent chemicals or when the transgenic product has a known degree of toxicity.



Allergenicity

Another food safety worry is the possibility that genetically modified foods will introduce allergies into the food chain. If the allergenicity of the substance is known, the review procedure is sped up. Gene products that are typically non-allergenic will not become allergic when produced in a transgenic plant. There are no known cases of allergies to plant ferritin, for example. Allergenicity assessment is significantly more difficult when the allergenicity of a transgenic protein is unknown. GFP is a nice example once more.

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