Question

The use of Agrobacterium tumefaciens has contributed enormously to the development of transgenic plants. Discuss this contribution and cite five examples of improvements in characteristics of crop plants resulting from genetic engineering. State 3 concerns raised about these genetically modified organisms?

Answer 1

Plasmids from the plant pathogenic bacterium Agrobacterium tumefaciens is chiefly responsible for the successful genetic engineering of plants.Normally infection in dicot plants cells by bacterium transform the cell in to tumor cells and crown gall diseases develop.Tumor is developed due to the insertion of bacterial gene in to the plant cell genome.

Only the strains of A.tumafaciens having large conjugative plasmid called Ti plasmid which are pathogenic.The plasmid transfers it's part known as T- DNA region.It is discovered that this region of Ti plasmid has a great potential to act as a vector for the insertion of recombinant DNA in to plant chromosomes.

Plasmids for recombination is prepared in such a way that tumor inducing regions have been deleted and genes required for actual infection of the plant cell by the plasmids are retained.

Gene of interest ie genes coding for herbicide or diseases resistance is inserted on to the T-DNA region.

Then the plasmid is returned to the A.tumafaciens.

Plant cells are infected with this transformed new bacterium and transformant are selected by screening of antibiotic resistance.

Finally whole plants are regenerated from the transformed cells which would be resistant against the infection.

This has made major contribution in the field agriculture by increasing the production via disease resistance.

This can be use to modify dicots such as tomato,celery,lettuce,alfalfa etc.This can be also introduced on to the monocot such as corn,wheat and other grains.

Capacity of Agrobacterium to infect monocots is limited to a narrow range of genotypes.But there are some studies recently showed how effectively monocot can be transformed.

Genetically Modified (GM) crops offer improved yields, enhanced nutritional value, longer shelf life, and resistance to drought, frost, or insect pests.

●Examples

•Corn varieties containing a gene for a bacterial pesticide that kills larval pests.

In the United States, GM corn is used in many common foods, including cornmeal, tortilla chips, and high-fructose corn syrup.

•Soybeans with an inserted gene that renders them resistant to weed-killers such as Roundup (brand name of a systemic, broad-spectrum glyphosate-based herbicide)

GM soy is used primarily in animal feed and in soybean oil.

• Squash
Zucchini and yellow summer squash have been commercially available in the U.S. since the mid- to late-'90s,.

•Papaya
Bred to withstand ringspot virus, which can destroy papaya plants, these genetically engineered 'Rainbow Papayas' were first commercially produced in the late 1990s. Much of the yield is grown in Hawaii.

•“Golden rice” genetically engineered to contain vitamin A and iron so as to prevent common nutritional deficiencies in developing countries.

• Vegetables with higher vitamin E content to help fight heart disease.GM crops under development include varieties of wheat free of gluten, a major cause of food allergy.

In the United States, GM corn is used in many common foods, including cornmeal, tortilla chips, and high-fructose corn syrup.

● The main 3 concerns raised about GM organisms are:

• Allergenicity

Potentials to provoke allergic reaction when consumed genetically modified crops.

Protocols for the testing of GM foods have been evaluated by the Food and Agriculture Organization of the United Nations (FAO) and WHO. No allergic effects have been found relative to GM foods currently on the market.

•Gene transfer

Gene transfer from GM foods to cells of the body or to bacteria in the gastrointestinal tract would cause concern if the transferred genetic material adversely affects human health.

• Out crossing

Issues of concern include ,the capability of the GMO to escape and potentially introduce the engineered genes into wild populations.

The mixing of crops derived from conventional seeds with GM crops, may have an indirect effect on food safety and food security.