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In-depth Notes on Controlling Plant Pests and Genetically Modified Crops

Engineering Insect Resistance

  • Global Agricultural Impact:

    • In 1994, pests consumed approximately 14% of global agricultural output. This figure may be an underestimation due to indirect losses.

    • Annual pesticide costs exceed USD 10 billion, with predictions of crop losses without pesticide application:

    • Wheat: 52%

    • Rice: 83%

    • Maize: 59%

    • Potato: 74%

    • Soybean: 58%

    • Cotton: 84%

Bt (Bacillus thuringiensis) Toxin

  • Bacillus thuringiensis (Bt) is a gram-negative bacterium that produces proteins toxic to specific insect larvae.

  • BT toxins are crystalline proteins that show species-specific toxicity, affecting:

    • Lepidoptera (butterflies and moths)

    • Diptera (flies)

    • Coleoptera (beetles)

  • Mechanism of Action:

    • Native Cry proteins are cleaved in the insect gut by proteolytic enzymes, forming active polypeptides of approximately 60-80 kD.

    • These bind to receptors in the epithelial brush border of the intestinal membrane, creating pores and leading to cell lysis.

    • Results in paralysis and death of the larva within 1-3 days.

Transgenic Plants Expressing Bt Toxin

  • Genes encoding the Bt toxin can be integrated into plants through methods like Agrobacterium transformation or Biolistics.

  • Transgenic plants expressing Bt proteins are toxic to target insect larvae while being harmless to beneficial insects (e.g., bees).

  • Example: Transgenic tobacco expressing Bt toxin is resistant to Manduca sexta (tobacco hornworm).

Transgenic Bt Crop Plants

  • Common crops:

    • Maize: Targets leptidopteran larvae.

    • Cotton: Cry1A toxin targets cotton bollworms.

  • In the U.S., BT maize accounts for >70% of plantings; BT cotton comprises ~90% of cotton grown in permissive countries (e.g., China, India, USA).

Targeting the European Corn Borer

  • Damage from the larvae is internal and challenging to assess; infestations are unpredictable.

  • Control: Single Bt toxin (Cry1A(b)) expressed in maize effectively controls European corn borer attacks.

  • Recent lines of BT maize contain multiple stacked transgenes targeting various pests.

SmartStax: Multi-trait Corn

  • Developers: Dow AgroSciences and Monsanto.

  • Launched in 2009, combines traits from Herculex XTRA and VT Triple Pro with multiple Bt toxins providing broad pest control.

  • Reduces refuge requirements for pest-management strategies.

  • Cry Toxins in SmartStax:

    • Cry3Bb1: Targets corn rootworms.

    • Cry1A.105 and Cry2Ab2: Control Lepidoptera, including European corn borer and corn earworm.

    • Also has herbicide tolerance to glyphosate and glufosinate.

Cotton Bollworm in India

  • >90% of cotton in India is BT transgenic, offering high protection against cotton bollworm.

  • Indian government mandates that patent owners allow local breeding to introduce BT genes into Indian varieties (>500 varieties now).

  • BT cotton significantly reduces insecticide use by ~50%.

Effects of BT Cotton

  • Post-introduction of BT varieties, insecticide applications on cotton decreased by ~50%.

  • China Findings (2012):

    • Introduction of BT cotton led to reduced insecticide use; increased predator densities of pests (e.g., ladybirds, lacewings).

    • Decreased densities of target pests such as aphids on cotton and non-BT crops (like soybean).

Breeding & Engineering Novel Products in Plants

  • Focus on bioengineering for healthier foods and as platforms for producing novel products.

Structures of Common Dietary Fatty Acids

  • Fatty Acids Explained:

    • Diacylglycerol

    • Phosphatidylcholine

    • Compositions of various fatty acids like palmitic (16:0), stearic (18:0), oleic (18:1;9), linoleic (18:2;9,12), and alpha-linolenic (18:3;9,12,15).

Manipulating Plant Lipids

  • Goal: Improve oil quality and health benefits.

  • Brassicaceae and other oil-producing plants contain high levels of long-chain monounsaturated fatty acids, notably erucic acid (22:1n-9), which is linked to heart disease.

  • Breeding programs initiated in the 1950s led to low-erucic acid rapeseed (now called ‘Canola’).

Edible Oils through Genetic Engineering

  • Monounsaturated oils (e.g., 18:1D9) are favored over polyunsaturates (18:2D9,12; 18:3D9,12,15) or saturated oils (e.g., 16:0, 18:0) for health.

  • Example: 18:1D15 (18:1 n-3) promotes beneficial lipid ratios in blood.

Biopharming and Protein Production

  • Plant-Derived Proteins (PDP): Useful in medical treatments (e.g., monoclonal antibodies for cancers, vaccines for viruses).

  • Antibody Production:

    • Through B-lymphocytes, produces unique antibodies.

    • Cloning genes from immortalized B-lymphocytes into plants for large-scale production is feasible.

ZMapp and Plant-Made Medicines

  • ZMapp: A mixture of three monoclonal antibodies for Ebola; demonstrated effective treatment success in 2013.

  • Growth in Nicotiana benthamiana for production simplifies and reduces costs in comparison to traditional methods.

Conclusion

  • Advances in biotechnology have significantly improved pest control, crop resistance, and the production of healthier food and medicines, underscoring the potential of genetic engineering in agriculture and health.