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.