Genetically Modified Plants

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Genetically Modified Plants
Biotechnology underlying science Potential
Risks vs. (Potential) Benefits
Assigned Reading Chapter 10.5
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Genetically Modified Organisms

• Types of GMOs?
• artificial selection and traditional breeding,
• transgenic organisms,
• other approaches,
• targeted mutagenesis,
• gene introgression,
• ?

• Old Science

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Desirable Agronomic Traits(traditional or modern)

• Increased yields, more nutritious, quality, etc.,
• More resistant to pestilence, weeds, water and
  nutrient deprivations,
• Ability to withstand marginal growth conditions,
• and thrive in new environmental ranges,
• Profit.

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Traditional Breeding
45,000 genes
25,000 genes

• technology is not essential,
• limited by species boundaries,
• all genes/traits are mixed.

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Introgression

• incorporation of genes of one genome into the
  genome of another cultivar,
• standard breeding techniques are laborious (if
  possible at all),
• genomics and related sciences greatly accelerates
  standard breeding techniques.

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Genome Era Traditional Breeding

• Wild tomato

Cultivar w/ 1 wild gene replacement
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Genetic Bottlenecks and Seed Preservation
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GMO
Introgression
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Transgenic Plants

• based on DNA technology,
• single genes/traits can be transferred,
• species boundaries are not limiting.

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How are GMOs generated?
insert into plant
via biolistics
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Biolistics
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Natural soil bacterium that infects
plants,hosts 160 Genera,families gt
60,effect poor growth, low yield.
Kalanchoe Stem w/ infection.
Agrobacterium tumefaciens
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Plant Cells
Ti-Plasmid
Transfer-DNA
Nature
Ti tumor inducing
Plasmid extrachromosomal DNA evolved for genetic
transfer.
Hormone genes
Opines genes
Agrobacterium
Any Gene
Selectable Markers, etc
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T-DNA (Transfer DNA)

• with gene of interest,
• b-carotene,
• herbicide resistance, etc..

Construct T-DNA
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T-DNA (Transfer DNA)
selection genes

• gene of interest,
• b-carotene,
• herbicide resistance, etc..

virulence genes
Construct T-DNA

• Virulence genes facilitate Agro infection, T-DNA
  transfer,
• not usually transferred in commercial
  applications,
• Selection genes (2) used to identify
  transgenics,
• usually antibiotic or herbicide resistance, etc.
  (i.e. only the organisms with the T-DNA live in a
  selection experiment),
• Gene of interest protein coding region, plus a
  promoter.

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Promoters Control Expression
Foreign DNA is common (via nature) in most
genomes,

• Transgenes must be expressed in order to
  function,
• Promoters control where, when and how much
  protein is produced.

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Gene Structure
chromosome (megabases)
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Promoter Specifies Expression
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Expression Protein Production
Protein and protein functions only present in
tissue with active promoter.
Tissue Specific Expression
Time Specific Expression
Suicide Promoters, etc.
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Brief History of Transgenic Organisms

• Transgenic E. coli,
• not demonstratively dangerous,
• demonstratively beneficial (probably).
• Transgenic virus,
• not demonstratively dangerous,
• demonstratively beneficial (probably).
• Transgenic plants,
• demonstratively dangerous? (not yet),
• demonstratively beneficial (?).

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Potential Risks

• Risk of invasion.
• Direct nontarget Effects
• Indirect nontarget Effects.
• New Viral Diseases.
• Variability and Unexpected Results.

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Potential Risks(risk of invasion)

• 50,000 invaders in USA the old fashioned ways,
• self-sustaining cultivars,
• low anticipated risk,
• hybridization with (native) neighbors,
• transgene introgression,
• introgression of domestic cultivar genes with
  natives has occurred, resulting in negative
  impacts on native species,
• time lags.

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Direct (nontarget)

• Risk to non-target species,
• pollinators,
• passers-by,
• soil ecosystems,
• decomposition rates,
• carbon cycle,
• nitrogen cycle.

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Indirect (nontarget)

• kill weeds kill species that live on or eat
  the weeds,
• bioaccumulation,
• nontarget species eat plants, store toxins,
• those species are eaten, amassing the toxin,
• on up the food chain.

Bee on Red Clover.
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New Viral Diseases

• virus resistant plants promote virulent strains,
• mutations,
• recombination,
• heteroencapsulation,
• virus move genes from one organism to another,
• not presently a risk, but a potential risk.

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Variability and Unexpected Results

• time scale,
• numbers,
• environmental and cultivar differences,
• application, culture and consistency.

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Other Issues

• Economic hegemony of GMP seed producing
  countries, companies,
• Cultural shifts in farming due to the
  introduction of GMOs,
• Potential allergies to genetically modified
  crops,
• The preservation of natural genetic crop-lines,
• The lack of an adequate risk assessment
  methodology to quantify unintended ecological
  consequences.

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The Precautionary Principle
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Biotechnology in General
Scenario 1
Scenario 2
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Transgenic Construct