Genetically Modified Plants
Biotechnology: underlying science
Potential Risks vs.(Potential) Benefits
Assigned Reading: Chapter 10.5
Genetically Modified Organisms
Types of GMOs?
- artificial selection
and traditional
breeding,
- transgenic organisms,
- other approaches,
- targeted mutagenesis,
- gene introgression,
- ?
Old Science
Humans (~30,000 years)
Humans (~30 years)
Bacteria (eons)
Humans (~15 years)
Bacteria (eons)
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.
Traditional Breeding
~25,000 genes
~45,000 genes
• technology is not essential,
• limited by species boundaries,
• all genes/traits are mixed.
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.
Genome Era Traditional Breeding
Wild tomato
Cultivar w/ 1 wild gene replacement
Genetic Bottlenecks and Seed Preservation
Introgression
GMO
Transgenic Plants
• based on DNA technology,
• single genes/traits can be transferred,
• species boundaries are not limiting.
How are GMOs generated?
...uses tools of
molecular genetics,
- i.e. applied
bacteria and
virus genetics.
insert into plant
…via biolistics - or - Agrobacterium tumefaceins
Biolistics
Kalanchoe Stem
w/ infection.
Agrobacterium tumefaciens
Natural soil bacterium
that infects plants,
hosts: 160 Genera,
families: > 60,
effect; poor growth, low
yield.
Nature
Ti-Plasmid
Transfer-DNA
Plant Cells
Ti: tumor inducing
Plasmid:
extrachromosomal
DNA evolved for
genetic transfer.
Agrobacterium
Hormone Opines
genes
genes
Lab
T-DNA
Out: Ti genes, opine genes,
In: DNA of choice.
Any Gene
Selectable Markers, etc
T-DNA (Transfer DNA)
…with gene of interest,
Construct T-DNA
bcarotene,
- herbicide resistance, etc..
transform, select for agro with T-DNA
Agrobacterium
infect plant, select for plants with T-DNA
Plant chromosome with T-DNA insert.
T-DNA (Transfer DNA)
selection genes
Construct T-DNA
virulence
genes
…gene of interest,
bcarotene,
- herbicide resistance, etc..
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”.
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.
Gene Structure
chromosome
(megabases)
gene (kilobases)
...ata cgt act atc...
...ttaggttctatc...
||||||||||||
...aatccaagatag...
||| ||| ||| |||
...tat gca tga tag...
promoter specific sequences.
protein coding
Promoter Specifies Expression
General Promoter: all tissues, all the time.
Vegetative Promoter: no flower, no fruit expression.
Root Promoter: only root expression.
Expression = Protein Production
Protein and
protein functions
only present in
tissue with
active promoter.
Tissue Specific Expression
Time Specific Expression
“Suicide” Promoters, etc.
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 (?).
Potential Risks
• Risk of invasion.
• Direct nontarget Effects
• Indirect nontarget Effects.
• New Viral Diseases.
• Variability and Unexpected Results.
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.
Direct
(nontarget)
• Risk to non-target species,
– pollinators,
– passers-by,
• soil ecosystems,
– decomposition rates,
– carbon cycle,
– nitrogen cycle.
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.
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.
Variability and Unexpected Results
• time scale,
• numbers,
• environmental and cultivar
differences,
• application, culture and
consistency.
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.
The Precautionary Principle
Biotechnology in General
Scenario 1
Scenario 2
Works great
Bad Environmental Consequences
Increase Carrying Capacity for Humans
Human Population Growth
Negative impacts on,
• select species,
• crops,
• ecosystems,
• etc.
Negative impacts on,
• select species,
• crops,
• ecosystems,
• etc.
Schedule
Quiz on Below, Bring Paper for 2 pts.
• Wednesday: Sugar and Genetics
– PDF of paper available on WEB page,
• print pp. 7 - 15.
Rest of Quarter
assignments
• June 1st: Chapter 8 and 9 reading assignments for
background.
• June 4th: Human and Chimps Paper.
• June 6th: Pheomone Paper.
• On Final: PCR, Northerns, Southerns,
Sequencing, and other relavant techniques.
GRADES
Quiz: 12.5
Midterm 2:
mean = 69 (150, high score).
Assignment
lecture 7
• Do a Punnett Square or a Split Fork Diagram
of,
Parent 1: wild-type for Chromosomes 14, 21
x
Parent 2: heterozygous for 14q;21q translocation.
Hint
gametes
Transgenic Construct
pBacR: piggyback vector, transposon derived
3xP3-EGFP-S40: Green fluorescent protein, eye specific promoter
AgCP promoter: mosquito promoter, activated by blood feast.
Signal: peptide sequence that sends protein to the midgut.
SM14: SM1 DNA sequence repeated 4 times, linked
What You Can Do
1. Pick one question on the exam that you missed,
answer completely for full credit,
•
•
must be clearly and completely answered,
Return Wednesday, 12 noon, stapled to exam.
2. Do better on the final, and get 1/2 the
difference between Exam 2 and the Final,
•
Example: 100 on E#2, 150 on Final, then add 25 pts.