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GMO’s and GENE FLOW:
A PLANT BREEDING PERSPECTIVE
Kendall R. Lamkey
Department of Agronomy
Iowa State University
Ames, IA 50010
http://www.agron.iastate.edu/corn
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Outline
• Conventional vs. Transgenic Crop Improvement
• Gene Flow
• Pollen Movement
• Current APHIS Regulations
• What Can Be Done
• Conclusions
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Conventional Plant Breeding
• The art and science of plant improvement
– Gene Exchange only occurs between sexually
compatible species
– Most of the genetic variation is created through
recombination (crossing)
– Selection is conducted by measuring plant
characteristics (yield, grain moisture, etc)
– Genes under selection are unknown
– Little is known about the changes that occur at
the DNA level with selection
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Transgenics
• The human mediated insertion of a synthetic gene
or genes into a plant
– Usually involves transfer of genes between sexually
incompatible species
– The gene produces a specific protein of interest – either
as an input or output trait
– Often referred to as “precise”, because we know the
DNA sequence and gene product
– Gene insertion into the genome is usually into a random
location
– Effect on other plant characteristics is unknown
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Gene Discovery
Gene Discovery: Where do the genes come from?
• Basic research in plant physiology and biochemistry
• Genome sequencing efforts such as the human
genome project
X
?
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Transformation
Parts of a transgene
The promoter • Usually taken from a corn gene
• Determines where and when the transgene will
function
• The gene can be Tissue Specific or Constitutive
P(BLA)
The coding sequence -
r-zein pro
Determines what the gene
does
APr
Porcine lactalbumin
3'UTR1
pAHC25/zein pro/lactal
Must be modified to
resemble a corn gene
7320 bp
ORI
P(LAC)
3'UTR1
Ubi pro
BAR
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“Gene
Gun”
Backcrossing
R
+/+
BC3F1 (93.75%)
½ +/+ : ½ +/Bt
R
+/+
x
D
Bt/Bt
F1 (50%)
x +/Bt
BC3F2 (93.75%)
R
BC1F1 (75%)
+/+ x ½ +/+ : ½ +/Bt
¼ +/+ : ½ +/Bt : ¼ Bt/Bt
BC3F3
Bt/Bt
R
BC2F1 (87.5%)
+/+ x ½ +/+ : ½ +/Bt
BC3F1 (93.75%)
½ +/+ : ½ +/Bt
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Conventional vs. Transgenic
• Genomes are fluid and dynamic – not stable and
static
• Difficult to distinguish between effects of
conventional breeding and a transgene insertion
event
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Conventional vs. Transgenic
• Transgenes result in novel phenotypes, but
present no new categories of risks
• Specific traits introduced by both
conventional and transgenic approaches can
pose unique risks
• It is the product and not the process we
should be concerned about
NCR (2002) Environmental effects of transgenic plants
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Gene flow
• Gene flow is movement between
groups that results in genetic
exchange
– Gene flow always results in contamination
– Contamination does not result in gene
flow, unless it is followed by gene
exchange
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Gene Flow
• Seed Dispersal
– Spillage
– Seed shattering
– Mechanical mixing
• Horizontal Transfer
– nonsexual transfer of genetic material
from one organism to another
• Pollen Movement
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Pollen Movement
• Crop to wild
– Grain crops have no wild relatives in the
US
– Needs to be assessed on a crop by crop
basis
• Crop to weed
– Must be assessed on a crop by crop basis
• Crop to crop
– Our primary concern
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Pollen Movement
• Primarily an issue with crosspollinated crops
• Dependent on environmental conditions
and the physical characteristics of
the pollen
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Pollen Movement - Corn
• Characteristics of Corn
– One plant produces 18,000,000 to
25,000,000 pollen grains
– One plant theoretically has enough pollen
to pollinate an acre of corn
– There have been surprisingly few studies
of pollen movement in corn, especially
long distance movement
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Pollen Movement - Corn
M. Garcia C., J. Figueroa M., R. Gomez L., R. Townsend, and J. Schoper. 1998. Pollen
control during transgenic hybrid maize development in Mexico. Crop Science 38:1597
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Pollen Movement - Corn
19 Meters
Yellow
Corn
Tassels
Removed
30 Meters
White
Corn
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Plants
With
Yellow
Seeds
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Pollen Movement - Corn
• Spatial isolation resulted in 0.01% contamination
from a pollen source > 184 m from the field
• Isolation in space and time resulted in no
contamination
• Pollen movement is best controlled when
transgenics are used as females
• Study is relevant only to breeding scale studies
• Difficult to apply results from Mexico to US
M. Garcia C., J. Figueroa M., R. Gomez L., R. Townsend, and J. Schoper. 1998. Pollen
control during transgenic hybrid maize development in Mexico. Crop Science 38:1597
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Pollen Movement - Corn
• Four recommendations
– Use transgenic plants as females and remove
tassels prior to pollen shed
– Spatial isolation > 185m
– Use temporal isolation by planting 1 or 2 weeks
later than surrounding corn
– Scout and destroy sexually compatible plants in
the area of presumed pollen movement
M. Garcia C., J. Figueroa M., R. Gomez L., R. Townsend, and J. Schoper. 1998. Pollen
control during transgenic hybrid maize development in Mexico. Crop Science 38:1597
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Pollen Movement - Corn
S. Luna V., J. Figueroa M., B. Baltazar M., R. Gomez L., R. Townsend, and J. B. Schoper. 2001. Maize Pollen
Longevity and Distance Isolation Requirements for Effective Pollen Control. Crop Sci. 41:1551–1557
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Pollen Movement - Corn
S. Luna V., J. Figueroa M., B. Baltazar M., R. Gomez L., R. Townsend, and J. B. Schoper. 2001. Maize Pollen
Longevity and Distance Isolation Requirements for Effective Pollen Control. Crop Sci. 41:1551–1557
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Pollen Movement - Corn
• It was clear maize pollen does not remain
viable in the atmosphere for longer than 2
h near San Jose del Valle.
• Actual measurements of pollen movement as
measured by outcrossing from research
scale plantings of material, indicated that
viable pollen was barely detectable at 200
m and nonexistant at 300 m from the pollen
source.
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Pollen Movement - Corn
• What is low?
– Assume 1% contamination (100 0f 10,000
kernels
– 1 lb corn = 1800 kernels
– 1 bushel corn = 100,800 kernels
– 1 semi = 750 bushels = 75,600,000
– 756,000 contaminating kernels per semi
– Or 7.5 bushels / semi
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What Can Be Done?
• Barriers to Pollen Movement
– Physical
– Biological
– Mechanical
– Spatial
– Temporal
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What Can Be Done?
• Physical barriers physically prevent
pollen movement
– Glass House
– Wind Breaks
– Mesh Nets
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What Can Be Done?
• Biological Barriers use genetic or
molecular aspects of the plant itself
– Apomixis
– Male Sterility
– Trangenes that render pollen grains in
which they are expressed inviable
– Terminator Technology
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What Can Be Done?
• Mechanical Barriers involves removal
of the pollen producing structures
– Removal of tassels
– Perhaps use of gameticides
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What Can Be Done?
• Spatial Barriers use distance to
prevent pollen movement
– Studies need to be done to determine
the spatial distances on a crop by crop
basis
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What Can Be Done?
• Temporal barriers take advantage of
known flowering patterns and sexually
isolate the crop from the crops
around it.
– Quite effective
– Used by Breeders
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What Do I Recommend?
• Four of the five barriers should be
used to prevent or eliminate pollen
movement.
– Management intensive
– Assumes no human errors (bad
assumption)
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What Does Aphis Require
• Transgenic corn must be planted at least 1 mile from
corn seed production
• Corn from previous season in a 0.25 mile radius must
be harvested and removed before planting
• The land within 25 feet of the transgenic plant area
must be fallow
• No other corn plants within a radius of 0.5 mile of
transgenic plants
• Transgenic corn must be planted no less that 21 days
before or 21 days after planting dates of corn in a
zone of 0.5 to 1 mile of transgenic plants
• Buffers reduce distances and times
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Other Issues
• Identity preservation for zero
tolerance
– Theoretically possible – practically
difficult
– Costly if areas of production are widely
separated
– Humans make mistakes
• Misappropriation
• Spillage
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Other Recommendations
• Both DNA and Protein tests of the
gene and the gene product should be
available before testing
• Genes should be constructed so they
are traceable to the lab of origin
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Conclusion
Gene Flow Happens
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