Gene flow and environmental risk assessment of GM crops ??????GM?????????

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Gene flow and environmental risk assessment of
GM crops??????GM?????????

• Alan Raybould, Ecological Sciences, Syngenta
• ??.???, ????, Syngenta??

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Outline ??

• What is gene flow?
• Methods to estimate gene flow
• Regulatory risk and environmental risk
• Hazard and exposure
• Gene flow in environmental fate
• Gene flow and weediness
• Gene flow and genetic resources
• Data requirements for risk assessment
• Risk assessment framework

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What is gene flow? ????????

• Encyclopaedia Britannica
• Introduction of genetic material (by
  interbreeding) from one population of a species
  to another, thereby changing the composition of
  the gene pool of the receiving population.
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What is gene flow? ????????

• A natural phenomenon helps maintain genetic
  variation
• Occurs within and between crops, weeds and wild
  plants
• In plants, the main agents of gene flow are
  pollen and seeds
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Gene flow via pollen ???????????

• Plants have mechanisms to disperse pollen
• Some species use wind
• Small, unspectacular flowers
• Produce large amounts of pollen

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Conifers?? Trees Grasse?
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Gene flow via pollen ???????????

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• Some plants use animal vectors
• Insects (birds, bats, other mammals, slugs)
• Attract animals by colour, scent and rewards
  (pollen and nectar)

Bee orchid mimicry??? ??
Dog rose colour, pollen
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Gene flow via pollen ???????????

• Some plants prevent or reduce self-fertilisation
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Hop male and female flowers on separate
plants ???-????
Maize separate male and female flowers on same
plant??-???????
Brassica self-incompatibilit ?? ????
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Gene flow via seed ???????????

• Many mechanisms to promote seed dispersal
• Wind
• Structures to keep seeds airborne
• Animals
• Structures to catch the fur of animals
• Fruits hard seed coat to protect seeds from
  digestion
• Man
• Weeds mimic crops
• Dispersal in time
• Dormancy

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Gene flow via seed ???????????
Tomato fruit and hard seeds?? ?????
Dandelion wind ??? ?
False oat mimicry ??? ??
Goose grass animal fur ??? ????
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Gene flow and dispersal ???????

• Gene flow and dispersal are not the same
• Pollen must effect fertilisation
• Seeds must germinate and produce reproductive
  plants
• Dispersal potential gene flow
• Fertilisation and production of fertile plants
  actual gene flow

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Methods to estimate gene flow
Method Parameter estimated
Seed traps1 Potential gene flow via seed
Pollen traps1 Potential gene flow via pollen
Male-sterile bait plants1 Potential gene flow via pollen
Parentage analysis1 Actual gene flow via pollen
Plants with genetic markers1 Actual gene flow via seeds and pollen
Genetic structure2 Actual gene flow via seeds and pollen
1Direct methods estimate contemporary dispersal
make few assumptions weak at detecting rare,
long-distance dispersal 2Indirect method
estimates of gene flow over many generations
detect effects of rare, long-distance dispersal
rely on (untestable) assumptions about demography
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Regulatory risk and environmental risk???????????

• Gene flow may lead to unintended presence of
  transgenes
• Presence may contravene regulations or permit
  conditions
• Unapproved Events outside field trials
• Events approved for animal feed in human food
  chain
• Approved Events above thresholds in unlabelled
  batches
• Co-existence of GM and organic farming

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Regulatory risk and environmental risk???????????

• Can lead to fines and compensation to affected
  parties
• Presence of the gene may have no effect on safety
• A regulatory (or economic) risk, not an
  environmental risk
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Gene flow and environmental risk?????????

• Gene flow is a natural phenomenon
• The process does not constitute a risk in itself
• The risk results from any harmful properties of
  the gene
• Hazard harmful effect of the gene
• Exposure presence of the gene where it can
  cause harm
• Gene flow is part of the exposure assessment

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Gene flow and environmental fate ?????????

• Environmental fate is the concentration,
  distribution and persistence of a chemical in the
  environment
• A fate assessment is carried out for GM proteins
• Determines which organisms are exposed to the
  protein
• See Exposure Characterization this afternoon
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Gene flow and environmental fate ?????????

• Gene flow can disperse the protein
• to other varieties of the same crop
  (crop-to-crop)
• to following crops (via dormancy and
  volunteering)
• to non-agricultural habitats (invasiveness or
  weediness)
• to other species (wild plants, horizontal gene
  transfer)
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Environmental fate crop-to-crop gene flow????
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• For Events for commercial sale, it is assumed
  that crop-to-crop gene flow will occur
• Sporadic, low frequencies of transgenes in non-GM
  crops
• Called adventitious presence
• Environmental safety assessment will cover this
  presence
• Assessment for intended cultivation is worst-case
• Intended concentration of protein gtgt adventitious
  concn

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Environmental fate crop-to-crop gene flow????
??-??????

• May need studies to show that protein does not
  affect properties of commodities
• E.g., maize expressing GM alpha-amylase
• No toxicity to humans, farm animals non-target
  organisms
• Product is intended for ethanol production
• Will adventitious presence affect maize for other
  uses?
• Food manufacture
• Other industrial uses
• Analyse fractions from wet and dry milling

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Environmental fate crop-to-crop gene flow????
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• Pharmaceutical and industrial chemicals are a
  special case
• Need to eliminate crop-to-crop gene flow in food
  crops
• Chemicals may not be harmful to humans
• If so, should be a regulatory problem
• But, perceived as a safety problem

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Environmental fate crop-to-crop gene flow????
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• Some options to reduce exposure
• Express chemicals in crops not used for food
• Isolate the GM crop from other crops in space or
  time
• Use male-sterile plants or prevent flowering
  altogether

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Environmental fate volunteers ????????

• Volunteers are crops that persist after harvest
  and appear in the following crop
• Can be regarded as gene flow in time
• Conclusions of the environmental risk assessment
  for cultivation should cover exposure via
  volunteers
• Volunteers that express pharmaceutical or
  industrial chemicals can cause problems
• Express these chemicals in plants with no
  dormancy and inability to over-winter

Volunteer soybean in a maize crop
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Environmental fate feral populations and wild
plants???? ?????????

• Feral Crops
• Crops growing outside cultivation
• Gene flow via seed (and pollen)
• Conclusions of the environmental risk assessment
  for cultivation should cover exposure via feral
  populations
• Only exception is if an NTO related to the target
  pest and not found in crop is exposed
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Feral oilseed rape ????
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Environmental fate feral populations and wild
plants???? ?????????

• Wild plants
• Sexually compatible with the crop
• Gene flow via pollen (and seed)
• Same conclusions as for feral crops
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Wild turnip ????
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Environmental fate horizontal gene transfer
(HGT)???? ?????? (HGT)

• HGT is the integration of DNA from one species
  into the genome of a sexually incompatible
  species
• Theoretical possibility of HGT of transgenes to
  soil microbes
• Extremely unlikely to affect the environmental
  risk assessment
• Not detected under field conditions
• Detected sporadically under optimum conditions
• High sequence identity, high selection for
  transformants

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Environmental fate horizontal gene transfer
(HGT)???? ?????? (HGT)

• Transgenes are optimised for plant expression
• Low sequence identity with microbial genes
• Recombination unlikely
• Transgenes have plant promoters
• In the unlikely event of recombination, no
  protein expressed
• What is the hazard?

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Gene flow and weediness (invasiveness)????????
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• Gene flow to wild relative may increase its
  weediness
• Transgene confers biotic or abiotic stress
  tolerance
• The stressor was limiting population growth rate
• Transgene removes or reduces the effects of the
  stressor
• Population growth rate increases increased
  weediness
• Same logic applies to weediness of the crop itself

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Gene flow and weediness (invasiveness)????????
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• Phenomenon is called ecological release
• Methods to predict the ecological release hazard
  of transgenes will be described in the next
  presentation

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Gene flow and genetic resources?????????

• Gene flow from transgenic crop to a wild relative
  that may contain valuable genetic variation for
  crop breeding
• Harm results from spread of the transgene causing
  a reduction in genetic variation in the wild
  relative

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Gene flow and genetic resources?????????

• Theoretical possibility under high gene flow or
  selection
• Will be limited to genes linked to the transgene
• Minimal effect in outcrossing species (e.g.,
  maize)
• Higher effect in inbreeding species (e.g., rice)
• For inbreeding species, this hazard is
  conceptually similar to weediness

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Data requirements for risk assessment?????????

• Null hypothesis is that the biology of the crop
  is unchanged by genetic modification
• A test of this hypothesis forms part of the
  hazard assessment for weediness and is described
  in the next presentation
• If the hypothesis is corroborated, information
  about the non-GM crop is valid for use in the
  risk assessment

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Data requirements for risk assessment?????????

• If sufficient information is available to assess
  adventitious presence, volunteering, weediness
  and gene flow to wild relatives, no new studies
  are required
• Likely to have sufficient knowledge for major
  crops

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What if insufficient knowledge? ???????????

• May have insufficient knowledge for minor crops
  or for major crops growing outside historical
  area of cultivation
• Consider experiments to assess
• Dormancy
• Volunteering
• Weediness
• Gene flow to wild relatives

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Dormancy ??

• Allows gene flow through time potential to
  volunteer
• Primary dormancy is an intrinsic physical or
  physiological state of the seed that prevents
  germination
• Secondary dormancy is imposed by environmental
  conditions unfavourable to germination
• Simple tests are available for both kinds of
  dormancy

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Primary dormancy ????

• Collect ripe seed and place in conditions
  favourable for germination
• Monitor cumulative germination
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Secondary dormancy/seed longevity????/????

• Bury seeds in soil in suitable bags (e.g., nylon
  mesh)
• Treat with fungicide
• High density of seeds makes fungal attack likely
• Recover bag periodically and germinate a sample
  of seed
• Compare with a reference sample to
• distinguish from
• primary dormancy

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Volunteering ????

• Sow seed in a cultivated fallow field to simulate
  optimum conditions
• Monitor plant development
• Safflower experiment in Illinois
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Germination in the autumn???????
No plants survived the winter?????????
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Feral populations ????

• Volunteer experiments simulate optimum conditions
  for establishment of feral populations
• Disturbed ground
• No plant cover
• If no volunteers, feral populations are unlikely
  to form
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Feral populations ????

• Can supplement with systematic surveys for feral
  populations in area surrounding cultivation
• Test whether long-distance dispersal is possible
• E.g., do seeds remain viable after passage
  through the gut of a bird?
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Gene flow to wild relatives ??????????

• Can assess using tiered tests
• Tier I test for hybridisation using lab methods
• If no hybrids, stop testing hybrids go to tier
  II
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Hand pollination????
Embryo rescue????
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Gene flow to wild relatives ??????????

• Tier II Test for spontaneous hybridisation
  (lab or field)
• If no hybrids, stop testing hybrids go to tier
  III
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Gene flow to wild relatives ??????????

• Tier III Search for naturally-produced hybrids
  in field
• No hybrids, stop testing
• If hybrids, need to assess hazard

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Risk assessment framework ??????

• Test that the biology of the GM plant is not
  significantly different from a non-GM equivalent
• (Used in the hazard assessment for weediness)
• If no different, use information on the biology
  of the non-GM plant to assess gene flow
  parameters
• Adventitious presence (crop-to-crop)
• Volunteer populations
• Feral populations
• Gene flow to wild plants and HGT

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Risk assessment framework ??????

• Usually sufficient information in published
  literature
• If not, data can be obtained by simple
  experiments
• Use this information to confirm that exposure to
  GM proteins via gene flow will be no higher than
  that via cultivation
• If so, and if toxicity risk from cultivation is
  acceptable, toxicity risk via gene flow will be
  acceptable

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Risk assessment framework ??????

• If biology of GM plant is not significantly
  different from non-GM equivalent, the weediness
  risk from volunteers and feral populations is
  acceptable
• However, extra experiments may be required to
  assess the weediness hazard of wild relatives
  containing the transgene

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Risk assessment framework ??????

• Risk assessment for pharmaceutical proteins is a
  special case
• Any unintended presence of the protein may be
  regarded as a serious safety problem even if low
  toxicity can be shown
• Strict control of gene flow will be necessary

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Risk assessment framework ??????

• Isolation of crop and rigorous control of
  volunteers and ferals
• If growing crop outside historical area of
  cultivation, check volunteering and ability to
  form feral populations is unchanged
• Similar studies will be required if using a
  minor, non-food crop for which little or no
  information exists

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