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Risk Assessment of GM Plants
Assoc. Prof. Dr. Wichai Cherdshewasart
Department of Biology, Faculty of Science, Chulalongkorn University
Tel 02-2185033 Fax 02-2185034
Modes of plant gene modification
1. Classical breeding (wild crossing)2. Mutation 3. Somaclonal variation 4. Protoplast fusion5. Embryo rescue 6. Gene transfer
1. Classical breeding (wild crossing) Advantage:
practical, low cost, stable, effective within species
Disadvantage:time-consumed, ineffective within different species
2. Mutation Advantage: practical, low cost Disadvantage:
randomized, needs long selection procedure, not totally stable, may initiate revertant
3. Somaclonal variation
Advantage: in vitro manipulation Disadvantage: takes time, randomized,
needs long selection procedure
4. Protoplast fusion Advantage: across species barrier Disadvantage: randomized, remote
species may success but fail for further development
5. Embryo rescue Advantage:
cross between different species is possible to initiate embryonic development.
Disadvantage: transfer pre-mature embryo to new environment could initiate fully developed plants, but sterile
6. Gene transfer
Advantage: precise genotype obtained, laboratory and industry practical
Disadvantage: Not possible for all species, especially monocot
Mode of gene transfer:
1. Vector-mediated gene transfer Agrobacterium-mediated Virus-mediated
2. Vectorless-mediated gene transfer (Direct gene transfer) Mechanical Physical Electrical Chemical
Analysis of transgenic plants
1. Phenotypic analysis2. Genotypic analysis3. Greenhouse condition
analysis4. Field trial condition analysis
Genotypic analysis PCR for rapid screening Southern blot for precise gene detection Northern blot for transcription analysis Western blot for translation analysis,
together with Ab-binding or enzymatic analysis
Mendelian analysis for insertion locus and linkage analysis
In situ hybridization for precise insertion locus analysis
DNA methylation analysis for silencing potential analysis
A generally accepted risk assessment method*,**,***
* UNEP International Technical Guideline for Safety in Biotechnology** The Cartegena Protocol*** EC Directive 2001/18/EEC
1. Identify potential adverse effects on human health and/or the environment
2. Estimate the likelihood of these adverse effects being realized
3. Evaluate the consequence should be identified effects be realized (the risk)
4. Consider appropriate risk-management strategies
5. Estimate the overall potential impact, including a consideration of potential impacts that may be beneficial to human health or the environment
Approaches to risk assessment
1. Trait analysis characteristics of the modified organism; transgene,
parental organisms, receiving environment less problem, if small scale more problem, if large scale
2. Familarity comparison of transgenic to similar organism(s)
derived from classical genetic methods assume that small genetic changes (1-4 genes)
exhibits no significant change in well-known organism, phenotype is still the same
3. Formulaic possible adverse effects; to human health or
the environment R = H x E R; Risk, H; Hazard, E; Exposure facilitates consideration of risk-management
options
4. Intuitive Reasoning use education, experience and reason to
promote knowledge for making decision with complete information
depends on what should be considered use of expert committees, independent
reviewers/assessors without a conflict of interest
Needs:1. Environmental friendly products2. Tight global regulatory requirements3. Trade barrier Methods:1. Product and country specification2. Science-based assessment3. Multi-tiered, complementary
approaches
Plant assessment:
1. Survival against wild type plants2. Stability of gene expression,
especially in the field vs. laboratory / greenhouse3. Distinct genotype over wild type plant4. Invasiveness of transgenic plants, the possibility to develop into weeds
Trait assessment:
1. Toxicity to non-target organisms2. In case of human consumption, no allergen / toxic substance3. Ecological impacts (outcrossing)
1. Field obseravationEmergence Order of testing relies on
degree of possible risk of the plant
Growth measurement
Transgenic plant growth / wild type, not greater than 1
Days of flowering
Transgenic plant days of flowering / wild type, not greater than 1
Length of flowering period
Transgenic plant length of flowering period / wild type, not greater than 1
Pollen dispersal distance
This is the reason why buffer zone has to be set up)
Shattering of seed from plant
Distance of seed shattering determines degree of risk
Reproductive success or yield (annual)
Reproductive success determines transmission risk
Reproductive success or yield (perennial)
Perennial risk determines more risk
Qualitative insect
Non-target insects = 0
Qualitative pathogens
Non-target pathogens = 0
Others
2. Plant testingDormacy/ germination
-shorter dormancy / germination determine front running risk-longer dormancy / germination determine latent risk
riskField seedbank longevity (dormancy x viability)
-increase longevity determines risk
Competition (Replacement or addition series)
-stronger competition determines risk
Replacement capacity
-higher replacement capacity determines risk
Gene flow (through pollen movement)
-wider pollen dispersal determines risk-outcrossing determines risk
Introgression (hybrid weediness)
-hybrid weediness determines long term risk
Alleopathy -Competitive of survival risk
Susceptibility to conventional management
-Competitive of agricultural risk
Genetic stability
-High genetic stability determines risk
Epistasis -Epistasis determines unexpected genetics-Horizontal gene transfer Gene transfer between plant nucleus and organelle Gene transfer between plant nucleus and genome of consumer, predator, Gene transfer between nucleus and organelle
Other
Regulatory principles:
1. Scientifically based, based on information of organism, used technology and effects to humans and environment
2. Product-based approach, use existing product-based legislation
3. Familiarity and substantial equivalence, experience with the use of that species. The determination is based on scientific literature and practical experience with the plant and similar plant varieties.
4. Case-by case, allow the development of knowledge that could inform criteria and requirement over time.
Regulatory principles:
5. Step-wise fashion, products should be assessed throughout the chain of development : From laboratory to greenhouse and finally large-scale field trial
6. Transparency7. Precautionary principle/approach, derived from
Rio Declaration, regulatory groups can make decisions about products based on scientific uncertainty.
8. Harmonization, sharing of or acceptance of another group’s review
1. Good laboratory practice Tightly control of GM-vectors, plasmids and
plant materials Apply no bacterial antibiotic resistant-
derived gene Apply bioluminescence gene from animal as
marker Apply antisense for pollen developmental
gene Limit level of toxic gene, eg, cry family
2. Good agricultural practice Controlled plantation area with standard
buffer zone and % sharing with wild type plants
Emasculation Flower bud elimination Closed-bag control Net protection of fruits and seeds from
insects, birds, bats, rodents Total fruit and seed collection Labeling and separation technique for
transgenic plant and seed Whole plant elimination after harvest
3. Good manufacturing practice
Labeling GM-products according to domestic and export regulations
Testing for allergen and toxicity of the products containing GM-materials
4. Good marketing practice
Fully-informed alien gene(s) and awareness of application
Evaluated for allergen and toxic molecule Labeling Post marketing record
5. Good consumption practice
For GM-food products: determine animals as primary consumer and human as secondary consumer
Study labeling Food safety criteria
References Head G. and Duan J. 2002. Environmental safety assessment
for transgenic crops. Wolf K. 1994. Gene transfer between organelles and the
nucleus in lower eukaryotes Copy P. Bazin C. Anxolabehere D. Langin T. 1994. Horizontal
transfer and the evolution of transposable elements Landmann J. Graser E. Riedel-Preuss A. van der Hoeven C.
1994. Can Agrobacteria be eliminated from transgenic plants? Hoffmann T. Golz C. Schieder O. 1994. Preliminary findings of
DNA transfer from transgenic plants to a wild-type strain of Aspergillus niger
Hansen L. C. Obryeki J.-J. L. 2000 Field deposition of Bt transgenic corn pollen: lethal effects on the monarch butterfly.