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

Environment Safety Assessment For Transgenic Crops:

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)

Guidelines for Plant Testing

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.