Genetically Modified Plants

Biotechnology: underlying scienceBiotechnology: underlying science

Potential Risks vs.(Potential) BenefitsPotential Risks vs.(Potential) Benefits

Assigned Reading: Chapter 11.3

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

• technology is not essential,

• limited by species boundaries,

• all genes/traits are mixed.

~45,000 genes~25,000 genes

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*.

Wild tomato

Genome Era Traditional Breeding

Cultivar w/ 1 wild gene replacement

Transgenic Plants

• based on DNA technology,• single genes/traits can be transferred,• species boundaries are not limiting.

How are GMOs generated?

insert into plant

…via biolistics - or - Agrobacterium tumefaceins

...uses tools of molecular genetics,

- i.e. applied bacteria and virus genetics.

Biolistics

Agrobacterium tumefaciens

Kalanchoe Stemw/ infection.

Natural soil bacterium Natural soil bacterium that infects plants,that infects plants,

hosts: 160 Genera,hosts: 160 Genera,families: > 60,families: > 60,

effecteffect; poor growth, ; poor growth, low yield.low yield.

Agrobacterium

Plant CellsNature

Ti-Plasmid Transfer-DNA

Hormonegenes

Opinesgenes

Lab

Selectable MarkersGenes

Out: Ti genes, opine genes,

In: DNA of choice.

T-DNA

Ti: tumor inducing

Plasmid: extrachromosomal DNA evolved for genetic transfer.

Construct T-DNA

infect plant, select for plants with T-DNA

T-DNA (Transfer DNA)

transform, select for agro with T-DNA

Agrobacterium

Plant chromosome with T-DNA insert.

…with gene of interest,

carotene,- herbicide resistance, etc..

Construct T-DNA

selection genes

virulencegenes

T-DNA (Transfer DNA)

…gene of interest,

carotene,- herbicide resistance, etc..

Virulence genes: facilitate Agro infection, T-DNA transfer,

• not usually transferred in commercial applications,

Selection genes: 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

Transgenes must be expressed in order to function,

Promoters control where, when and how much protein is produced.

Foreign DNA is common (via nature) in most genomes,

Gene Structure

chromosome

(megabases)

gene (kilobases)

...ata cgt act atc...

||| ||| ||| |||

...tat gca tga tag...

protein coding

...ttaggttctatc...

||||||||||||

...aatccaagatag...

promoter specific sequences.

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

“Suicide” Promoters, etc.

Time Specific Expression

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