Transcript Introduction

How transgenic plants are made
• Original approach used a natural plant system
• Current plasmid based with various delivery
systems
• Currently many traits engineered or under
development
• Now augmented by newer high throughput
genome sequencing techniques
• Highly politicized, especially in EU
Agrobacterium causes crown galls
In the field
…and in the lab
A plasmid transfers DNA to the plant
Used to make transgenic plants in 1983
Only small part of plasmid is transferred
Transferred DNA
~30 KB
Transfer region
controls
excision and
integration of
DNA into plant
host
Direct repeats
200 KB
Growth factor
stimulates
gall growth in
plant
Transferring new genes to plant cells
EXCISION
SITES
KanR
KanR
INTO PLANT GENOME
KanR
Antibiotic
resistance
genes
included
Two classes of plants require different methods
MONOCOTS
DICOTS
Electroporation
Agrobacterium
Corn
Rice
Wheat
Soy
Cotton
Aubergine
Yams
Tomato
Potato
SOME ORIGINAL TRANSGENIC CROPS
Crop and release date
Name
Company
Novel properties
Tomato (1994)
Flavr Savr
Calgene
Vine-ripened
flavour, shelf life
Zeneca
Consistency of
tomato paste
Tomato (1995)
Cotton
Potato
Maize (1996-97)
Bollgard
Monsanto
Bacillus
thuringiensis toxin
for insect
resistance
Soybean
Canola (rape seed)
Cotton (1995-96)
Corn
Soy Beans
Many others
Roundup
Ready
Monsanto
Glyphosate
herbicide
resistance
New GMO crops are being approved
Number of GMOs per crop
Adoption in US is very high
WHAT GENES ARE TRANSFERRED INTO PLANTS?
• HERBICIDE RESISTANCE
• DROUGHT RESISTANCE
• SALT RESISTANCE
• INHIBITORS OF RIPENING
• NUTRITIONAL SUPPLEMENTS
• PHARMACEUTICALS
• INCREASED HEAVY METAL UPTAKE
GMOs vary by trait
Transferring bioluminescence gene
Bacillus thuringenensis (Bt) - Insect Resistance
• SPORE FORMING BACTERIA
• SAME AS B. anthracis AND B. cereus
PLASMIDS ONLY DISTINGUISH
• PLASMIDS PRODUCE CRYSTALS OF CRY PROTEINS
• MANY DIFFERENT KINDS OF CRY
• SMALL PROTEIN = EASY MOLECULAR METHODS
• MOST Bt HAVE SEVERAL TOXINS
• TOXIC TO DIFFERENT INSECTS
LONG HISTORY IN ORGANIC AGRICULTURE
Microbial pesticides registered by EPA
ONE Bt TOXIN STRUCTURE
BINDS SPECIFICALLY
TO A RECEPTOR
INSERTS INTO GUT WALL
PROTECTS THE PEPTIDE
FROM DEGRADATION
Bt proteins dissolve the insect gut lining
TOXIN BINDS TO
SPECIFIC RECEPTORS
IN GUT WALL
PROTEIN CLEAVED
DISSOLVES
GUT LINING
NO TOXIN
TOXIN
Huge Diversity of Different Proteins
SIMILAR MODES
OF ACTION
DIFFERENT
INSECT
SPECIFICITIES
Bt CRYSTAL PROTEINS AND THEIR TARGET SPECIES
Gene
Insect Activity
cryI; A(a), A(b), A(c), B, C, D, E,
F,G
Lepidopteran larvae
(BUTTERFLIES)
cryII; A, B, C
Lepidopteran and
Dipteran Larvae (FLIES)
cryIII; A, B,
Coleopteran larvae (BEETLES)
cryIV; A, B,C,D
Dipteran larvae
cryV - cryIX
Various
MANY Bt-RICE VARIETIES HAVE BEEN MADE
CHANGES IN GUT PROTEIN CAN MEDIATE RESISTANCE
DIFFERENT TRANSGENIC GOAL – ADD NUTRIENTS
• POLISHED RICE IS MAINLY CARBOHYDRATE
• STAPLE FOOD IN AREAS WHERE VITAMIN
DEFICIENCIES ARE COMMON
• ADD VITAMIN A TO RICE ENDOSPERM?
• RICE HAS ENZYMES TO MAKE VITAMIN A
PRECURSOR
CONVERT GGPP INTO CAROTENE WITH GENES FROM OTHER PLANTS
LIMIT IN NORMAL RICE
DAFFODIL
ERWINIA
DAFFODIL
Herbicide Resistance - most common in US
• Glyphosate = Roundup
• Inhibits an enzyme needed to synthesize
aromatic amino acids ( Phe, Tyr and Trp)
• Roundup ready plants carry a bacterial
version of the enzyme that is naturally
resistant to Roundup
• Animals do not have this system, so not toxic
to humans
• Resistance can evolve in a variety of ways in
plants exposed to Roundup
Diverse Methods & Goals, Many Controversies