crop biotechnology Flashcards
1
Q
what has conventional plant breeding achieved?
A
- yield has increased 3x this century
- increased harvest index (percentage of plant harvested)
- increased length of growing cycle
- increased reliability
- resistance to abiotic and biotic stress
- increased range of cultivation
- e.g. introducing rye genes into wheat in UK, increasing disease resistance ‘naturally’
- will not be replaced by GM or gene editing
2
Q
GMOs
A
= organisms in which the genetic material has been altered in a way that does not occur naturally by mating and/or recombination
- applies to all life except humans
- other names include GM, LMO, GE, transgenic etc
3
Q
increase in yields due to synthetic pesticides
A
- yield increases since WW2 (also due to semi-dwarf varieties)
- global pesticide use increased 15-20x
- increased food safety, fewer toxins from fungal diseases and weeds
- herbicides very effective in reducing potential crop loss
4
Q
auxin herbicides
A
- made from synthetic auxin, a plant hormone naturally found in meristematic locations that drives growth
- weeds undergo too quick undifferentiated growth, collapsing them by exhausting them
- useful in dicot weeds
- monocot weeds e.g. grass less sensitive as smaller leaves
5
Q
herbicides, finale 150
A
- contains glufosinate, irreversible glutamine synthetase inhibitor
- glutamine cannot be synthesised, key amino acid, leads to plant death as proteins cannot be made
- glufosinate is produced by certain streptomyces bacteria
6
Q
herbicides, glyphosate
A
- most potent herbicide, used to be found in Roundup
- inhibits EPSP synthase of ‘shikimate pathway’, competes for enzyme binding sites and permanently deactivates enzymes
- EPSP needed for the synthesis of key aromatic amino acids, flavonoids, lignin, auxin
- very short lived, specific to plants, inexpensive, kills most plants
- have to spray pre crop establishment as kills crops
7
Q
discovery of glyphosate resistant EPSP synthase
A
- glyphosate resistant bacterial strain CP4 isolated from glyphosate production waste
- CP4 EPSP synthase Gly to Ala mutation at active site allows normal reaction but glyphosate does not interfere
- can genetically modified crop plants with CP4 EPSP synthase gene to create glyphosate resistant crops
8
Q
to make a GM crop we need
A
- defined gene sequences of known function or synthesised artificially (synthetic biology)
- effective vectors including promoters, targeting sequences, terminators and selectable markers
- effective transformation systems (to make gene ‘readable’ to plant e.g. if bacterial)
9
Q
common methods of gene transmission
A
- soil bacterium Agrobacterium tumefaciens Ti plasmid
- gene gun
10
Q
GM using Agrobacterium tumefaciens
A
- soil bacterium, casual agent of crown gall disease
- infects the plant through its Ti plasmid (tumour inducing), integrates T-DNA (transfer DNA) into chromosomal DNA of its host cells that triggers hormonal growth to produce a carbon source only the bacteria can use
- to use in GM can strip out tumour inducing genes, keep T-DNA and add genes to be transferred
- can add to callus (undifferentiated cells), plant then generates with the added DNA
11
Q
GM using a gene gun
A
- elemental particle of a heavy metal e.g. gold can be coated with plasmid DNA
- biolistic particle delivery system used to inject callus with particles
- now often use helium to shoot particles into cells
12
Q
Roundup-ready GM crops
A
- Monsanto developed Roundup-ready soybean, maize, cotton
- modified to carry additional copy of CP4 glyphosate resistant EPSP synthase gene
- increased rates of roundup use
- very low impact on broader environment, net positive outcome
13
Q
glyphosate resistant weeds
A
- 8.6bn kg applied globally since 1974
- 16 resistant weed species found in Roundup-ready cropping systems
- one resistance mechanism is over-production of EPSP synthase
14
Q
higher yield potential in cotton
A
- triple stack-herbicide tolerance technology
- resistant to dicamba, glyphosate and glufosinate herbicides
- hard for weeds to evolve resistance to 3 herbicides simultaneously
15
Q
‘Bt’ cotton
A
- cotton bollworm moth is the worst single insect pest costing >$5bn annually
- historically sprayed broad sprectum insecticides
- then Bt toxin used as an organic pesticide but expensive to culture and short lived
- ‘Bt’ toxin gene (cloned from bacteria) in Monsanto’s ‘Bollgard II’ GM cotton
- decreased insecticide use, increasing survival of other insects
- highly specific, only insects who eat cotton die
- 80% global cotton is GM
16
Q
‘Bt’ toxin in ‘Bt’ cotton
A
- Bacillus crystal toxins on leaves eaten by insects, kills insect (reproductive strategy)
- ‘Cry’ genes produce endotoxin crystals solubilised in midgut and activated by proteolysis
- inserted into GM cotton by T-DNA, only functional part of gene used optimised for plant expression
- cotton produces endotoxin, cotton bollworm moth feeds on plant and dies
17
Q
which traits are engineered
A
- > 30 traits currently engineered for commercial use
- most popular are herbicide tolerance, insect resistance and both together (stacking)
- many other examples e.g. non-browning apples, papaya ringspot virus resistance, anthocyanin rich pink pineapple
18
Q
where are GM crops grown
A
- mainly US
- some Spain and Portugal
- rarely in Africa, lobbied by Greenpeace etc
19
Q
why do farmers choose to grow GM crops
A
- increased yields
- decreased pesticide use
- production cost slightly higher but does not outweigh decrease in cost from increased yields and reduced pesticides
- increased profit, especially important in developing countries
20
Q
Hawaii, RRSV papaya ringspot virus
A
- 1992-1997
- virus spread by aphids kills trees
- nearly eliminated papaya production, one of main farming industries
- production halved by end of decade
- private and public sector innovation (not for profit) created GM ‘rainbow’ papayas resistant to RRSV
- recovered industry, 85% Hawaiian papayas GM
21
Q
‘rainbow’ GM papayas
A
- gene from papaya ringspot virus engineered into crop and expressed forming segments of double stranded RNA
- dsRNA triggers plant defense mechanism, cleaved into short strands of RNA
- short RNA complementary to RNA from virus, so the virus triggers the plant defense mechanism, stopping it from replicating
22
Q
Thailand, RRSV papaya ringspot virus
A
- Cornell university transferred virus resistance gene into Thai varieties of papaya
- 2004 field trials established in Thailand
- local farmers ‘stole’ the fruit from the research stations
- Greenpeace launches campaign against GM plants as ideologically against GM plants (linked to funding)
- Thai government destroys all GM plants so to not have negative publicity (reliant on tourism)
23
Q
genome editing
A
= techniques for genome engineering that involve DNA repair mechanisms and/or replication for incorporating site-specific modification into a genomic DNA
e.g.
- mega nucleases (MN)
- zinc-finger nucleases (ZFN)
- transcription activator-like effector nucleases (TALEN)
- clustered regularly interspaced short palindromic repeats (CRISPR) coupled with a CRISPR-associated protein (Cas e.g. Cas9)
- oligonucleotide-directed mutagenesis (ODM)
24
Q
rise of genome editing
A
- CRISPR/Cas system initially discovered in E.Coli genome in 1987, adapted system used to edit human and mouse cells in 2013
- first GE humans born in China in october 2018, twins Lulu and Nana (researcher fined and imprisoned)
- first GE crop grown in USA in 2019, Cibus’ ultra-high oleic oil canola
- GE organisms still classed as GMO in EU but not England (classed as precision bred organisms, PBOs, allowed to be commercially sold)
25
UK, high vitamin D tomatoes
- average intake of vitamin D for UK adult 7.2 micrograms below RDA of 10 micrograms
- research at John Innes Centre (JIC) Norwich found removing one gene (SL7-DR2 enzyme) boosts vitamin D levels
- 2 tomatoes would meet full RDA
- FSA in process of approving PBOs, need to determine whether nutritional content can be harmful
