L11- Improving Food Quality Flashcards
Why has conventional breeding and mutation breeding not been as successful in enhancing food quality?
- There is no genetic variation in crop population to select for
- Multiple gene families/ quality traits cannot be easily removed
- Some traits need to be specifically switched on/ off in specific organs/ tissues
- Not a targeted approach
What is the difference between Antisense, co-suppression, and RNAi?
ANTISENSE:
- Only adds the genes in reverse complementary direction
CO-SUPPRESSION
- Additional copy of a gene is added
RNAi
- Sense and antisense added
- RNA molecules inhibit gene expression or translation, by neutralising targeted mRNA molecules
Mechanism of Antisense
- Put another similar gene into the cell, but swap the coding region, which gets netralised and there’s no protein production
Example of antisense
• E.g. Removing allergens in Rye grass
- Lol p 5 is a protein in pollen that causes allergens in humans
Approach:
- Down regulation of allergen production (Lol p 5) with an antisense construct targeted to the gene in ryegrass
Mechanism of co-suppression
- insert another gene that already exists in the plant
- this leads to supression of the gene which is originally present in the plant
Example of co-suppression
• E.g. Reduction of allergen in food crops
Soybean- major seed allergy
(Gly m Bd 30K, <1% total seed protein)
Approach:
- Co-suppression using seed specific promotor (Coglycinin promotor)
Transgenic plants:
- No accumulation of the Gly m Bd 30K
- Transgenic Development similar to WT
- No effect on seed size and shape, or protein and oil content
- Sera from individuals allergic to soybean tested
Mechanism of RNAi
- Entry of long double stranded RNA, such as an introduction of a transgene
- Results in the recruitment of enzyme Dicer - Dicer cleaves the dsRNA into short 20-25 basepairs long, fragments, called small interference RNA (siRNA)
- An RNA induced silencing complex (RISC) then distinguises between the two siRNA strands as either sense or antisense
- The sense strands are degraded - The antisense are incorporated to the RISC
- Used to guide messenger RNA (mRNA) - Messenger RNAs (mRNA) which codes for amino acids, are cleaved by RISC
- The activated RISC can repeatedly participate in mRNA degradation, inhibiting protein synthesis
Example of RNAi
E.g. Silencing of Major apple allergen, Mal D 1
Approach:
- RNAi using constitutive promotor (35S)
• Transgenic plants: Expression of Mal D 1 in leaves - Skin prick test - Human IgE antibodies - Monoclonal antibodies
Applications of plant biotechnology to improve food quality?
Tomatos
FLAVR SAVR tomatos:
- Reduction of cell wall-degrading enzyme (polygalacturonase) activity with an antisense gene construct
- > more resistant to cracking and mechanical damage than normal varieties
- > FLAVR SAVR don’t need to be picked until a later stage of ripening when flavour is better
- > These tomatoes yield extracts with the commercially desirable characteristics of higher viscosity and high solid contents
Applications of plant biotechnology to improve food quality?
BT CORN
BT CORN:
Decreased risk of lower grain quality from Mycotoxin (indirect benefit)
- Research showed ears and grain from YieldGard corn were less contaminated by fusarium and fumonisin than conventional corn
What approaches have been used to decrease cotton seed toxicity?
Gossypol:
- Naturally occurring terpenoid toxin in cotton plant
- Toxin affects the heart, liver and reproductive systems (human and animals (Monogastric)
- Toxin higher in seeds
• Protect cotton plants from insects and pathogens
Conventional Breeding
- Glandless cotton lacking gossypol production
Commercial failure:
- Increased Susceptibility to insects and pests
Solution:
- Switch off gossypol production in cotton seeds only (seed specific promotor)
Elimination of gossypol from cottonseed meal
- RNAi- mediated gene silencing of δ-cadinene synthase gene in seeds (highly seed specific promotor from cotton)
• Transgenic plants:
- Seed gossypol levels well below the toxic threshold for human consumption
- No general inhibition of terpenoid production in the rest of the plant
- Stable low-gossypol trait
- Transmitted to the next generation
- Opening a new source of nutrition for millions of people
Why use genetic engineering to produce Golden Rice?
- Only way to produce rice that can synthesise carotenoids in endosperm
- > No variability detected in rice germplasm collections for this trait
- > Rice plants can synthesise carotenoids in leaves, not expressed in endosperm
- Transgenic approach feasible due to:
- > Development of rice transformation technologies
- > Understanding of carotenoid biosynthetic pathway
What is Golden Rice?
Golden Rice
- genetically modified rice that produces beta-carotene (provitamin A) (yellow colour) in the endosperm
- response to vitamin A deficiency (VAD) in developing nations
Steps in the Carotenoid pathway
- GGPP (Geranylgeranyl phyrophosphate) is produced in grain endosperm of white rice
- Conversion to phytoene does not occur
- Phytoene synthase (Psy) enzyme not expressed in grain
- Golden Rice 1- uses Psy from daffodil
- Golden Rice 2- uses Psy from maise
- Control (carotene desaturase- Ctrl) from soil bacterium
- Endogenous rice enzyme in endosperm
Amount of expression of B-carotene in GR1 and GR2
GR1
- produced more B-carotene, but not enough to make an impact on VAD
GR2
- Provides significant levels of vitamin A, based on a 12:1 factor for the conversion of B-carotene to vitamin-A
