Lecture 8 - Improving food quality - Gray Flashcards Preview

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Who is this benefiting?

Consumer, not just producer


What are some examples of improved food?

- foodstuffs with improved protein
- nutriceuticals eg margarines, designer tomatoes, and golden rice
- longer lasting fruit and veg


Where does human protein come from

65% from plants - mostly cereal and legumes. this also supplies livestock fodder.


how many amino acids does human produce

10 of the 21. rest must be consumed


what are some sources of proteins

- seeds!
- legume storage proteins GLOBULINS are low in methionine and cysteine
- cereal PROLAMINS lack lysine


how can we improve amino acid composition of seeds?

alter the amino acid seq of endogenous gene - BUT this can make protein unstable
Could also express lysine or methionine rich proteins from other plants BUT albumin from brazil nuts had allergenic risk.


What are potatoes low in?

Lysine, cysteine. methionine.


What had a good amino acid comp?

Amaranth albumin seed protein


What did they do?

Expressed gene in potato on starch synthase tuber specific promoter - increased lysine and sulphur containing amino acids


What are innate potatoes?

Potatoes with lower levels of acrylamide formation when cooked. Also less prone to bruising and spots due to reduced polyphenol oxidase. RNAi was used to silence asparagine synthetase and polyphenol oxidase genes.


What enzyme makes fruit soft and how?

Polygalacturonase. Cell walls are stuck together with middle lamella (made up of pectate). When this breaks down, fruit gets soft. Polygalacturonase catalyses this softening.


Describe the principle behind antisense

Put gene in backwards, transcript is backwards, then this would stick to the endogenous transcript, and you get dsRNA. This isn't transcribed, as it triggers RNA interference in plants.


What promoter and terminator did they use here?

CaMV35S promoter, nopaline synthase terminator.


What effects does overexpression have?

Also silences expression of the gene


Was the antisense polygalacturonase successful?

Moderately. Delayed 'overripening' but didn't change softening. Kept tomatoes in tact for longer, and resistant to splitting. Stopped cells breaking down cell wall, therefore increased solids, good for sauces etc. Also, no need to heat sauce to denature enzymes.


What was the first GM food for human consmption?

Flavr Savr tomatoes (1994). V successful. Withdrew in 1997 due to bad transport.
But - 1995 processed market, increased yields of paste. Cold break - no heating needed. AntiGM debate halted sales.


What gives plants their colour?



What is the rate limiting step?

Phytoene synthase - mutant fruit are yellow.


What happened when we attempted to overexpress colour?

YELLOW fruit - due to RNAi. Natural surveillance system for viruses.


What did this lead to?

This identified the gene responsible for phytoene synthesis. This codes for provitamin A.


What can vitamin A deficiency lead to?

Loss of sight, poor immune system.


Why is rice low in nutrients

We remove the husk by polishing


What are carotenoids?

Precursors to vit A. Pigment involved in photosynthesis, fruit and flower colour.


Is vitamin A toxic?

Yes. So we produce proVitA (beta-carotene) in endosperm.


Describe how golden rice was developed

PSY gene (codes for phytoene synthase) was added on to rice promoter. This joins two geranylgeranyl-diphosphate molecules together, forming phytoene. PDS converts it to zeta-carotene. ZDS converts this to lycopene. Lycopene cycled to form beta carotene. Using CRTI from Erwinia skips PDS and ZDS.


What was different about golden rice 2?

They tested PSY genes from different sources, to find one with the highest activity. Found it on maize gene instead of daffodil.
Also used selection without antibiotic resistance.
Ferritin and phytase genes also expressed to increase levels of available iron in the rice.


What are some objections to golden rice?

Vit A can be solved by food supplements and home gardening
GR will contaminate non-GMO rice and affect export markets
It may have unknown health consequences
Greenpeace say this is a Trojan horse that will usher in use of GMOs by multinationals
Does the community want it?


How does fruit ripen?

Burst of ethylene triggers fruit ripening. If you could turn that off/down, you could slow down ripening


How is ethylene made?

Made from methionine. Need ACC synthase and ACC oxidase.


What technique was employed to slow fruit ripening? Did it work?

ACC oxidase antisense. It did, less than 5% ethylene. Fruit intact 30-40 days on plant. Lasted for 5 months picked. Ethylene gas then triggered ripening.