Lecture 8 - Improving food quality - Gray

Question 1

Who is this benefiting?

Answer 1

Consumer, not just producer

Question 2

What are some examples of improved food?

Answer 2

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

Question 3

Where does human protein come from

Answer 3

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

Question 4

how many amino acids does human produce

Answer 4

10 of the 21. rest must be consumed

Question 5

what are some sources of proteins

Answer 5

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

Question 6

how can we improve amino acid composition of seeds?

Answer 6

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.

Question 7

What are potatoes low in?

Answer 7

Lysine, cysteine. methionine.

Question 8

What had a good amino acid comp?

Answer 8

Amaranth albumin seed protein

Question 9

What did they do?

Answer 9

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

Question 10

What are innate potatoes?

Answer 10

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.

Question 11

What enzyme makes fruit soft and how?

Answer 11

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

Question 12

Describe the principle behind antisense

Answer 12

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.

Question 13

What promoter and terminator did they use here?

Answer 13

CaMV35S promoter, nopaline synthase terminator.

Question 14

What effects does overexpression have?

Answer 14

Also silences expression of the gene

Question 15

Was the antisense polygalacturonase successful?

Answer 15

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.

Question 16

What was the first GM food for human consmption?

Answer 16

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.

Question 17

What gives plants their colour?

Answer 17

Carotenoids

Question 18

What is the rate limiting step?

Answer 18

Phytoene synthase - mutant fruit are yellow.

Question 19

What happened when we attempted to overexpress colour?

Answer 19

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

Question 20

What did this lead to?

Answer 20

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

Question 21

What can vitamin A deficiency lead to?

Answer 21

Loss of sight, poor immune system.

Question 22

Why is rice low in nutrients

Answer 22

We remove the husk by polishing

Question 23

What are carotenoids?

Answer 23

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

Question 24

Is vitamin A toxic?

Answer 24

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

Question 25

Describe how golden rice was developed

Answer 25

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.

Question 26

What was different about golden rice 2?

Answer 26

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.

Question 27

What are some objections to golden rice?

Answer 27

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?

Question 28

How does fruit ripen?

Answer 28

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

Question 29

How is ethylene made?

Answer 29

Made from methionine. Need ACC synthase and ACC oxidase.

Question 30

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

Answer 30

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.

Question 31

How can this be applied to cut flowers?

Answer 31

Ethylene also controls senescence - so if we limit this, we can extend the life of cut flowers