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Genetics as it applies to evolution, molecular biology, and medical aspects.

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Postby ngfok » Thu Mar 16, 2006 12:56 am

hi i have a question on GM golden rice? Does this process taken inside the bacteria. Cause i don't understand how endosperm can have promotor. Isn't promoter only in bacteria and not in plants.


"Golden rice was designed to produce Vitamin A precursor beta-carotene in the part of rice that people eat, the endosperm. The rice plant can produce beta-carotene, it is a carotenoid that occurs in the leaves and is involved in photosynthesis, however the plant does not normally produce the pigment in the endosperm since the endosperm is not a tissue where photosynthesis takes place.
Golden rice was created by transforming rice with three beta-carotene biosynthesis genes:
1. psy (phytoene synthase)
2. lyc (lycopene cyclase) both from daffodil (Narcissus pseudonarcissus), and
3. crt1 from the soil bacterium Erwinia uredovora
The psy, lyc and crt1 genes were transformed into the nuclear genome and placed under the control of an endosperm specific promoter, so that they are only expressed in the endosperm. The lyc gene transfomed into the rice has a transit peptide sequence attached so that it is targeted to the plastid where geranylgeranyl diphosphate formation occurs. It was important to use the bacterial gene crt1 since it can catalyze multiple steps in the synthesis of carotenoids, these steps require more than one enzyme in plants.[3] The end product of the engineered pathway lycopene, if the plant accumulated lycopene the rice would be red. Recent analysis has shown that the plant endogenous enzymes process the lycopene to beta-carotene in the endosperm, giving the rice the distinctive yellow colour for which it is named.[4] The original Golden rice was called SGR1, under greenhouse conditions it produced 1.6µg/g of carotenoids."
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Postby canalon » Thu Mar 16, 2006 3:26 am

Promoter is a genetic that regulates he expression of a gene. They are found in every organisms (although they can be different fom one to another). So GM golden rice express its genes without help from any bacteria.
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Postby gumshoes_15 » Wed Mar 22, 2006 12:04 am

Canalon wrote:Promoter is a genetic that regulates he expression of a gene. They are found in every organisms (although they can be different fom one to another). So GM golden rice express its genes without help from any bacteria.


i don't think that's correct, or else what is the purpose of the agrobacteria. isn't agrobacteria helps transform the rice.
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Postby LilKim » Wed Mar 22, 2006 2:22 am

Like Canalon said.... a promotor is simply a region that's 5' to the coding sequence of a gene. This element (promotor) controls when, and where a particular gene is expressed.

A promotor (or gene regulatory region) is present 5' to every gene and in ALL living organisms . . . Bacterial/Plant/Animal ....

Since the 3 genes (PSY, lyc, crt1) were transformed into the GM rice genome. (... in this situation transformation means that the 3 genes were introduced to the nucleus and actually integrated into the chromosomes in the GM rice genome)

...Therefeore, their expression must be regulated by the GM rice plant itself! I don't know much about plants (so i have no idea were the endosperm is ...) but, if you transform a gene with a specific promotor... the gene will only be expressed when that promotor is on.

Therefore... these 3 gene will be expressed whenever and whereever endosperm specific genes are expressed in the rice plant cells

kewl beans!
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Postby canalon » Wed Mar 22, 2006 3:26 am

gumshoes_15 wrote:i don't think that's correct, or else what is the purpose of the agrobacteria. isn't agrobacteria helps transform the rice.


That is correct! :evil: :wink:
The bacteria are used to assemble and replicate in huge quantity the genes that you want to insert (usually you do that in E. coli because they are easy to grow) then you insert them in Agrobacterium tumefasciens whose Ti plasmid is able to transfer the genes into the plant genome. End of the role of bacteria. The specificity of the promoter of your construct will now determine where and when your newly inserted genes will be expressed.
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Postby Nithin » Thu Apr 06, 2006 4:03 am

Agrobacterium tumifaciens is a soil bacteria which affects plants and causes tumour in them. As Patrick said there is a Ti plasmid which means tumour inducing plasmid. This tumour inducing plasmid as the name indicates causes tumour. But before using this bacteria the tumour inducing characteristics are removed. This is called a disarmed Ti plasmid. After bacterial infection and transfer of the gene of interest which is incorporated into the Ti plasmid bacterial role is complete and bacteria becomes say (excess baggage)And I have a small doubt. I know the Agrobacterium tumifaciens does not affect all the plants. In fact it affects either monocots only or dicots only. I dunno which ( I think that monocots only) Which one please???
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