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Sridharan S Transgenic plants_traits for improved quality.pptx

The document discusses transgenic plants, focusing on biofortification to enhance micronutrient levels, particularly through the development of 'Golden Rice' that synthesizes β-carotene to address vitamin A deficiency. It outlines the genetic modifications used to produce β-carotene in rice grains via the introduction of specific genes from daffodils and bacteria. Additionally, it addresses methods to improve fruit shelf life by inhibiting ethylene production through genetic modifications.

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TRANSGENIC PLANTS: TRAITS FOR IMPROVED QUALITY SRIDHARAN S 2021009024 Course Teacher Dr.K.Hemaprabha Assoc. Professor(Biotechnology) ABT301 PLANT BIOTECHNOLOGY (2+1)
BIO-FORTIFICATION • Biofortification is the process of breeding food crops that are rich in bio-available micronutrients • These crops “biofortify” themselves by loading higher levels of minerals and vitamins in their seeds and roots, which are then harvested and eaten. • Biofortified crop varieties could naturally reduce nutritionally related health problems in hundreds of millions of people.
PROVITAMIN A  Vitamin A deficiency (VAD) mainly affects pre-school children and pregnant women in the world.  VAD causes blindness in children. Cure for this is to provide vitamin A supplements as capsules  An alternative and viable approach to alleviate this problem is to provide β-carotene (Provitamin A) in the grains.  Human can synthesize vitamin A if provided with the precursor molecule β - carotene (also known as provitamin A).  Beta-carotene is assumed to be converted to retinol (vitamin A) in the animal gut.  Milled rice is normally devoid of β-carotene
• The rice plant can naturally produce beta-carotene in its leaves, where it is involved in photosynthesis. The β-carotene is an accessory pigment that is essential to photosynthesis. It is synthesized from the isoprenoid pathway in all green tissue. • Carotenoids are 40-carbon compounds produced from the precursor molecule via a biochemical pathway localized in plastids. • The 40-carbon backbone of β-carotene is phytoene, which is assembled by combination of two 20-carbon geranly geranyl diphosphate (GGPP) molecules by the enzyme Phytoene synthase . • Double bonds are then added to phytoene through a series of desaturation steps to produce lycopene, an antioxidant compound found in most plants that contribute to the red color of tomatoes. • Finally, lycopene can be converted to the β-carotene by the enzyme, lycopene cyclase. Plant does not normally produce the pigment in the endosperm, where photosynthesis does not occur.
 Dr. Ingo Potrykus in Switzerland and Peter Beyer in Germany are the two person responsible for transforming rice with two additional genes to produce β-carotene in rice endosperm •Although rice seed does not contain β-carotene, a precursor, geranyl geranyl diphosphate (GGPP) is produced. •GGPP is not converted further into β-carotene as it lacks enzymes Phytoene synthase, Phytoene desaturase, and Zeta carotene desaturase.
 Hence, to synthesize β-carotene in rice seed, transgenic rice plants were generated that express two additional genes in the endosperm of rice seed.  Golden rice was created by transforming rice with only two beta-carotene biosynthesis genes:  First gene that codes for phytoene synthase (obtained from daffodil plant Narcissus pseudonarcissus) was expressed using rice endosperm specific glutelin (seed storage protein in cereals) promoter, Gt1 (show tissue specific expression, expressed only in endosperm) for the production of phytoene in rice grains.  Because the daffodil gene products are normally found in plastids, they already contain sequence for a plastids transit peptide to direct newly synthesized phytoene synthase enzymes to plastids.
 Second gene, ctr1, carotene desaturase gene (obtained from the bacterium, Erwiniauredovora) was expressed under cauliflower mosaic virus 35S promoter  This enzyme adds double bonds to phytoene to produce lycopene. This bacterial enzyme does the function of two plant enzymes viz.,phytoene desaturase and zeta carotene desaturase.  The bacterial gene encoding desaturase was modified by addition of a transit peptide to direct it to plastids following translation.  Finally, lycopene is converted in rice grains by an endogenous lycopene cyclase to β-carotene, yellow product. Transgenic rice produced golden colored seed that accumulated up to 1.6 μg of total carotenoids per gram dry weight, with about 50% of this found as β-carotene (0.8 μg of β-caroteneper gram).
Further work saw the development of “Golden rice II” in which the daffodil phytoene synthase gene was replaced with its more efficient maize phytoene synthase (psy) gene along with the Erwiniauredovora carotene desaturase (crt1) gene expressed under a rice glutelin specific promoter, Gt1. Transgenic rice yielded up to 37 μg of total carotenoids per gram (preferentially accumulates β- carotene up to 31 µg/g), thus produced 23 fold increase in carotenoid, compared to the first generation of Golden rice. It is estimated that by eating modest amount of Golden rice 2, enough β- carotene can be provided to overcome vitamin A deficiency.
Normal rice lacks β-carotene Golden rice rich in β-carotene The precursor of Vitamin A
IMPROVING FRUIT SHELF LIFE  Shelf life of fruits increased by inhibiting the expression of ethylene biosynthesis gene by antisense technology or RNAi technology.  Ethylene is synthesized in higher plants from methionine via S- adenosylmethionine and aminocyclopropane- 1-carboxylic acid.  The two key enzymes of the pathway are ACC synthase (ACS; ACC-1-aminocyclopropane-1-carboxylic acid) and ACC oxidase (ACO)  In tomato, the ACC synthase gene active during ripening was silenced using the antisense techniques effectively reducing the production of ethylene by the ripening fruit by 99.5% .  While control fruits begin to produce ethylene 48-50 days after pollination and immediately undergo a respiratory burst, genetically modified tomatoes produced minimal levels of ethylene and failed to produce the respiratory burst thereby improved fruit shelf life.
Methionine S-Adenosylmethionine (AdoMet) ACC synthase 1-Aminocyclopropane- 1-carboxylic acid (ACC) ACC oxidase Ethylene Shelf life of tomato fruits increased by inhibiting the expression of ethylene biosynthesis gene by antisense technology or RNAi technology. Climacteric fruit depend on ethylene for fruit ripening Example: banana, melon, tomato
IMPROVING FRUIT SHELF LIFE. First commercially grown genetically modified food Released by Calgene in 1994 Harboured antisense construct of tomato polygalaturonase (PG)- a cell wall pectin degrading enzyme Antisense inhibition of gene expression Flavr Savr tomato
Transgenic plant-Delayed ripening Normal plant
REFERENCE  Bernard R.Glick, Jack J.Pasternak, Cheryl L.Patten Molecular Biotechnology Principles and Applicatons of Recombinant DNA  Yunbi Xu Molecular Plant Breeding
THANK YOU SRIDHARAN S 2021009024