Flavr Savr tomato (Anti sense RNA technology)

Flavr Savr tomato is a transgenic variety of tomato projected to contain,
Enhanced flavor & color
Improved shelf life.
Antisense RNA technology is applied to the Polygalacturonase gene to achieve this.
To understand this technology and its background to use in this product, we must be aware of the following three components.
1. Climacteric fruit physiology
Climacteric is the final physiological process that marks the end of fruit maturation and the beginning of fruit senescence. Sudden rise in respiration and level of ethylene are the characteristic features of this process.
Sensory attributes
The peak of edible ripeness
Best taste and texture for consumption.
2. Biochemical changes during tomato ripening
 Sudden rise in respiration of the fruit without any external influences.
 Sudden rise in the level of ethylene; the growth hormone
 Change in pigment compositions: Decrease in the level of chlorophylls (Green) and increase Lycopene level (Red).
 Change in Carbohydrate composition: accelerated conversion of starch into sugar.
After effects
 Respiration rates dip below the pre-climacteric rates.
 Fruits are prone to fungal invasion.
 This leads to senescence.
3. Ripening related genes.
Ripening process-related studies showed 3 important groups of clones induced by ethylene.
 The first clone pTOM5 gives Phytoene synthase as a gene product which synthesizes Lycopene the substance responsible for red coloration.
 The second clone pTOM6 gives Polygalacturonase as a gene product that degrades the cell wall resulting in softening of the fruit.
 The third clone pTOM13 produces ACC oxidase as a gene product that is involved in ethylene formation the main triggering hormone.
Genetic manipulation involved manipulating these genes to get desired traits.
Antisense RNA technology is used to get Flavr Savr tomato.
Antisense RNA is obtained by transcribing template (Noncoding) strand of DNA. Essentially this will be complementary to the normal mRNA.
Usage of this technology in Flavr Savr tomato is outlined like this.
The construct:
1.Polygalacturonase is responsible for the degradation of the cell wall. So blocking its expression will retain the desi
The clone pTOM6 which gives Polygalacturonase as a gene product and responsible for the degradation of the cell wall has been blocked by preparing and inserting antisense RNA into the agrobacterium-based system.
2.The gene of the polygalacturonase enzyme is isolated from the tomato. This is the first desired gene.
3.Antisense RNA coding gene is prepared with the help of a Ti-plasmid by turning the gene in the opposite direction. This is the second desired gene.
4.Ti-promoter is employed to insert the complementary DNA with new constructs into the genome of the cell.
The Process:
 During the ripening process of the flavr savr tomato, both genes coded by sense strand and antisense strand are translated into messenger RNA.
 This results in two complementary mRNAs.
 Due to this complementary nature, they fit together to form a double-stranded mRNA.
 This will lead to the blocking of the production of polygalacturonase.
The output:
Flavr Savr tomato which is with intact cell walls and appealing looks.
Significance
Though is product never introduced to the market and it is an economically nonviable venture, the technology established by this work has significant biotechnological applications in various fields.