The correct answer is (4) Polygalacturonase.

Explanation of each option

1. 1-Amino cyclopropane-1-carboxylic acid synthase (ACC synthase)

• ACC synthase catalyzes the formation of ACC, the precursor of ethylene, and silencing it can reduce ethylene production and delay ripening.

• However, this is NOT the strategy used in the original Flavr Savr tomato; other experimental lines used ACC synthase antisense, but Flavr Savr specifically targeted polygalacturonase.

2. 1-Amino cyclopropane-1-carboxylic acid oxidase (ACC oxidase)

• ACC oxidase converts ACC to ethylene; down‑regulation also reduces ethylene biosynthesis.

• Again, this was not the gene engineered in the Flavr Savr variety.

3. Expansin

• Expansins are proteins that loosen cell walls and can influence growth and softening.

• They were not the primary target in Flavr Savr; the commercial product did not use expansin gene manipulation.

4. Polygalacturonase – Correct

• Flavr Savr tomato was created by introducing an antisense copy of the tomato polygalacturonase (PG) gene.

• PG degrades pectin in the cell wall during ripening, causing softening. Antisense PG mRNA hybridizes with the normal PG mRNA and blocks its translation, sharply reducing PG activity.

• As a result, pectin degradation slows, the fruit softens more slowly, and shelf life is extended while allowing vine ripening for better flavor.

SEO‑oriented introduction (for article use)

The famous Flavr Savr tomato, the first commercially approved genetically engineered food crop, was developed by targeting the enzyme polygalacturonase, which is responsible for pectin breakdown and fruit softening. By inserting an antisense copy of the polygalacturonase gene, scientists drastically reduced PG activity, slowing tomato softening and extending shelf life, rather than altering ethylene biosynthesis enzymes like ACC synthase, ACC oxidase, or cell‑wall–loosening expansins.