192. Given below are two statements one is labelled as Assertion A and the other is labelled as
Reason R:
Assertion A: Phosphomannose isomerase (PMI) from E. coli was used as selection marker to
develop ‘golden rice 2’.
Reason R: When mannose is added in the selection media, endogenous hexokinase converts
mannose into mannose-6-phosphate which blocks glycolysis, ATP production, and represses
transcription of photosynthetic genes, resulting in slower growth of non-transformed plants. PMI,
on the other hand, converts mannose-6-phosphate to fructose-6-phosphate.
In the light of the above statements, choose the correct answer from the options given below:
A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not the correct explanation of A
C. A is true but R is false
D. A is false but R is true

Explanation:

❌ Assertion A: PMI from E. coli was used as selection marker to develop ‘Golden Rice 2’

• False.

• Golden Rice 2 was developed using genes psy (phytoene synthase from maize) and crtI (phytoene desaturase from Pantoea ananatis).

• The selection marker commonly used was hpt (hygromycin resistance gene), not PMI.

• Therefore, PMI was not used as a selection marker in Golden Rice 2.

✅ Reason R: When mannose is added… PMI converts mannose-6-phosphate to fructose-6-phosphate

• True.

• Mannose is phosphorylated by endogenous hexokinase into mannose-6-phosphate, which accumulates and inhibits glycolysis, reducing energy availability and gene expression, thus hindering non-transformed plant growth.

• Plants transformed with PMI convert mannose-6-phosphate into fructose-6-phosphate, feeding back into the glycolytic pathway and allowing growth.

• This makes PMI a positive selection marker in many transformation systems (but not specifically in Golden Rice 2).

Conclusion:

• PMI is a valid plant selection marker, but was not used in Golden Rice 2.

• Thus, the Assertion is false, but the Reason is scientifically accurate.