Given below are two statements one is labelled as Assertion A and the other is labelled as Reason R: Assertion A: Phosphomannose isomerase (PMI)…
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:
Select an option to attempt
Correct Answer: Option A
Explanation
PMI selectable marker in Golden Rice 2 transformation:Assertion: PMI (phosphomannose isomerase) was used as a selectable marker in Golden Rice 2.Reason: PMI converts mannose-6-phosphate (M6P) to fructose-6-phosphate (F6P), rescuing transformed cells on mannose-containing medium.Mechanism of PMI selection:• Mannose (present in growth medium) is taken up and phosphorylated to mannose-6-phosphate by hexokinase in plant cells.• M6P cannot enter glycolysis further (no plant phosphomannose isomerase) → M6P ACCUMULATES → blocks glycolysis → non-transformed cells starve and die.• Transformed cells expressing PMI convert M6P → F6P → can enter glycolysis → SURVIVE and GROW.• This is a POSITIVE selectable marker system (growth advantage, not antibiotic resistance).Advantages: No antibiotic resistance genes → better regulatory acceptance for food crops.Both Assertion A and Reason R are true, and R correctly explains A.Answer: Both A and R are true; R is the correct explanation of A.