Delayed-ripening tomatoes: These engineered lines express antisense RNA directed against which key softening enzyme?
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APolygalacturonase (cell-wall pectinase)
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BGlycerol-1-phosphate acyltransferase (lipid enzyme)
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CACC deaminase (ethylene pathway enzyme)
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DSucrose-phosphate synthase (carbon partitioning enzyme)
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EPectin methylesterase specifically
Answer
Correct Answer: Polygalacturonase (cell-wall pectinase)
Explanation
Introduction / Context:Fruit softening is driven in part by cell-wall pectin degradation. A landmark strategy for delaying tomato softening targeted the polygalacturonase gene using antisense RNA, reducing enzymatic breakdown of pectin.
Given Data / Assumptions:
- Antisense RNA reduces target mRNA accumulation.
- Polygalacturonase catalyzes pectin depolymerization.
- Other enzymes listed are not the classical target for the first delayed-ripening tomatoes.
Concept / Approach:By lowering polygalacturonase, the integrity of the middle lamella and primary wall polysaccharides is maintained longer, slowing softening while allowing other ripening processes to proceed.
Step-by-Step Solution:
Identify the enzyme most directly tied to pectin breakdown.Match with historical antisense target: polygalacturonase.Choose option (a) as the accurate description.Verification / Alternative check:Published analyses of Flavr Savr tomatoes document antisense polygalacturonase constructs and the resulting firmness retention.
Why Other Options Are Wrong:
Glycerol-1-phosphate acyltransferase: lipid metabolism; not the softening enzyme targeted.ACC deaminase: reduces ethylene by degrading ACC; a different, later strategy.Sucrose-phosphate synthase: carbon allocation; not primarily softening.Pectin methylesterase: modulates pectin esterification but was not the original antisense target in the classic example.Common Pitfalls:Conflating ethylene-pathway manipulations with cell-wall enzyme suppression; both can delay ripening but via distinct mechanisms.
Final Answer:Polygalacturonase (cell-wall pectinase).