Metabolic engineering of potato — which bacterial gene has been used to elevate tuber starch content?

Introduction / Context:
Improving starch yield in potato (Solanum tuberosum) has been a classic target of metabolic engineering. The committed step in starch biosynthesis is catalyzed by ADP-glucose pyrophosphorylase (AGPase), which converts glucose-1-phosphate and ATP to ADP-glucose, the direct glucosyl donor for starch synthases.

Given Data / Assumptions:

• Bacterial AGPase (e.g., E. coli glgC/glgD) has been expressed in tubers.
• Goal is higher flux through ADP-glucose formation → more starch deposition.
• Other genes (SPS, PG, invertase) regulate different steps or polymers.

Concept / Approach:

Overexpressing AGPase elevates ADP-glucose supply, increasing starch granule biosynthesis. Bacterial AGPase can be engineered for reduced allosteric inhibition, further enhancing carbon flux to starch. SPS modulates sucrose synthesis in source tissues; PG affects pectin degradation in fruit softening; invertase cleaves sucrose and can decrease starch accumulation by diverting carbon.

Step-by-Step Solution:

Verification / Alternative check:

Peer-reviewed studies report increased tuber starch content after expressing modified bacterial AGPase in potato, validating the strategy.

Why Other Options Are Wrong:

SPS adjusts sucrose metabolism but does not directly commit carbon to starch in tubers. PG targets pectin breakdown (fruit softening), not starch. Invertase often reduces starch by diverting sucrose.

Common Pitfalls:

Assuming any sugar-related enzyme increases starch; in practice, the committed step (AGPase) is critical.

Final Answer:

ADP-glucose pyrophosphorylase (AGPase) gene