The efficiency gap
Photosynthesis is the biological process by which plants, algae and some bacteria capture sunlight and use it to convert carbon dioxide and water into glucose and oxygen. Every calorie of food on Earth traces back to it.
Yet the process is remarkably inefficient. Leaves reflect some light, absorb only some wavelengths, and lose energy to heat and to a process called photorespiration. Under real field conditions, major crops like wheat and rice convert only 1–2% of the sunlight they receive into edible biomass.
With global population projected to reach 10 billion by 2050, and with climate change reducing arable land, researchers believe improving this efficiency could be one of the highest-impact agricultural interventions available.
See our cells and organelles guide for background on the chloroplast, where photosynthesis takes place.
The photorespiration problem
The central enzyme in carbon fixation is RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase). It evolved over three billion years ago, when the atmosphere had far more CO₂ and far less O₂ than today.
The problem: RuBisCO cannot perfectly distinguish CO₂ from O₂. When it binds oxygen — which happens frequently in hot conditions when plant stomata close to prevent water loss — it triggers photorespiration: a futile cycle that consumes energy and releases CO₂ already fixed, reducing yield by up to 30%.
Engineering a solution
The RIPE (Realizing Increased Photosynthetic Efficiency) project, based at the University of Illinois and funded by the Gates Foundation and USAID, has demonstrated several approaches:
- Photorespiration bypass: inserting shorter metabolic routes to recover carbon lost during photorespiration. In greenhouse trials, tobacco plants engineered with this bypass showed 40% greater yield.
- VPZ (chloroplast protection): overexpressing three proteins (VDE, PsbS, ZEP) that allow plants to adjust light-harvesting more rapidly as clouds pass — reducing wasted light energy by 15–20%.
- SBPase overexpression: increasing the amount of the enzyme sedoheptulose bisphosphatase to accelerate the Calvin cycle.
C4 rice — the long game
Maize, sugarcane and sorghum use a more efficient form of photosynthesis called C4, which concentrates CO₂ around RuBisCO and nearly eliminates photorespiration. C4 plants are typically 30–50% more productive than C3 plants like rice and wheat under high temperatures.
The C4 Rice Consortium — a global effort funded by the Gates Foundation — is attempting to engineer C4 characteristics into rice. This requires reorganising leaf anatomy and rewiring carbon metabolism. It is estimated to require at least another decade of work, but the potential yield gain for the world's most important staple crop is enormous.