Photosynthetic Efficiency and Photorespiration in Crop Plants

Photosynthetic efficiency in crop plants is governed by the capacity to convert light energy into chemical energy and to fix atmospheric CO₂ into biomass. Central to this process is Rubisco, the enzyme that catalyses the carboxylation of ribulose-1,5-bisphosphate but also reacts with O₂ in a competing oxygenation reaction known as photorespiration. Photorespiration drains energy and releases previously fixed CO₂, yet also plays protective roles under stress by dissipating excess excitation energy. In C₃ crops, inefficiencies arise from suboptimal light harvesting, limitations in electron transport, and Rubisco’s poor discrimination between CO₂ and O₂. Strategies to enhance productivity have targeted improved light capture, strengthened electron transport chains, optimisation of Calvin–Benson cycle enzyme kinetics, elevation of CO₂ concentration at the reaction site and synthetic bypasses of the photorespiratory pathway. Genetic stacking of traits, modelling of canopy photosynthesis and exploitation of natural variation have further revealed routes to increase biomass accumulation and yield under field conditions. Advances in synthetic biology now allow introduction of microbial CO₂-concentrating modules into chloroplasts, and precision breeding is uncovering avenues to modulate photorespiration for both stress tolerance and resource use efficiency. Collectively, these approaches aim to meet global food security challenges by tailoring photosynthetic processes to the demands of a changing climate.

Research from Nature Portfolio

A proof-of-concept study has shown that expression of nine carboxysome components from proteobacteria in tobacco chloroplasts yields functional microcompartments that elevate CO₂ at the site of Rubisco, thereby supporting autotrophic growth under elevated atmospheric CO₂. This work demonstrates the feasibility of engineering complete CO₂-concentrating mechanisms into C₃ chloroplasts to boost carboxylation rates.

Investigations into manipulation of sedoheptulose-1,7-bisphosphatase (SBPase) in tomato have revealed that increased SBPase activity enhances photosynthetic rates, sucrose and starch accumulation, total biomass and leaf area, while also conferring greater tolerance to chilling stress. These findings underscore the potential of targeting individual Calvin–Benson cycle enzymes to improve both productivity and stress resilience in crops.

Photosynthetic Efficiency and Photorespiration in Crop Plants publication trend

The graph below shows the total number of articles in photosynthetic efficiency and photorespiration in crop plants across all publications each year (not limited to Nature Index journals).

Technical terms

Photosynthetic efficiency: Ratio of chemical energy stored as carbohydrates to the incident light energy absorbed by the plant.

Photorespiration: Metabolic pathway initiated by Rubisco’s oxygenation of ribulose-1,5-bisphosphate, resulting in CO₂ release and consumption of ATP and reducing power.

Rubisco: The enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, responsible for the first step in CO₂ fixation and also catalysing a competing oxygenation reaction.

Calvin–Benson cycle: Series of enzymatic reactions in the chloroplast stroma that convert CO₂ into triose phosphates using ATP and NADPH from the light reactions.

Carboxysome: Proteinaceous microcompartment in some bacteria that concentrates CO₂ around Rubisco to increase carboxylation efficiency.

CO₂-concentrating mechanism: Biological system that elevates local CO₂ concentration at the site of Rubisco to suppress photorespiration and enhance carbon assimilation.

Sedoheptulose-1,7-bisphosphatase (SBPase): Key enzyme in the Calvin–Benson cycle that catalyses the dephosphorylation of sedoheptulose-1,7-bisphosphate, promoting ribulose-1,5-bisphosphate regeneration.

References

1. Engineering α-carboxysomes into plant chloroplasts to support autotrophic photosynthesis. Nature Communications (2023).
2. Changes in SBPase activity influence photosynthetic capacity, growth, and tolerance to chilling stress in transgenic tomato plants. Scientific Reports (2016).
3. Perspectives on improving photosynthesis to increase crop yield. The Plant Cell (2024).
4. Feeding the world: improving photosynthetic efficiency for sustainable crop production. Journal of Experimental Botany (2019).