CRISPR-Cas9 technologies and photosynthetic efficiencies

CRISPR-Cas9 technology has the potential to enhance photosynthetic efficiency and increase crop yields. CRISPR-Cas9 is a gene editing process where genetic engineers can target specific genes in the photosynthesis pathway by turning them off or changing their function. Photosynthesis involves a series of complex reactions, and key genes regulating these processes can be edited to optimize plant performance.

Any step of the photosynthetic pathway can be altered by biotechnology, and has the potential to increase crop yields.

The following sections will look at a few specific examples.

Light is crucial for photosynthesis. If the ability of a plant to harvest light is increased this can increase photosynthetic efficiencies and therefore crop yield.
Genes responsible for light capture, such as light-harvesting complex protein B1 (Lhcb1), can be modified to improve the absorbance of specific wavelengths of light. The Lhcb1 genes encode major components of the light-harvesting chlorophyll-binding protein complexes of the thylakoid membrane, which plays a critical role in light capture during photosynthesis. Targeted modifications to these can improve their ability to convert light energy to chemical energy. This has been shown to improve plant growth.
This is particularly useful in regions where plants grow in low light or in controlled environments like greenhouses.
Rubisco is a key enzyme in the Calvin cycle but is inefficient as it often fixes to oxygen instead of carbon dioxide. This process of oxygen fixation is known as photorespiration and results in a loss of energy efficiency. There are a number of ways that biotechnology can be used to minimise photorespiration:
1. Improve Rubisco efficiency
  Using the enzyme CRISPR-Cas9, scientists can edit genes such as RBCS (RuBisCo small subunit genes) to enhance Rubisco’s specificity for carbon dioxide or alter its active site to improve catalytic efficiency.
2. Enhance CO2 concentration
  To bypass RuBisCO’s inefficiency, CRISPR-Cas9 can introduce or enhance carbon dioxide concentrating mechanisms from C4 plants, such as modifying genes like PEPC (phosphoenolpyruvate carboxylase). These edits increase the concentration of carbon dioxide around RuBisCO, reducing oxygen competition and photorespiration.
3. Reducing photorespiration
  CRISPR-Cas9 can edit genes involved in the photorespiratory pathway, such as GOX1 (glycolate oxidase), to decrease energy waste. Alternatively, genes that allow for more efficient recycling of photorespiratory byproducts can be optimised to redirect them into productive metabolic pathways.
The stomata control water loss and carbon dioxide capture in a plant. There are a number of genes that control the stomatal density on a leaf. Two such genes are EPF1 and EPF2 (Epidermal patterning factors). These genes can be edited to improve water efficiency without compromising photosynthesis.

The methods described above are just a few ways in which photosynthesis can be modified using biotechnology. For every gene involved in photosynthesis there is the potential to modify it using CRISPR-Cas9 to increase its efficiency, resulting in increased photosynthesis and crop yields.

An image of two plants of the same species. The one on the left is smaller, and has not been modified using CRISPR-Cas9. It therefore has less energy for photosynthesis and more energy is lost as heat. The modified plant on the right has an approximate 15% increase in photosynthesis efficiency and less energy lost to heat. This results in approximately 15% more plant growth.

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CRISPR-Cas9 technologies and photosynthetic efficiencies

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