BioTechniques News
Beatrice Bowlby
The quest for new and improved plant-based meat alternatives has taken an unexpected turn, as researchers engineer lettuce and tobacco plants to produce pig muscle protein in their chloroplasts.
Scientists from Imperial College London, the Bezos Centre for Sustainable Protein and biotechnology startup Kyomei (all London, UK) have inserted the porcine gene for myoglobin into plant cells, enabling the crops to produce muscle proteins that could one day be used to create plant-based meat products. The plants grew normally, flowered and even passed their newfound meaty genes to the next generation, highlighting their potential as a more sustainable and scalable source of protein that could help reduce our reliance on animal agriculture.
Livestock farming is an incredibly resource-intensive practice, requiring large amounts of land and water, as well as contributing to greenhouse gas emissions, deforestation and biodiversity loss. Swapping to alternative protein sources, such as engineered meat proteins, may offer a solution to this, providing similar nutritional profiles and flavor to traditional meat with fewer unsavory environmental and ethical ramifications.
A promising candidate is myoglobin, which is found in the cardiac and skeletal muscle of vertebrates and gives meat its characteristic red color and metallic taste. Previous work has expressed myoglobin in bacteria and yeast; however, these organisms cannot produce their own food, meaning their role in protein production is limited as they require expensive and energy-intensive bioreactors and feedstocks.
Hoping to bypass these hurdles, the new study turned its attention to plants, specifically chloroplasts, because their bacterial ancestry and high number of copies per cell make them ideal for churning out large amounts of protein. The team first cloned pig myoglobin genes before using a gene gun and gold microcarrier delivery system to introduce them into the chloroplasts of the model plant Nicotiana tabacum (tobacco) and cultivated crop Lactuca sativa (lettuce).
For comparison, the researchers also expressed porcine myoglobin in the nuclei of these plants and bovine myoglobin in the chloroplasts of the green alga Chlamydomonas reinhardtii.
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Southern blotting analysis and genome sequencing were used to confirm transformation of the tobacco and lettuce and ensure that all copies of mitochondrial DNA were identical. Successfully engineered plants had normal morphology and were able to produce flowers and functional seeds.
Next, myoglobin accumulation was estimated by SDS-PAGE and immunoblotting, which revealed that total soluble protein was much higher in chloroplast-engineered tobacco (2.7%) and lettuce (1.5%) than in C. reinhardtii (<0.25%). Expression in tobacco chloroplasts was also superior to tobacco nuclear expression.
Porcine myoglobin was then purified from tobacco plants using anion-exchange chromatography followed by size-exclusion chromatography, and was found to have similar physical properties to other mammalian myoglobin proteins in terms of size, folding and heme binding.
Lastly, liquid chromatography–mass spectrometry analysis demonstrated that tobacco plants with engineered chloroplasts produced around 800 mg per kg of dry weight, while lettuce produced approximately 810 mg. Although animal meat contains roughly ten times that, plant cultivation is far more efficient, so the team argues that the yield per hectare could still rival, or potentially exceed, that of livestock farming, while also benefitting the planet.
“The myoglobin could be extracted from leaves and purified using industrial protein purification methods. Since it is identical to animal myoglobin, it could then be added as an ingredient to plant-based meat products to improve their color, flavor and nutritional value,” posited study author Alexia Groff.
According to Rodrigo Ledesma-Amaro, director of the Bezos Centre for Sustainable Protein, this latest development marks an “important advance on earlier plant and algal research.” However, he cautioned that “further research must confirm food functionality and safety, field performance, processing requirements and clear economic and environmental benefits at scale.”
The post Lettuce engineered to produce pig protein, planting the seed for future meat substitutes appeared first on BioTechniques.
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