Scientists have engineered tobacco and lettuce plants that carry the gene for the protein myoglobin, a molecule abundant in animal muscle fibers, in the genome of their chloroplasts. This makes it possible to mass-produce myoglobin in crops to give a meaty flavor and color to meat alternatives. The expected yield at scale could rival those from livestock farming, while greatly reducing water use and greenhouse gas emissions.
Possibly the most effective personal choice we can make to reduce our environmental footprint is to eat less meat. This is because livestock farming requires setting aside valuable land to grow fodder, while using up vast amounts of freshwater and contributing to global warming through the emission of methane and nitrous oxide. At least as important for many consumers is the desire to prevent animal suffering. For these reasons, the global market for meat alternatives is currently worth between €6.7bn and €8.1bn per year, and is projected to grow between 8.1% and 12.3% each year over the next decade.
One common method for producing fake meat is microbial engineering, where genes coding for animal proteins are inserted into the genome of bacteria or yeast for mass production in bioreactors. But now, scientists have developed a promising alternative as a proof-of-principle.
“Here we show that plants can be engineered to produce the animal protein myoglobin (Mb) in their chloroplasts, the energy factories for photosynthesis. This could provide a more sustainable way to produce an important ingredient for plant-based meat products,” said Dr Alexia Groff, a researcher at Imperial College London. The results are published in Frontiers in Plant Science.
Carniferous plants
Myoglobin is an important components of the heart and skeletal muscle of vertebrates. Myoglobin is rich in iron, which is why meat has a metallic and umami flavor, while the oxygen bound to it gives meat its red color. Groff and colleagues first cloned the genes for pig and cattle myoglobin. They then used a so-called ‘gene gun’ to shoot gene copies physically into the chloroplasts of tobacco and lettuce seedlings in the laboratory. Tests confirmed that some seedlings had subsequently integrated the gene into the short ring-like genome of their chloroplasts. The plants were then grown to adulthood and flowered and set seed, with their offspring inheriting the transgene.
For comparison, the authors also inserted the gene into the much larger nuclear genome of both plant species, as well as into the chloroplast of the unicellular alga Chlamydomonas reinhardtii.
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“Due to their bacterial ancestry and their high number of copies per cell, chloroplasts are generally much better at making large amounts of protein than the cell nucleus,” said Groff. “Here, we used tobacco because it is the best model plant for developing this technology, and lettuce because it is an edible crop that could eventually be used for food ingredient production.”
Measurements done by liquid chromatography-mass spectrometry showed that the yield in myoglobin was approximately 800 mg per kilogram dry weight of tobacco and 810 mg per kilogram dry weight of lettuce. This was at least three times higher than the yield from tobacco plants with the transgene spliced into the nuclear genome. Real meat contains between 8.1 and 11.2 mg myoglobin per gram dry weight.
“Despite this, plant cultivation is far more resource efficient than livestock production; consequently, plant-derived Mb could achieve protein yields per hectare that rival – or even potentially exceed – those of animal agriculture, while also benefiting from substantially lower water use and greenhouse gas emissions,” wrote the authors.
Planting a seed for future production
What are the next steps before the discovery can be commercialized?
“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,” explained Groff.
“We hope that edible lettuce, modified to express myoglobin, could also one day serve as a heme-iron-enriched biofortified food, depending on legislative approval,” added coauthor Dr Kyoko Morimoto, chief scientific officer at Kyomei, a Cambridge-based plant biotechnology startup which partially funded the research.
This article originally appeared in Frontiers.
