After years of exploring alternative ways to produce animal proteins and reduce reliance on livestock farming, scientists on Thursday said they had paved the way for producing plant-grown meat by engineering tobacco and lettuce to make myoglobin, a key muscle protein that gives meat its flavour and colour.
Published in Frontiers in Plant Science, the research marks a step beyond creating meat in laboratories, popularly known as lab-grown meat.
As a proof of principle, scientists from Imperial College London, Kyomei Ltd, the University of California, and Nanchang University in China have engineered tobacco and lettuce plants to carry the gene for myoglobin (Mb)—a protein abundant in animal muscle fibres—in the genome of their chloroplasts, the structures responsible for photosynthesis, using a “gene gun”. This makes it possible to mass-produce myoglobin in crops, giving plant-based meat alternatives a more meat-like flavour and colour.
Myoglobin is a key component of the heart and skeletal muscles of vertebrates.
The expected yield at scale could rival that from livestock farming while greatly reducing water use and greenhouse gas emissions, the authors said in the paper titled Sustainable production of myoglobin meat protein in plant chloroplasts.
The need for alternatives arose because livestock farming requires setting aside valuable land to grow fodder, while using vast amounts of freshwater and contributing to global warming through the emission of methane and nitrous oxide. According to the paper, the global market for meat alternatives is currently worth between €6.7 billion and €8.1 billion per year and is projected to grow by 8.1% to 12.3% annually over the next decade.
One common method for producing fake meat is microbial engineering, in which genes coding for animal proteins are inserted into the genomes of bacteria or yeast for mass production in bioreactors. But now, scientists have developed a promising alternative as a proof of principle, they said.
“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, in a statement.
According to the paper, Groff and colleagues first cloned the genes for pig and cattle myoglobin. They then used a so-called “gene gun” to physically shoot gene copies 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, flowered, and set seed, with their offspring inheriting the transgene.
“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.”
According to the authors, measurements showed that the yield of myoglobin was approximately 800 mg per kilogram of dry-weight tobacco and 810 mg per kilogram of dry-weight lettuce. Real meat contains between 8.1 and 11.2 mg of myoglobin per gram of dry weight.
“…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.
“Overall, our work describes the first report of stable Mb production in higher plants and its effect on photosynthesis and heme levels. This provides a foundation for future plant-made animal proteins for food applications,” they added.
Explaining the next steps before the discovery can be commercialised, Groff said, “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.”
Co-author Dr Kyoko Morimoto, chief scientific officer at Kyomei, a Cambridge-based plant biotechnology startup that partially funded the research, added, “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.”
