Scientists Grew Meat Protein Inside Lettuce, No Animals Involved

A head of lettuce that delivers the iron-rich protein behind a burger’s color, its savory depth, and its nutritional punch sounds like science fiction. That idea just moved considerably closer to reality. For the first time, scientists have permanently grown myoglobin, the protein responsible for meat’s distinctive red color, metallic flavor, and absorbable iron, inside the cells of living lettuce plants.

Myoglobin is not a minor player in what makes meat taste and look like meat. It gives beef its red hue, contributes to that characteristic savory richness, and supplies a form of iron that the human body absorbs far more easily than the iron found in spinach or beans. Companies like Impossible Foods have already recognized its importance, using a related protein to make their plant-based burgers “bleed.” But producing myoglobin sustainably and at scale remains a challenge. Most current methods rely on bacteria or yeast grown in expensive, energy-hungry industrial tanks, which limits how far the technology can realistically go.

This new research, published in the journal Frontiers in Plant Science and led by scientists at Imperial College London and the biotech company Kyomei Ltd., offers a different route: engineering the protein directly into the green machinery of plants themselves. The work opens a potential path toward food plants that carry meat-like properties without the environmental cost of raising livestock.

How Scientists Put Meat Protein Inside a Plant

To pull this off, the research team rewrote the instructions inside the plant’s chloroplasts, the tiny structures in plant cells responsible for converting sunlight into energy. Chloroplasts carry their own separate genetic material, distinct from the plant’s main DNA, and scientists can insert new genes directly into that system. This approach tends to produce much higher levels of the target protein than standard plant engineering methods, partly because each plant cell contains many chloroplasts, each carrying multiple copies of the modified genetic instructions.

For tobacco, a standard laboratory workhorse for this kind of research, the team inserted the gene for the pig version of myoglobin. For lettuce, they did the same. As a point of comparison, they also inserted a gene for the bovine version of myoglobin into a single-celled green alga called Chlamydomonas reinhardtii. Tobacco is not edible, but it is widely used in plant science because it grows quickly and accumulates proteins at high levels. Lettuce, on the other hand, is a real food crop, which is what makes its inclusion here stand out.

What the Meat-Protein Plants Actually Produced

Once transformed, the plants were grown under controlled conditions and tested to confirm the myoglobin was genuine and being produced consistently. In tobacco, myoglobin accumulated to roughly 2.7% of the plant’s total soluble protein. In lettuce, it reached about 1.5%. In real-world terms, that works out to an estimated 94 milligrams of myoglobin per kilogram of fresh tobacco leaves and 48 milligrams per kilogram of fresh lettuce. By dry weight, both plants came in at around 800 milligrams per kilogram.

Animal muscle contains far more myoglobin, roughly 8,000 to 11,000 milligrams per kilogram of dry tissue, depending on the cut. So plants are not matching beef anytime soon on a pound-for-pound basis. The researchers point out, though, citing earlier life-cycle research, that plant farming is far more resource-efficient than raising cattle, which is why they argue the protein yield per acre of farmland could one day rival animal agriculture with substantially lower water use and greenhouse gas emissions.

Among the three organisms tested, the single-celled alga performed worst, accumulating less than 0.25% of total soluble protein, and the myoglobin showed signs of breaking down. Both tobacco and lettuce outperformed the alga, and both also outperformed standard plant engineering methods that insert genes into the plant’s main DNA rather than into the chloroplasts. Of 37 plants engineered using those more conventional methods, myoglobin accumulation was consistently at least three times lower than what the chloroplast approach achieved.

Getting the protein to accumulate is one thing. Getting it to carry heme is another. Heme is the iron-containing molecule that gives myoglobin its color and the meat-like qualities that make the protein worth producing in the first place, and myoglobin needs it to deliver those properties. When the team purified myoglobin from tobacco leaves and analyzed it closely, they found the protein was correctly folded, a good sign. A highly sensitive technique that identifies molecules by their weight confirmed the protein was the right size and showed little evidence of chemical damage. However, only about 35% of the purified myoglobin had heme properly attached. By comparison, myoglobin produced in bacteria had 80% heme attachment under the same analysis. The plants do respond to the demand for heme, as total heme levels in myoglobin-producing tobacco plants were roughly double those in control plants, but not enough to fully load all the myoglobin being made. The authors note that this shortfall would most likely compromise the color, taste, and nutritional value of the plant-produced protein until it is improved.

Despite the incomplete heme loading, expressing myoglobin in tobacco chloroplasts did not meaningfully disrupt the plant’s ability to photosynthesize. Key measures of how efficiently the plants captured light and converted it to energy remained similar between the myoglobin-producing plants and the controls.

Why the Lettuce Result Changes the Conversation

From a food-systems perspective, the lettuce result is the headline finding. Tobacco cannot be eaten, so it serves primarily as a research tool. Lettuce is a different story. The deeper biochemical work, including purification, folding, and heme analysis, was carried out in tobacco, while the lettuce results establish that stable production in an edible plant is possible. Edible crop plants that accumulate functional animal proteins could, in theory, be incorporated into food products with far less processing than would be required if the protein were produced in a tank and then extracted and purified separately. The authors also note that this is the first reported case of any heme-binding protein being stably expressed in lettuce.

Regulatory frameworks around plant-made animal proteins are still being worked out globally, and practical questions remain. The analysis was conducted on a single independent plant line for each species, and the measurement method itself can vary in its readings, so confirming these findings across multiple independently derived plant lines and with additional measurement approaches would strengthen the conclusions. The authors also did not analyze the lettuce plants’ internal responses to producing this foreign protein in the same depth as in tobacco, leaving some questions open.

Improving heme availability within the plants, potentially by engineering them to produce more of it or by using different genetic control switches, is likely to be an important next step. The researchers also call for future work testing the meat-like color, taste, and nutritional performance of the plant-produced protein in actual food systems, the true test of whether this approach can travel from a laboratory to an ingredient on a shelf.

Livestock farming currently accounts for substantial shares of global greenhouse gas emissions, land use, and freshwater consumption. Plant-based proteins that could eventually help deliver the sensory and nutritional properties that make meat appealing rank among the more promising tools available for reducing that footprint. Getting myoglobin to grow permanently inside lettuce does not solve that problem on its own, but it is a meaningful step in a new direction.

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