To obtain the result, the researchers took a lettuce, a tiny particle of gold and a kind of gene gun. They loaded the gene onto the particles that contains the instructions for making pig myoglobin, then shot them into leaf cells. The plant grew, produced seeds and, above all, began to manufacture a protein that we normally find in animal muscles.
It is the experiment carried out by researchers from Imperial College London and the British startup Kyomei and published on Frontiers in Plant Science. Scientists have managed to make lettuce and tobacco produce myoglobin by modifying the DNA of their chloroplasts. The goal, one day, could be to use plants as small factories to obtain one of the ingredients capable of making plant-based alternatives to meat more similar to the original. That “one day”, however, is still very important.
Why myoglobin
Myoglobin is a protein present mainly in the muscles of vertebrates. It contains heme, a molecule that binds iron, and contributes to the color of meat and some of the characteristics we perceive when we eat it.
This is why it is of great interest to those who work on plant-based alternatives. Making a burger with pea or soy protein is relatively simple; reproducing the texture, color, aroma and flavor of meat at the same time is another job. Myoglobin could become one of the useful ingredients to get closer to that result.
The researchers chose chloroplasts, the structures of plant cells that allow plants to carry out photosynthesis. They also have their own little DNA, and within a single cell, there are several of them. In very simple terms: if you want to convince a plant to produce a protein, having many copies of the “factory” can come in handy.
And this is exactly what happened. In tobacco, the production of myoglobin obtained by modifying the chloroplasts was at least three times higher than that obtained by inserting the gene into the DNA of the cell nucleus.
How much “meat” does lettuce produce? Much less than it seems
Here it is best to keep your imagination at bay: the lettuce did not turn into steak and no one in the study tasted it to see if it tasted like meat.
In dried lettuce leaves, the researchers estimated about 810 milligrams of myoglobin per kilogram; in tobacco about 800 milligrams. In real meat the concentrations are decidedly higher: the study cites values in the order of several milligrams per gram of dry weight. The same authors also point out that the quantities obtained in plants are estimates based on a limited number of samples and still need to be optimised.
Then there is a second obstacle. A useful myoglobin must be able to bind heme, the iron-containing part, well. In the protein extracted from tobacco only about 35% was bound to heme, compared to about 80% of the myoglobin produced for comparison in the bacterium Escherichia coli. The plant protein still had a structure compatible with the correctly folded one, but the authors indicate the availability of heme as one of the problems to be solved.
In short, the factory works. The assembly line still has a few pieces to fix.
Why use lettuce to produce animal proteins
Today, proteins of animal origin intended for new foods can also be produced through modified microorganisms, such as bacteria and yeasts, grown in bioreactors. It is the so-called precision fermentation, a technology that already has much more established industrial processes.
Plants might offer another avenue. The biomass is grown, the leaves are harvested and the desired protein is extracted. In the case of lettuce there is an obvious advantage: it is already an edible plant. According to the authors, this could potentially make some purification steps easier compared to a plant like tobacco.
The team also hypothesizes that the modified lettuce could be studied in the future as a heme iron-enriched food. We are still in the field of possibilities: first we would need checks on safety, on the behavior of the protein in food, on the flavor and of course the authorizations required for genetically modified organisms and new food ingredients.
The environmental benefit is a possibility for now
Finally, there is the question that makes this work particularly interesting for meat alternatives. Livestock requires land, water and feed and is responsible for a significant share of greenhouse gas emissions. The researchers believe that producing myoglobin in plants may require many fewer resources than obtaining it from animals and estimate that by increasing yields, production per hectare could become competitive.
The study, however, did not directly measure the environmental footprint of industrial production. We don’t yet have acres of myoglobin lettuce, large-scale functioning extraction facilities, or a comprehensive analysis of the water, energy and emissions needed to get to the final ingredient. The possible environmental advantage will therefore have to be demonstrated along the entire supply chain.
There is also an industrial connection to be aware of: two authors work for Kyomei and the doctorate of the study’s first author, Alexia Groff, was funded in part by the same company together with the British Engineering and Physical Sciences Research Council. Everything is stated in the scientific article.
For now there remains a much simpler result than the steak grown in the garden, and perhaps for this very reason interesting: a lettuce has managed to stably produce a protein typical of animal muscle and transmit this ability to its seeds. To know if it will really end up inside a veggie burger, several experiments are still needed. The lettuce, meanwhile, did its part.
