Making fruits that don’t spoil.
This is Codon, a newsletter about biology, technology, and the future. In this essay, I talk about gene-edited bananas that don’t turn brown for many weeks.
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At 8 o’clock on a February morning, Eli Black smashed a hole in a window on the 44th floor of New York City’s MetLife building and jumped.
It was 1975, and the chairman of United Brands was responsible for a sizable fraction of the world’s banana trade. An associate later told The New York Times that Black was “under great strain because of business pressures.”
Those pressures were not related to irksome employees or dwindling revenues. The problem was, rather, that Black had planned to bribe Honduran officials in exchange for favorable tax rates on banana exports, and the U.S. government found out about it.
Honduras was set to impose a slight tax hike on 40-pound banana crates, which would have cost United Brands (then the largest shareholder in the United Fruit Company, now Chiquita) some $7.5 million per year. A lawsuit alleged that Black’s company had failed “to disclose substantial payments to officials of foreign governments in order to secure favorable treatment.” In 1978, the company pleaded guilty to conspiring to pay $2.5 million to a Honduran economic minister. (In 1954, the C.I.A. deposed a democratically-elected government in Guatemala at the behest of the same company.)
Just a few decades ago, the greatest threats to bananas were political maneuverings and military coups. Today, the greatest threats are biological: Fungi that wipe out fields, and spoiled fruits that slash into razor-thin margins. To combat these threats, genetic engineers are making bananas that fend off fungi or ripen slower than natural varieties. Their work could save five billion bananas from being thrown in the trash each year in the United States alone.
A British company, called Tropic Biosciences, raised $35 million last year to make gene-edited bananas that don’t brown like a normal fruit. But questions abound: How long do “non-browning” bananas really last? Is banana spoilage an actual problem? And will these bananas — designed for a hungry planet that seems to prize “naturalness” over everything else — even make it to the dinner table?
The Death of Gros Michel
There are over 1,000 types of bananas in the world, but men live and die for the Cavendish, a staple crop for 40 percent of people. The Cavendish makes up about half of all bananas grown on Earth, but accounts for 99 percent of exports.
Our modern reliance on the Cavendish only happened because of a historical accident. Until the 1950s, the Gros Michel was the main banana export. It had sweet flesh and thick skin, which made it easy to ship. (Every time you eat banana-flavored candy — like a Laffy Taffy or Runts — you are tasting an artificial flavor based upon the Gros Michel). By 1965, though, these bananas nearly vanished from Latin America.
The Gros Michel trees were destroyed by a fungus, called Fusarium oxysporum Tropical Race 1, which clings to boots and survives in soil for many years. It invades plants through their roots, spreads through the xylem, and turns the leaves yellow. Dying trees smell like rotten flesh.
As banana plantations collapsed, Dole and Chiquita switched over to the Cavendish, mainly because of its natural resistance to Tropical Race 1. Evolution cannot be defeated for long, though, and a new type of fungus has now arrived. In 2013, a Fusarium fungus — called Tropical Race 4 — was identified in Mozambique. From there, it “travelled to Lebanon, Israel, India, Jordan, Oman, Pakistan and Australia,” according to an article in WIRED. “In 2018, it was found in Myanmar.” This new fungus now threatens the Cavendish banana, and scientists worry that it may already be in Latin America. The race is on to make a resistant Cavendish using gene-editing tools.
A group of Australians were the first to make that happen; in 2017, they took a single gene from a nematode, pasted it into the genome of a Cavendish tree, and showed that the gene-edited plants were completely resistant to the fungi.
Gene-edited bananas are not yet being grown commercially, to my knowledge, but a Dole plantation in Central America is starting field trials for a disease-resistant variety that was developed by Elo Life Systems, an American company. Kenya, Malawi, and Uganda are also gearing up for gene-edited banana trials.
Money is also pouring into the field, fast. The Gates Foundation gave $7.6 million to Australian scientists to make Cavendish bananas enriched in vitamin A for cultivation in Uganda (where about 9 percent of people are vitamin A deficient). And two Israeli companies — called Evogene and Rahan Meristem — teamed up to make gene-edited bananas that are resistant to another disease, called Black Sigatoka, which is caused by a different type of fungus.
There is clearly a need for gene-edited bananas, and we have the technology to make them a reality. But crafting bananas that don’t go brown, and then growing them at scale, will prove a greater challenge.
Be Still, My Spoiled Fruits
The U.S. eats something like 7 billion pounds of bananas every year. Most are imported from Costa Rica, Guatemala, and Ecuador. After a banana is picked from the tree, it is stocked on grocery store shelves within two weeks. The fruits are shipped on large container vessels; tightly packed in refrigerated crates so that they don’t ripen during transit. When the bananas arrive at a port, the crates are filled with ethene gas to initiate ripening. A single overripe banana in a large crate “can cause a chain reaction that may wreck as much as 15 percent of a shipment.”
Of all the bananas shipped to the United States, we throw away about 5 billion of them. This fruit is discarded more than any other food in grocery stores, according to a 2018 study from Sweden. This may not seem like a big deal (bananas naturally decompose into fertilizer!), but it means that we waste a lot of water and burn a lot of diesel to grow and ship bananas that people don’t end up eating.
It takes 1.28 kilograms of CO2 and 330 liters of water to make one kilogram of bananas, according to a 2015 study from Ecuador. This, ultimately, is the reason why Tropic Biosciences and other companies are trying to make bananas that don’t ripen so quickly: The economic impacts could be massive.
They are also fortunate, in part, because scientists have been studying bananas, and why they ripen, for more than fifty years. Most fruits brown when you pinch them because an enzyme, called polyphenol oxidase, turns phenols into quinones, which then react with other molecules to make melanin, a dark pigment. Polyphenol oxidase is produced in banana cells very early during development, and then its levels decline once ripening starts.
But this is not the whole story. When bananas are ready to ripen, they begin to produce ethene gas, a plant hormone. This gas is produced by an enzyme that is encoded by a gene, called MA-AC01. This gene is regulated, in turn, by a small arsenal of other proteins from the MaMADS family. (Yes, I know. Biology is a chaotic mess!)
These are the basics of how bananas ripen. Now, how do we make them stop?
Haya Friedman, an Israeli biologist, is probably the world’s foremost expert on this niche subject. In 2016, her team demonstrated that, by adding short snippets of DNA or RNA — which can target and “shut down” the MaMADS regulatory proteins — to bananas, it is possible to slow their ripening. (The idea came from tomatoes, which ripen in much the same way.) Friedman’s engineered bananas stay yellow for more than a month after being plucked from a tree.
Tropic Biosciences, the UK company, is undoubtedly familiar with Friedman’s work, because they are using a similar method to make their own gene-edited bananas. Their approach, however, is a clever improvement over everything that came before.
We know what happens to bananas when they ripen, and scientists like Friedman have shown how we might slow down this process. But there is just one problem with all this: If you add any genetic material to a banana, the fruit will be regulated as a GMO in many countries, and would then have to pass through intense safety and field trials. Companies obviously want to avoid this, and Tropic Biosciences figured out how:
Every living thing (even bananas!) has a genome made of DNA. Most of this genetic material codes for proteins: DNA is transcribed into RNA, which is then translated into proteins. A significant portion of the genome, though, does not encode proteins. These “other” bits of DNA are called non-coding regions, and some of them make non-coding RNAs.
Now, these non-coding RNAs float around the cell and occasionally match up with a messenger RNA. When the two strands bind together, the messenger RNA is “blocked” from being translated into a protein.
Tropic Biosciences’ gene-editing technology harnesses these non-coding RNAs in a really clever way. Instead of altering a protein-coding gene directly, the company changes the sequences of non-coding RNAs to redirect them to a new protein target. A non-coding RNA that normally blocks Protein X, for example, could be altered to shut down MaMADS proteins instead.
This technology is incredibly intriguing. Since the company does not add DNA to the genome, or alter any protein-coding genes, their plants are not regulated as GMOs in the United States, Canada, Japan, Argentina, or a dozen other countries.
Another advantage: There are many non-coding RNAs that are only expressed in specific parts of a plant, such as the leaves, fruit, or roots. Tropic’s technology can be used to alter non-coding RNAs that are only present in the banana fruit, while leaving the rest of the tree relatively unchanged.
This technology is already being used to make low-caffeine coffee and rice with higher yields, and it has been licensed to an animal engineering company that is making chickens resistant to Avian flu.
Genetic engineering is the only technology that can make the “perfect” banana for our Anthropocene future. But it is not a panacea for our troubles.
Companies are making bananas that ripen slowly or fend off fungi because those are the only things we’ve been studying for decades upon decades. We still don’t know how most genes in bananas work, though, so don’t expect scientists to make jumbo bananas or other “super fruits” any time soon.
There’s also no way to know whether these gene-edited bananas will be commercially adopted. The banana business is dominated by Chiquita, Dole, and Del Monte, which together own most of the banana plantations in Ecuador and Costa Rica. Chiquita alone controls about one-third of the entire banana export market. If Tropic wants to make an actual impact on carbon emissions, they will need buy-in from one of these companies. (As far as I know, Tropic’s gene-edited bananas are not yet being cultivated.)
Despite these concerns, the future of gene-edited bananas is promising. The regulatory tide is shifting.
The Philippines recently revamped their biotechnology policies for gene-edited crops; non-browning bananas were the first application submitted for consideration under the new rules. If the Philippines (a top five global banana exporter) rules that Tropic’s bananas are not GMO, then the company will be able to cultivate fruits on the island. Ecuador and Colombia regulate gene-edited crops that do not carry DNA from another species in much the same way as a normal plant.
In the United States, there is also a track record of lenient gene-editing regulations, including for foods that are engineered to ripen more slowly.
In 2016, the U.S. Department of Agriculture decided not to regulate a gene-edited mushroom that browns more slowly, and ruled that they “can be cultivated and sold” in the United States without federal oversight. In May 2021, Tropic also applied for — and later received — an exemption for a non-browning potato developed with their gene-silencing technology.
These gene-edited mushrooms can stay on shelves longer than normal mushrooms and don’t have to be handled as delicately during shipments. They’re expected to reach grocery stores in the U.K. as early as this year.
Now, if you have made it this far in my little essay about bananas and gene-editing, and you happen to be looking for your purpose in life, then let me say this: Look to biology, and plants in particular. Gene-edited crops are a great way to leave a lasting impact on the world. We are entering a renaissance in gene-editing technologies that perfectly coincides with a tidal shift in biotechnology regulations. We are now approaching the Second Green Revolution, and there is room for you here.
And consider this: A small company in the U.K. has made a handful of changes to a banana’s DNA and, in the process, made them last twice as long on grocery store shelves. These bananas could save millions of gallons of water (and billions of fruits) from going to waste each year. The company estimates that their “bananas could reduce food waste and CO2 equivalent emissions along the supply chain by over 25%,” which “could support an annual reduction in CO2 emissions of over 9 million tonnes in the banana export market alone.” By engineering plants, in other words, it is possible to achieve so much with so little.
Alas, gene-editing is not a panacea for the world’s woes. In fifty years, some new fungus will emerge that even an engineered Cavendish banana cannot withstand. Biology will continue to adapt and evolve; it will always win the arms race against our human designs. But when the next threat emerges, I will not look to the politicians or Eli Blacks of the world to quash my fears and devise solutions. My head will turn to the biologists — to you. ◼️
Disclosure: The views expressed in this blog are entirely my own and do not represent the views of any company or university with which I am affiliated.