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Isn’t it just so disappointing when you pick out a nice, red tomato at the supermarket only to find out it’s watery and bland when you slice into it? Well, it turns out that’s kind of a recent problem.

Back in the day, when your parents or grandparents were kids, tomatoes actually tasted better. Our obsession with perfectly red tomatoes is what made them taste so... meh. Once upon a time, and by that I mean way back in the early to mid 20th century, tomatoes sold in supermarkets often had a green ring around the stem, which customers didn’t like.

But farmers noticed some tomatoes didn’t have it. So over time, they bred their tomatoes from stocks without this ring, eventually creating uniformly colored tomatoes in a process called artificial selection. And they did this in basically all varieties of the plant, from little cherry tomatoes to big beefsteaks.

But what growers didn’t know is that one gene was responsible for this uniform coloring, a gene that was later conveniently named “uniform”. And it also controls a tomato’s sweetness. The variant of the uniform gene that makes tomatoes uniformly red works by disabling a protein called golden 2-like protein 2, or GLK2.

GLKs are what scientists call transcription factors, which means they alter the expression of other genes. Some of the genes GLK2 controls are involved in making chlorophylls, the pigments that make plants green and absorb light so they can use the sun’s energy to transform carbon dioxide and water into sugars. These sugars are how plants store energy for later use, and unsurprisingly, they’re also a big part of what gives tomatoes their flavor.

Other genes affected by GLK2 are involved in producing pigments called carotenoids. They’re what make tomatoes red when ripe, and they affect flavor, too. So by selecting for wholly red tomatoes, farmers accidentally made them blander.

Scientists confirmed the connection between redness and the GLK2 genes in tomatoes in a paper published in the journal Science in 2012. They inserted sections of DNA into the genomes of tomato plants that turned their GLK2s back on. The fruits of these genetically modified plants turned a dark green before ripening because they contained three to six times the chlorophyll of regular tomato plants.

And when those fruits ripened, they contained 21% more sugar and 10-60% more of the carotenoid lycopene than the unmodified tomatoes. People could just sell similarly modified plants if they wanted yummier tomatoes. But farmers and scientists are looking for ways to breed GLK2 back in without using genetic engineering.

That’s part of why there’s been a surge in interest in heirloom tomatoes wild varieties which haven’t had their GLK2 genes silenced. They tend to be more flavorful because of their characteristic green or yellow patches. And hopefully, their not-so uniform genes can help make those really red Romas a little yummier, too.

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