Bland Tomatoes Born That Way?

Photo by Manjith Kainickara under the creative commons license for attribution 2.0

“Supermarket tomatoes that look good but taste bland? Maybe this is why:

Yes, looks can be misleading and the same could be the case with flavourless tomatoes. Or rather, looks could even be the cause of their bland taste.

Tomatoes vary a lot in their colours or their shades of green to be precise when they are still unripe. Some tomatoes are uniformly pale green, others not so evenly coloured an
d will be dark around the ‘shoulders’. It was around 70 years ago that marketers first got to know something that farmers knew already: a tomato on the vine that’s uniformly light green is not ripened, but by the time it’s packed, shipped, and displayed on shelves, it will have turned into a perfect evenly red-coloured tomato. Whereas tomatoes that are not evenly coloured do not give such clear-cut indicators and are also less “aesthetically appealing”, and they were much easier to farm as they gave clear indications of when they were ready to harvest.

Hence, farmers crossed only the tomatoes that were evenly coloured and were “perfect” to be displayed on shelves and easy to harvest, and the uneven coloured solid green tomatoes were forgotten. But in a recent study made by Ann Powell from the University of California, it was discovered that this form of selective breeding has resulted in the loss of taste of tomatoes.

The trait of ripening is governed by a cluster of genes called the “uniform ripening locus” or simply “u”. Powell showed that this region includes at least eight genes, including one called SIGLK2 that affects the tomato’s colour.

SIGLK2 also controls the activity of hundreds of other genes and is chiefly involved in the production of chloroplasts, which in turn determines the level of sugars produced but it also gives a dark green colour (chloroplasts have chlorophyll) around the ‘shoulders’. Hence, wherever SIGLK2 is active, tomatoes are a dark, intense green and unevenly so, and this was the type that wasn’t selected by the farmers. In the wild tomatoes (denoted by a capital U), SIGLK2 is at least 8 times more active near the stem than the bottom, while is why the top half is a darker shade of green giving the tomato an uneven colour.

But in the evenly coloured fruits (denoted by a small u), SIGLK2 has picked up a single mutation – a difference in just one single DNA letter. Although this may seem as a tiny change, it means that the gene encodes a stunted, broken protein. This in turn means that the there’s no proper production of chloroplasts, hence no chlorophyll, and it also doesn’t make the tomatoes any greener which makes these u-tomatoes light green, and evenly so. And if there is decrease in the number of chloroplasts, there is reduction in photosynthesis and hence reduction in overall levels of sugar, thus solving the taste mystery.

But wait, there’s more to it. When a working copy of SIGLK2 from a different plant was stuck into a u-tomato, there was an increase in the sugar levels by 40%!”

Courtesy of Evolution on Facebook



**Bonus: Eating Tomatoes is Shown to Slash Stroke Risk in Half


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