Soft, juicy, delicious tomatoes were a feature of my childhood and are still available from the plants I grow each summer. However, they've largely vanished from stores. The ripe fruits don't hold up well to shipping, so producers have focused on growing variants where mutations have partially blocked the ripening process. These tomatoes stay firm longer, but it comes at the cost of texture and flavor—as well as a decline in their nutritional value.

Now, researchers seem to have identified an enzyme that specifically helps soften the tomato during the ripening process. By knocking its activity down, they've interfered with softening while leaving other aspects of the ripening process intact. The result is a ripe fruit that can sit at room temperature for two weeks and still remain firm.

In some ways, the surprise of these results isn't that they happened; it's that they took so long. A high-quality tomato genome sequence was first published in 2012, and it allowed researchers to identify more than 50 genes that were likely to encode proteins that could modify the plant cell wall. Four of these genes appeared to be active at high levels in the ripening fruit, and so these genes were targeted through genetic engineering.

The results were, well, less than impressive. "Silencing their expression in transgenic tomato lines has yielded very small or no detectable changes in fruit softening," the researchers wrote.

The team behind the new work instead decided to take their cues from strawberries, where targeting a specific gene is able to reduce the softening of the fruit. That gene encodes a protein (pectate lyase) that breaks down pectin, a complex polymer built from sugars. Pectin is a key part of the plant cell wall, and it helps form the glue that allows these cells to stick together. (Though you probably know it as part of the gel that makes jellies gelatinous.)

People had looked at pectin breakdown in tomatoes, but the earliest attempts didn't work out, so researchers stopped paying attention to it. A quick search for transcribed genes, however, showed that tomatoes activate at least five pectin-digesting genes in their fruit, and one of them is expressed at high levels during ripening. The team targeted this gene with a technique (called RNA interference) that limits the gene's ability to be made into a protein.

It worked. Tomatoes where the gene was knocked down remained firm during the ripening process and were clearly more robust than their wild-type peers. This was shown most dramatically by simply leaving both types of tomato out for two weeks at room temperature. The non-engineered tomatoes started to decay, while the ones with the gene knockdown remained intact.

Better still, the other aspects of ripening appeared to be occurring normally. Weight and color of the engineered fruit were normal, and they still produced all the chemicals that we know are involved in tomato color, smell, and taste.

The researchers themselves, however, admit they haven't done one rather critical test: the taste test. And a key part of the tomato-eating experience is their texture. If all the researchers have produced is some tomato-tasting cardboard, then it's not clear if their engineered plant represents much progress.

For the most part, the authors (some of whom work at the ag-biotech company Syngenta) focus on ways to minimize the genetic engineering involved by simply eliminating the gene entirely, rather than just knocking it down. Presumably, by avoiding any inserted DNA, they will avoid any stigma associated with GMO foods. But this may be a case where more engineering will produce a better product—one that stays firm through shipping and storage but can go through the ripening process once, say, left at room temperature for two days.

All of this is speculation at this point, though. But if Syngenta wants to mail a few, I'll happily compare them to the best that my plants have to offer.

Nature Biotechnology, 2016. DOI: 10.1038/nbt.3602 (About DOIs).