agriculture Feeding the world Genetics Plants

The Taste of Tomatoes + Tomato Mutagenesis

An anonymous indian tomato vendor in Chennai, Tamal Nadu. photo mckaysavage, flickr (click to see photo in it's original context)

First, since I didn’t explicitly state it in my previous post, the paper on the longer lasting tomatoes developed by India’s National Institute for Plant Genome Research didn’t report any data on how the RNAi knock-down tomatoes actually taste.* The tomatoes are nearly twice as firm as tomatoes in which these genes are NOT knocked down, so it’s possible they’d seem unpleasantly crunchy, I don’t know how doubling the firmness of a tomato translates into the feeling when a person bites into one.

On the other hand, if the tomatoes do turn out to be tasty and delicious, it’s quite possible the trait could be replicated without genetic engineering. And if that turns out to be true, it’s absolutely the approach anyone developing longer lasting farmers to Indian farmers, or farmers anywhere, should take (for why I’m saying this, check out the bit in bold further into this post).

agriculture biology Genetics Plants

Scientists at India’s NIPGR Create a Longer-Lasting Tomato (Studying The Regulation of Fruit Ripening)

Author’s note: This would seem to be the week for vegetables I hated as a kid. Yesterday was onion, today tomato, if there’s a story about brinjal/eggplant in the next few days we’ll have hit all the big ones. 😉

Ripening tomatoes. Photo: Photos_by_Lina, fickr (click to see photo in its original context)

I was recently pointed to an early publication paper that went up on the Proceedings of the National Academy of Sciences website on Monday, where a research group at India’s National Institute of Plant Genome Research describes two genes from tomato that, when knocked down by RNAi*, result in tomatoes that can remain ripe but not spoiled for up to three times as long as tomatoes where these two genes function normally.

Their approach targets specific genes involved in breaking down certain proteins found in the cell walls of tomatoes (in fact in the cell walls of all plants). Breaking down the cell wall is a key part of ripening in fruits (which the tomato is, botanically if not culinarily). Which makes sense if you’ll think about it for a moment. One of the traits we associate with ripening is getting softer, from bananas to peaches if it’s still crunchy when you bite into it, it wasn’t ripe. What makes plants stiff and crunchy? The strength of their cell walls. Since, unlike vegetables, fruits WANT to be eaten**, as they ripen they begin to break down their cell walls to make themselves more appealing to passing animals. Unfortunately, ripening and spoiling are, in a lot of ways, the same process. If fruits aren’t eaten when they become ripe, they continue to get softer, transitioning from delicious looking -> unappetizing -> inedible -> a puddle of mush on your kitchen counter.

Preventing ripening entirely is relatively easy, and there are plenty of known mutants in tomatoes and other species that never ripen (these naturally mutant tomatoes stay green and hard no matter how long you wait). But getting part of the way to ripeness but stopping before crossing the line into spoiled is a much less tractable problem.

Feeding the world Fun With Numbers

Could we feed ourselves with tomatoes?

Obviously no one is suggesting turning the US into a tomato monoculture, but tomatoes seem like a easy, if not necessarily accurate, proxy for the sort of fresh vegetable passed diets that some people advocate as a solution for the entire nation. If the did the same calculation for lettuce, the numbers would likely be much worse. If I did it for sweet potatoes, I’m guessing they would be substantially better.

There is a very useful resource on growing tomatoes made available by the Iowa State extension service. They estimate yields of 12,000-16,000 pounds of tomato per acre. A pound of tomatoes contains 86 calories.

agriculture Genetics Plants

Domestication Bottlenecks

Driveway tomato garden. How much diversity do these plants contain?
Driveway tomato garden. How much diversity do these plants contain?

Crops like tomatoes, even heirloom tomatoes, aren’t found in the wild. Domestication of crops usually involves only a relative handful of individual plants. Narrowing the species down to a few hundred (or possibly even a few dozen plants) means only a limited number of copies of each gene will be carried through and many of the variant copies of the genes present in the wild population won’t be included in that number. Keeping the population small for multiple generation reduces variability even more as by chance some rare version of genes in one generation won’t be passed to any of the offspring in the next.

Genetic bottlenecks happen in the animal world as well. Skin grafts between unrelated Cheetahs aren’t rejected because the animals are so genetically similar their immune system can’t distinguish the grafted skin as being different from its own skin. Even less fortunate are the tasmanian devils who have so little genetic diversity that they are being decimated by a transmissible cancer. After fighting with an infected devil, which has tumors on its face and neck, tiny bits of the cancer will get into an uninfected devil’s wounds, and since the immune system can’t distinguish the foreign cancer cells from the devil’s own cells, the cancer cells reproduce unchecked, the trait that makes normal cancers, produced by mutated versions of our own cells, so deadly. And the solution mentioned in the article, to save the species by protecting 200 individuals, while better than letting them all die, will sacrifice even more genetic variability by subjecting the already inbred devils to a new population (and genetic) bottleneck.

agriculture Plants

The Real GM Tomato

In my previous post I mentioned that the only people who actually knew what GM tomatoes tasted like where a few who’d lived in California in the mid-90s. That was when Calgene, a biotech start-up founded in the university town of UC-Davis, introduced a tomato that would last longer without tasting like cardboard. And the trait wasn’t the result of a gene from fish or deadly nightshade* but simply a copy of a gene already in tomatoes, reversed so it would reduce the effect of the existing copies. But how did it taste? Click read more to find out: