February 8, 2005
ScienCentral
Gene Machine
Researchers at the Samuel Roberts Nobel Foundation were able to produce hardier tomatoes by inserting an animal gene into an ornamental variety of tomatoes not usually eaten called micro-toms.
Writing in Proceedings of the National Academy of Sciences, Marilyn Roossinck, Pin Xu and Stephanie Rogers reported that the gene controls a growth mechanism called apoptosis or "programmed cell death." "It's a suicide mechanism for cells, " says Roossinck, but one "that is very tightly regulated and controlled." She notes that in humans, for example, "if you look at your hand and you see that you have all these fingers on your hand, separated—the reason you have separate fingers is because of programmed cell death during development. During development human hands start as paddles, the fingers then form, and the skin between the fingers then dies.
The modified tomatoes resist a disease called the Cucumber Mosaic Virus, which, along with a parasitic piece of RNA called satellite RNA, takes advantage of the programmed cell death process to kill the tomato plant. It has led to tomato crop failures in some countries around the world. The virus is quite widespread and can infect more than 1,200 varieties of plants.
In a plant, programmed cell death is important in, among other things, creating the phloem, the tubular bundles of cells which carry nutrition throughout the plant. The researchers have found that the virus takes advantage of the normal cell death and sends it spinning it out of control. Says Roossinck, "this is just a strange case where it's gone wrong and so we have cells dying that shouldn't be dying. And once those initial cells die they seem to send a trigger or signal to the rest of the plant and then the whole plant dies."
By inserting an animal gene they were able to stop the RNA from triggering the apoptosis process. Roossinck adds the use of the animal gene is important, noting, "we don't know what the proteins in plants normally are that are involved in this process. We know that it's similar to the process in animals because it looks the same. We see all these characteristic events that go on in plant cells just like they do in animal cells, where it's very well characterized. But, we don't know what the proteins are in plants. We know now that they must be similar to the ones in animals because these anti-apoptosis proteins, that is the proteins that inhibit this kind of cell death, work in plants even if they come from an animal source."
The idea of using an animal gene is not new. Roossinck says their tests follow similar animal-to-plant gene transfers in experiments designed to stop fungal diseases.
The genetic modification did not kill the virus. Roossinck says tests show that, "it was there in similar levels as when there was no anti-apoptosis gene. So, we're making the plants tolerant of the virus."
What did happen as an additional benefit was that the tomatoes were also more tolerant of colder temperatures. "We found that they survived very well at four degrees Centigrade (39 Fahrenheit) and if they had already had flowers on them then they could set fruit at that temperature," she says. "At seven degrees (Centigrade, 45 degrees Fahrenheit) they could flower and set fruit completely."
But Roossinck says, to her, "the most interesting thing is that plants and animals have a lot of similarity in this pathway of programmed cell death. If they didn't then these animal genes would not function in plants like they do. So I think that's the most significant thing."
This research appeared in the November 2, 2004 issue of Proceedings of the National Academy of Sciences and was funded by the SR Noble Foundation.
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