Animal genes help tomatoes

Tomato plants expressing two animal antiapoptotic genes can better fend off a common lethal virus and cold temperatures, researchers report in the early edition of PNAS this week.The work represents another step forward in the study of plant programmed cell death (PCD), an essential process for plant growth and development, according to senior author Marilyn Roossinck, from the Samuel Roberts Noble Foundation. And for tomatoes, which are very sensitive to the cold and harbor no known natural resistance to the virus used in the report, it represents a potentially valuable agricultural method.People are very excited by idea of a more cold-tolerant tomato plant, Roossnick told The Scientist. "We are also very optimistic about being able to sort out more details about PCD in plants with this system," she said.Roossinck, lead author Ping Xu, and Stephanie Rogers began with a molecular parasite of cucumber mosaic virus (CMV), called D satRNA, which when present together with CMV, kills tomatoes. "We were originally interested in this small RNA molecule that induces a lethal disease in tomatoes," said Roossinck. "We thought it was very curious that this little RNA molecule could kill a plant."In 2000, the group discovered that D satRNA was capable of inducing PCD in tomatoes. However, little is currently known about the proteins that participate in plant PCD pathways, and at the primary sequence level, homologs of animal antiapoptotic genes have yet to be found in plants. So Roossinck and colleagues instead asked how animal antiapoptotic genes might affect D satRNA-induced PCD.The expression of worm ced-9 and human bcl-xL in tomato plants did slightly affect plant growth and seed development, but upon infection with CMV/D satRNA, these plants also showed few or no symptoms of infection. D satRNA could still be found in these plants, suggesting they were more tolerant of the RNA molecule, as opposed to resistant to the infection itself. In addition, plants expressing a loss-of-function mutant of bcl-xL still showed symptoms of the disease. In another set of experiments, the group found that ced-9 and bcl-xL expressing plants were more tolerant of chilling at 4°C, with no necrotic lesions forming in these plants. At 7°C, ced-9 and bcl-xL plants were also still able to bear fruit, while non-transgenic plants were not. "This shows, once again, the high level of conservation between animals and plants in their responses to stress or pathogenic attack," said Martin Dickman, from the University of Nebraska, who was not involved in the study. "The fact that people can take animal genes and demonstrate they function in a similar manner in plants, is remarkable confirmation that function extends from humans all the way to plants." Eric Lam, from Rutgers University, who was also not involved in the study, agreed that the work extends the understanding of the conserved nature of PCD across kingdoms. "A key observation is that the point mutant of bcl-xL suppressed its effect in planta, thus suggesting that the effects observed may relate to its known function in animal cells," Lam told The Scientist.CMV/D satRNA infection is a significant disease in tomatoes, and in colder regions of the world, a cold-tolerant tomato could prove a useful crop. Thus, although preliminary, Lam comments that the results do "suggest that cell death regulators from animal systems could be exploited for improving tolerance of certain crop plants to viral diseases and low-temperature stress."Although Roossinck and colleagues did not set out to make a more tolerant tomato, Dickman and colleagues are carrying out similar work with different plants expressing various animal antiapoptotic genes. "If you can modulate cell death to protect plants from stress, you have an important field application that could help you to control certain diseases through tolerance," said Dickman.

Animal genes help tomatoes

Worm and human antiapoptotic genes protect tomatoes from cold temperatures and infection

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