Subscribe rss-microbe
Home Current Topics Cecropin-Producing Tomatoes Resist Bacterial Wilt, Spot
Cecropin-Producing Tomatoes Resist Bacterial Wilt, Spot Print E-mail

 

As part of an effort to fight several bacterial diseases that can lead to 10% losses of tomato crops, researchers from the Republic of China on Taiwan moved genes encoding the antibacterial cecropin B peptides from lepidoptera into tomatoes.  The resulting transgenic tomatoes now show resistance to two key diseases, namely bacterial wilt and spot, according to Hueih-Min Chen of National Nano Device Laboratories in Hsinchu, Taiwan, and his collaborators. Details of the research appear in the February Applied and Environmental Microbiology (76:769-775).

"Twenty-five percent of all crops are destroyed by disease," says Robert Hancock of the University of British Columbia in Vancouver, Canada. Wilt and spot, caused by the gram-negative pathogens Ralstonia solanacearum and Xanthomonas campestris pv. vesicatoria, respectively, are particularly costly for tomato growers. Moreover, pesticides are largely ineffective against these diseases, particularly X. campestris-caused spot. Chen and his collaborators found that, at low concentrations, the positively charged, 31-to-39-amino-acid cecropins, which derive from the giant cecropia moth, exhibit lytic antibacterial activity against a number of gram-negative and some grampositive bacteria, whose membranes are negatively charged, but not against eukaryotic cells, which have neutral membranes.

cecropiaThus, for example, extracts of cecropin B expressed in the transgenic tomatoes showed broad-spectrum antimicrobial activity, according to Chen and collaborators. Moreover, the transgenic tomatoes are resistant to the two bacterial diseases, he says. Their work arises from general Taiwanese efforts to promote the transformation of antibacterial peptide genes into crops of global importance, through the Taiwan National Science and Technology Program for Agricultural Biotechnology, and a foundation, the Development Program of Industrialization for Agricultural Biotechnology. Ironically, however, that apparent resistance to Ralstonia probably results from the transgenic peptides acting as immunomodulators, rather than from their antibacterial activity, according to Hancock. "Ralstonia is almost completely resistant to cationic peptides," he says. "We've done a bunch of studies showing that different [antimicrobial] peptides work in plants-primarily potato, but also cotton and tobacco." The study by Chen confirms similar work by researchers at St. Louis-based Monsanto, Hancock further notes.

In vitro, chemically synthesized cecropin B is far more effective against X. campestris, with an S50 of 0.29 μg/ ml, than against R. solanacearum, for which S50 is 529.6 μg/ml. Nonetheless, the levels expressed in the transgenic plants, roughly 0.05 μg in 50mg of leaf material, are smaller even than the S50 for X. campestris, leading the researchers in Taiwan to suggest that the compound may be acting by boosting innate immune defenses in the plants.

Genes encoding cecropins are also used to transform tobacco and potato plants. In the case of the potatoes, inserting the cecropin gene induced a range of changes in the host plant, including its shape, size, and color, Chen says. However, transformed tomato plants maintain their usual physical attributes.

Transgenic plants have such a bad name-especially in Europe, despite a lack of data showing risks to consumers- that these cecropin-producing tomatoes are unlikely to gain a market, according to Hancock. "We were unable to raise enough money or find a large partner for our own company [which aimed to commercialize these transgenic crops], because of the bad reputation attached to genetically modified plants," he says. "We have also had huge resistance to this idea from food producers."

David Holzman
David Holzman is the Microbe Journal Highlights Editor.