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Researchers develop super-toxic Bt genes

In the world of plants genetically engineered to resist insects, up to 90 percent use Bt toxins. That?s why European and African researchers joined forces to create an ?ber-Bt, one that would work even if insects developed resistance to Bt toxins. The authors noted that as of yet, no insect has shown resistance to ?traditional? Bt toxins.

The team, led by Paul Christou of the University of Lleida in Spain, combined Cry toxins (components of Bt toxin) and ricin B-chain proteins to form BtRB. ?Transgenic rice and maize plants engineered to express the fusion protein were significantly more toxic in insect bioassays than those containing the Bt gene alone,? the scientists wrote in their article, appearing in the online early edition this week of the Proceedings of the National Academy of Sciences.

In fact, after four days, the fusion protein resulted in the deaths of 78 percent of cotton leaf worm larvae that had infested corn plants. When just one of the proteins was applied, larvae death was less than 20 percent. BtRB was also more toxic toward the stem borer and the leafhopper, a pest usually unaffected by Bt toxins.

The standard Bt toxin is regularly applied to nonorganic crops of cotton, corn and potatoes. Cry toxins have not been tested for their toxicity to mammals, and haven?t yet been used in commercially available crops. They?re being considered for use in GE rice, though. Ricin, which is produced naturally by castor beans, can be deadly if inhaled, injected or ingested, and is often considered an agent of chemical or biological warfare. It consists of two protein chains, ricin A and ricin B. Only ricin B was considered for use in transgenic agriculture in this study.

?If transgenic crops expressing fusion proteins like BtRB were adopted by farmers, it would be necessary to establish that the insecticidal activity of the unique toxin retained some specificity, to avoid deleterious effects on nontarget and beneficial insect species,? the researchers cautioned.

?Lessons learned after the indiscriminate and irresponsible use of chemical pesticides for the control of insect pests over the past several decades call for reason and caution in how we deploy transgenic plants expressing insecticidal genes in the present and in the future,? they warned later in the paper.

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