Crop Tech Corner

By Emily Unglesbee
DTN Staff Reporter

ROCKVILLE, Md. (DTN) — This bi-monthly column condenses the latest news in the field of crop technology, research and products.


A new technique that rapidly produces new Bt proteins is making waves in the entomology world. The technique, called Phage-Assisted Continuous Evolution (PACE), was developed by scientists from Harvard, Cornell and Monsanto. In their abstract, the researchers claim the technique will allow scientists to overcome Bt resistance in insects.

Bt resistance is a growing problem in the U.S., particularly in the Western corn rootworm, where several populations of the pest can survive a number of Bt proteins on the market. According to a news release from Harvard, the PACE technique will combat this problem by allowing scientists to quickly produce and deploy new, altered Bt proteins that attack resistant insects in slightly different ways.

Bt proteins work by binding to a specific protein in an insect’s gut. To combat insect resistance in the past, researchers have had the time-consuming task of finding new Bt proteins that target new parts of the insect’s gut. The PACE technique could speed that search up dramatically, according to its developer, Harvard chemistry professor David Liu. "… We evolved new Bt toxins containing dozens of amino acid changes over 500 generations in 22 days of PACE," he said in the Harvard news release. "To do that many generations of protein evolution with traditional stepwise methods, at the rate of about one generation per week, might take a decade."

Liu and his graduate student co-authored the study with graduate student Ahmed H. Badran. To test the effectiveness of their new Bt-generating technique, they fed some of their newly evolved Bt toxins to cabbage loopers that had shown resistance to currently available Bt toxins. The insects, which could tolerate enormous amounts of traditional Bt toxins, were much more susceptible to the new PACE-generated proteins, the scientists reported.

While promising, the new PACE technique probably doesn’t make Bt technology bulletproof, Liu conceded in the press release. Insects could likely develop resistance to the new PACE-produced Bt proteins. However, the method should help researchers find new and effective Bt proteins and perhaps even find ones that target multiple proteins in an insect’s gut, which would make it harder for an insect population to quickly evolve resistance.

More research will be needed to determine the future of Liu and Badran’s PACE technique, and questions remain. Will it work against insects beyond the cabbage looper? How will the regulatory system evaluate and test the new PACE-evolved proteins? Even if Bt production is sped up, how quickly can industry actually move the technology through the time-consuming regulatory process?

The PACE technique holds great promise beyond agriculture, the Harvard release noted. Much of the initial research on the technique has actually targeted the healthcare industry, where the need for new therapeutic proteins is equally valuable. "In an ideal world, all of it should end up benefitting people somehow," Liu said in the release, before singling out the agricultural benefits: "This collaboration is a great example of a project that is not aimed at the development of new therapeutics, but instead at another important goal, namely trying to protect and improve our ability to feed people."

Funding for the research came from the National Institutes of Health, the Department of Defense’s Defense Advanced Research Projects Agency (DARPA), the Howard Hughes Medical Institute, the Harvard Chemical Biology Program, a National Science Foundation Graduate Research Fellowship and Monsanto, which has an "ongoing research collaboration" with Liu’s laboratory.

For more information, see the Harvard release here:…, and the study abstract here:….

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