Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Smarter toxins help crops fight resistant pests

11.10.2011
A slight change in molecular structure introduced by genetic engineering gives crop-protecting proteins called Bt toxins a new edge in overcoming resistance of certain pests, a UA-led team of researchers reports in Nature Biotechnology

One of the most successful strategies in pest control is to endow crop plants with genes from the bacterium Bacillus thuringiensis, or Bt for short, which code for proteins that kill pests attempting to eat them.

But insect pests are evolving resistance to Bt toxins, which threatens the continued success of this approach. In the current issue of Nature Biotechnology, a research team led by UA Professor Bruce Tabashnik reports the discovery that a small modification of the toxins' structure overcomes the defenses of some major pests that are resistant to the natural, unmodified Bt toxins.

“A given Bt toxin only kills certain insects that have the right receptors in their gut,” explained Tabashnik, head of the UA’s entomology department in the College of Agriculture and Life Sciences. “This is one reason why Bt toxins are an environmentally friendly way to control pests,” he said. “They don’t kill indiscriminately. Bt cotton, for example, will not kill bees, lady bugs, and other beneficial insects.”

Unlike conventional broad-spectrum insecticides, Bt toxins kill only a narrow range of species because their potency is determined by a highly specific binding interaction with receptors on the surface of the insects’ gut cells, similar to a key that only fits a certain lock.

“If you change the lock, it won’t work,” Tabashnik said. “Insects adapt through evolutionary change. Naturally occurring mutations are out there in the insect populations, and those individuals that carry genes that make them resistant to the Bt toxins have a selective advantage.”

The more a toxin is used, the more likely it is pests will adapt. Bt toxins have been used in sprays for decades. Crops that make Bt toxins were commercialized 15 years ago and covered more than 140 million acres worldwide in 2010, according to Tabashnik.

In a joint effort with Alejandra Bravo and Mario Soberón at the Universidad Nacional Autónoma de México (UNAM), Tabashnik’s team set out to better understand how Bt toxins work and to develop countermeasures to control resistant pests.

“Our collaborators developed detailed models about each step at the molecular level,” Tabashnik said, “what receptors the toxins bind to, which enzymes they interact with and so on.”

Previous work had demonstrated that binding of Bt toxins to a cadherin protein in the insect gut is a key step in the process that ultimately kills the insect. Results at UNAM indicated that binding of Bt toxins to cadherin promotes the next step - trimming of a small portion of the toxins by the insect's enzymes. Meanwhile, Tabashnik's team identified lab-selected resistant strains of a major cotton pest, pink bollworm (Pectinophora gossypiella), in which genetic mutations altered cadherin and thereby reduced binding of Bt toxins.

The findings from UNAM and UA considered together implied that in resistant strains of the pest, naturally occurring genetic mutations changed the lock -- the cadherin receptor -- so that Bt toxin – the key – no longer fits. As a result, the trimming does not occur, the whole chain of events is stopped in its tracks, and the insects survive.

Said Tabashnik: “So our collaborators in Mexico asked, ‘Why don’t we trim the toxin ourselves, by using genetic engineering to create modified Bt toxins that no longer need the intact cadherin receptor to kill the pests?’”

In initial tests, the researchers found that the modified toxins killed caterpillars of the tobacco hornworm, Manduca sexta, in which production of cadherin was blocked by a technique called RNA interference. The modified toxins also killed resistant pink bollworm caterpillars carrying mutations that altered their cadherin.

“Those experiments led us to hypothesize that any insect carrying a mutant cadherin receptor as a mechanism of resistance would be killed by the modified Bt toxins,” Tabashnik said.

To find out, the team invited colleagues from all over the world to participate in an ambitious experiment. “We sent them native and modified toxins without telling them which was which and asked them to test both types of toxins against the resistant strains they have in their labs,” Tabashnik said.

It turned out things are more complicated than the hypothesis predicted. The modified toxins did not always work on insects with cadherin mutations, and they worked surprisingly well against some insects whose resistance was not caused by a cadherin mutation.

“We still don’t know why the modified toxins were so effective against some resistant strains and not others” Tabashnik said. “The take-home message is we need to look at this on a case-by-case basis.”

Tabashnik pointed out that “based on the lab results, we think the modified Bt toxins could be useful, but we won’t know until they're tested in the field.” He said the results are promising enough that Pioneer, a major agriculture and biotechnology company, made a significant investment to pursue the technology.

Through the UA’s Office of Technology Transfer, the UA's stake in the technology has been licensed to UNAM, which in turn selected Pioneer as their commercial partner in exploring its potential for commercialization.

“At the very least, we've learned more about the pests and their interactions with Bt toxins, ” Tabashnik said. “In a best-case scenario, this could help growers sustain environmentally friendly pest control.”

In addition to Tabashnik, Bravo and Soberón, the following co-authors have contributed to this study: Fangneng Huang, B. Rogers Leonard and Mukti Ghimire at Louisiana State University Agricultural Center in Baton Rouge, La.; Blair Siegfried and Murugesan Rangasamy at the University of Nebraska in Lincoln, Neb.; Yajun Yang and Yidong Wu at Nanjing Agricultural University in Nanjing, China; Linda Gahan at Clemson University in Clemson, S.C.; David Heckel at the Max Planck Institute for Chemical Ecology in Jena, Germany.

The report, "Efficacy of genetically modified Bt toxins against insects with different genetic mechanisms of resistance," will be published as an advance online publication on Nature Biotechnology's website on Oct. 9, 2011.

The DOI for the paper will be 10.1038/10.1038/nbt.1988. Once the paper is published electronically, the DOI can be used to retrieve the abstract and full text (abstracts are available to everyone, full text only to subscribers) by adding it to the following URL: http://dx.doi.org/

Daniel Stolte | EurekAlert!
Further information:
http://www.arizona.edu

More articles from Agricultural and Forestry Science:

nachricht Climate change, population growth may lead to open ocean aquaculture
05.10.2017 | Oregon State University

nachricht New machine evaluates soybean at harvest for quality
04.10.2017 | University of Illinois College of Agricultural, Consumer and Environmental Sciences

All articles from Agricultural and Forestry Science >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Electrode materials from the microwave oven

19.10.2017 | Materials Sciences

New material for digital memories of the future

19.10.2017 | Materials Sciences

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>