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.”
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.
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!
Back to Nature: Palm oil plantations are being turned back into protected rainforest
21.03.2019 | Forschungsverbund Berlin e.V.
The inner struggle of the evening primrose: Chloroplasts are caught up in an evolutionary arms race
14.03.2019 | Max-Planck-Institut für Molekulare Pflanzenphysiologie
DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.
The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
25.03.2019 | Trade Fair News
25.03.2019 | Life Sciences
25.03.2019 | Information Technology