Toxins from Bacillus thuringiensis bacteria (Bt toxins) are used in organic and conventional farming to manage pest insects. Sprayed as pesticides or produced in genetically modified plants, Bt toxins, used in pest control since 1938, minimize herbivory in crops, such as vegetables, maize or cotton.
Tobacco budworm (Heliothis virescens)
Melanie Marr, MPI for Chemical Ecology
Cotton bollworm (Helicoverpa armigera)
Suyog Kuwar, MPI for Chemical Ecology
Since 1996, Bt producing transgenic crops have been grown, which successfully control pests like the European corn borer, the tobacco budworm, the Western corn rootworm, and the cotton bollworm. Over the years, Bt resistant insects have emerged in organic and conventional farming. Scientists have therefore modified the molecular structure of two Bt toxins, Cry1Ab and Cry1Ac, in order to overcome resistance. The novel toxins, Cry1AbMod and Cry1AcMod, are effective against five resistant insect species, such as the diamondback moth, the cotton bollworm, and the European corn borer. Cry1AbMod and Cry1AcMod can be used alone or in combination with other Bt toxins for plant protection. (NATURE Biotechnology, advance online publication, DOI: 10.1038/nbt.1988)
New insights into the mechanisms of action of Cry1Ab and Cry1Ac served as the basis for development of the modified Bt toxins. The primary question had been why the Cry proteins, which naturally occur in B. thuringiensis, have such a resoundingly toxic effect on many different herbivorous insects. Researchers had previously found a protein in the caterpillars’ midgut that binds Bt toxins – with fateful consequences for the insects, because binding the toxins causes the gut cells to die. This protein is one of the many types of cadherin proteins in the cell. Binding to cadherin also causes the removal of a structural element of the Cry protein called an alpha helix, which triggers cell death; this is probably due to a Cry-mediated formation of pores in the cell membranes.
Scientists in the groups of David G. Heckel at Clemson University, South Carolina, USA, and at the University of Melbourne, Australia, then discovered that mutated cadherins cause Bt resistance. If cadherin mutations or the absence of cadherin were the causal factors of Bt resistance in certain pest insects, it should be possible to break this resistance by means of Bt toxins that did not have the crucial alpha helix and could therefore be effective without cadherin. Mexican researchers led by Mario Soberón and Alejandra Bravo developed these novel toxins, called Cry1AbMod and Cry1AcMod.
“When we studied the new Bt toxins in 12 resistant and non-resistant strains of five major pest species, the results of our experiments were encouraging but surprising. The new toxins are also effective against strains whose Bt resistance is not based on cadherin mutations,” says David G. Heckel, director of the Department of Entomology at the Max Planck Institute for Chemical Ecology in Jena, Germany, and co-author of the study. Especially interesting was the finding that the new toxins were specifically effective against a super-resistant strain of tobacco budworm carrying both the cadherin mutation and another mutation affecting an ABC transporter which was discovered by the Max Planck researchers last year.
Particularly striking was the effect of Cry1AbMod and Cry1AcMod on a Bt resistant corn borer and a resistant diamondback moth strain that was 350 times stronger compared to that of the natural toxins. On the other hand, the new toxins had only a weak effect on some strains whose Bt resistance is due to a mutated cadherin.
If both novel Bt toxins prove to be useful in agriculture, they can be used in combination with different Bt toxins to guarantee a reliable effect on herbivorous pests. Biologists also agree that measures to reduce the occurrence of resistant insect pests must be strictly adhered to and that farmers should be informed in detail. Such measures would mainly include the use of different pesticides, crop rotation, and simultaneous sowing of non-Bt plants in fields, where transgenic Bt varieties are grown. [JWK, AO]Original Publication:
Bare bones: Making bones transparent
27.04.2017 | California Institute of Technology
Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
27.04.2017 | Life Sciences
27.04.2017 | Physics and Astronomy
27.04.2017 | Earth Sciences