Genetic engineers create smarter toxins to help crops fight resistant pests

Oct 09, 2011
The diamondback moth (Plutella xylostella), one of the world's most destructive vegetable pests, has evolved resistance to native Bt (Bacillus thuringiensis) toxins, but it can be killed with genetically modified Bt toxins. Credit: Marshall Johnson, University of California, Riverside

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 are evolving resistance to Bt toxins, which threatens the continued success of this approach. In the current issue of , 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 only kills certain insects that have the right 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. , for example, will not kill bees, lady bugs, and other ."

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 . Naturally occurring mutations are out there in the , 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 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 – 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."

Explore further: Scientists sequence complete genome of E. coli strain responsible for food poisoning

More information: 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.

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Nanobanano
2 / 5 (4) Oct 09, 2011
Bt cotton, for example, will not kill bees, lady bugs, and other beneficial insects."


Are you SURE?

Hey, it's not like the BEES haven't damn near disappeared in the past decade or so. SOMETHING is killing them.

How much more SHIT do you want to put in people's food at the genetic molecular level?

You think all the POISON you artificially MUTATED the plants to produce might have something to do with the diabetes, hypertension, neurological, and developmental disorders being out of control in the U.S. and Europe?

Who cares if it's targeted to insects?

Put enough of ANY foreign substance that is not part of the natural food cycle into people's diets and you're going to start creating illnesses eventually.

Even if it was 100 percent safe, does the reader REALIZE WHAT THESE PEOPLE ARE CAPABLE OF?

They could make a HUMAN toxin in the food to target PEOPLE on a genetic basis, and nobody would even know it was happening.
Nanobanano
1 / 5 (3) Oct 09, 2011
Imagine if a MUSLIM engineered some corn with a HUMAN TOXIN in it, and grew the POLLEN and got in an aircraft and spread it over our farmland.

They could kill tens of thousands,maybe even a lot more, of people gradually and contaminate the entire food supply with something like poison corn, or poison wheat, etc.

Any entity smart enough to make this stuff could target to a specific skin color or eye color or some other genetic anomaly as modern day eugenics...

any gentic disease

What is to prevent some modern Hitler from exterminating everyone by modifying the food to kill all people with genes deemed "inferior"?

I mean, if they want health insurance to cost less, the purely vaccuum utilitarian thing to do would be to eliminate the genetic bases for hereditary diseases. Any self-respecting NAZI or Muslim, or even an American hyper-progressive, would be glad to take that approach.

Is everyone at the mercy of the insane people who are playing God with this stuff?
Isaacsname
not rated yet Oct 09, 2011
Don't be rediculous NB, BT that's targeted to act on specific pests would be a benefit. That way it could spare pollinators while effecting specific targets.
jamesrm
not rated yet Oct 09, 2011
"Imagine if a MUSLIM engineered some corn with a HUMAN TOXIN in it, and grew the POLLEN and got in an aircraft and spread it over our farmland."

A good target but not for the group you mentioned.
"G6PDH is the most common human enzyme defect, being present in more than 400 million people worldwide. African, Middle Eastern and South Asian people are affected the most along with those who are mixed with any of the above." see favism
HealingMindN
not rated yet Oct 09, 2011
I wonder if the genetic engineers are also working on GMO BT resistant humans with shrimp heads who don't care if they eat GMOs because BT has been found in an over whelming number of pregnant women as of late.
aroc91
not rated yet Oct 09, 2011
Imagine if a MUSLIM engineered some corn with a HUMAN TOXIN in it, and grew the POLLEN and got in an aircraft and spread it over our farmland.


Now I KNOW you're trolling.
Kev_C
1 / 5 (1) Oct 09, 2011
No he's not. He's making a very valid and pertinent point. It would be all to easy to alter some food source material genetically as he says so that it takes out the relevant sub set of humans. As for the distribution method it could well be pollen. After all it is how the genes for glyphosate resistance first transferred horizontally.
I personally feel that it is high time the biotechs were outlawed before they totally screw the ecosystem functionality of the entire planet with their bioological equivalents of computer viruses. Problem is that these things would be even harder to stop once out there. Thankfully though we are slower at evolving than insects so with any luck any serious damage we do will eradicate us entirely long before we could adapt. The rest of the planetary life forms would do okay in the end.
I wonder what other creative way they will invent for us humans to die painfully? We've tried most other methods. War, Plague, Pestilence, Famine. Wonder what's next?
gareth_Ph
not rated yet Oct 09, 2011
Bioweapons are nothing new. Been around since WW2. In fact it's probably easier to make weaponised bio-agents than useful ones like this article describes.

Many new technologies have the potential for destruction - it doesn't mean we should quash new discoveries.

Also a fine display of typical (American?) bigotry - assuming that MUSLIMS / NAZIs would do this sort of thing
Walfy
1 / 5 (1) Oct 10, 2011
It's creepy that such reports never cover the whole story. They always assume that genetically modified organisms are a simple and clean manipulation of a living, breathing life form's genetics: "Yes, we just add this gene that creates this toxin that only affects this certain pest! Hmmm., it's wonderful, isn't it?" What they leave out is that they barely know how it works and when something does seem to work, it's done very sloppy with the side affects downplayed and swept under the rug. Study GMOs with an open mind and you'll see how sick in the head it all is. Billions of years of life evolving in its special way, then the likes of Monsanto, with its profit motive, forces genes from disparate life forms together, crams and crushes them together until they see something they might like in the living, f****d up adult. Really sick in the head.
LivaN
2 / 5 (1) Oct 10, 2011
Kev_C
I personally feel that it is high time the biotechs were outlawed before they totally screw the ecosystem functionality of the entire planet with their bioological equivalents of computer viruses.
It is good that decisions like these are not made based on personal feelings biased by fear stemming from ignorance.

Thankfully though we are slower at evolving than insects so with any luck any serious damage we do will eradicate us entirely long before we could adapt.
Pitiful sentiment that betrays you as weak. You are the cancer of your race.

The rest of the planetary life forms would do okay in the end.
No, unless another intelligent life form evolves, all life will inevitably be destroyed. Absolutely no point.

I wonder what other creative way they will invent for us humans to die painfully?
And while doing that you forget the significantly greater number of ways in which we have protected ourselves from meeting such a fate.
Doug_Huffman
1 / 5 (1) Oct 10, 2011
Why bother? Let the Luddites eschew but raw foods solely. They cannot differentiate in principle, but in process only, from evolution. Will their Soylent Green survival rations be acceptable, now that maize is corrupted?
Humpty
1 / 5 (1) Oct 10, 2011
A speech by Percy Schmeiser, a Canadian farmer sued by Monsanto because pollen from GM canola blew onto his field.
Percy Schmeiser Part 1
http://www.youtub...LZSCsRLs
Percy Schmeiser Part 2
http://www.youtub...response
Percy Schmeiser Part 3
http://www.youtub...response
Ricochet
not rated yet Oct 10, 2011
My major concern is what to do when these insects develop resistance to this and other future strains of toxins, and what effects will their byproducts have on the plant life, and more importantly, those who eat them...
Will it escalate to a point where they basically have to use a major broad-spectrum toxin on the plants grown in biodomes, which then have to be administered an antidote before their harvested? Or worse yet, will we have to innoculate ourselves before we can eat the crops?
Kev_C
1 / 5 (1) Oct 10, 2011
LivaN posted:
Pitiful sentiment that betrays you as weak. You are the cancer of your race.

Ooh! Meow. Not!
Pity that people like you exist to insult the independent thinking of people like me who are not in the least bit interested in profit at all costs. Its just a pity people like you are. And the cost is almost all life.
May I recommend that you re-read what I said and think first before you comment.
Its people like you that, through your irresponsible experimenting, cause cancer in the ordinary people like those who become the unsuspecting victims of your madcap experiments.
Trouble comes to you when people like me, who represent the ones who know what your game is, object to your tawdry experiments. Then your only weapon is to resort to cheap shot insults because you have lost the ability to communicate with any sane human. To you and your kind we are merely a hinderance to your full spectrum dominance of the planet.
Pitying you is not even worth the effort.
LivaN
not rated yet Oct 11, 2011
Kev_C
Pity that people like you exist to insult the independent thinking of people like me

with any luck any serious damage we do will eradicate us entirely
Independent thinkers who consider it lucky for an entire race to be wiped out, because of the sins of the few, are entirely deserving of insult.

not interested in profit at all costs. Its just a pity people like you are
Fallacy. Please reference where I stated/implied such an ideology.

the cost is almost all life
Please validate this assertion that profit at all costs directly results in [death of] almost all life. Then please show how that assertion has anything to do with my post.

I recommend that you re-read what I said and think first before you comment
Re-read. The points I quoted are still trash.

Its people like you that cause cancer in the ordinary people like those who become the unsuspecting victims of your madcap experiments.


cont...
LivaN
not rated yet Oct 11, 2011
Cancer is a result of our current lifestyle, not genetically engineered (GE) product. You drink coffee, smoke cigarettes, eat fast food, sleep with your cell phone under your pillow and relish in modern day luxuries, all the while pointing to GE and shouting cancer.

Trouble comes to you when people like me, who represent the ones who know what your game is, object to your tawdry experiments.
You object out of ignorance and fear, rather than valid reasons.

your only weapon is to resort to cheap shot insults because you have lost the ability to communicate with any sane human.
You assign me an ideology then proceeded to attack me based on that belief. Next time, quote what Ive said that you disagree with. Otherwise you are merely arguing points that were not made.
To you and your kind we are merely a hinderance to your full spectrum dominance of the planet.
Fallacy. Please reference where I stated/implied such an ideology.
aroc91
not rated yet Oct 14, 2011
sleep with your cell phone under your pillow


Although I agree with you, I just had to point out that there's absolutely no link between the weak microwave radiation that phones put out and cancer.
LivaN
not rated yet Oct 14, 2011
sleep with your cell phone under your pillow


Although I agree with you, I just had to point out that there's absolutely no link between the weak microwave radiation that phones put out and cancer.


Agreed, but I still wouldn't sleep with a cellphone under my pillow, while I have no problem eating GE food.
godistruth
not rated yet Oct 14, 2011
You cannot outsmart nature which has had a few billion years of a head start. All this GM nonsense should be concerneing us all. When you meddle with nature you truly are playing with fire.
Ricochet
not rated yet Oct 14, 2011
Potatoes used to be posionous...

No it wasn't direct genetic engineering, but when you breed out specific traits in plants/animals you're still tampering with nature.