What's Up UA? - Scientists Discover Genetic Basis of Pest Resistance to Biotech Cotton - Tucson Local Media: University Of Arizona

What's Up UA? - Scientists Discover Genetic Basis of Pest Resistance to Biotech Cotton

Print
Font Size:
Default font size
Larger font size

Posted: Tuesday, May 27, 2014 8:24 am | Updated: 8:29 am, Tue May 27, 2014.

An international team led by scientists at the University of Arizona and the U.S. Department of Agriculture has discovered what happens on a molecular basis in insects that evolved resistance to genetically engineered cotton plants.

The findings, reported in the May 19 issue of the journal PLOS ONE, shed light on how the global caterpillar pest called pink bollworm overcomes biotech cotton, which was designed to make an insect-killing bacterial protein called Bt toxin. The results could have major impacts for managing pest resistance to Bt crops.

Caterpillars of the pink bollworm are one of the most detrimental pests to cotton production worldwide. First detected in the U.S. in 1917, this invasive insect species wreaked havoc on Arizona's cotton-growing industry, with larvae infesting as many as every other cotton boll (the fruit capsule containing the valuable fibers).

A breakthrough came in 1996 with the introduction of Bt cotton, a genetically engineered crop containing a gene transferred from the bacterium, Bacillus thuringensis, endowing the plants with a protein that kills some, but not all insects. Organic growers have used Bt proteins in sprays for decades because they kill certain pests but are not toxic to people and most other organisms. Pest control with Bt proteins – either in sprays or genetically engineered crops – reduces reliance on chemical insecticides. Although Bt proteins provide environmental and economic benefits, these benefits are cut short when pests evolve resistance.

"Bt crops have had major benefits for society," said Jeffrey Fabrick, the lead author of the study and a research entomologist at the USDA Agricultural Research Service in Maricopa, Arizona. "By understanding how insects adapt to Bt crops we can devise better strategies to delay the evolution of resistance and extend these benefits."

"Many mechanisms of resistance to Bt proteins have been proposed and studied in the lab, but this is the first analysis of the molecular genetic basis of severe pest resistance to a Bt crop in the field," said Bruce Tabashnik, one of the paper's authors and the head of the Department of Entomology in the UA College of Agriculture and Life Sciences. He also is a member of the UA's BIO5 Institute.

Based on laboratory experiments aimed at determining the molecular mechanisms involved, scientists knew that pink bollworm could evolve resistance against the Bt toxin, but they had to go all the way to India to observe this happening in the field.  

Farmers in the U.S., but not in India, adopted tactics designed to slow evolution of resistance in pink bollworm. Scientists from the UA and the USDA worked closely with cotton growers in Arizona to develop and implement resistance management strategies such as providing "refuges" of standard cotton plants that do not produce Bt proteins and releasing sterile pink bollworm moths. Planting refuges near Bt crops allows susceptible insects to survive and reproduce and thus reduces the chances that two resistant insects will mate with each other and produce resistant offspring. Similarly, mass release of sterile moths also makes it less likely for two resistant individuals to encounter each other and mate.

As a result, pink bollworm has been all but eradicated in the southwestern U.S.  Suppression of this pest with Bt cotton is the cornerstone of an integrated pest management program that has allowed Arizona cotton growers to reduce broad-spectrum insecticide use by 80 percent, saving them over $10 million annually. In the U.S., pink bollworm populations have not evolved resistance to Bt toxins in the wild.

In India, however, resistant pink bollworm populations have emerged.

The emergence of resistant pink bollworm in India provided the researchers an opportunity to test the hypothesis that insects in the field would evolve resistance to Bt toxin by the same genetic mechanism found previously in the lab. In the lab strains, the scientists had identified mutations in a gene encoding a protein called cadherin. Binding of Bt toxin to cadherin is an essential step in the intoxication process. Mutations that disrupt cadherin block this binding, which leaves the insect unscathed by the Bt toxin.

"We wanted to see if field-resistant pink bollworm from India harbored these same changes in the cadherin gene," Fabrick said. He said that by collaborating with Indian scientists, "we discovered that the same cadherin gene is associated with the resistance in India, but the mutations are different and much more numerous than the ones we found in lab-selected pink bollworm from Arizona."

Tabashnik added: "In 17 years of research and screening more than 10,000 individuals from Arizona, we identified four cadherin-based resistance mutations. And in just eight individuals from India, we found 19 different cadherin variants that confer resistance. It blew our minds." 

By sequencing the DNA of resistant pink bollworm collected from the field in India –which grows the most Bt cotton of any country in the world – the team found that the insects produce remarkably diverse disrupted variants of cadherin. The researchers learned that the astonishing diversity of cadherin in pink bollworm from India is caused by alternative splicing, a novel mechanism of resistance that allows a single DNA sequence to code for many variants of a protein. "Our findings represent the first example of alternative splicing associated with Bt resistance that evolved in the field," said Fabrick, who is also an adjunct scientist in the Department of Entomology at the UA. 

Mario Soberón, a Bt expert at the Universidad Nacional Autónoma de México in Cuernavaca, who was not an author of the study, commented, "This is a neat example of the diverse mechanisms insect possess to evolve resistance. An important implication is that DNA screening would not be efficient for monitoring resistance of pink bollworm to Bt toxins."

In addition to Fabrick and Tabashnik, the following authors collaborated on the study: Jeyakumar Ponnuraj from the National Institute of Plant Health Management in Hyderabad, India, who studied pink bollworm resistance as a visiting scholar in Tabashnik's lab; Amar Singh and Raj Tanwar of the National Centre for Integrated Pest Management at the Indian Agricultural Research Institute in New Delhi; and Gopalan UnnithanAlex YelichXianchun Li and Yves Carrière from the UA Department of Entomology.

© 2014 Tucson Local Media. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

More about

More about

Welcome to the discussion.

Oro Valley Audiology

Oro Valley AudiologyAddress: 2542 E Vistoso Commerce Loop Rd, Oro Valley, AZ 85755Phone:(520) ...

Monday 12/15/2014

Arts and Sciences Are Writing a New Love Story Together

Thursday 12/11/2014

More hardware for UA's Wright

Wednesday 12/10/2014

S.H.I.E.L.D half season finale delivers Cats get a glimpse of the future in blowout

Friday 11/14/2014

UA Eller College To Share Economic Outlook for 2015-2016

Wednesday 11/12/2014

UA Humanities Seminars

Tuesday 11/04/2014

What's Up UA? - Hiring Interns? Top 8 Tips for Companies

Wednesday 10/15/2014

What's Up UA? - Close Encounter 'One in a Million'

Monday 10/13/2014

What's Up UA? - Austin Hill: The Comeback Kid

Monday 10/06/2014

What's Up UA? - Health, Wellness Practices Highlighted by Chinese Culture Festival

Thursday 10/02/2014

What's Up UA? - Ready for a Super-Fast Internet? UA Scientists Are Fast at Work on It

Tuesday 09/30/2014

What's Up UA? - Using the Force: UA Police Officer Completes NASA Project

Monday 09/29/2014

What's Up UA? - How New Social Movements Take Root

Friday 09/26/2014

What's Up UA? - PBS 'NewsHour' to Feature Inspirational UA Student

Wednesday 09/24/2014

What's Up UA? - UA Paves Way to Redefine STEM Education

Monday 09/22/2014

What's Up UA? - Wildcats Rally, Hail Mary TD Defeats Cal, 49-45

Thursday 09/18/2014

What's Up UA? - When Job Loss Equals Weight Gain

Monday 09/15/2014

What's Up UA? - Don’t Underestimate Your Mind’s Eye

Thursday 09/11/2014

What's Up UA? - 'What I Wish I Had Known as a Freshman'

Tuesday 09/09/2014

What's Up UA? - UA Undergraduate Researchers Take to the Radio

Thursday 09/04/2014

What's Up UA? - Send Your Tweet – and Your Name – to an Asteroid

Tuesday 09/02/2014

What's Up UA? - Brown Foundations' $2.5 Million Kicks Off Catapult Corp

Thursday 08/28/2014

What's Up UA? - New Veterinary Degree Program Made Possible by $9M Gift is Critical for State

Monday 08/25/2014

What's Up UA? - Laser 'Lightning Rods' Channel Electricity Through Thin Air

Thursday 08/21/2014

What's Up UA? - UA Fall Enrollment Sets Record for Diversity, Number of Freshmen

Tuesday 08/19/2014

What's Up UA? - Remarkable Résumé: UA Student Journalist's Career Includes CNN, NYT Phoenix

Friday 08/15/2014

What's Up UA? - Through Innovative Partnership, 'Hot Shot' Team Tackles Yuma Produce Perils

Wednesday 08/13/2014

What's Up UA? - The UA Named a Top College by The Princeton Review

Monday 08/11/2014

What's Up UA? - UA Researchers Study Increasing Lifespan and Immune Function What's Up UA? - UA Undergrads Conducting Microgravity Research Aboard NASA's G-Force One

Monday 06/09/2014

What's up UA? - UA to Host U.S. and Mexico Officials Exploring Collaborations in Education, Innovation, Research

Thursday 06/05/2014

What's Up UA? - New Wilderness Medicine Class Hones Patient Care Skills in Rugged Conditions

Tuesday 06/03/2014

Track Cats Send Eight Athletes to TrackTown USA

Monday 06/02/2014

What's Up UA? - Bringing a Spacecraft Back From the Dead

Friday 05/30/2014

What's Up UA? - Heart Attack Patient Defies Odds with Tailored Surgical Treatment at UA Medical Center

Thursday 05/29/2014

What's Up UA? - UA Marketing Students Win National AT&T Competition

Tuesday 05/27/2014

What's Up UA? - Scientists Discover Genetic Basis of Pest Resistance to Biotech Cotton

Friday 05/23/2014

What's up UA? - Four UA Students Picked for Pat Tillman Foundation Scholarships

Wednesday 05/21/2014

What's Up UA? - Scientists Discover Genetic Basis of Pest Resistance to Biotech Cotton

Monday 05/19/2014

What's Up UA? - UA Tunnels Get Carbon Fiber Makeover

Thursday 05/15/2014

What's Up UA? - Earning a UA Degree, in a Grandfather’s Memory

Tuesday 05/13/2014

What's Up UA? - UA's Phoenix Cancer Center is 'Topped Off,' Joins Award-Winning Medical School Building

Thursday 05/08/2014

What's Up UA? - University of Arizona to Offer Nation’s First Bachelor of Arts in Law

Monday 05/05/2014

What's Up UA? - UA Combating Health Disparities to Build Healthier Communities

Wednesday 04/30/2014

What's Up UA? - Scientists at the UA Make Critical End-Stage Liver Disease Discovery

Friday 04/25/2014

What's Up UA? - A Century-Long Track Record of Serving Arizona and Benefiting the State's Economy

Wednesday 04/23/2014

What's Up UA? - UA Opens Nation’s First Resource Center for Student Vets Studying Health Care UA Wildcat Instant Decision Days at PCC campuses April 29-May 2

Monday 04/21/2014

What's Up UA? - UA Scientists to Begin Construction on NASA Spacecraft that will Visit Asteroid in 2018

Thursday 04/10/2014

What's Up UA? - Spring Fling Celebrates 40th Anniversary With Return to UA Mall

Catalina Bighorn Sheep Releases

Arizona Game and Fish released 30 Bighorn Sheep in a 2-Day period into the Catalina Mountains ...

More Featured Videos
Spacer4px

Follow us on Facebook

Online poll