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College of Liberal Arts and Sciences team uses TALEN technology to alter a gene in rice to make the plant resistant to bacterial blight.

Bing Yang, center, examines a greenhouse rice plant with Bo Liu, left, and Ting Li.
AMES, Iowa – In 2010, Iowa State University researcher Bing Yang led a team that developed a group of hybrid proteins that he believed could lead to a highly-efficient method for modifying plant and animal DNA.

Now Yang’s team has demonstrated the hybrid proteins do indeed “edit” genes. His team of researchers have been able to modify a specific gene in rice to make the plant resistant to bacterial blight, a destructive disease that affects the food staple that feeds nearly half the world.

The researchers are the first to use the so-called TALEN technology to change a plant that benefits society, Yang said. “We demonstrated we could move this technology to the real world, to make a change in the rice DNA. It’s a proof of concept.”

Yang is an assistant professor of genetics, development and cell biology in the College of Liberal Arts and Sciences at Iowa State.

Applications to Midwest crops
The discovery shows that scientists can use the TALEN-based technology to efficiently locate and remove a speck of undesirable or defective DNA from a plant or animal cell. Yang said this new process is applicable for any plant species, including important Midwest crops corn and soybeans, and animal system.

“It’s a landmark experiment,” said Martin Spalding, associate dean in the College of Liberal Arts and Sciences and one of the project’s collaborators. “Yang’s research group is making a specific modification in DNA that converts a plant that is susceptible to a certain pathogen to one that’s resistant to it.”

Yang’s research appeared in the journal Nature Biotechnology in May. In addition to Yang and Spalding, the paper’s authors are Ting Li, Iowa State graduate student; Bo Liu, assistant scientist in the Department of Genetics, Development and Cell Biology; and Donald P. Weeks of the Department of Biochemistry at the University of Nebraska-Lincoln.

Two years ago Yang’s team developed this group of hybrid proteins that could make breaks at specific sites in double-stranded DNA in living cells. Their modified proteins are fusions of two bacterial proteins – the TAL (transcription activator-like) effector and an enzyme called a nuclease. (Hence the name TALEN, a technology now widely used in biotechnology.) Like a pair of “molecular scissors”, the TAL effector binds to the exact spot on the DNA to be cut and the nuclease cuts the DNA strands.

Yang’s team aimed to fight a rice bacterial pathogen called Xanthomonas, which causes blight in rice and other plants. The virulent pathogen uses an endogenous TAL effector to target a specific DNA segment in rice by activating – or switching on – genes that make the plant susceptible to disease. Then, Yang said, the specially designed TALEN, when introduced into the rice plant, bonded with and cut the targeted DNA segment out of rice genome.

The cuts in the DNA repair themselves naturally but alter the recognition sequence slightly so the pathogen is unable to recognize the disease susceptibility gene. The result is that the blight is unable to get a toehold in the rice plant.

“We changed it to resistant rice by disrupting this interaction between the bacteria [Xanthomonas] and the rice disease susceptibility genes and prevented the disease from occurring,” Yang explained. “We used a designer, or artificial, TAL effector to make this change. It’s kind of like fighting fire with fire. We’re taking advantage of the pathogen.”

More efficient method
The new approach is an improvement over current tools for genome modification, said Yang, and could lead to a new era in crop breeding. It is faster and less expensive to use the TALEN method than other technologies, and it’s relatively simple to design proteins to recognize specific DNA sequences.

Yang said an important benefit of his hybrid protein is that the altered rice plant will have new traits through modified DNA, but, because the TALEN gene can be eliminated in genetic crosses, under current regulations the plant should not be considered a genetically modified organism (GMO).

The work of Yang’s team is based on previous research conducted at Iowa State by Adam Bogdanove, professor of plant pathology and microbiology, and former graduate student Matthew Moscou. They determined that endogenous TAL effectors used a simple code to bind to a specific DNA sequence. The findings were also followed by research by a group of scientists led by Bogdanove and former ISU professor Dan Voytas, now at the University of Minnesota, Twin Cities. They also showed that TAL effector proteins could be fused to a DNA cutting enzyme, suggesting the potential for manipulating genes and their functions.

Yang’s research is funded by grants from the National Science Foundation, the College of Liberal Arts and Sciences and the Iowa State University Research Foundation.

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College of Liberal Arts and Sciences (www.las.iastate.edu)
Iowa State University

Contacts:
Bing Yang, Genetics, Development and Cell Biology, 515-294-2968, byang@iastate.edu
Steve Jones, Liberal Arts & Sciences Communications, (515) 294-0461, jones@iastate.edu