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Improving a Solution

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Posted Jul. 10, 2018

Advanced gene editing techniques offer new hope for scientists seeking to provide farmers with new tools that advance land stewardship.

People since the beginning of time have bred plants and animals for desirable traits. The first farmers would have propagated the largest, tastiest berries. Even man’s best friend, the dog, has been bred for specific skills like hunting and protecting.

In traditional breeding, including that of the Noble Research Institute’s 66-year-old small grains breeding program, the best plants in each generation are used as parents for the next.

Perhaps the best known example of traditional selection is maize, or corn, which started out as a wild grass called teosinte more than 10,000 years ago. While ancient civilizations in Mexico and Central America developed corn, no one knew until the 20th century that DNA was the secret behind this process.

Medicago truncatulaNoble Research Institute plant scientists use Medicago truncatula (pictured here) among other plant species to study how to use CRISPR-Cas9 to produce plants with desirable traits. Medicago truncatula is the model species used to study legumes, like clover and soybean.

DNA is the instruction code for life. It tells living creatures how to function, and within it lies potential. If plant scientists can adjust these instructions, whether through traditional breeding or more precise methods, they can produce varieties better prepared to overcome challenges faced by farmers and society at large. They can coax plants into using nutrients more efficiently, into growing longer or stronger in the face of drought and disease.

In the 1980s and ’90s, genetically modified organisms, or GMOs, were born. Scientists had learned how to copy a desirable gene (a section of DNA) from one organism and insert it into another so that it could express a beneficial trait. By 2015, about 444 million acres of GMO crops were planted across the world. GMOs, which most commonly provide insect and herbicide resistance, have been associated with yield increases and the rise in conservation tillage, according to a U.S. Department of Agriculture soybean study. Conservation tillage practices, including no-till, help prevent erosion and other environmental degradation.

But, though the National Academy of Sciences has found “no substantiated evidence of a difference in human health risks” when comparing GMOs with conventionally bred crops, some people are uncomfortable with this type of breeding. GMOs have been subject to scrutiny and governmental oversight. This regulation has made it difficult and expensive to bring improved crops to market, which has limited access for smaller companies and to only a few crop species.

While traditional breeding and genetic engineering are two tools for crop improvement, another is showing great promise. Gene editing, specifically a technique called CRISPR-Cas9, is casting new vision in the timeless quest to grow plants that meet societal needs.

Zengyu Wang, Ph.D., director of core research and transformation at the Noble Research Institute, is taking the emerging technology one step further.

One Step Further

CRISPR-Cas9 has gained the interest of scientists in many fields, from medicine to agriculture. In 2013, Wang decided to integrate it into his forage research.

CRISPR stands for “clustered regularly interspaced short palindromic repeats,” and refers to a biological system based on a natural defense mechanism in bacteria. Cas9 is the associated protein. While a GMO expresses beneficial traits through a process that introduces genetic information from another species, the CRISPR-Cas9 method produces beneficial traits as the result of a precise edit made within the target species’ own DNA.

Typically, when CRISPR is used to improve plants, a strand of CRISPR-Cas9 DNA and a guide RNA are inserted into the plant genome. The guide RNA directs the Cas9 protein, which acts as a pair of scissors, to accurately snip out a specified portion of the plant’s DNA. This tweak in the plant’s instruction manual enables the plant to produce a desired trait – such as drought tolerance.

After adopting CRISPR in a variety of plant species, Wang and Miao Chen, Ph.D., a postdoctoral fellow, decided to try something new. Instead of inserting DNA as used in conventional CRISPR approaches, they inserted RNA. The outcome is the same except RNA, unlike DNA, does not integrate itself into the plant genome. By nature, it is a messenger that lasts only as long as it takes to deliver its instructions. This approach eliminates the need for later, additional steps, for example, backcrossing to remove inserted DNA material, before delivering field-ready, commercial plants for evaluation or use.

“Essentially, we are inducing a natural variation within the plant, comparable to what happens in the field, with much more precision, efficiency and reliability than we’ve ever had,” Wang says.

Wang’s variation has proven successful in trials, and he and his team will work to apply it in agriculturally important crop, like wheat.

“Farmers and ranchers need crop varieties that will help them produce food using less water, fertilizers and pesticides,” Wang says. “CRISPR is one of our most exciting new tools to help us deliver these solutions to producers for their benefit as well as that of our environment and society as a whole.”

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10 Things to Know About CRISPR

  1. CRISPR is the most precise, most affordable and fastest way available today to conduct advanced plant breeding. The crop varieties it produces could have been bred in the field as part of a traditional breeding program. But CRISPR is much faster.
  2. Traditional breeding, genetic engineering (used to create genetically modified organisms, or GMOs) and gene editing (including CRISPR) are all tools for crop improvement.
  3. When used to edit plant genes, the system essentially snips out a specified piece of DNA within the plant while the cell seamlessly repairs the site using its natural abilities. This enables the plant to generate desirable traits.
  4. CRISPR stands for “clustered regularly interspaced short palindromic repeats.” It refers to a system based on a naturally occurring defense mechanism in bacteria. This mechanism protects bacteria from invading viruses by enabling a scissor-like reaction that cuts and destroys the attacking virus’s DNA.
  5. There are different CRISPR systems. The most common is CRISPR-Cas9. The “Cas9” refers to an associated protein that acts as the scissors in the reaction. It’s bundled with a piece of guide RNA that tells it where to cut.
  6. A new waxy corn variety from DuPont is expected to be one of the first CRISPR-edited plant varieties on the market, sometime around 2020. Waxy corn is used in paper adhesives and food thickeners. Other potential CRISPR applications include crops that taste better, yield more, are resistant to diseases and pests, and better tolerate drought.
  7. Conventional methods of CRISPR initially insert a piece of foreign DNA to kick-start the editing process; however, the foreign DNA is segregated out in thenext generation. This means the foreign DNA is not in seeds that would be sold for planting. For this reason, CRISPR-edited crop varieties will notbe regulated as GMOs by the U.S. Department of Agriculture at this time.
  8. One of the downfalls of genetic engineering, which creates GMOs, is that it has been limited to companies that can afford to jump through expensive regulatory hoops. CRISPR opens doors for smaller companies and nonprofit organizations, including those that work on less-funded crops like vegetables and forages, to use the technology for the benefit of a more diverse set of agricultural crops and producers.
  9. CRISPR is also being used in medical research to explore ways the mechanism can help treat, and potentially cure, diseases in people.

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