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Technology

Genome-edited rice gets a step closer to the kitchen

Scientists in Japan await first harvest of crop developed using new GMO technology

Seedlings of genome-edited rice strains are planted outdoors to test their real-world viability. (Courtesy NARO)

TOKYO   Japan has begun its first outdoor test-planting of rice strains developed using genome editing. This technology, which allows scientists to make changes to specific genes, promises a more efficient method for improving agricultural strains of all types.

On May 23, the National Agriculture and Food Research Organization, or NARO, planted two modified strains of rice in a paddy at its facility in Tsukuba, Ibaraki Prefecture. The main purpose is to determine whether the plants will show the desired improvements in yield when grown outdoors rather than in a lab environment.

NARO modified one of the strains to produce larger grains, and the other to produce more grains per ear. The organization plans to harvest the rice as early as October to analyze crop volume and other factors.

"With this technology we can reduce the time needed to develop new strains from between three and five years, at best, to just one," said Hiroshi Ezura, a professor at the University of Tsukuba who specializes in genome editing.

AN ELEGANT SOLUTION   Genome editing changes how genes work by removing and altering targeted pieces of the genome. Like text editing, it allows specific changes to be made in targeted locations, making it possible to produce improvements with a single edit.

Conventional methods of strain improvement use induced genetic mutation triggered by, for example, dipping amounts of rice in a chemical solution. Any resulting plants that manifest the desired trait, like larger grains, are selected for further breeding. This approach, however, involves a large degree of chance. As a result, it usually takes a long time to obtain a strain with the exact intended trait.

The first genome-editing technology was unveiled in 1996. Steady improvements have led to the current CRISPR/Cas method, and research in the field has blossomed. Genome editing has been used to improve not only crops, but also fish and other farmed products. Much is also expected from its application in the medical field.

But the technology is currently most effective in agriculture, where much progress has been made in analyzing the genomes of various crops. This analysis has helped identify genes that influence yield, sweetness and other characteristics of grains, rice in particular, and of tomatoes and vegetables. Targeting these genes for editing makes strain improvement more efficient.

Corporations in the U.S., too, are using genome editing to improve crop strains. DuPont Pioneer, for instance, has developed a high-yield strain of corn and test-grown it outdoors. The company expects to commercialize the product in four years. Seed giant Monsanto recently formed a partnership with the Broad Institute of MIT and Harvard, which develops genome editing technologies.

Crop improvements announced in Japan include herbicide-resistant rice and tomatoes that require no pollination, but cultivation of all of these new strains remains limited to closed greenhouses.

The two strains of rice planted by NARO were tested in a climate-controlled greenhouse last year, and it is not yet clear whether the hoped-for characteristics will develop in the more stressful outdoor environment. If they do, it will be a major step toward commercialization.

REGULATION QUESTIONS   Like conventional cross-breeding, genome editing uses genes from within a single species. This is different from genetic recombination, which introduces genes from other species. While it is technically possible to use another species' genes for genome editing, such an approach has not yet been employed to improve agricultural cultivars.

Discussions on regulating agricultural products created using genome editing are ongoing.

A scientist conducts genome editing in a laboratory.

In September 2015, a study group under the Ministry of Agriculture, Forestry and Fisheries published a report recommending advance consultation with the government when growing agricultural products developed using genome editing. No decision has been made on regulations regarding the commercialization of such products.

In the U.S., researchers at the Pennsylvania State University developed mushrooms that are slow to discolor. The Department of Agriculture decided that these mushrooms do not require USDA approval because they do not contain any foreign DNA.

But as professor Masashi Tachikawa of Nagoya University, a close observer of global trends in genome editing, points out, "The U.S. Food and Drug Administration has not made a decision on the product's safety as a food, and there are moves to review the regulations."

Before beginning its outdoor experiment, NARO obtained government approval under rules for genetic recombination, as the method it used to develop the new strains involved introducing outside genetic material in the form of an enzymatic gene. If this gene is removed, the genetic modification will be no different from conventional methods. This makes the development of technology to confirm whether the enzyme's genetic material has been completely removed an important issue.

KEYWORD: CRISPR/Cas

Genome editing alters genetic information by using an enzyme like a pair of scissors to cut DNA strands. The first generation of the technology appeared in 1996, but both it and the improved second generation required different enzymes for each targeted gene. As a result, only a small number of research laboratories were able to successfully employ these methods.

CRISPR/Cas, the third generation of the technology, was developed in 2012. This method cuts DNA by targeting nucleic acids, which are polymers attached to DNA. Because this requires only changing the sequence of nucleic acids, a common enzyme can be used to cut different genes, making editing much simpler.

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