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Genetic Engineering, Silencing Boost Plant Output

Growing test plants

Donald Ort, left, with co-authors Paul South, center, and Amanda Cavanagh, right, study how well tobacco plants modified to boost photosynthesis perform beside unmodified plants in real-world conditions. (Claire Benjamin, RIPE, Univ of Illinois – Urbana)

18 Feb. 2019. An agricultural research lab uses genetic engineering and gene silencing to produce crop plants that increase their yields by more than 40 percent. A team from University of Illinois in Urbana described their techniques and results on Saturday at the American Association for Advancement of Science or AAAS annual meeting, and last month in the journal Science.

Researchers from the University of Illinois genomic biology institute led by plant biologist Donald Ort, with colleagues from the Agricultural Research Service at U.S. Department of Agriculture, are seeking more efficient photosynthesis processes that convert sunlight, carbon dioxide, and nutrients into larger and more plentiful plant life. While advances in plant science called the Green Revolution produce significantly more crops than before, say the researchers, the photosynthesis process remains inefficient, requiring large energy inputs. A more efficient photosynthesis process could make it easier and cheaper to produce more crops, needed to feed an exploding global population.

A key stumbling block in making photosynthesis more efficient is the plant enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase or Rubisco that absorbs and converts carbon dioxide in the air to sugar. But that process is slow and prone to errors, since Rubisco cannot always discriminate between oxygen and carbon dioxide. The confusion between oxygen and carbon dioxide leads to toxic by-products in the plants, requiring an additional process known as photorespiration to recycle those by-products. That extra process involves 3 different parts of plant cells to recycle the toxins, which needs considerable energy and detracts from the plant’s photosynthesis.

“Crops like soybean and wheat waste more than 30 percent of the energy they generate from photosynthesis dealing with this glitch,” says Ort in a statement from the project’s sponsor Realizing Increased Photosynthetic Efficiency or RIPE, “but modeling suggested that photorespiratory shortcuts could be engineered to help the plant conserve its energy and reinvest it into growth.” That modeling led Ort and colleagues to try 3 different methods to make a plant’s metabolic system more efficient.

The researchers worked with tobacco plants to test these different techniques, since tobacco is easier to modify and it produces larger leaves than most plant crops. The team engineered the tobacco genome with combinations of genes governing metabolic processes in algae and E. coli bacteria, a well-researched microorganism. Initial greenhouse tests showed some increases in photosynthesis efficiency, but another part of the recycling process in the plant’s metabolism, which restricts the elimination of the toxins, limited those gains.

As a result, the researchers added another step to the process called RNA interference. RNA is made up of nucleic acids produced by genes with the instructions to cells coded from DNA to produce proteins. With RNA interference, those instructions are interrupted or silenced, preventing production of proteins from specific genes, while limiting the effects on other genes, RNA, and proteins.

The team then tested the most promising genetic engineering strategy, both with and without RNA interference. In tobacco plants grown under real-world conditions in the field over 2 growing seasons, plants with both the re-engineered photorespiration processes and RNA interference grew more than 40 percent more biomass than wild-type tobacco, while genetic engineering alone yielded 25 percent more biomass.

Ort expects that translating these techniques into food crops could take as long as 15 years, due in part to regulatory approvals. But RIPE, funded by the Bill and Melinda Gates Foundation and others, says small growers in developing regions will have royalty-free access to seeds produced with this technology.

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