Science

Using CRISPR on Grapes

New technologies like gene editing hold promise for improving the fruit’s resistance to disease

Photo illustration by Jeff Quinn.

In 1863 winemakers in the Rhône Valley of France noticed that the leaves were falling off their vines, new shoots were stunted, and ultimately, the plants were dying off. Within 10 years, the blight had spread throughout the country, and the government offered a reward of 300,000 francs (the equivalent of more than $1 million U.S. today) to anyone who could cure it. The botanist Jules Émile Planchon identified the cause: a yellow aphid visible only through a magnifying glass. He named the bug Phylloxera vastatrix, “the devastator.” Planchon and his colleagues announced that the way to save French wine was to rip up the vines, replace the infected plants with resistant rootstock from a different species of grape imported from America, and graft old vines onto the healthy new roots.

After long exposure to the bugs, the American vines had evolved numerous defensive tactics that the European species didn’t have. When the Phylloxera aphid punctures the root of a European vine, the plant simply succumbs to the wound; the American root, on the other hand, secretes a thick protective sap when punctured, then grows a woody covering over the wound.

A century and a half later, we’ve learned that it’s their genes that make the European and American grape species different in such an important way—and in the last few years, we’ve learned much more than that. New technologies, such as CRISPR (clustered regularly interspaced short palindromic repeats), allow for the precise manipulation of genes, or “genome editing,” by means of enzymes that snip DNA strands and insert or remove genes with a degree of ease and accuracy that was unheard of a decade ago. Genome editing is a very young and very powerful technology that’s still confined to the testing stage—where it has already been applied in thousands of laboratory studies on a wide variety of species, from yeasts to rats to human cells.

How Genome Editing Works

“Let’s say we have one scrubby variety [of a plant],” says Adam Bogdanove, Ph.D., a professor of plant pathology at Cornell University, who created one of the first methods for genome editing, called TALEN (transcription activator-like effector nucleases), and has applied it extensively in rice genomes. The example he describes from his work involving rice could just as well apply to wine grapes. “It’s low-yield, but you can throw any pathogen at it and it’s disease resistant as all get-out,” he says. “And we have another variety with great yield, but it’s extremely susceptible to disease. Traditionally, we could breed them together and get a cross with moderate yield, and then select and backcross, and do this eight or nine times, until we’ve gotten rid of almost all the DNA from the scrubby variety except the resistance.”

Bogdanove explains that if the idea with wine grapes is to breed, for example, Pinot Noir and maintain its characteristics but also provide resistance to a certain nematode, that outcome is difficult to achieve by breeding. “It’ll take forever to get back to Pinot Noir.” With genome editing, however, scientists can just open up the genome, go in with their tools, and drop the gene that gives the plant resistance into the right place. “It’s more precise,” he says. “There’s no chance of bringing in any unwanted DNA, and it’s enormously faster.”

Challenges with Public Perception

Far more than the remaining technical challenges, fear on the part of the public about genetic technologies—which, Bogdanove says, often dictates how those technologies are eventually regulated, particularly in Europe—is probably the primary barrier to genetically engineered grapes getting into bottles anytime soon. “Between things like Flavr Savr tomatoes and ‘terminator’ seeds, which linked transgenics to corporate greed, and Roundup Ready Corn, which leads to more pesticide use, the industry has done a really bad job of giving a good impression,” says Bogdanove. “But genome editing itself is much more precise and predictable than the conventional mutagenesis with chemicals or radiation that breeders have been doing since the early 1900s, which is generally regarded as safe and routine.”

Before Carole Meredith, Ph.D., and her husband started Lagier Meredith Vineyard in Napa Valley, California, she was a professor in the field of grape genetics at U.C. Davis’s Department of Viticulture and Enology, where she still holds emerita status. “The big advantage of gene editing over transgenic genetic modification,” she says, “is that no foreign DNA is introduced, which might allay some concerns. Small genetic differences are already well accepted within classic wine grape varieties [such variants are called clones], so precise and controlled gene editing is no cause for alarm.” Still, she says, “I think there will be considerable resistance among consumers and the wine trade. People fear that which they do not understand, and very few nonscientists have any understanding of genetic modification.”

Carole Meredith
Photo courtesy of Carole Meredith.

A number of scientists are currently working on genomic editing of disease-resistant grapes, including Rong Di, Ph.D., an associate research professor in the Department of Plant Biology at Rutgers University in New Jersey, who has conducted research editing the Chardonnay genome to add resistance to downy mildew, and Lance Cadle-Davidson, Ph.D., at the USDA Agricultural Research Service’s Grape Genetics Research Unit, whose research focuses on developing new grape varieties that are resistant to fungal and oomycete diseases.

Making a Case for CRISPR

Chad Vargas, who founded NewGen Vineyard Services after 10 years of managing the vineyards at Adelsheim in Oregon, is excited about genetic innovations. “I would welcome an edited version of any wine grape variety that would result in tolerance to powdery mildew and botrytis—and still hold the quality and character of that variety,” he says. “There is a stigma against genetic engineering [among] some in our industry, but most of us who make our living by growing wine grapes are sensitive to the fact that more tools are needed to sustain our industry through challenges involving climate change and the introduction of new pests.”

In 19th-century France, although grafting ultimately saved the industry, the growers deplored and resisted the idea of bringing in new rootstocks, concerned that the American plants would taint the flavors they were used to getting from their generations-old vines. Alternatives that were seriously considered included digging 50,000 holes in every planted acre and filling them with carbon disulfide solution once per season in the hope that it would kill enough of the aphids to save the plants.

Bogdanove tells the story of one of the first deployments of transgenic technology, introduced in 1998 when Hawaii’s papaya crop was being wiped out by ringspot virus. In research conducted by the University of Hawaii, and closely scrutinized by the USDA, FDA, and EPA, a gene from the virus was inserted into papaya plants (using genetic-engineering technology much less precise than CRISPR), enabling the plants to develop resistance to the virus. Bogdanove believes that it may take another do-or-die situation before the wine industry could bring itself to accept such a change.

“I myself would have no qualms about growing and vinifying a grape carrying a genome that had been edited to improve mildew resistance,” says Meredith, “and I would certainly drink the wine, but I would probably have trouble finding buyers for the wine.” Wine in particular, she points out, is an ancient beverage that’s strongly tied to history and tradition. “I think that makes modern genetic tinkering even less acceptable to consumers than it is in crops like corn and soybeans.”

Paul Adams is the senior science research editor at Cook’s Illustrated. He lives in New York City, where he writes about food and drinks.

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