Killing Pierce’s Disease

Scientists have managed to kill Pierce’s disease, a disease that is currently incurable in winegrapes. It was done through a fusion process in which scientists combined a lytic peptide, a protein, with a molecule, elastase, that recognizes Xylella fastidiosa, the bacteria that causes Pierce’s disease.

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However, though extremely successful in the lab as well as ongoing field trials, it will be a while before immune grapevines are commercially available, says Goutam Gupta, a staff scientist at Los Alamos National Laboratory in New Mexico who has spent many years in this area of research. Elastase comes from a human gene, and while the amount is very low, he recognizes that some people will have a problem with the idea. The most extreme among them refer to such crops as “Frankenfoods.”

In this instance, it came down to expedience, says Gupta. The human genome had already been mapped, so he and his colleagues knew where to look for the genetic material they needed. “Now the grape genome is being fully sequenced, and should be complete in a few months,” he says. “Then we might be able to take a grape gene.”

Blocking The Disease

But first researchers had to make sure the procedure would work, and of that they now have no doubt, says Gupta. “This hybrid protein can very rapidly clear the bacterium in the lab, but to do it in the vine we needed to express it in the xylem of the vines,” he says. “We used a special genetic approach to make sure this is delivered in the grapevine xylem, and indeed we found in greenhouse studies we could block the disease.”

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This satisfying result has been a long time in coming. Gupta said they began with two years of study to design the procedure in a test tube. Then they studied it in tobacco plants, a crop in which it is very easy to observe disease systems. A disease that might take years to fully express in grapes can take months in tobacco. They then spent five years working in grapes.

The concept is actually a simple one, says Gupta. If anything, plants have it tougher because while human beings have both adoptive immune defense and innate immune defense, plants have only the latter. The plant recognizes danger in a process called signalling.

“These days we use antibiotics to protect against diseases, but resistance develops,” he says. “Can we enhance the immune system of the host, in this case, the plant? That was the notion we started with.”

Currently the research, which is being funded by the California Department of Food and Agriculture and the Pierce’s Disease Research Program, is focused on replacing the human genetic material with that from grapes, so it should be palatable to all consumers. “We have a lot of homework to do until we get the vines to market,” he said.

Citrus, Almonds May Be Next

It’s not like the gene fusion process used to kill Pierce’s disease in grapes will be limited to only that particular disease or crop. The bacteria that causes Pierce’s disease in grapes, Xylella fastidiosa, causes citrus variegated chlorosis and almond leaf scorch, albeit different strains.

In fact, Gupta says his team originally presented their research project to citrus groups. “They liked the idea, but didn’t have enough funding,” he said, “so they forwarded our application to the winegrape growers for their problem with Xylella fastidiosa, i.e. Pierce’s disease.”

Now Gupta has every intention of turning his attention back to citrus. He is co-chair of the national Citrus Health Response Program. His next target is the scourge of Florida orange growers, a disease that just a couple months ago was found in California: citrus greening.

Online Assistance

The California Department of Food and Agriculture has been working hard the past couple years to help grape growers combat Pierce’s disease. Its Pierce’s Disease Control Program has an excellent Web resource that’s worth checking out. Go to www.cdfa.ca.gov/pdcp/ for more information.

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