A Pierce’s Disease breakthrough?

February 21, 2012 11:39am

•  UC Davis scientists use ‘fused genes’ to battle plant killer

•  Engineered 'super gene' kills the bacteria

After years of research, science may have had a breakthrough in efforts to combat the deadline grapevine killer known as Pierce’s Disease.

Currently, there is no remedy once a vine is infected. In some parts of Southern California, the insect-spread disease has wiped out swaths of vineyards.

Now, researchers at the University of California, Davis, say a gene fusion research project delivers a one-two punch to Pierce's disease.

The study is set for publication this week in the early edition of the Proceedings of the National Academy of Sciences.

"Many disease-causing microbes can evade one defensive action by a host plant, but we believe that most microbes would have difficulty overcoming a combination of two immune-system defenses," says UC Davis plant sciences professor Abhaya Dandekar, the lead researcher.

He and his colleagues tested this hypothesis on Xylella fastidiosa, the bacteria responsible for Pierce's disease in grapevines. Strains of the bacteria also attack and damage other host plants, including citrus, stone fruits, almonds, oleander, and certain shade trees, such as oaks, elms, maples and sycamores.

Pierce's disease in grapevines is now known to exist in 28 California counties. From 1994 to 2000, the disease destroyed more than 1,000 acres of northern California grapevines, causing $30 million in damages.

In grapevines, Xylella fastidiosa is carried from plant to plant by half-inch-long insects known as sharpshooters. The bacteria infect and clog the plant's water-transporting tissue, or xylem. Grapevines with Pierce's disease develop yellow and brown leaves and die within a few years.

To block such infections, the researchers engineered a hybrid gene by fusing together two genes that are responsible for two key functions of the plant's innate immune response: recognizing Xylella fastidiosa as a bacterial invader and destroying its outer membranes, causing the bacteria to die.

The researchers then inserted this hybrid gene into grapevines.

They found that sap from plants genetically engineered with the hybrid gene effectively killed Xylella fastidiosa in the laboratory. Grapevines engineered to carry the hybrid gene had significantlyless leaf scorching and xylem clogging, indicating resistance to Pierce's disease, the university says.

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