UC Davis tackles Pierce's disease with genetic engineering

A gene fusion research project could help fight Pierce's disease in California. The grapevine disease was first noted in California around 1884 and is now known to exist in 28 Californian 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.

There is currently no known cure for Pierce’s disease but researchers at UC Davis have tested the hypothesis that disease-causing microbes can evade one defensive action by a host plant but believed that most microbes would have difficulty overcoming a combination of two immune-system defenses.

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 fastidios, (the bacteria responsible for Pierce's disease) 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. And grapevines engineered to carry the hybrid gene had significantly less leaf scorching and xylem clogging, indicating resistance to Pierce’s disease.