Enzyme Discovery Helps Explain Grapevine Damage Caused By Pierce's Disease

A new enzyme that figures in Pierce's disease, a widespread bacterial infection spread by insects, was recently discovered by researchers from the University of California, Davis. Their finding could save California's grape and wine industries millions of dollars each year. 

"With a bacterial disease, much like cancer, if you understand how the virulent form spreads, you can better control or remove it," Abhaya Dandekar, a professor of plant sciences and senior author on the new study, said in a news release. "We anticipate this discovery could open new ways to think about dealing with Pierce's disease and highlight other areas of immune response, in general, that haven't yet been considered."

Pierce's disease, first identified in the 1890s, is caused by the bacterium Xylella fastidiosa and spread between grapevines by xylem-feeding leafhoppers known as blue-green sharpshooters. When infected with this deadly disease, leaves generally turn yellow or red along the edges, before dying and falling from the vine.  

Pierce's disease was a serious threat to California agriculture in 1996 when the glassywinged sharpshooter was discovered in the state's Temecula Valley. Since then, the disease has spread north where it has become well-established and has cost California's grape and wine industries more than $100 million annually on average.

When Xyllela fastidiosa invades a grapevine, it produces a biofilm or gel in the xylem that blocks the xylem, preventing the flow of water to the leaves, which turn color and then die.

However, there is more to the story and that is what researchers from UC-Davis reveal in their new study. They set out to find how else Xyllela fastidiosa alters a vine's physiology.

When reserachers analyzedg the bacteria's secretome, or secreted proteins that actually trigger the disease, they discovered an enzyme, subsequently named LesA, that was abundant during Xyllela fastidiosa infections. LesA shared characteristics with similar enzymes known to be capable of breaking down plant cell walls.

"The LesA enzyme has the ability to move through cell membranes, equipping the Xyllela fastidiosa bacteria to invade the grapevine and to live in its xylem tissues, where it feeds on fatlike compounds called lipids," Dandekar added in the university's release. 

The LesA enzyme helps explain why, for example, some infected grapevines exhibit severe symptoms but have little to no blockage in their xylem.

Researchers confirmed this point by creating a mutant strain of Xyllela fastidiosa bacteria that lacked the ability to cause infection in grapevines.

Their study was recently published in the journal Scientific Reports. 

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