A transgenic approach to fighting Xylella Fastidiosa bacterial disease in grapevines

Effects of Pierce’s Disease (photo: PR Newswire/Los Alamos National Laboratory)

In a new study published February 21, 2012 ahead of print in the Proceedings of the National Academy of Sciences, researchers from Los Alamos National Laboratory, University of California, Davis and the USDA’s Agricultural Research Service revealed a new transgenic approach to blocking infection by Xylella Fastidiosa (Xf), the insidious bacteria that can cause major harm to commercially important California crops such as grapes, citrus and almonds.

The strain of Xf that impacts grapevines is deadly Pierce’s Disease, which chokes the vine by blocking the xylem, the water-conducting tissue in the plant.

After analyzing the genome sequencing on various Xf strains, researchers discovered a common protein to all of the strains called MopB.  They then sought a therapeutic approach to help plants defend themselves against MopB rather than to rely on chemical treatments after the fact.

Via instructions from a new hybrid gene inserted into the grapevine, a therapeutic protein recognizes and destroys MopB to prevent infection of the host plant.  Initial studies showed the effectiveness of this gene on preventing Pierce’s Disease.

In interviews by phone and email, research corresponding author Goutam Gupta of the Los Alamos National Laboratory said that field work is still being conducted in California and Texas to monitor how the grapevines react “in a natural environment and what kind of effects … the transgene[s] have on the plant health and the grape quality.”  He also indicated that any commercial availability is at least 2-3 years down the line.

When asked if the therapeutic protein could affect other, potentially beneficial bacteria, Gupta said that few bacteria reside in the xylem which is where the therapeutic protein is targeted, because the xylem contains no live cells; i.e., there are few nutrients for bacteria to live on.  In terms of other potentially negative affects on the grapevine, Gupta said that the protein is highly specific to Xf so “only a little amount is needed for Xf clearance.  This significantly reduces any toxic effect on the plant.  In addition, the possibility of plant toxicity is also minimized since the hybrid protein is mainly released in the xylem which has no live cells.”

This transgenic approach contrasts with natural cross-breeding approaches to cultivating disease-resistant vines conducted by researchers like Dr. Andrew Walker in the Department of Viticulture & Enology at UC Davis.  According to Jim Fullmer, Executive Director of Biodynamic certifying agency Demeter USA, genetically-engineered vines would not be allowed in either Biodynamic or USDA NOP organic production.

So why is Los Alamos National Laboratory – an institution known for strategic research geared towards national security – creating such genes?  Apparently, after 9-11 and the Anthrax incidence, several government agencies including the Center for Disease Control, the National Insitute of Health and others, came together to identify and prioritize potential bio-threats to the nation, especially those fungi, viruses and bacterias engineered to be drug or chemical-resistant and therefore virulent.  According to Gupta, “the hybrid protein is not defeated by the pathogen factors that cause drug resistance.”  So while Xf itself may not pose an imminent danger in terms of national security, the immune defense approach can certainly be applied  to other potentially dangerous pathogens.

The publication of the paper draws attention to the scope of work being conducted at Los Alamos National Laboratory.  According to Nancy W. Ambrosiano, PIO, their broad, multidisciplinary work covers not only nuclear and bio- threats, but also economic threats covered in this research.  It has also made contributions to the evolution of the Human Genome Project, HIV vaccine research and a large influenza database.

The full text of the paper “An engineered innate immune defense protects grapevines from Pierce’s disease,” by Abhaya M. Dandekar, et al is located on the website www.pnas.com.


previously published on examiner.com (edited)