The technique holds promise for creating genetically engineered trees and vines that can stave off crown gall, a costly disease that affects many perennial fruit and nut crops, including walnuts, apples and grapes.
Professor Abhaya Dandekar and doctoral candidate Matthew Escobar, both of the UC Davis pomology department, discovered that gene silencing can be used to interrupt the process of tumor formation in crown gall disease. Their findings will appear in the Oct. 30 issue of the Proceedings of the National Academy of Sciences.
"Gene silencing is one of the most exciting things happening in the plant sciences," said Dandekar, an authority on genetically engineered tree crops. "There have been clues that this technique might be used to produce disease resistance in plants, but we were surprised to discover just how well it actually works in the case of crown gall disease."
Crown Gall Disease
Crown gall is caused by the common soil bacterium Agrobacterium tumefacians, which has the unique ability to transfer its own DNA into the DNA of the plant it infects in a process known as "horizontal gene transfer."
The bacteria usually invade the plant at a spot where it has been wounded. The wounded plant cells release certain chemicals that make it possible for the bacterial DNA to be incorporated into the plant's DNA. Genes contained in this bacterial DNA then become active in the nuclei of the plant cells.
This molecular takeover of the plant's genetic code causes the plant to produce the proteins that trigger tumor formation. The tumors appear as galls or lumps of tissue near the base of the plant's stem. Galls can damage the plant by blocking transport of nutrients and water up and down the plant stem or tree trunk.