A molecular mechanism for plant disease resistance has been identified for the first time by two separate research teams at Berkeley and UC Davis and at Purdue.

Studying bacterial speck disease in tomato plants as a model, both teams of researchers confirmed a decades-old notion that disease resistance in plants is triggered by the interaction of proteins produced by both a resistance gene in the plant and an " avirulence" gene in the disease-causing micro-organism.

The avirulence protein acts much like an antigen in animals, eliciting an immune response from the plant.

Researchers suspect that this resistance mechanism observed in tomatoes also occurs in many other plants.

The results of both the UC and Purdue studies appeared in the Dec. 20 issue of the journal Science, accompanied by a related commentary.

" This is the first demonstration that there is a lock-and-key mechanism at the molecular level involved with the plant's ability to recognize and mount a resistance response to a pathogen," said UC study co-author Steven Scofield, a research geneticist at the UC Davis Center for Engineering Plants for Resistance Against Pathogens.

" These findings set the stage to allow us to genetically engineer disease-resistant crops," added co-author Brian Staskawicz, a professor of plant and microbial biology at Berkeley.

For some 40 years, researchers have known that a plant's ability to fend off an attacking bacterial or viral disease is somehow linked to the complementary activity of genes in both the plant and the pathogen -- the disease-causing agent.

Previous genetic research has suggested that an avirulence gene in the pathogen triggers a resistance response in the infected plant.

Having identified this basic gene-for-gene resistance mechanism, the UC researchers plan to further explore the phenomenon by following the chain of events to understand the full mechanism of resistance.

"We've been looking at the top of the chain of events that occur when a plant perceives a pathogen," said Scofield.