Study reveals how plants and bacteria 'talk' to thwart disease

When it comes to plants' innate immunity, like many of the dances of life, it takes two to tango. A receptor molecule in the plant pairs up with a specific molecule on the invading bacteria and, presto, the immune system swings into action to defend against the invasion of the disease-causing microbe.

Unwrapping some of the mystery from how plants and bacteria communicate in this dance of immunity, scientists at the University of California, Davis, have identified the bacterial signaling molecule that matches up with a specific receptor in rice plants to ward off a devastating disease known as bacterial blight of rice.

The researchers, led by UC Davis plant pathologist Pamela Ronald, will publish their findings in the Nov. 6 issue of the journal Science.

"The new discovery of this bacterial signaling molecule helps us better understand how the innate immune system operates," Ronald said.

"Because similar pairs of receptors and bacterial signaling molecules are known to exist not only in rice but also in other plants, as well as animals and humans, we are hopeful that this work will lead to new strategies for controlling diseases in plants and people," she said.

Disease resistance background

In 1995, Ronald's laboratory identified the XA21 gene, which produces a receptor protein that recognizes Xanthomonas oryzae pv. Oryzae, also known as Xoo, which causes bacterial blight disease. Xoo and other species of Xanthomonas infect virtually every crop species in the world.

Subsequent discoveries revealed that receptors with striking structural similarities to the XA21 receptor protein exist in other plants, flies, mice and even humans. These receptors were later named pattern recognition receptors or PRRs because they have the ability to recognize molecules that occur across species in a large class of disease-causing microbes. These receptors then can launch a protective immune defense on behalf of the plant or animal.