Plant, animal immunity: We are family

UC DAVIS (US) — Plants and animals detect microbial invasions and resist diseases in surprisingly similar ways, according to a new study.

The findings are a result of 15 years of research by teams of scientists from seemingly disparate fields using classical genetic studies to unravel the mysteries of disease resistance.

Details are published in Nov. 19 issue of the journal Science.

“Increasingly, researchers will be intent on harnessing knowledge of resistance and immune responses to advance plant and animal health,” says Pamela Ronald, a plant pathologist at University of California, Davis.

“Some of the resistance mechanisms that researchers will discover will likely serve as new drug targets to control deadly bacteria for which there are currently no effective treatments.”

Ronald’s study describes how research use common approaches to tease apart the secrets of immunity in species ranging from fruit flies to rice.

Receptors—protein molecules usually found on cell membranes—recognize and bind to specific molecules on invading organisms, signaling the plant or animal in which the receptor resides to mount an immune response and fend off microbial infection and disease, Ronald says.

The current research illustrates descriptions of the disease-resistance or immunity pathways in the mouse, Drosophila fruit fly, rice, and a common research plant known as Arabidopsis. These represent the immune defense systems of vertebrates, insects, monocotyledons (grasslike plants) and dicotyledons (plants such as beans that have two seed leaves.)

Plant biologists have previously discovered receptors that sense and respond to infection. The 1980s brought about an intense hunt for the genes that control production of the receptor proteins, followed by an “avalanche” of newly discovered receptor genes and mechanisms in the 1990s.

Another milestone included discovery in 2000 of the immune receptor in Arabidopsis known as FLS2—which demonstrated that a plant receptor could bind to a molecule that is present in many different microbial invaders.

The review also discuses how plant and animal immune responses have evolved through the years and which mechanisms have remained the same.

While the past 15 years have been rich in significant discoveries related to plant and animal immunity, Ronald and colleague Bruce Beutler, an immunologist and mammalian geneticist at The Scripps Research Institute, are quick to point out that researchers have just scratched the surface.

“If you think of evolution as a tree and existing plant and animal species as the leaves on the tips of the tree’s branches, it is clear that we have examined only a few of those leaves and have only a fragmentary impression of what immune mechanisms exist now and were present in the distant past,” Beutler says.

They say as results from new gene sequencing projects become available, scientists will likely find that some plant and animal species emphasize specific resistance mechanisms while having little use for others.

For example, the researchers point out that the Drosophila’s immune system depends on only one immunologically active receptor, known as the Toll receptor, to sense invasion by fungi and gram-positive bacteria. In contrast, Arabidopsis has dozens of sensors to protect against microbial infections, and rice has hundreds.

The review study was supported with funding from the National Institutes of Health.

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