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Biological Sciences Division
Research Highlights

May 2014

How a Plant Beckons the Bacteria That Will Do It Harm

Work on microbial signaling offers a window into better biofuels, human health

Infection of tomatoes by Pseudomonas syringae.

Results: A common plant puts out a welcome mat to bacteria seeking to invade, and scientists at the University of Missouri and Pacific Northwest National Laboratory have discovered the mat's molecular mix.

The study, published in the Proceedings of the National Academy of Sciences, reveals new targets during the battle between microbe and host that researchers can exploit to protect plants.

The team showed that the humble and oft-studied plant Arabidopsis puts out a molecular signal that invites an attack from a pathogen. It's as if a hostile army were unknowingly passing by a castle, and the sentry stood up and yelled, "Over here!"—focusing the attackers on a target they would have otherwise simply passed by.

"This signaling system triggers a structure in bacteria that actually looks a lot like a syringe, which is used to inject virulence proteins into its target. It's exciting to learn that metabolites excreted by the host can play a role in triggering this system in bacteria," said Dr. Thomas Metz, an author of the paper and a chemist at PNNL.

The findings come from a collaboration of scientists led by Dr. Scott Peck of the University of Missouri that includes researchers from the university, the Biological Sciences Division at PNNL, and EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research (BER) and located at PNNL.

Why It Matters: The research examines a key moment in the relationship between microbe and host, when a microbe recognizes a host as a potential target and employs its molecular machinery to pierce it, injecting its contents into the plant's cells—a crucial step in infecting an organism.

The work focused on bacteria known as Pseudomonas syringae pv. tomato DC3000, which can ruin tomatoes as well as Arabidopsis. The bacteria employ a molecular system known as the Type 3 Secretion System, or T3SS, to infect plants. In tomatoes, the infection leads to unsightly brown spots.

The findings also could have implications for people. The same molecular machinery employed by Pseudomonas syringae is also used by a host of microbes to cause diseases that afflict people, including salmonella, the plague, respiratory disease, and chlamydia.

On the energy front, the findings will help scientists grow plants that can serve as an energy source and are more resistant to infection. Also, a better understanding of the signals that microbes use helps scientists who rely on such organisms for converting materials like switchgrass and wood chips into useable fuel.

See the entire news release at


Sponsors: This work was supported by the National Science Foundation and an EMSL User Proposal. Portions of this research were enabled by capabilities developed by the PNNL Pan-omics Program under support from the DOE-BER Genome Science Program.

User Facility: EMSL

Research Team: Jeffrey C. Anderson, Ying Wan, and Scott C. Peck, University of Missouri; Young-Mo Kim, Ljiljana Paša-Tolic, Thomas O. Metz, PNNL.

Research Area: Biological Systems Science

Reference: Anderson JC, Y Wan, YM Kim, L Pasa-Tolic, TO Metz, and SC Peck. 2014. "Decreased Abundance of Type III Secretion System-Inducing Signals in Arabidopsis mkp1 Enhances Resistance Against Pseudomonas syringae." Proceedings of the National Academy of Sciences 111(18):6846-6851. DOI: 10.1073/pnas.1403248111.

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