The disease-causing bacterium Pseudomonas syringae on a tomato. (Credit: Scot Nelson/Flickr)

With plants and pathogens, it’s a back-and-forth battle for control

Researchers have found two new players in the “seek-and-destroy” struggle between plants and microbes.

Plants’ innate immunity relies on the ability of molecular receptors on the surface of the plant cells to identify specific groups of molecules on the invading microbe or pathogen. When a plant cell receptor recognizes such a group of molecules, it triggers the plant’s immune response to swing into action and battle the invading pathogen.

"In effect, the plant and the attacking bacteria battle to take control of the biochemical process that initiates the plant's antibacterial immunity," Benjamin Schwessinger explains. (Credit: Tuomas Puukko/Flickr)
“In effect, the plant and the attacking bacteria battle to take control of the biochemical process that initiates the plant’s antibacterial immunity,” Benjamin Schwessinger explains. (Credit: Tuomas Puukko/Flickr)

“In this study, we showed that a biochemical process known as tyrosine phosphorylation is important to the plant’s immune signaling system,” says co-author Benjamin Schwessinger, a Human Frontier Science Program postdoctoral fellow in the University of California, Davis Department of Plant Pathology. Schwessinger initiated the work when at the Sainsbury Laboratory in Norwich, UK.

“Furthermore, we demonstrated that a certain plant receptor that recognizes the presence of the Pseudomonas syringae bacterium also becomes the target for a counterattack when that bacterium attempts to fight back and suppress the plant’s immune system,” he says.

Using the Arabidopsis plant as a model, the researchers showed for the first time that tyrosine phosphorylation is an important part of the “molecular code” for how a plant immune receptor, known as EFR, signals the presence of the EF-TU protein on Pseudomonas syringae, a disease-causing bacterium that infects a wide range of plant species. Findings from the study are published online in the journal Science.

Attacking bacteria, not to be outwitted by the plant’s immune response, tend to launch something of a counter-offensive by injecting proteins inside the plant cell.

The researchers found that the Pseudomonas syringae bacterium delivers its counter-punch to the plant’s immune response in the form of an enzyme called HopAO1. The enzyme has been known to researchers for about a decade, but this study was the first to identify which molecules it targets inside the plant cell.

“In effect, the plant and the attacking bacteria battle to take control of the biochemical process that initiates the plant’s antibacterial immunity,” Schwessinger says.

Other researchers from the Sainsbury Laboratory, Michigan State University, the University of Illinois, Urbana, and Chungnam National University contributed to the research.

The Gatsby Charitable Foundation, European Research Council, United Kingdom Biotechnology and Biological Sciences Research Council, US Department of Energy, US National Institutes of Health, the Gordon and Betty Moore Foundation, National Science Foundation, and the US Department of Agriculture funded the study.

Source: UC Davis

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