Plants have effective mechanisms aimed at protecting themselves against bacteria and fungi. Research funded by the National Science Foundation (NSF) and published in the February 28 issue of Nature uncovers the molecular basis by which this resistance occurs. The work holds promise for designing hardier crops.
“We’ve identified a key molecular pathway within plant cells,” says scientist Jen Sheen of the molecular biology department at Massachusetts General Hospital (MGH), who authored the Nature paper with several of her colleagues. “If we activate this pathway in leaves, we’ve found that we can make them more resistant to pathogens like bacteria and fungi.”
Adds Jane Silverthorne, program director in NSF’s biological sciences directorate, “This is an exciting step forward. For the first time, we have a detailed description of an important plant signaling pathway. This information will bevaluable to furthering our understanding of basic signaling mechanisms in plants, as well as for developing crops with improved resistance to pathogens."
Sheen says plants have an effective and sophisticated immune system. Their first line of defense is a thick cell wall covered with cuticle layers that acts somewhat like human skin. If a pathogen is able to penetrate this physical barrier, for example through a wound, the pathogen will usually be detected by receptors on the surface or inside of the plant cells. One of the best characterized pathogen receptors has a feature characteristic of other plant receptors known as a Leucine-rich repeat (LRR) receptor kinase. This receptor kinase can recognize a structure on bacterial pathogens called flagellin that makes the bacteria motile.
“There’s a conserved region in the flagellin that’s present on a wide range of bacterial pathogens, so plants are very effective at detecting pathogens. Highlighting the conservation and similarity of immune systems in plants and animals, bacterial flagellin can also trigger innate immune response through a LRR receptor in mammals,” explains Sheen.
When the plant receptor binds flagellin, a complex set of cellular events follow, resulting in the expression of key immune response genes.
“The receptor in plant cells is connected to a signaling cascade that activates gene expression through what’s known as transcription factors,” Sheen says. In particular, these transcription factors may trigger the production of certain plant signals, reminiscent of cytokines in mammals, that then turn on a lot more downstream genes directly involved in the defense mechanism of the plant, Sheen explains.
The whole process is a complicated cascade of events that Sheen and her colleagues are continuing to unravel. “We are currently investigating the downstream genes involved in this cascade. Ultimately, it looks like the end result is that the plant is able to produce a variety of anti-microbial proteins, enzymes and chemicals.” Sheen adds that the ultimate goal of this type of research is to be able to engineer plants to become more pathogen-resistant.
The study was also supported by the U.S. Department of Agriculture, the National Institutes of Health, the Toyobo Biotechnology Foundation, and the Uehara Memorial Foundation.
NSF is an independent federal agency that supports fundamental research and education across all fields of science and engineering, with an annual budget of about $4.8 billion. NSF funds reach all 50 states, through grants to about 1,800 universities and institutions nationwide. Each year, NSF receives about 30,000 competitive requests for funding, and makes about 10,000 new funding awards. NSF also awards over $200 million in professional and service contracts yearly.
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