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Plant Immunity
Mustard Shows Backbone in Its Own Defense
Plants, Vertebrates Appear to Share Elements of Innate Immune System
When a pathogenic microbe tickles a cell, plants react with a series of molecular conversations that order the immune system to fight back. Eavesdropping researchers at Massachusetts General Hospital have reported the details of a complete relay of conversations from a pathogen-detecting receptor to action-triggering transcription factors in a paper in the Feb. 28 Nature.
Fred Ausubel, Jen Sheen, Joulia Plotnikova, Matthew Willmann, Guillaume Tena (left to right, in a rooftop greenhouse), and colleagues detailed the network of signals Arabidopsis plant cells use to detect a pathogen and turn on its defense response. Photo by Steve Gilbert
The molecular conversation follows a pattern strikingly similar to the more complex and less understood innate immune system of people and other vertebrates, suggesting the immune mechanisms have been conserved throughout evolution.
The details from danger signal to action were worked out in isolated cells of the mustard Arabidopsis thaliana. In the study, leaves infected with bacterial or fungal pathogens stayed green and healthy-looking when the newfound molecular signaling pathway was activated, but the leaves deteriorated with disease and died when the signaling pathway was blocked. The pathway is mediated by a MAP kinase cascade.
When it comes to self-defense, plants and animals show similar footwork. First, a receptor on the cell membrane detects the tickle of flagellin on pathogenic bacteria. Inside the cell, protein links and kinase cascades pick up and carry the danger signal to the transcription factor. Then, early immune genes launch a defense response general enough to fight both bacteria and fungi. Step by step, this pathway was detailed for the first time in plants in a Nature paper by Massachusetts General researchers and their colleagues. Apparently conserved from early evolution, the signaling pathway is related to more complex and less well understood innate immune signals in animals. Animals have receptors with similar pathogen-recognition parts, as well as MAP kinase-mediated signaling to transcription factors that kick-start general pathogen-fighting mechanisms.
Jen Sheen, HMS associate professor of genetics and senior author on the paper, and her eight co-authors represent seven nationalities and come from four laboratories. Much of the work was done in two of the three plant research groups who share greenhouses at MGH.
--Carol Cruzan Morton
Copyright 2002 by the President and Fellows of Harvard College
