Rooting out plant stress responses

Plant cellular responses are much more locally and temporally specialized than previously thought, a new study suggests. In growing Arabidopsis roots, different tissue layers respond to stressful conditions in highly cell-type specific ways, according to linkurl:research;http://www.sciencemag.org/cgi/content/abstract/115379 published online today (April 24) in Science. "By and large, plants have been viewed as single, uniform entities," said linkurl:Philip Benfey;http://www.biology.duke.edu/b

Written byElie Dolgin

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Plant cellular responses are much more locally and temporally specialized than previously thought, a new study suggests. In growing Arabidopsis roots, different tissue layers respond to stressful conditions in highly cell-type specific ways, according to linkurl:research;http://www.sciencemag.org/cgi/content/abstract/115379 published online today (April 24) in Science. "By and large, plants have been viewed as single, uniform entities," said linkurl:Philip Benfey;http://www.biology.duke.edu/benfeylab/ of Duke University in Durham, North Carolina, who led the study. "But we saw dramatic differences between cell types that we could trace back to physiological — and probably adaptive — differences." "They can actually distinguish stress-specific and development-specific cis-regulatory elements," said linkurl:Hans Bohnert;http://www.life.uiuc.edu/bohnert/ of the University of Illinois at Urbana-Champaign, who was not involved in the research. "They're on their way to explaining the whole plant." Plants grown on marginal linkurl:agricultural;http://www.the-scientist.com/news/home/52943/ lands are often exposed to high levels of salt or low levels of essential nutrients, which can have complex effects on root physiology. It has been unclear, however, how different cell types responded to these linkurl:environmental stresses.;http://www.the-scientist.com/news/display/24263 Now, Benfey and colleagues from Duke University and the University of Michigan, Ann Arbor, have gotten to the root of this problem. Benfey's team used a series of genome-wide microarrays to investigate levels of gene expression in different parts of the Arabidopsis root. In one test, they subdivided the root lengthwise into four longitudinal zones to examine developmental stages, and in another, they cross-sectioned the root into six radial zones to study different cell types. Under two stressful conditions — either linkurl:high salinity;http://www.the-scientist.com/2003/6/2/S27/1/ or iron deficiency — the researchers found that the majority of genes were expressed in a highly zone-specific and stress-specific manner. "It wasn't like there was a [universal] type of dedicated cell response," said Benfey. linkurl:Michael Deyholos;http://www.biology.ualberta.ca/faculty/michael_deyholos/uploads/lab/Deyholos_Lab.htm of the University of Alberta in Edmonton, Canada, who was not involved in the research, said the study was long overdue. "No one had gone down to cellular resolution," he told The Scientist. But he said that with such a large genome-wide dataset, it was "hard to interpret or even see the details," and that the study was "just scratching the surface" of cell-type specific responses in plants. The researchers also found a large number of genes that were explicitly expressed in certain cell-types, but whose activity levels didn't change considerably under stress. Benfey thinks that two different classes of genes probably function in cell identity: those involved in what he called "core identity," and are independent of the environment, and those that contribute to the cell's "responsive identity" to external stimuli. His team is now working to engineer more stress-resistant plants by pinpointing the key gene networks involved in stress responses.