LA JOLLA, CAIn analyzing the molecular sensor for the plant growth hormone brassinolide, researchers at the Salk Institute for Biological Studies discovered that although plants took an evolutionary path different from their animal cousins, they arrived at similar solutions to a common problem: How to reliably receive and process incoming signals.
The team's findings, published in the February 1, 2011 issue of Genes and Development, revealed that so-called tyrosine phosphorylationused as an "on" or "off" switch and long thought to be a feature unique to animal cellsis a mechanism conserved across the animal and plant kingdoms.
"There seem to be only so many ways to build a robust signaling system," says Howard Hughes Medical Institute investigator Joanne Chory, Ph.D., professor and director of the Plant Molecular and Cellular Biology Laboratory and holder of the Howard H. and Maryam R. Newman Chair, "and plants and animals have hit upon the same mechanisms."
As different as they may seem, both mammalian and plant cells need to be able to perceive small molecule hormones to respond to changes in the environment. While human cells draw on a wide variety of sensor molecules, including more than 800 different G-protein-coupled receptors, 48 known nuclear hormone receptors and 72 receptor kinases, plants rely mostly on the latter.
"This group of receptors is by far the largest one in plants," says postdoctoral researcher and co-first author Michael Hothorn, "but we don't know much about the activation mechanism apart from 'there's a bunch of new phosphorylations.'"
Kinases transfer phosphate groups to proteins and come in two principal flavors: They either attach the phosphate group to the amino acid tyrosine within the protein or to serine or threonine. The vast majority of receptor kinases in animals possess tyrosine kinase activity, while only a few are specific for serine-threonine.
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