Purdue University researchers found that this group of plants produces, but does not respond to, the molecule that triggers the infection response used by nearly all other plants. The molecule does, however, allow this group of plants, called metal hyperaccumulators, to store high levels of metal in their tissues, rendering them pathogen resistant.
These findings, reported in today's (Friday, March 11) issue of the journal Plant Physiology, shed new light on the evolution of these plants and may have implications for the development of crops that may one day remove metal and other contaminants from the environment.
"Our goal is to find the high-level regulator - the one gene or group of genes that turns a plant into a hyperaccumulator," said David Salt, associate professor of plant molecular physiology in Purdue's horticulture department. "But we have no way to know what that gene is, so we need to deconstruct the process, starting with things we can measure, which are these visible traits, and then we work backwards."
A question that has long stymied Salt and his colleagues centers on the origins of this trait. While essential as micronutrients, metals are toxic in high levels. Most plants have mechanisms that keep metals in the environment out of their tissues. So what would have driven some plants to do just the opposite?
"The existing explanation is that metal accumulation evolved to protect these plants from pathogens," Salt said. "Yet most other plants don't accumulate metals, and they resist infection just fine. It never really made sense to me. If everyone's already resisting pathogens, why do you need an extra mechanism? There has to be more to it."
It turns out the plants Salt studies - a group of small, weedy alpine flowers called Thlaspi - lack the standard pathog