Researchers identify proteins making up mechanosensitive io...( Researchers at Washington University...),Health

Researchers at Washington University in St. Louis are the first to identify two proteins responsible for mechanosensitive ion channel activities in plant roots. Scientists have long known that plant cells respond to physical forces. Until now, however, the proteins controlling the ion channel response remained a mystery.

As the name suggests, mechanosensitive channels are paths through the cell membrane that respond to mechanical forces such as gravity, pressure, or touch. Under certain forces, a channel opens, allowing the flow of ions, such as calcium and potassium ions, into and out of the cell. Different forces might close the channel, stopping the flow.

This cross-membrane ion flow has been measured electrophysically, using a technique called the patch-clamp method. But the molecular nature of the channels themselves was not known. Now, knowing the proteins involved makes it possible to discover what the channels do for the whole plant.

"People have been characterizing mechanosensitive channels in plants for 20 years," said Elizabeth Haswell, Ph.D., assistant professor of biology at Washington University in St. Louis and lead investigator of this project, "This is the first time anybody has been able to show which proteins underlie these activities."

The two proteins governing ion channels in Arabidopsis root are MSL9 and MSL10, according to the study published in the May 20 issue of Current Biology. MSL stands for MscS-Like proteins because of their similarity to a family of bacterial channels known as MscS (mechanosensitive channels of small conductance). Even though bacteria and plants are not closely related in terms of evolution, this study shows that bacterial and plant cells are probably using the same types of proteins to respond to mechanical forces.

To establish that the channels were in fact mechanosensitive, Haswell's French colleagues used the patch-
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