Keeping plant-cell motors on track

Within both plant and animal cells, motor proteins act like the engines in a busy train system. They shuttle material in the cell from one location to another. And just as commuter trains travel a predictable route in a defined direction, their volume of transport is commensurate with need. At rush hour, more trains are in operation. At midnight, there’s no point in running trains every 10 minutes.

In a growing plant cell, motor proteins called kinesins work as transporters that haul materials built in one part of the cell to the place where they are needed. Kinesins travel along tracks of polymers known as microtubules to get where they are going. Moving cargo costs the cell energy and resources, and this process is closely controlled to prevent waste.

Biologists at Washington University in St. Louis have discovered the molecular brakeman that holds kinesins in check until it’s their turn to move. (From left:) Ram Dixit, Anindya Ganguly, Graham Burkart and Yuanwei Fan. (Photo: Joe Angeles/Washington University).

Now biologists at Washington University in St. Louis have discovered the molecular brakeman that holds kinesins in check until their cargo is needed.

The importing IMB4 is a regulator that controls a kinesin specifically involved with building the plant cell wall. It works by physically binding to the kinesin, said Ram Dixit, associate professor of biology in Arts & Sciences. IMB4 holds the kinesin in an inactive state — protecting it from degrading while it waits — and prevents the kinesin from traveling along a microtubule until its cargo is needed. The new research is published in the journal Developmental Cell.

“The cell wall is like the plant’s exoskeleton, and building it is one of the growing plant’s most important functions. We have identified a key molecular regulator that closely controls cell wall deposition by physically binding to a kinesin,” Dixit said. “We still don’t know what signals cause IMB4 to release the brakes, but we now understand how it holds kinesins back until they are needed.”

Read more at Washington University in St. Louis (Talia Ogliore)