Root or shoot? EAR calls the shots( La Jolla CA Controlled by a tightl...)

La Jolla, CA Controlled by a tightly regulated choreography that determines what should go up and what should go down, plants develop along a polar axis with a root on one end and a shoot on the other.

While studying why a defective TOPLESS gene causes plant embryos to develop into a seedling topped with a second root instead of a stem with leaves, researchers at the Salk Institute for Biological Studies hit upon the linchpin that ensures that plants are neither all root nor all shoot.

Turns out the question, Root or shoot" literally hinges on the EAR domain, a short protein sequence only six amino acids long.

The Salk researchers findings, published in the February 7 issue of Science Express, explain how mutations in TOPLESS can switch a plant cells fate from shoot to root and in the process clarify the purpose of the so-called EAR motif, a protein domain whose function has puzzled plant scientists for several years.

Weve known for a while that the EAR domain can turn off transcription, but how it did this was an open question, says the studys lead author, Jeffrey A. Long, Ph.D., an assistant professor in the Plant Molecular and Cellular Biology Laboratory. We didnt set out to fish for molecules that bind to the EAR domain, but when we used TOPLESS as a bait, thats what we found.

Scientists and home gardeners alike have been messing with plants basic architecture for years: Permanently switch on a gene called BODENLOS (or bottomless) and plants forgo root development altogether. Dip plant cuttings into hormone rooting powder and roots start to sprout where none have been. The active ingredient, a synthetic version of the plant hormone auxin that regulates root growth in plants, overrides the molecular switch that keeps auxin-responsive genes turned off in parts of the plant that are above ground.

In an earlier study, Long and his team had discovered that the switch is none other than TOPLESS, the
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