Gibberellin Receptor Found

PLANT BIOCHEMISTRY

A target of the plant hormones known as gibberellins has been identified.

Gibberellins induce many well-characterized responses in plants, including stem elongation, but how they do so is not known. Now, Japanese researchers led by Nagoya University's Makoto Matsuoka have discovered a receptor for these compounds, called GID1, and propose a mechanism for gibberellin signaling.

GID1 can bind to all biologically active gibberellins, including gibberellic acid. Its discovery is "extremely important" and "very exciting," says Mark Estelle of Indiana University. His is one of two teams that recently discovered a receptor for auxin, another key plant hormone (C&EN, May 30, page 11). ";Gibberellins have been known for decades and have a central role in plant growth and development," he adds.

GID1 is a soluble protein in the nuclei of rice plant cells. That it is a gibberellin receptor is based on several lines of evidence (Nature 2005, 437, 693). The work is "so complete—it has all the data to demonstrate that this protein is a receptor," Estelle says.

The researchers suggest that, when bound to a gibberellin, GID1 interacts with another protein that represses the expression of gibberellin-dependent transcription factors. The interaction leads to destruction of the repressor protein by the plant’s protein-degrading machinery and release of the transcription factors. Liberated, the transcription factors activate certain genes required for plant development.

The proposed mechanism parallels that advanced for auxin, notes botany professor Peter McCourt of the University of Toronto. In both cases, small organic molecules initiate a protein-protein interaction that eventually destroys one of the proteins. "We now know the core biochemistry of these small molecules,"McCourt says. "What's next is to figure out how that core biochemistry regulates development."