Secret is out

How gibberellins work

Published: Tuesday 15 November 2005

gibberellins are no gibberish for plants. In fact, they are plant growth regulators that influence a range of developmental processes including germination, stem elongation, flowering, leaf ageing and fruit formation. Numbering 126, gibberellins have been known for several decades, but scientists were clueless about how they work. No more.

Makoto Matsuoka and his team at Nagoya University in Japan have discovered that gibberellins work through a protein called gid1. They suggest that when bound to a gibberellin, gid1 interacts with another protein that has the opposite effect -- to repress the expression of gibberellin. gid 1 is invariably the winner of the cellular war -- the repressor protein is destroyed and gibberellins set free to activate certain genes required for plant development. The study, for which rice plants were used, appears in Nature (Vol 437, No 7059, September 29, 2005).

The work of the Japanese scientists is "so complete -- it has all the data to demonstrate that this protein is a receptor," says Mark Estelle, an Indiana University Bloomington biologist who led the team that discovered the tir1 protein that binds auxin, another key plant hormone. The discovery of tir1, about six months ago, culminated 70 years of efforts to understand auxin's role in cell growth and division.

Plants are known to have an astounding ability to respond to external conditions. For example, a bonsai illustrates how a potential tree can be duped into growing only a few centimetres tall over decades. This developmental plasticity has been manipulated throughout agricultural history, most notably during the 'green revolution' during which plant breeders often doubled grain production by selecting for semi-dwarf varieties of wheat and rice. But the underlying developmental mechanisms responsible have been unclear. It is this gap that the discovery of gid1 protein seeks to plug.

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