How does your garden grow roots?

A gene that activates cell division regulates the tempo of plant root growth, researchers report. Moreover, by manipulating the gene, scientists may someday speed up root development. Certain proteins, encoded by a group of genes called cyclin, trigger plant cell division. In the new study, Peter Doerner and his colleagues at the Salk Institute for Biological Studies in La Jolla, Calif., spliced cyclin1 onto a regulatory sequence of DNA, forcing cyclin1 to make its protein throughout the cell cycle instead of just before cell division. They then transferred this gene package into Arabidopsis, a much-studied weed.

These transgenic plants reached a standard size, but they grew faster than other Arabidopsis plants. Although their roots grew about 40 percent faster than those of unaltered Arabidopsis, the plants had regular root patterns, the team reports in the April 11 Nature.

The researchers don't know whether the altered cyclin1 gene stimulated growth throughout the plant or the speedy root development gave the rest of the plant a boost.

However, they do know that having the gene active throughout the cell cycle reduces the effectiveness of a mechanism that normally turns off growth. When treated with auxin, a growth hormone, the altered Arabidopsis grew for a longer period than the unaltered plants.

Because they were able to influence growth rates simply by souping up the cyclin1 gene, the researchers conclude that plant growth depends entirely on cell division. In contrast, promoting cell division in animals increases only the likelihood of cancer, not normal growth.

In a few years, the team's findings may enable scientists to genetically engineer plants that grow roots more quickly and therefore tolerate dry conditions better, Doerner asserts. Before that happens, he says, the researchers need to understand the role of the eight other cyclin genes, which are probably also involved in cell division.