Plant "Dwarf" Gene Found By Salk Scientists

The gene, called BAS-1, can potentially serve as a "volume knob" that would allow growers to set the height of grass, trees and other plants. Think of hedges that never need pruning. Or instant bonsai.

"BAS-1 appears to control the level of an important steroid hormone that stimulates growth in plant cells," said Joanne Chory, Salk professor and senior author of a study describing the new gene in the December 20 issue of the Proceedings of the National Academy of Sciences.

She added that steroid hormones have only recently been appreciated as playing a significant role in plant growth and that, as in humans, steroid production causes plants to "pump up."

The product of the BAS-1 gene (the full name is phyB activation-tagged suppressor1) breaks down an abundant growth hormone, the steroid brassinolide. In the Salk study, its effects were observed mainly in plant stems, and to a lesser degree in leaves and flowers.

"The findings suggest that by manipulating BAS-1, it may be possible to make short or 'dwarf' plants that are completely normal in every other way," said Chory.

Finding BAS-1 also answers a basic question in plant biology. Researchers knew that the brassinolide hormone and its receptor are present throughout the plant, and therefore it was a mystery as to how it -- or other steroids -- could influence growth in a manner specific to individual tissues. The current study indicates a mechanism that regulates brassinolide in a tissue-specific way.

"It appears that brassinolide is made through the plant and then growth is controlled by selectively inactivating it," said Chory. "BAS-1 performs this step in stems, and so switching on BAS-1 will halt stem elongation.

"Presumably, additional genes will be found that regulate steroid-induced growth in other parts of the plant, such as leaves and petals," she added. "By tinkering with the entire set, it should eventually be possible to influence every aspect of plant growth and appearance."

Chory and her colleagues found the BAS-1 gene by searching for genes that would reverse the effects of a mutation in the phyB gene, which senses and reacts to red light. The phyB mutant plants grow overly long stems, an effect corrected by high levels of BAS-1 activity. BAS-1 is the first gene identified that interacts with both the steroid hormone and light-detecting pathways, two of the major systems that control plant growth.

First author of the study is Michael M. Neff, a former postdoctoral fellow in Chory's laboratory. Other Salk authors include Serena M. Ngyugen and Elizabeth J. Malancharuvil. The study was done in collaboration with Suguru Takatsuto at Joetsu University in Nigata, Japan; Masayoshi Tsubuki and Toshio Honda at Hoshi University in Tokyo, Japan; and Shozo Fujioka, Takahiro Noguchi and Hideharu Seto at The Institute of Physical and Chemical Research in Saitama, Japan. The study, titled "BAS1: A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis," was supported by the National Institutes of Health and by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan. Neff was supported by a National Research Service Award, and Chory is a Howard Hughes Medical Institute investigator.

The Salk Institute for Biological Studies, located in La Jolla, Calif., is an independent nonprofit institution dedicated to fundamental discoveries in the life sciences, the improvement of human health and conditions, and the training of future generations of researchers. The Institute was founded in 1960 by Jonas Salk, M.D., with a gift of land from the City of San Diego and the financial support of the March of Dimes Birth Defects Foundation.