New Clue About Plants' Sunlight Sensors Revealed

Plants can’t see, but they can sense sunlight--with molecules called phytochromes. Now, in a letter in the August 19 issue of Nature, California researchers report discovering a new clue to a mostly mysterious process: how do phytochromes switch on genes to command a plant to respond to sunlight? The genes may trigger the plant to flower, for instance, or to make sugar--for energy--from sunlight, air and water.

The scientists, with the University of California at Berkeley, have discovered that a type of phytochrome known as phytochrome B will, when activated by sunlight, bind to a protein called PIF3. They made the discovery in Albany, Calif., at the Plant Gene Expression Center, a joint venture of the university and the Agricultural Research Service, USDA's chief research agency.

The binding of sunlight-activated phytochrome B to PIF3 is a previously unknown step. Phytochrome B doesn't bind if it is kept in the dark, according to lab tests by Min Ni, James M. Tepperman and Peter H. Quail at Albany.

The scientists expect their investigations may eventually lead to new ways to change when and how plants respond to sunlight. This could speed development of genetically engineered plants that, for example, germinate or flower at times controlled by growers. What's more, new clues about how phytochrome B interacts with PIF3 to control genes should serve as a helpful new model of how other signaling pathways might work, such as those that control genes for resistance to drought or insects.

Phytochromes detect light in the red or far-red parts of the spectrum. They can determine the ratio of red to far-red light, and accordingly become active or inactive. This allows seeds to tell whether they are close to the soil surface, for example, and allows plants to time daylength, so that they can flower at the correct time of year.

Scientific contact: Peter H. Quail, ARS/University of California at Berkeley Plant Gene Expression Center, 800 Buchanan St., Albany, CA 94710, phone (510) 559-5900, fax (510) 559-5678, quail@nature.berkeley.edu.