As Wang explained: "We've known for some time what happens at the cell's surface, so understanding what is happening in the nucleus is very important for unraveling this mystery of plant growth. We found that in the model plant Arabidopsis, a protein in the cell nucleus called BZR1, which is activated when the BR hormone is present, has a previously unknown segment where molecular binding occurs. Instead of stimulating an activity, the protein binds to a DNA sequence (named brassinosteriod-response element or BRRE), which stops the process of transcription--the transfer of genetic information from the DNA template molecule to messenger RNA--for a gene named CPD. Because the CPD gene orders the production of an enzyme needed for BR synthesis, this suppression stops the production of BR conferring a feedback regulation of BR production. When the BR steroid level is high, BZR1 is activated and BR synthesis is reduced. When the level is low, the synthesis is high. This feedback regulation is critical for maintaining an optimal steroid level for plant growth.
Using sophisticated microarray analyses of mutant Arabidopsis plants, which produce a more active version of BZR1, the scientist also found that in addition to coordinating equilibrium in plants, BZR1 also promotes growth, thus playing a dual role. The researchers further identified other genes controlled by BZR1, and studies of these genes will enhance the understanding of how steroid hormones regulate plant growth.
The Carnegie Institution (www.CarnegieInstitution.org) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.
Authors of the study are the following:Jun-Xian He1*, Joshua M. Gendron1,2*, Yu Sun1, Srinivas S. L. Gampala1, Nathan Gendron1, Catherine Qing Sun1, and Zhi-Yong Wang1†
1.Department of Plant Biology, Carnegie Institution, Stanford, CA 94305
2. Department of Biological Sciences, Stanford University, Stanford, CA 94305.
Copies of the embargoed paper may be obtained from the AAAS at 202-326-6440, or scipak@aaas.org
Journal
Science