Cooperative State Research, Education and Extension Service (CSREES) Research Results

Plant steroids play an essential role in plant growth and development and provide stress protection. Scientists at the Salk Institute for Biological Studies, in La Jolla, CA, and the Howard Hughes Medical Institute, Chevy Chase, MD, are unlocking the mysteries between plant steroids and plant growth. Their research, funded by USDA, could lead to new plant varieties with desirable growth traits.

Joanne Chory and colleagues identified a new protein that stops the growth process in plants when there is an absence of brassinosteroids, a type of plant steroid. These steroids induce a signaling mechanism in plant cells that flips a proverbial switch causing the plant to grow and develop properly.

For a signal to be transmitted to a plant cell, brassinosteroids attach to a receptor on the plasma membrane of the cell, like a lock and key mechanism. The brassinosteroid receptor on the plasma membrane is called BRI1. Once BRI1 is activated by brassinosteroid binding, it interacts with BAK, a co-receptor that continues the reception chain.

In the absence of brassinosteroids, BRI1 kinase binds with the newly identified protein, BKI1 instead of BAK, shutting down the receptor and stopping the signal. This stunts growth and produces mutant dwarf plants.

During testing, the researchers found that reintroducing brassinosteroids into the system causes BRI1 to bind to the brassinosteroid, and BKI1 rapidly dissociates from the plasma membrane. The reception chain continues from there and normal growth resumes.

BKI1-like genes are present in many plant species, including economically important crops, such as rice, maize, and soybean. Over- or under-expression of BKI1 in these species will provide a valuable tool to control the strength of brassinosteroid signaling in plant cells and will allow the creation of novel plant varieties with desirable traits.

This research was published in August 25 th issue of Science in the article titled “ Brassinosteroids regulate dissociation of BKI1, a negative regulator of BRI1 signaling, from the plasma membrane.”

The USDA’s Cooperative State Research, Education and Extension Service funded this research project through the National Research Initiative (NRI) Genetic Processes and Mechanisms of Agricultural Plants Program. The NRI is the largest peer reviewed, competitive grants program in CSREES. It supports research, education, and extension grants that address key problems of national, regional, and multi-state importance in sustaining all components of agriculture.

CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education, and extension programs in the Land-Grant University System and other partner organizations. For more information, visit http://www.csrees.usda.gov.