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USDA Funds Research Clarifying the Path Steriod Signal Follows in Plants

Media Contact:
Jennifer Martin, CSREES Staff (202) 720-8188

Stacy Kish, CSREES Staff (202) 690-5716
August 7, 2006

The word 'steroids' may not conjure up images of agriculture, but steroid hormones make the difference between a healthy, robust plant and one diminished in growth with abnormal development and reduced fertility. Application of this knowledge to agricultural practices may lead to improved productivity and healthier crop plants. Steroid applications in agriculture are limited because scientists are still deciphering steroid interactions in plants at the cellular level.

Steroid behavior in plant cells follows a unique pathway that scientists are only beginning to unlock and understand. In plant cells, steroids bind to receptors at the cell surface, like the space shuttle docking with the space station . The binding activates a chain reaction in which proteins in the cell's cytoplasm interact transferring the signal to the cell's nucleus. This signaling pathway activates gene expression in the nucleus. When a gene is activated, it produces morphological effects in the plant, such as plant height and leaf width. The signaling pathway can be negatively regulated by an inhibitor blocking the path.

Scientists believe the inhibitor does not block the signal path directly. Instead, a target protein of the inhibitor acts on a member in the signal path. For example, imagine that a long line of dominoes standing on end represents the signal path in the plant cell. The target protein effectively removes or disables a protein from the signal path. This is the same as removing a domino from the middle of the domino line. The signal initiated by the steroid stops where the target protein affected the signal path, much as falling dominoes stop at a gap in the line. The exact sequence of events leading to a blocked signal in plant cells is controversial.

Joanne Chory and colleagues from the Plant Biology Laboratory at the Salk Institute for Biological Studies and the Howard Hughes Medical Institute examined the signaling pathway of brassinosteroids, a group of plant steroids that play an important role in plant growth and development. Specifically, they wanted to determine how certain target proteins function to block the signal pathway. Previous research suggested the target protein of the inhibitor was translocated, or moved, into the plant cell's nucleus from the surrounding cytoplasm. The Salk group determined that the target protein was not translocated into the nucleus, but was already present in the nucleus of the plant cell.

This study provides scientists insight as to how the signaling pathway functions in plants and provides new opportunities to explore alternate methods to combat factors that interrupt the signal path in the cell. The results of this research are presented in an article entitled 'Downstream nuclear events in brassinosteroid signaling,' which is featured in the May 4 th edition of the journal Nature .

The USDA's Cooperative State Research, Education and Extension Service (CSREES) funded this research through its 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.

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