A key missing link in the so-called signaling pathway for plant steroid hormones has been discovered by researchers at the Carnegie Institution's Department of Plant Biology.
Many important signaling pathways are relays of molecules that start at the cell surface and cascade to the nucleus to regulate genes.
This discovery marks the first such pathway in plants for which all the steps of the relay have been identified.
Steroids are important hormones in both animals and plants. Brassinosteroids regulate many aspects of growth and development in plants.
Mutants deficient in brassinosteroids are often stunted and infertile. Brassinosteroids are similar in many respects to animal steroids, but appear to function very differently at the cellular level.
Animal cells usually respond to steroids using internal receptor molecules within the cell nucleus, whereas in plants the receptors, called receptor-like kinases, are anchored to the outside surface of the cell membranes.
For over a decade, scientists have tried to understand how the signal is passed from the cell surface to the nucleus to regulate gene expression.
Now, the research team unraveled the pathway in cells of Arabidopsis thaliana, a small flowering plant related to cabbage and mustard often used as a model organism in plant molecular biology.
"This is the first completely connected signaling pathway from a plant receptor-like kinase, which is one of the biggest gene families in plants," said Carnegie's Zhi-Yong Wang, leader of the research team.
"The Arabidopsis genome encodes over 400 receptor-like kinases and in rice there are nearly 1,000. We know the functions of about a dozen or so. The completely connected brassinosteroid pathway uses at least six proteins to pass the signal from the receptor all the way to the nuclear genes expressed. This will be a new paradigm for understanding the functional mechanism of other receptor-like kinases," Wang added.
Understanding the molecular mechanism of brassinosteroid signaling could help researchers develop strategies and molecular tools for genetic engineering of plants with modified sensitivity to hormones, either produced by the plant or sprayed on crops during cultivation, resulting in higher yield or improved traits.
"We perhaps could engineer plants with altered sensitivity in different portions of the plant," said Wang.