Plant steroids more complex than those inside people


Washington : Steroids boost plants just as they do humans, but the molecular signals that activate such genes in plant cells are a lot more complex than in human cells.

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A new study by Carnegie Institution plant biologists used an emerging molecular approach called proteomics to identify key links in the steroid signalling chain.

Zhi-Yong Wang and Wenqinag Tang of the Carnegie Institution conducted the study with seven co-authors.

Plant steroids, called brassinosteroids, are key hormones throughout the plant kingdom. They regulate many aspects of growth and development.

Mutants deficient in brassinosteroids are often extremely stunted and infertile. Brassinosteroids are similar in many respects to animal steroids, but appear to function very differently at the cellular level.

Animal cells respond to steroids using internal receptor molecules within the cell’s nucleus, whereas in plants the receptors are anchored to the outside surface of the cell membranes.

A challenge for researchers has been to piece together the steps by which the hormonal signal is transmitted from the cell surface receptor to its action in the nucleus, where genes are the targets of regulation.

Traditionally, genetic methods have been used to identify several components of the BR signalling pathway. However, the genetic approach cannot identify all the components of a signalling pathway largely because of genetic redundancy (many genes play the same role in the cell).

To identify the links in the signal transduction chain, researchers used the techniques of proteomics. “Proteomics is analogous to genomics,” said Wang.

“In genomics, we aim for a comprehensive survey of all the genes in genome. In proteomics, we’re mapping the proteins.” Because there can be hundreds of thousands of different proteins in a single organism, proteomics requires techniques, such as 2-dimensional gel electrophoresis, which can process and segregate thousands of proteins at a time based on differences in their size and charge.

But even with these methods, isolating the low-abundance signalling proteins was a daunting task. “Earlier attempts to identify these molecules failed, because the analyses were swamped by the more abundant proteins,” said Wang.

“But because we knew the proteins would be associated with the cell membrane, we tried separating the membranes from the rest of the cell material and just analysed that fraction. And that worked.”

These findings have been published in the July 25 issue of Science.