Atomic insights into how plant steroid hormone makes plants grow

Aug 08, 2013
Left: This is the LLR domain of the receptor BRI1 (blue). In a first step, BRI1 binds the steroid hormone (yellow) to a surface pocket. This creates a docking platform for the smaller and shape-complementary LRR-domain of SERK1 (orange), which binds on top, with the steroid acting as a molecular glue. Credit: Julia Santiago.

If one wants to better understand how plants grow, one must analyse the chemistry of life in its molecular detail. Michael Hothorn from the Friedrich-Miescher-Laboratory of the Max Planck Society in Tübingen and his team are doing just that. Their latest work now reveals that a plant membrane receptor requires a helper protein to sense a growth-promoting steroid hormone and to transduce this signal across the cell membrane.

Every cell is surrounded by a greasy . Signals from other cells and from the environment must be sensed at the cell surface, transduced across this membrane and translated into a specific response inside the cell. All organisms have evolved membrane to get these complex tasks done, but plant membrane receptors look drastically different from the well-studied players in animals and bacteria. The plant steroid receptor BRI1, which can sense a small promoting , belongs to the family of leucine-rich repeat (LRR) receptor , which are responsible for most membrane signalling events in plants. It was previously shown that BRI1 directly binds the small steroid hormone with its LRR-domain at the cell surface.

Julia Santiago, a in the Hothorn lab, could now demonstrate that BRI1 requires a helper protein to correctly sense the hormone and transduce the signal across the membrane. The helper SERK1 is a known player in the brassinosteroid signalling pathway, but it came as a surprise to see how early on it is required. By hitting containing the ternary BRI1 – steroid hormone – SERK1 complex with intense X-rays, Santiago could see that SERK1 contributes directly to the formation of the hormone binding pocket, with both proteins interacting with the hormone. The steroid thus acts as a molecular glue which promotes association of the BRI1 and SERK1 LRR domains at the . This then causes interaction of the cytoplasmic kinases domains in the cell interior, which in turn activates a well characterized signalling pathway triggering the growth response.

The interesting feature of SERK1 is that it can help activate several seemingly unrelated plant receptor kinases, which bind vastly different ligands and trigger different responses. The new structures provide a first glimpse on how SERK1 might be able to do that. Instead of shaking hands with BRI1, it only uses a few 'finger tips' to contact the receptor. Other, strictly conserved surface patches remain available for the interaction with other plant receptor kinases and, potentially their ligands. "There must be some advantage to having all this different functions combined into a single helper protein", Hothorn speculates. Notably, the use of a shared helper protein could allow different signalling pathway to communicate with each other.

The atomic models offer other novel insights too: "Looking at our models, we can now predict pretty well, which mutation in the receptor or helper protein should have an effect on the down-stream signalling pathway. We also know what parts of the hormone are really important to make it bind to the receptor or to the helper protein". Such detailed insights may promote the rational design of synthetic plant steroid hormones and receptor antagonist with applications in basic research, and perhaps someday in the field.

Explore further: Two-armed control of ATR, a master regulator of the DNA damage checkpoint

More information: Julia Santiago, Christine Henzler, Michael Hothorn, Molecular mechanism for plant steroid receptor activation by somatic embryogenesis co-receptor kinases, Science Express; 9 August, 2013

Related Stories

Mastermind steroid found in plants

Nov 15, 2010

Scientists have known for some time how important plant steroids called brassinosteroids are for regulating plant growth and development. But until now, they did not know how extensive their reach is. Now researchers, including ...

In plants, small changes make big impact

Oct 07, 2010

(PhysOrg.com) -- You can’t see them or feel them, but right now countless biochemical interactions in your body affect your life in countless ways. These interactions are important because if they go ...

Recommended for you

Japanese scientist resigns over stem cell scandal

Dec 19, 2014

A researcher embroiled in a fabrication scandal that has rocked Japan's scientific establishment said Friday she would resign after failing to reproduce results of what was once billed as a ground-breaking study on ...

'Hairclip' protein mechanism explained

Dec 18, 2014

Research led by the Teichmann group on the Wellcome Genome Campus has identified a fundamental mechanism for controlling protein function. Published in the journal Science, the discovery has wide-ranging implications for bi ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.