Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Plant Receptors Reflect Different Solutions for a Fundamental Signaling Problem

15.06.2011
Salk Institute researchers follow twists and turns of plant steroid signaling

Birds do it, bees do it, and for most things biological, even plants do it. But not necessarily like their animal counterparts. A study led by Salk Institute scientists shows that a plant receptor does one of the most fundamental cellular “its”—the delivery of a hormonal signal from outside the cell to the nucleus—in a radically different way than its animal cousins. Knowing that could aid creation of techniques to speed plant growth and enhance agricultural production.


Image: Courtesy of Michael Hothorn and Jamie Simon, Salk Institute for Biological Studies
Atomic model of the plant steroid receptor BRI1 A molecule of brassinolide (yellow wire model) binds to the extracellular domain of the receptor (in light-blue). Binding ultimately causes phosphorylation of the receptor's cytoplasmic kinase domain (in dark blue), thereby transducing the signal across the membrane.

In a study published in the June 12, 2011, advance online edition of the journal Nature, a team led by Joanne Chory, Ph.D., professor and director of the Plant Molecular and Cellular Biology Laboratory and a Howard Hughes Medical Institute investigator, reports the three-dimensional structure of a plant steroid hormone receptor known as BRI1.

Since the late 90’s the Chory lab has conducted landmark studies revealing that plant and animal steroids are made via similar pathways and that, like animals, plants use steroids to become bigger, regulate sexual development, and control physiology.

The new study caps that work with a molecular analysis of a receptor that transduces the plant steroid signal. "Our genetics studies previously showed that unlike animal steroid receptors, which bind steroids inside cells, plant steroid receptors are membrane proteins, a completely different class of protein,” says Chory, holder of the Howard H. and Maryam R. Newman Chair in Plant Biology. “Now that we know the precise contacts made between the steroid and its receptor, we can propose how the BRI1 receptor works.”

The new work reports the atomic structure of BRI1 and then superimposes it with a distant structural cousin, the mammalian membrane protein TLR3, which activates an innate immune response in mice and humans. The TLR3 structure was determined in 2005 by Ian Wilson, Ph.D., professor in the Department of Molecular Biology and member of the Skaggs Institute at The Scripps Research Institute (TSRI) and a co-author of the current study.

The comparison affirms that, although somewhat similar to TLRs architecturally, the domain of BRI1 that pokes out through the cell membrane and monitors the extracellular environment exhibits twists and turns unique to plants. “We thought BRI1 would look like TLR3, which is shaped like a horseshoe,” says Michael Hothorn, Ph.D., a postdoctoral fellow in the Chory lab and the study’s first author. “But instead BRI1 was twisted into a superhelical spiral.”

To visualize those twists, the group employed a technique called x-ray diffraction. That method requires that scientists first grow highly purified crystals of BRI1 extracellular “antenna”—in this case derived from the mustard plant Arabidopsis thaliana—and then bombard the crystals with x-rays. The way x-rays bounce off, or “diffract” from, the crystal enables researchers to construct a three-dimensional, Lego-like representation of the protein’s architecture in the presence or absence of steroid activator.

One prediction was that structural shifts caused by binding of the brassinolide steroid might resemble conformation changes made by TLR when it initiates an immune response. “We knew that when the TLR3 horseshoe binds an activator another horseshoe becomes glued on top of it,” says Hothorn. “But BRI1 contains an island domain that first binds steroid onto the twisted structure and then provides a platform for a different protein to interact and relay the signal.”

Although the job of proteins like TLR3 and BRI1 is to alter gene expression patterns in response to environmental stimuli, their structural differences likely reflect the fact that those stimuli are fundamentally different molecules. “In mammals TLR3 is an innate immunity receptor activated when large ligands such as viral RNA bind to a highly repeated area called the LRR or Leucine-Rich Repeat domain,” says Wilson. “BRI1 is also an LRR protein but its structure is highly specialized to recognize and respond to smaller plant steroid hormones.”

“Michael’s structural work is the final brick in the wall,” says Chory, noting that BRI1 serves as the prototype for a large class of similar proteins expressed in plants. Interestingly, BRI1 is an exception in that family: while its job is to relay growth-promoting signals, many of its look-alikes actually stimulate immune responses in plants, protecting them from insects, worms or bacteria. Whether BRI1’s sibling receptors display such a twisted structure opens new avenue of investigation.

Many common herbicides were designed to mimic the structure of plant hormones. “Because brassinosteroids are hormones, knowing the structure of their receptor will allow us to rationally design herbicides that could block interaction between hormone and receptor,” says Chory. “This would enable us to manipulate how fast plants grow and how large they become—traits that are important in crops that must soon feed 10 billion people.”

Also contributing to the work were Youssef Belkhadir and Tsegaye Dabi of the Chory lab, Joseph Noel of Salk, and Marlene Dreux of The Scripps Research Institute in La Jolla.

Support for the work was from the Howard Hughes Medical Institute, the National Science Foundation, the European Molecular Biology Organization, the International Human Frontier Science Program Organization, the Philippe Foundation, the National Institutes of Health, and the Skaggs Institute for Chemical Biology at TSRI.

About the Salk Institute for Biological Studies:
The Salk Institute for Biological Studies is one of the world's preeminent basic research institutions, where internationally renowned faculty probe fundamental life science questions in a unique, collaborative, and creative environment. Focused both on discovery and on mentoring future generations of researchers, Salk scientists make groundbreaking contributions to our understanding of cancer, aging, Alzheimer's, diabetes and infectious diseases by studying neuroscience, genetics, cell and plant biology, and related disciplines.

Faculty achievements have been recognized with numerous honors, including Nobel Prizes and memberships in the National Academy of Sciences. Founded in 1960 by polio vaccine pioneer Jonas Salk, M.D., the Institute is an independent nonprofit organization and architectural landmark.

Kat Kearney
Kkearney@salk.edu
858.453.4100 x1226

Kat Kearney | Newswise Science News
Further information:
http://www.salk.edu

More articles from Life Sciences:

nachricht Cryo-electron microscopy achieves unprecedented resolution using new computational methods
24.03.2017 | DOE/Lawrence Berkeley National Laboratory

nachricht How cheetahs stay fit and healthy
24.03.2017 | Forschungsverbund Berlin e.V.

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>