UC Riverside scientists discover auxin sensing and signaling complex on plant cell surface that explains why leaf epidermal cells have jigsaw puzzle-piece shapes
Auxin, a small molecule, is a plant hormone discovered by Charles Darwin about 100 years ago. Over the years that followed it became understood to be the most important and versatile plant hormone controlling nearly all aspects of plant growth and development, such as bending of shoots toward the source of light (as discovered by Darwin), formation of new leaves, flowers, and roots, growth of roots, and gravity-oriented growth. Just how a small molecule like auxin could play such a pivotal role in plants baffled plant biologists for decades.
Then, about ten years ago, an auxin sensing and signaling system was discovered in the cell's nucleus, but it could not explain all the diverse roles of auxin.
Now, plant cell biologists at the University of California, Riverside have discovered a new auxin sensing and signaling complex, one that is localized on the cell surface rather than in the cell's nucleus. The discovery provides new insights into the mode of auxin action, the researchers say.
"This is a new milestone in auxin biology and will ignite interest in the field," said Zhenbiao Yang, a professor of cell biology in the Department of Botany and Plant Sciences, and the leader of the research project. "Our findings conclusively demonstrate the existence of an extracellular auxin sensing system in plants, which had long been proposed but remained elusive. Further, we have uncovered the decades-long mystery of how ABP1, an auxin-binding protein, works to control plant developmental processes."
ABP1 was identified more than 40 years ago, but its role was hotly debated among plant biologists because its mode of action remained unclear — until the recent discovery by Yang's team.
The team also showed that the cell surface auxin sensing system involves "transmembrane receptor kinases" (TMKs) — enzymes widespread throughout eukaryotes that typically act as cell surface sensors for extracellular stimuli and translate them into intracellular responses.
"This breakthrough discovery of the cell surface ABP1/TMK auxin sensing system dramatically elevates the level of our understanding of how auxin plays diverse roles," said Natasha Raikhel, a distinguished professor of plant cell biology at UC Riverside, who was not involved in the research. "This signaling mechanism now serves as a paradigm for elucidating the molecular mechanisms underlying various auxin-modulated developmental processes and patterns. In addition to their major impact on the field of plant development and morphogenesis and plant signal transduction, Yang's discoveries also provide novel means of engineering plants with desired morphological traits and growth patterns."
Study results appear in the Feb. 28 issue of Science.
Yang's lab has been studying molecular mechanisms for the formation of the jigsaw puzzle-piece shape of pavement cells in leaf epidermis of the Arabidopsis plant, a small flowering plant widely used in plant biology laboratories as a model organism. It is the interlocking feature of these cells that provides the required physical strength and integrity for flat, thin leaves.
In previous work, the lab found that auxin activated the formation of the puzzle piece shape through ABP1 and ABP1-dependent activation of "ROP GTPases," which are pivotal regulatory proteins that act as a molecular switch in gating incoming signals from the cell surface. It was unclear, however, whether ABP1 was a cell surface auxin receptor. Also, just how it led to the activation of ROP GTPases remained unknown.
"But now we have identified a family of TMKs that physically and functionally interact with ABP1 to perceive and transduce auxin signal at the cell surface," Yang said. "We show that ABP1 and TMKs form a new auxin sensing complex at the cell surface and that TMKs transmit extracellular auxin signals to ROP GTPases located just inside of the cell membrane. This novel auxin sensing and signaling system makes possible the formation of the jigsaw shape of leaf epidermal cells and many other auxin-mediated processes."
Next, Yang's team plans to investigate whether there are additional components in the cell surface auxin sensing complex, what specific pathways are regulated by the cell surface auxin sensor, and why plants need both the nuclear and extracellular auxin sensors.
Yang was joined in the study by researchers at UCR; the National University of Singapore; the Chinese Academy of Sciences; the University of Wisconsin; Ghent University, Belgium; the Institute of Science and Technology, Austria; the University of North Carolina, Chapel Hill; and Masaryk University, the Czech Republic.
The research was supported by a grant to Yang from the National Institute of General Medical Sciences.
The University of California, Riverside is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion. A broadcast studio with fiber cable to the AT&T Hollywood hub is available for live or taped interviews. UCR also has ISDN for radio interviews. To learn more, call (951) UCR-NEWS.
Iqbal Pittalwala | EurekAlert!
Polymers Based on Boron?
18.01.2018 | Julius-Maximilians-Universität Würzburg
Bioengineered soft microfibers improve T-cell production
18.01.2018 | Columbia University School of Engineering and Applied Science
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
The oceans are the largest global heat reservoir. As a result of man-made global warming, the temperature in the global climate system increases; around 90% of...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
18.01.2018 | Life Sciences
18.01.2018 | Life Sciences
18.01.2018 | Earth Sciences