In recent years, scientists learned a lot about the different components that transmit ethylene signals inside cells. But a central regulator of ethylene responses, a protein known as EIN2, resisted all their efforts.
Finally, after more than a decade of constant probing, a team of researchers led by Joseph Ecker, Ph.D., a professor in the Plant Biology laboratory and director of the Salk Institute Genomic Analysis Laboratory, successfully pinned down the elusive protein. Turns out, the presence of ethylene stabilizes the otherwise ephemeral EIN2 allowing it to gather up enough strength to pass on ethylene’s message.
Their findings, published in the Feb. 15, 2009 edition of the journal Genes and Development, are an important step toward defining EIN2’s role in growth and development and modifying key processes to improve agriculture, preventing crop losses due to ethylene related processes.
“Ethylene is involved in a wide variety of processes and we knew from genetic experiments that EIN2 is right at the center of ethylene signaling pathway, but for the longest time we were unable to figure out how it is regulated,” says Ecker. “Now that we know that EIN2 is negatively regulated by protein degradation, we can begin to understand how it triggers all these different ethylene responses in plants.”
All aspects of a plant’s life are influenced by ethylene: It induces seed germination and the so-called triple response in seedlings, which helps them to push past obstructions. It regulates root hair growth in general and nodulation in nitrogen-fixing legumes. It stimulates fruit ripening, floral fading and abscission, which allows plants to drop fruits, leaves and flowers. But it also protects against pathogens and environmental stress.
While ethylene’s power has been harnessed since the ancient Egyptians discovered that scoring figs hastens the ripening process, it also causes significant losses for florists, markets, suppliers and growers. A single rotting apple’s ethylene production will accelerate the ripening process in nearby apples causing them to spoil as well. Stress during shipping and handling increases ethylene production in cut flowers inducing premature floral fading.
“Ethylene plays a big role in our daily life and ethylene overproduction causes huge economic losses every year,” says first author Hong Qiao, Ph.D., a postdoctoral fellow in Ecker’s lab. “Once we fill in the gaps in our understanding of the ethylene signaling pathway, we can use this knowledge to improve pathogen or drought resistance in plants.”
In the absence of ethylene, a protein called CTR1—short for constitutive triple response 1—shuts down the ethylene pathway through the repression of a protein known as ETHYLENE INSENSITIVE 2 or EIN2. As soon as ethylene binds to its receptors, though, CTR1 looses its paralyzing grip on EIN2 and EIN2 becomes active. But nobody knew how.
Since the activity of the gene, which was isolated in Ecker’s lab in 1995, doesn’t change, Qiao took a closer look at protein levels. It quickly became clear that EIN2 is a short-lived protein that is constantly recycled. When she treated the plants with ethylene, however, EIN2 was no longer degraded and started to accumulate.
Further experiments revealed that two so-called F-box proteins, ETP1 and ETP2 (EIN2 targeting protein 1 and 2), flag EIN2 for degradation when it is not needed for signal transmission. In the presence of ethylene, both F-box proteins are inactivated and EIN2 is no longer sent to the cell’s recycling plant.
“Protein degradation is an emerging theme in plant biology and has been linked to several signaling pathways,” explains Ecker. “This type of regulation is like having your foot on the accelerator and the brake at the same time, then letting up on the brake. It allows cells to respond quickly to incoming information.”
When Qiao inactivated both ETP1 and ETP2 the ethylene signaling pathway was permanently active. When she increased their levels above normal the plants did not respond to the presence of ethylene at all because they couldn’t shake off ETP1 and ETP2. “It really confirmed the central role of EIN2,” say Qiao. “Now we can follow this route and fill in the gaps between EIN2 and downstream components of the pathway.”
Graduate student Katherine N. Chang, and postdoctoral researcher Junshi Yazaki, Ph.D., both in Ecker’s lab also contributed to the study.
The work was funded by the National Science Foundation.
The Salk Institute for Biological Studies in La Jolla, California, is an independent nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health, and the training of future generations of researchers. Jonas Salk, M.D., whose polio vaccine all but eradicated the crippling disease poliomyelitis in 1955, opened the Institute in 1965 with a gift of land from the City of San Diego and the financial support of the March of Dimes.
Gina Kirchweger | Newswise Science News
Closing the carbon loop
08.12.2016 | University of Pittsburgh
Newly discovered bacteria-binding protein in the intestine
08.12.2016 | University of Gothenburg
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
08.12.2016 | Life Sciences
08.12.2016 | Physics and Astronomy
08.12.2016 | Materials Sciences