What Turns Ethylene On

The gaseous phytohormone ethylene is a major manipulator of plant growth processes. It is best known for its roles in fruit ripening and flower fading. It also induces seed germination and protects the plant against pathogens and environmental stress. The hormone, however, causes significant losses to agriculture and the cut flower industry. Ethylene produced by a single rotting fruit will hasten the ripening process of nearby fruits causing them to spoil as well. During delivery and handling, ethylene production is increased in cut flowers inducing premature floral fading.

In recent years, scientists have learned a lot about the ethylene signaling in cells. Researchers at the Salk Institute for Biological Studies in the US have now identified the role of EIN2, a key regulator in ethylene response. EIN2’s elusiveness has resisted previous efforts to completely elucidate the ethylene signaling pathway.

The Salk scientists, led by Joseph Ecker, found out that the presence of ethylene stabilizes the short-lived EIN2 allowing it to gather enough strength to relay ethylene’s message. In the absence of ethylene, a protein called CTR1 binds EIN2 repressing the ethylene pathway. As soon as ethylene binds to its receptor, EIN2 is activated but the mechanism of EIN2 activation remains unclear. At the root of it all are two F-box proteins: ETP1 and ETP2. These proteins mediate the degradation of EIN2 when it is not needed. The presence of ethylene inactivates these proteins and EIN2 is no longer degraded.

“This type of regulation is like having your foot on the accelerator and brake at the same time, and then letting up on the break,” explains Ecker. “It allows cells to respond quickly to incoming information.”  The discovery may also be used to improve pathogen and drought resistance in plants.

The complete article is available at http://www.salk.edu/news/pressrelease_details.php?press_id=340