Gaseous Hormone Hypothesis

The gaseous hormone ethylene is perceived by the ethylene receptors which reside at the endoplasmic reticulum membranes4. In the genetic model plant Arabidopsis, there are five ethylene receptors (ETR1, ERS1, ETR2, ERS2, and EIN4), that fall into two subfamilies depending on functional kinase activity, and a subset of the receptors contains a receiver domain which promotes interaction with CTR15, 6. Interestingly, the receiver domain of ethylene receptors has a remarkable structural similarity with the Ras protein in mammalian. The Ras is a small GTP-binding protein and is a critical regulator of RAF kinase function7. In the absence of ethylene, the receptors have inverse agonistic roles and suppress the ethylene signaling. This negative regulation of the ethylene signaling by ethylene receptors is, subsequently, transmitted to downstream component, CTR1 by direct interaction. …show more content…
While the elements in the ethylene signaling pathway have been identified, we are only beginning to understand the mechanism by which these proteins interact to mediate ethylene responses, especially the early steps in the pathway: receptorsCTR1EIN2. Genetic studies revealed that the kinase activity of CTR1 is essential for its function and proteomics analysis identified several phosphorylation sites on the EIN2 proteins, a subset of which were enriched in the air as compared to ethylene; subsequent analysis revealed direct phosphorylation of EIN2 by CTR110, 11. This phosphorylation blocks an activating proteolytic cleavage of EIN2. The cleavage of EIN2 in response to ethylene results in the release of the C-terminal domain of