Ethylene in smoke has long been used to ripen fruit; this practice has included ripening pears in the smoke from incense. Gashing of unpollinated figs has also been practiced; the ethylene produced upon wounding induces ripening
When germinating in the dark, impeded seedlings produce ethylene which confers a characteristic “triple response”
Reduced elongation
Hypocotyl swelling
Apical hook exaggeration
1901
Dimitry Neljubow traced the source of the strange growth patterns of his dark-grown pea seedlings to the ethylene produced by gas-burning lamps
Ethylene was identified as a compound that affects plant growth
1959
Gas chromatography (GC) was used to measure ethylene levels
Types and Structure of Ethylene
Biosynthesis of Ethylene
Core Enzyme
AdoMet synthetase
ACC synthase
ACS genes have unique and common functions
ETO1 is a component of a ubiquitin-ligase complex
ETO1 targets ACS proteins for ubiquitination and proteolysis
ACC oxidase
Synthetic pathway
Regulation and Metabolism of Ethylene
ACS and ACO activities are tightly regulated transcriptionally and post-transcriptionally and sensitive to developmental cues, wounding and pathogen attack
Transport of Ethylene
ACC moving from root to shoot induces ethylene formation and epinasty
In some plants ACC moves through the xylem into the shoot where it is converted to ethylene by ACC oxidase
Leaf epinasty, caused by differential growth of the petiole, reduces light absorption by the leaves
Perception and signaling
Receptor
The ethylene receptors structurally resemble the cytokinin receptors.
Subfamily
1
ETR1
ETR2
2
EIN4
ETR2
ERS2
Downstream of EIN2 a transcriptional cascade controls gene expression
EIN3 and EIL1 are transcription factors that bind an ethylene binding site (EBS) in the promoter of ERF1.
ERF1 encodes another TF that targets ethyleneresponsive genes
CTR1 is a negative regulator of ethylene signaling
In the absence of ethylene, CTR1 is active and inhibits the ethylene responses
