Ethylene signaling pathway

Although structurally diverse, the ethylene gasoreceptors all exhibit similarity (homology) to two-component regulatory system in bacteria, indicating their common ancestry from bacterial ancestor.

Although homodimers of the gasoreceptors are required for functional state, only one ethylene molecule binds to each dimer.

There is also non-canonical pathway in which ethylene activates cytokinin gasoreceptor, and thereby regulate seed development (stomatal aperture) and growth of root (the apical meristem).

[1] Ethylene binds to it specific transmembrane gasoreceptor present on the cell membrane of endoplasmic reticulum.

[17] However, the main membrane localization is done by the transmembrane domain, which can also bind ethylene with the help of copper as a cofactor.

[1] The C-terminus is basically a bacterial two-component system with kinase activity and response regulator.

[21] Ethylene gasoreceptors are functionally similar to bacterial two-component system which has two activation sites named response regulator and histidine kinase.

The cytoplasmic carboxy-terminal part of ethylene gasoreceptor is similar in amino acid sequence to these response regulator and histidine kinase in bacteria; although the N-terminal region is altogether different.

[23][24] Phylogenetic analysis also shows the common origin of the ethylene gasoreceptor in plants and ethylene-binding domain in cyanobacteria.

[6] In 2016, Randy F. Lacey and Brad M. Binder at the University of Tennessee discovered that a cyanobacterium, Synechocystis sp.

[1] The functional difference however is that kinase activity is not compulsory for ethylene binding in plants, but is the key role of SynEtr1.

[10] EIN2 is required for ethylene signalling and is part of the NRAMP (natural resistance-associated macrophage protein) family of metal transporters; it comprises a large, N-terminal portion containing multiple transmembrane domains (EIN2-N) in the ER membrane and a cytosolic C-terminal portion (EIN2-C).

[27] TRP1 is genetically related to transmembrane and coiled-coil protein 1 (TCC1) in animals that is involved F actin function and competes with Raf-1 for Ras binding.