text: Ethylene receptors 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 receptor is similar in amino acid sequence to these response regulator and histidine kinase in bacteria; although the N-terminal region is altogether different. Such genetic and protein relationships indicate that receptors and bacterial two-component receptors as well as phytochromes and cytokinin receptors in plants evolved from and were acquired by plants from a cyanobacterium that gave rise to plastids, the power organelles in plants and protists.
  Phylogenetic analysis also shows the common origin of the ethylene receptor in plants and ethylene-binding domain in cyanobacteria. In 2016, Randy F. Lacey and Brad M. Binder at the University of Tennessee discovered that a cyanobacterium, Synechocystis sp. PCC 6803 response to ethylene signal and has a functional ethylene receptor, which they named Synechocystis Ethylene Response1 (SynEtr1). They further showed that SynEtr1 acts similar to plant ethylene receptor in binding ethylene, indicating the origin of ethylene receptor from Synechocystis-related cyanobacterium. The functional difference however is that kinase activity is not compulsory for ethylene binding in plants, but is the key role of SynEtr1.