This Research in Focus is written by science writer Peter Minorsky (ASPB and Mercy College) who writes the monthly On the Inside column for Plant Physiology. This summary describes a paper by Lacey and Binder, to be published in the July 2016 issue. The authors examine a putative ethylene receptor in cyanobacteria; this protein had been previously characterized as having a role in light signaling and possibly ethylene signaling (Rodgriguez et al., 1999; Song et al., 2011; Narikawa et al., 2009). In this work, the protein is demonstrated to bind ethylene and to be required for ethylene response in cyanobacteria.
Ethylene is a gaseous hormone that influences the growth and development of plants. Previous research suggests that ethylene signaling probably evolved in plants prior to the colonization of land. In plants, the perception of ethylene is mediated by a family of receptors that show homology to bacterial two-component receptors. Plants acquired many proteins from cyanobacteria as a result of an endosymbiotic event approximately 1.5 billion years ago that led to chloroplasts. Because of the endosymbiotic gene transfer that occurred, it has been proposed that components of several two-component-like receptors in plants, such as ethylene receptors and phytochromes, were acquired from the cyanobacterium that gave rise to the chloroplasts of plants. In a search of sequenced genomes, Lacey and Binder have found that many bacterial species contain putative ethylene receptors. They provide data that the cyanobacterium Synechocystis has a functional receptor for ethylene, Ethylene response1 (SynEtr1). They demonstrate that SynEtr1 directly binds ethylene. Moreover, treatment of Synechocystis with ethylene or disruption of SynEtr1 caused measurable changes in physiology including faster movement towards light, slower cell sedimentation, enhanced biofilm production, a larger number of type IV pili, and higher levels of PSII. Prior research showed that SynEtr1 also contains a light responsive phytochrome-like domain. Thus, SynEtr1 is a bifunctional receptor that mediates responses to both light and ethylene. This is the first demonstration of a functional ethylene receptor in a non-plant species and suggests that that the perception of ethylene is more widespread than previously thought.
Lacey, R.F. and Binder, B. (2016). Ethylene Regulates the Physiology of the Cyanobacterium Synechocystis sp. PCC 6803 via an Ethylene Receptor. Plant Physiology.
Narikawa, R., Suzuki, F., Yoshihara, S., Higashi, S.-i., Watanabe, M. and Ikeuchi, M. (2011). Novel Photosensory Two-Component System (PixA–NixB–NixC) Involved in the Regulation of Positive and Negative Phototaxis of Cyanobacterium Synechocystis sp. PCC 6803. Plant and Cell Physiology. 52: 2214-2224.
Rodrı́guez, F.I., Esch, J.J., Hall, A.E., Binder, B.M., Schaller, G.E. and Bleecker, A.B. (1999). A Copper Cofactor for the Ethylene Receptor ETR1 from Arabidopsis. Science. 283: 996-998.
Song, J.-Y., Cho, H.S., Cho, J.-I., Jeon, J.-S., Lagarias, J.C. and Park, Y.-I. (2011). Near-UV cyanobacteriochrome signaling system elicits negative phototaxis in the cyanobacterium Synechocystis sp. PCC 6803. Proceedings of the National Academy of Sciences. 108: 10780-10785.