<i>Synechocystis</i>: Low Dosage and Rapid Response to Ethylene

Ethylene is a well-studied plant hormone, that has been shown to affect different aspects throughout the life cycle of plants. The ethylene receptors in plants resemble two component signaling models found in bacteria. Recent studies have identified a functional ethylene receptor, ethylene response 1 (Etr1), in sp. Strain PCC 6803. Etr1 is known for its two component signaling photoreceptor capabilities. The light signaling pathway from Etr1 involves two proteins that serve as response regulators (Slr1213 and Slr1214) and a small RNA, carbon stress-induced RNA1 (csiR1). It has been shown that Etr1 plays a role in how Synechocystis respond to ethylene and that this receptor affects phototaxis and biofilm formation. The focus of this thesis was to attain more details about cell surface changes, sensitivity to ethylene, and timing of these response in Synechocystis. Ethylene alters physiological changes on the cell surface. Application of ethylene also caused a rapid, but temporary, decrease in the transcript levels of Etr1, slr1213, and slr1214 and a rapid and prolonged decrease in csiR1 transcript. This data combined with prior reports indicate that ethylene affects a variety of processes in Synechocystis cells. Based on the data presented in this thesis, Synechocystis cells have a rapid response to ethylene and at very low dosages that are generally lower than what plants have been shown to respond to. Even at low dosages, ethylene is able regulate the transcription of many genes, causing alterations in both intra‐ and extracellular processes in Synechocystis. These changes lead to a variety of physiological changes and provide a good description of how these cells respond to ethylene.