A major challenge in biology is to understand how events at the biochemical level lead to changes at the organismal level. In cyanobacteria, light stimulates movement towards (positive phototaxis) and away from (negative phototaxis) light. This is an important survival mechanism in cyanobacteria. The cyanobacterium Synechocystis contains a protein (SynETR) that has characteristics of both photoreceptors (important for phototaxis) and ethylene receptors. In plants, ethylene receptors mediate many responses that impact plant survival, but it is unknown what these receptors do in cyanobacteria. Prior results have shown that ethylene regulates phototaxis in Synechocystis via the SynETR protein. However, no detectable biosynthesis of ethylene was found. It is known that sunlight can interact with dissolved organics to abiotically produce ethylene in the concentration range where physiological effects on phototaxis are seen. Thus, this project tests the hypothesis that Synechocystis uses ethylene as an external chemical cue to influence phototaxis behavior. The overall goal is to elucidate the mechanism by which ethylene affects SynETR function in Synechocystis to modulate phototaxis. A combination of biochemistry, chemistry, physiology, and molecular biology will be used to address this goal. This combination of approaches has yielded a great deal of information about the ethylene receptors in plants and provides a paradigm for determining the function of SynETR in Synechocystis. The multifaceted research will increase our understanding about links between ethylene binding events at the biochemical level with physiological changes that occur at the organismal level. This, in turn, will provide a broader understanding about how cyanobacteria respond to their environment and integrate environmental cues to modulate phototaxis.
The research will enhance research and educational infrastructure by broadening opportunities for high school, undergraduate and graduate students to engage in research. Since cyanobacteria contribute significantly to atmospheric oxygen levels and fix a large portion of carbon in the atmosphere, it is important to understand the effects of ethylene on these organisms because levels of ethylene in the atmosphere continue to rise as an air pollutant from industrial activities. Additionally, a better understanding about ethylene and its impact on cyanobacteria will help us determine how to maximize their use for bioenergy needs.
